1.1 --- a/src/share/vm/runtime/synchronizer.cpp Mon Oct 18 09:33:24 2010 -0700
1.2 +++ b/src/share/vm/runtime/synchronizer.cpp Fri Oct 22 15:59:34 2010 -0400
1.3 @@ -32,15 +32,12 @@
1.4 #define ATTR
1.5 #endif
1.6
1.7 -// Native markword accessors for synchronization and hashCode().
1.8 -//
1.9 // The "core" versions of monitor enter and exit reside in this file.
1.10 // The interpreter and compilers contain specialized transliterated
1.11 // variants of the enter-exit fast-path operations. See i486.ad fast_lock(),
1.12 // for instance. If you make changes here, make sure to modify the
1.13 // interpreter, and both C1 and C2 fast-path inline locking code emission.
1.14 //
1.15 -// TODO: merge the objectMonitor and synchronizer classes.
1.16 //
1.17 // -----------------------------------------------------------------------------
1.18
1.19 @@ -53,16 +50,6 @@
1.20 jlong, uintptr_t, char*, int, long);
1.21 HS_DTRACE_PROBE_DECL4(hotspot, monitor__waited,
1.22 jlong, uintptr_t, char*, int);
1.23 -HS_DTRACE_PROBE_DECL4(hotspot, monitor__notify,
1.24 - jlong, uintptr_t, char*, int);
1.25 -HS_DTRACE_PROBE_DECL4(hotspot, monitor__notifyAll,
1.26 - jlong, uintptr_t, char*, int);
1.27 -HS_DTRACE_PROBE_DECL4(hotspot, monitor__contended__enter,
1.28 - jlong, uintptr_t, char*, int);
1.29 -HS_DTRACE_PROBE_DECL4(hotspot, monitor__contended__entered,
1.30 - jlong, uintptr_t, char*, int);
1.31 -HS_DTRACE_PROBE_DECL4(hotspot, monitor__contended__exit,
1.32 - jlong, uintptr_t, char*, int);
1.33
1.34 #define DTRACE_MONITOR_PROBE_COMMON(klassOop, thread) \
1.35 char* bytes = NULL; \
1.36 @@ -99,61 +86,300 @@
1.37
1.38 #endif // ndef DTRACE_ENABLED
1.39
1.40 -// ObjectWaiter serves as a "proxy" or surrogate thread.
1.41 -// TODO-FIXME: Eliminate ObjectWaiter and use the thread-specific
1.42 -// ParkEvent instead. Beware, however, that the JVMTI code
1.43 -// knows about ObjectWaiters, so we'll have to reconcile that code.
1.44 -// See next_waiter(), first_waiter(), etc.
1.45 +// This exists only as a workaround of dtrace bug 6254741
1.46 +int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
1.47 + DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
1.48 + return 0;
1.49 +}
1.50
1.51 -class ObjectWaiter : public StackObj {
1.52 - public:
1.53 - enum TStates { TS_UNDEF, TS_READY, TS_RUN, TS_WAIT, TS_ENTER, TS_CXQ } ;
1.54 - enum Sorted { PREPEND, APPEND, SORTED } ;
1.55 - ObjectWaiter * volatile _next;
1.56 - ObjectWaiter * volatile _prev;
1.57 - Thread* _thread;
1.58 - ParkEvent * _event;
1.59 - volatile int _notified ;
1.60 - volatile TStates TState ;
1.61 - Sorted _Sorted ; // List placement disposition
1.62 - bool _active ; // Contention monitoring is enabled
1.63 - public:
1.64 - ObjectWaiter(Thread* thread) {
1.65 - _next = NULL;
1.66 - _prev = NULL;
1.67 - _notified = 0;
1.68 - TState = TS_RUN ;
1.69 - _thread = thread;
1.70 - _event = thread->_ParkEvent ;
1.71 - _active = false;
1.72 - assert (_event != NULL, "invariant") ;
1.73 +#define NINFLATIONLOCKS 256
1.74 +static volatile intptr_t InflationLocks [NINFLATIONLOCKS] ;
1.75 +
1.76 +ObjectMonitor * ObjectSynchronizer::gBlockList = NULL ;
1.77 +ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL ;
1.78 +ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL ;
1.79 +int ObjectSynchronizer::gOmInUseCount = 0;
1.80 +static volatile intptr_t ListLock = 0 ; // protects global monitor free-list cache
1.81 +static volatile int MonitorFreeCount = 0 ; // # on gFreeList
1.82 +static volatile int MonitorPopulation = 0 ; // # Extant -- in circulation
1.83 +#define CHAINMARKER ((oop)-1)
1.84 +
1.85 +// -----------------------------------------------------------------------------
1.86 +// Fast Monitor Enter/Exit
1.87 +// This the fast monitor enter. The interpreter and compiler use
1.88 +// some assembly copies of this code. Make sure update those code
1.89 +// if the following function is changed. The implementation is
1.90 +// extremely sensitive to race condition. Be careful.
1.91 +
1.92 +void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock, bool attempt_rebias, TRAPS) {
1.93 + if (UseBiasedLocking) {
1.94 + if (!SafepointSynchronize::is_at_safepoint()) {
1.95 + BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD);
1.96 + if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) {
1.97 + return;
1.98 + }
1.99 + } else {
1.100 + assert(!attempt_rebias, "can not rebias toward VM thread");
1.101 + BiasedLocking::revoke_at_safepoint(obj);
1.102 + }
1.103 + assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
1.104 + }
1.105 +
1.106 + slow_enter (obj, lock, THREAD) ;
1.107 +}
1.108 +
1.109 +void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) {
1.110 + assert(!object->mark()->has_bias_pattern(), "should not see bias pattern here");
1.111 + // if displaced header is null, the previous enter is recursive enter, no-op
1.112 + markOop dhw = lock->displaced_header();
1.113 + markOop mark ;
1.114 + if (dhw == NULL) {
1.115 + // Recursive stack-lock.
1.116 + // Diagnostics -- Could be: stack-locked, inflating, inflated.
1.117 + mark = object->mark() ;
1.118 + assert (!mark->is_neutral(), "invariant") ;
1.119 + if (mark->has_locker() && mark != markOopDesc::INFLATING()) {
1.120 + assert(THREAD->is_lock_owned((address)mark->locker()), "invariant") ;
1.121 + }
1.122 + if (mark->has_monitor()) {
1.123 + ObjectMonitor * m = mark->monitor() ;
1.124 + assert(((oop)(m->object()))->mark() == mark, "invariant") ;
1.125 + assert(m->is_entered(THREAD), "invariant") ;
1.126 + }
1.127 + return ;
1.128 }
1.129
1.130 - void wait_reenter_begin(ObjectMonitor *mon) {
1.131 - JavaThread *jt = (JavaThread *)this->_thread;
1.132 - _active = JavaThreadBlockedOnMonitorEnterState::wait_reenter_begin(jt, mon);
1.133 + mark = object->mark() ;
1.134 +
1.135 + // If the object is stack-locked by the current thread, try to
1.136 + // swing the displaced header from the box back to the mark.
1.137 + if (mark == (markOop) lock) {
1.138 + assert (dhw->is_neutral(), "invariant") ;
1.139 + if ((markOop) Atomic::cmpxchg_ptr (dhw, object->mark_addr(), mark) == mark) {
1.140 + TEVENT (fast_exit: release stacklock) ;
1.141 + return;
1.142 + }
1.143 }
1.144
1.145 - void wait_reenter_end(ObjectMonitor *mon) {
1.146 - JavaThread *jt = (JavaThread *)this->_thread;
1.147 - JavaThreadBlockedOnMonitorEnterState::wait_reenter_end(jt, _active);
1.148 + ObjectSynchronizer::inflate(THREAD, object)->exit (THREAD) ;
1.149 +}
1.150 +
1.151 +// -----------------------------------------------------------------------------
1.152 +// Interpreter/Compiler Slow Case
1.153 +// This routine is used to handle interpreter/compiler slow case
1.154 +// We don't need to use fast path here, because it must have been
1.155 +// failed in the interpreter/compiler code.
1.156 +void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) {
1.157 + markOop mark = obj->mark();
1.158 + assert(!mark->has_bias_pattern(), "should not see bias pattern here");
1.159 +
1.160 + if (mark->is_neutral()) {
1.161 + // Anticipate successful CAS -- the ST of the displaced mark must
1.162 + // be visible <= the ST performed by the CAS.
1.163 + lock->set_displaced_header(mark);
1.164 + if (mark == (markOop) Atomic::cmpxchg_ptr(lock, obj()->mark_addr(), mark)) {
1.165 + TEVENT (slow_enter: release stacklock) ;
1.166 + return ;
1.167 + }
1.168 + // Fall through to inflate() ...
1.169 + } else
1.170 + if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
1.171 + assert(lock != mark->locker(), "must not re-lock the same lock");
1.172 + assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock");
1.173 + lock->set_displaced_header(NULL);
1.174 + return;
1.175 }
1.176 -};
1.177
1.178 -enum ManifestConstants {
1.179 - ClearResponsibleAtSTW = 0,
1.180 - MaximumRecheckInterval = 1000
1.181 -} ;
1.182 +#if 0
1.183 + // The following optimization isn't particularly useful.
1.184 + if (mark->has_monitor() && mark->monitor()->is_entered(THREAD)) {
1.185 + lock->set_displaced_header (NULL) ;
1.186 + return ;
1.187 + }
1.188 +#endif
1.189
1.190 + // The object header will never be displaced to this lock,
1.191 + // so it does not matter what the value is, except that it
1.192 + // must be non-zero to avoid looking like a re-entrant lock,
1.193 + // and must not look locked either.
1.194 + lock->set_displaced_header(markOopDesc::unused_mark());
1.195 + ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD);
1.196 +}
1.197
1.198 -#undef TEVENT
1.199 -#define TEVENT(nom) {if (SyncVerbose) FEVENT(nom); }
1.200 +// This routine is used to handle interpreter/compiler slow case
1.201 +// We don't need to use fast path here, because it must have
1.202 +// failed in the interpreter/compiler code. Simply use the heavy
1.203 +// weight monitor should be ok, unless someone find otherwise.
1.204 +void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) {
1.205 + fast_exit (object, lock, THREAD) ;
1.206 +}
1.207
1.208 -#define FEVENT(nom) { static volatile int ctr = 0 ; int v = ++ctr ; if ((v & (v-1)) == 0) { ::printf (#nom " : %d \n", v); ::fflush(stdout); }}
1.209 +// -----------------------------------------------------------------------------
1.210 +// Class Loader support to workaround deadlocks on the class loader lock objects
1.211 +// Also used by GC
1.212 +// complete_exit()/reenter() are used to wait on a nested lock
1.213 +// i.e. to give up an outer lock completely and then re-enter
1.214 +// Used when holding nested locks - lock acquisition order: lock1 then lock2
1.215 +// 1) complete_exit lock1 - saving recursion count
1.216 +// 2) wait on lock2
1.217 +// 3) when notified on lock2, unlock lock2
1.218 +// 4) reenter lock1 with original recursion count
1.219 +// 5) lock lock2
1.220 +// NOTE: must use heavy weight monitor to handle complete_exit/reenter()
1.221 +intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
1.222 + TEVENT (complete_exit) ;
1.223 + if (UseBiasedLocking) {
1.224 + BiasedLocking::revoke_and_rebias(obj, false, THREAD);
1.225 + assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
1.226 + }
1.227
1.228 -#undef TEVENT
1.229 -#define TEVENT(nom) {;}
1.230 + ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
1.231
1.232 + return monitor->complete_exit(THREAD);
1.233 +}
1.234 +
1.235 +// NOTE: must use heavy weight monitor to handle complete_exit/reenter()
1.236 +void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) {
1.237 + TEVENT (reenter) ;
1.238 + if (UseBiasedLocking) {
1.239 + BiasedLocking::revoke_and_rebias(obj, false, THREAD);
1.240 + assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
1.241 + }
1.242 +
1.243 + ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
1.244 +
1.245 + monitor->reenter(recursion, THREAD);
1.246 +}
1.247 +// -----------------------------------------------------------------------------
1.248 +// JNI locks on java objects
1.249 +// NOTE: must use heavy weight monitor to handle jni monitor enter
1.250 +void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) { // possible entry from jni enter
1.251 + // the current locking is from JNI instead of Java code
1.252 + TEVENT (jni_enter) ;
1.253 + if (UseBiasedLocking) {
1.254 + BiasedLocking::revoke_and_rebias(obj, false, THREAD);
1.255 + assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
1.256 + }
1.257 + THREAD->set_current_pending_monitor_is_from_java(false);
1.258 + ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD);
1.259 + THREAD->set_current_pending_monitor_is_from_java(true);
1.260 +}
1.261 +
1.262 +// NOTE: must use heavy weight monitor to handle jni monitor enter
1.263 +bool ObjectSynchronizer::jni_try_enter(Handle obj, Thread* THREAD) {
1.264 + if (UseBiasedLocking) {
1.265 + BiasedLocking::revoke_and_rebias(obj, false, THREAD);
1.266 + assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
1.267 + }
1.268 +
1.269 + ObjectMonitor* monitor = ObjectSynchronizer::inflate_helper(obj());
1.270 + return monitor->try_enter(THREAD);
1.271 +}
1.272 +
1.273 +
1.274 +// NOTE: must use heavy weight monitor to handle jni monitor exit
1.275 +void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
1.276 + TEVENT (jni_exit) ;
1.277 + if (UseBiasedLocking) {
1.278 + BiasedLocking::revoke_and_rebias(obj, false, THREAD);
1.279 + }
1.280 + assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
1.281 +
1.282 + ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj);
1.283 + // If this thread has locked the object, exit the monitor. Note: can't use
1.284 + // monitor->check(CHECK); must exit even if an exception is pending.
1.285 + if (monitor->check(THREAD)) {
1.286 + monitor->exit(THREAD);
1.287 + }
1.288 +}
1.289 +
1.290 +// -----------------------------------------------------------------------------
1.291 +// Internal VM locks on java objects
1.292 +// standard constructor, allows locking failures
1.293 +ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) {
1.294 + _dolock = doLock;
1.295 + _thread = thread;
1.296 + debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);)
1.297 + _obj = obj;
1.298 +
1.299 + if (_dolock) {
1.300 + TEVENT (ObjectLocker) ;
1.301 +
1.302 + ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
1.303 + }
1.304 +}
1.305 +
1.306 +ObjectLocker::~ObjectLocker() {
1.307 + if (_dolock) {
1.308 + ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
1.309 + }
1.310 +}
1.311 +
1.312 +
1.313 +// -----------------------------------------------------------------------------
1.314 +// Wait/Notify/NotifyAll
1.315 +// NOTE: must use heavy weight monitor to handle wait()
1.316 +void ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
1.317 + if (UseBiasedLocking) {
1.318 + BiasedLocking::revoke_and_rebias(obj, false, THREAD);
1.319 + assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
1.320 + }
1.321 + if (millis < 0) {
1.322 + TEVENT (wait - throw IAX) ;
1.323 + THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
1.324 + }
1.325 + ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
1.326 + DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
1.327 + monitor->wait(millis, true, THREAD);
1.328 +
1.329 + /* This dummy call is in place to get around dtrace bug 6254741. Once
1.330 + that's fixed we can uncomment the following line and remove the call */
1.331 + // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
1.332 + dtrace_waited_probe(monitor, obj, THREAD);
1.333 +}
1.334 +
1.335 +void ObjectSynchronizer::waitUninterruptibly (Handle obj, jlong millis, TRAPS) {
1.336 + if (UseBiasedLocking) {
1.337 + BiasedLocking::revoke_and_rebias(obj, false, THREAD);
1.338 + assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
1.339 + }
1.340 + if (millis < 0) {
1.341 + TEVENT (wait - throw IAX) ;
1.342 + THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
1.343 + }
1.344 + ObjectSynchronizer::inflate(THREAD, obj()) -> wait(millis, false, THREAD) ;
1.345 +}
1.346 +
1.347 +void ObjectSynchronizer::notify(Handle obj, TRAPS) {
1.348 + if (UseBiasedLocking) {
1.349 + BiasedLocking::revoke_and_rebias(obj, false, THREAD);
1.350 + assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
1.351 + }
1.352 +
1.353 + markOop mark = obj->mark();
1.354 + if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
1.355 + return;
1.356 + }
1.357 + ObjectSynchronizer::inflate(THREAD, obj())->notify(THREAD);
1.358 +}
1.359 +
1.360 +// NOTE: see comment of notify()
1.361 +void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
1.362 + if (UseBiasedLocking) {
1.363 + BiasedLocking::revoke_and_rebias(obj, false, THREAD);
1.364 + assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
1.365 + }
1.366 +
1.367 + markOop mark = obj->mark();
1.368 + if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
1.369 + return;
1.370 + }
1.371 + ObjectSynchronizer::inflate(THREAD, obj())->notifyAll(THREAD);
1.372 +}
1.373 +
1.374 +// -----------------------------------------------------------------------------
1.375 +// Hash Code handling
1.376 +//
1.377 // Performance concern:
1.378 // OrderAccess::storestore() calls release() which STs 0 into the global volatile
1.379 // OrderAccess::Dummy variable. This store is unnecessary for correctness.
1.380 @@ -188,44 +414,73 @@
1.381 static int MonitorScavengeThreshold = 1000000 ;
1.382 static volatile int ForceMonitorScavenge = 0 ; // Scavenge required and pending
1.383
1.384 +static markOop ReadStableMark (oop obj) {
1.385 + markOop mark = obj->mark() ;
1.386 + if (!mark->is_being_inflated()) {
1.387 + return mark ; // normal fast-path return
1.388 + }
1.389
1.390 -// Tunables ...
1.391 -// The knob* variables are effectively final. Once set they should
1.392 -// never be modified hence. Consider using __read_mostly with GCC.
1.393 + int its = 0 ;
1.394 + for (;;) {
1.395 + markOop mark = obj->mark() ;
1.396 + if (!mark->is_being_inflated()) {
1.397 + return mark ; // normal fast-path return
1.398 + }
1.399
1.400 -static int Knob_LogSpins = 0 ; // enable jvmstat tally for spins
1.401 -static int Knob_HandOff = 0 ;
1.402 -static int Knob_Verbose = 0 ;
1.403 -static int Knob_ReportSettings = 0 ;
1.404 + // The object is being inflated by some other thread.
1.405 + // The caller of ReadStableMark() must wait for inflation to complete.
1.406 + // Avoid live-lock
1.407 + // TODO: consider calling SafepointSynchronize::do_call_back() while
1.408 + // spinning to see if there's a safepoint pending. If so, immediately
1.409 + // yielding or blocking would be appropriate. Avoid spinning while
1.410 + // there is a safepoint pending.
1.411 + // TODO: add inflation contention performance counters.
1.412 + // TODO: restrict the aggregate number of spinners.
1.413
1.414 -static int Knob_SpinLimit = 5000 ; // derived by an external tool -
1.415 -static int Knob_SpinBase = 0 ; // Floor AKA SpinMin
1.416 -static int Knob_SpinBackOff = 0 ; // spin-loop backoff
1.417 -static int Knob_CASPenalty = -1 ; // Penalty for failed CAS
1.418 -static int Knob_OXPenalty = -1 ; // Penalty for observed _owner change
1.419 -static int Knob_SpinSetSucc = 1 ; // spinners set the _succ field
1.420 -static int Knob_SpinEarly = 1 ;
1.421 -static int Knob_SuccEnabled = 1 ; // futile wake throttling
1.422 -static int Knob_SuccRestrict = 0 ; // Limit successors + spinners to at-most-one
1.423 -static int Knob_MaxSpinners = -1 ; // Should be a function of # CPUs
1.424 -static int Knob_Bonus = 100 ; // spin success bonus
1.425 -static int Knob_BonusB = 100 ; // spin success bonus
1.426 -static int Knob_Penalty = 200 ; // spin failure penalty
1.427 -static int Knob_Poverty = 1000 ;
1.428 -static int Knob_SpinAfterFutile = 1 ; // Spin after returning from park()
1.429 -static int Knob_FixedSpin = 0 ;
1.430 -static int Knob_OState = 3 ; // Spinner checks thread state of _owner
1.431 -static int Knob_UsePause = 1 ;
1.432 -static int Knob_ExitPolicy = 0 ;
1.433 -static int Knob_PreSpin = 10 ; // 20-100 likely better
1.434 -static int Knob_ResetEvent = 0 ;
1.435 -static int BackOffMask = 0 ;
1.436 -
1.437 -static int Knob_FastHSSEC = 0 ;
1.438 -static int Knob_MoveNotifyee = 2 ; // notify() - disposition of notifyee
1.439 -static int Knob_QMode = 0 ; // EntryList-cxq policy - queue discipline
1.440 -static volatile int InitDone = 0 ;
1.441 -
1.442 + ++its ;
1.443 + if (its > 10000 || !os::is_MP()) {
1.444 + if (its & 1) {
1.445 + os::NakedYield() ;
1.446 + TEVENT (Inflate: INFLATING - yield) ;
1.447 + } else {
1.448 + // Note that the following code attenuates the livelock problem but is not
1.449 + // a complete remedy. A more complete solution would require that the inflating
1.450 + // thread hold the associated inflation lock. The following code simply restricts
1.451 + // the number of spinners to at most one. We'll have N-2 threads blocked
1.452 + // on the inflationlock, 1 thread holding the inflation lock and using
1.453 + // a yield/park strategy, and 1 thread in the midst of inflation.
1.454 + // A more refined approach would be to change the encoding of INFLATING
1.455 + // to allow encapsulation of a native thread pointer. Threads waiting for
1.456 + // inflation to complete would use CAS to push themselves onto a singly linked
1.457 + // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
1.458 + // and calling park(). When inflation was complete the thread that accomplished inflation
1.459 + // would detach the list and set the markword to inflated with a single CAS and
1.460 + // then for each thread on the list, set the flag and unpark() the thread.
1.461 + // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
1.462 + // wakes at most one thread whereas we need to wake the entire list.
1.463 + int ix = (intptr_t(obj) >> 5) & (NINFLATIONLOCKS-1) ;
1.464 + int YieldThenBlock = 0 ;
1.465 + assert (ix >= 0 && ix < NINFLATIONLOCKS, "invariant") ;
1.466 + assert ((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant") ;
1.467 + Thread::muxAcquire (InflationLocks + ix, "InflationLock") ;
1.468 + while (obj->mark() == markOopDesc::INFLATING()) {
1.469 + // Beware: NakedYield() is advisory and has almost no effect on some platforms
1.470 + // so we periodically call Self->_ParkEvent->park(1).
1.471 + // We use a mixed spin/yield/block mechanism.
1.472 + if ((YieldThenBlock++) >= 16) {
1.473 + Thread::current()->_ParkEvent->park(1) ;
1.474 + } else {
1.475 + os::NakedYield() ;
1.476 + }
1.477 + }
1.478 + Thread::muxRelease (InflationLocks + ix ) ;
1.479 + TEVENT (Inflate: INFLATING - yield/park) ;
1.480 + }
1.481 + } else {
1.482 + SpinPause() ; // SMP-polite spinning
1.483 + }
1.484 + }
1.485 +}
1.486
1.487 // hashCode() generation :
1.488 //
1.489 @@ -290,416 +545,272 @@
1.490 TEVENT (hashCode: GENERATE) ;
1.491 return value;
1.492 }
1.493 +//
1.494 +intptr_t ObjectSynchronizer::FastHashCode (Thread * Self, oop obj) {
1.495 + if (UseBiasedLocking) {
1.496 + // NOTE: many places throughout the JVM do not expect a safepoint
1.497 + // to be taken here, in particular most operations on perm gen
1.498 + // objects. However, we only ever bias Java instances and all of
1.499 + // the call sites of identity_hash that might revoke biases have
1.500 + // been checked to make sure they can handle a safepoint. The
1.501 + // added check of the bias pattern is to avoid useless calls to
1.502 + // thread-local storage.
1.503 + if (obj->mark()->has_bias_pattern()) {
1.504 + // Box and unbox the raw reference just in case we cause a STW safepoint.
1.505 + Handle hobj (Self, obj) ;
1.506 + // Relaxing assertion for bug 6320749.
1.507 + assert (Universe::verify_in_progress() ||
1.508 + !SafepointSynchronize::is_at_safepoint(),
1.509 + "biases should not be seen by VM thread here");
1.510 + BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
1.511 + obj = hobj() ;
1.512 + assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
1.513 + }
1.514 + }
1.515
1.516 -void BasicLock::print_on(outputStream* st) const {
1.517 - st->print("monitor");
1.518 + // hashCode() is a heap mutator ...
1.519 + // Relaxing assertion for bug 6320749.
1.520 + assert (Universe::verify_in_progress() ||
1.521 + !SafepointSynchronize::is_at_safepoint(), "invariant") ;
1.522 + assert (Universe::verify_in_progress() ||
1.523 + Self->is_Java_thread() , "invariant") ;
1.524 + assert (Universe::verify_in_progress() ||
1.525 + ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant") ;
1.526 +
1.527 + ObjectMonitor* monitor = NULL;
1.528 + markOop temp, test;
1.529 + intptr_t hash;
1.530 + markOop mark = ReadStableMark (obj);
1.531 +
1.532 + // object should remain ineligible for biased locking
1.533 + assert (!mark->has_bias_pattern(), "invariant") ;
1.534 +
1.535 + if (mark->is_neutral()) {
1.536 + hash = mark->hash(); // this is a normal header
1.537 + if (hash) { // if it has hash, just return it
1.538 + return hash;
1.539 + }
1.540 + hash = get_next_hash(Self, obj); // allocate a new hash code
1.541 + temp = mark->copy_set_hash(hash); // merge the hash code into header
1.542 + // use (machine word version) atomic operation to install the hash
1.543 + test = (markOop) Atomic::cmpxchg_ptr(temp, obj->mark_addr(), mark);
1.544 + if (test == mark) {
1.545 + return hash;
1.546 + }
1.547 + // If atomic operation failed, we must inflate the header
1.548 + // into heavy weight monitor. We could add more code here
1.549 + // for fast path, but it does not worth the complexity.
1.550 + } else if (mark->has_monitor()) {
1.551 + monitor = mark->monitor();
1.552 + temp = monitor->header();
1.553 + assert (temp->is_neutral(), "invariant") ;
1.554 + hash = temp->hash();
1.555 + if (hash) {
1.556 + return hash;
1.557 + }
1.558 + // Skip to the following code to reduce code size
1.559 + } else if (Self->is_lock_owned((address)mark->locker())) {
1.560 + temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned
1.561 + assert (temp->is_neutral(), "invariant") ;
1.562 + hash = temp->hash(); // by current thread, check if the displaced
1.563 + if (hash) { // header contains hash code
1.564 + return hash;
1.565 + }
1.566 + // WARNING:
1.567 + // The displaced header is strictly immutable.
1.568 + // It can NOT be changed in ANY cases. So we have
1.569 + // to inflate the header into heavyweight monitor
1.570 + // even the current thread owns the lock. The reason
1.571 + // is the BasicLock (stack slot) will be asynchronously
1.572 + // read by other threads during the inflate() function.
1.573 + // Any change to stack may not propagate to other threads
1.574 + // correctly.
1.575 + }
1.576 +
1.577 + // Inflate the monitor to set hash code
1.578 + monitor = ObjectSynchronizer::inflate(Self, obj);
1.579 + // Load displaced header and check it has hash code
1.580 + mark = monitor->header();
1.581 + assert (mark->is_neutral(), "invariant") ;
1.582 + hash = mark->hash();
1.583 + if (hash == 0) {
1.584 + hash = get_next_hash(Self, obj);
1.585 + temp = mark->copy_set_hash(hash); // merge hash code into header
1.586 + assert (temp->is_neutral(), "invariant") ;
1.587 + test = (markOop) Atomic::cmpxchg_ptr(temp, monitor, mark);
1.588 + if (test != mark) {
1.589 + // The only update to the header in the monitor (outside GC)
1.590 + // is install the hash code. If someone add new usage of
1.591 + // displaced header, please update this code
1.592 + hash = test->hash();
1.593 + assert (test->is_neutral(), "invariant") ;
1.594 + assert (hash != 0, "Trivial unexpected object/monitor header usage.");
1.595 + }
1.596 + }
1.597 + // We finally get the hash
1.598 + return hash;
1.599 }
1.600
1.601 -void BasicLock::move_to(oop obj, BasicLock* dest) {
1.602 - // Check to see if we need to inflate the lock. This is only needed
1.603 - // if an object is locked using "this" lightweight monitor. In that
1.604 - // case, the displaced_header() is unlocked, because the
1.605 - // displaced_header() contains the header for the originally unlocked
1.606 - // object. However the object could have already been inflated. But it
1.607 - // does not matter, the inflation will just a no-op. For other cases,
1.608 - // the displaced header will be either 0x0 or 0x3, which are location
1.609 - // independent, therefore the BasicLock is free to move.
1.610 - //
1.611 - // During OSR we may need to relocate a BasicLock (which contains a
1.612 - // displaced word) from a location in an interpreter frame to a
1.613 - // new location in a compiled frame. "this" refers to the source
1.614 - // basiclock in the interpreter frame. "dest" refers to the destination
1.615 - // basiclock in the new compiled frame. We *always* inflate in move_to().
1.616 - // The always-Inflate policy works properly, but in 1.5.0 it can sometimes
1.617 - // cause performance problems in code that makes heavy use of a small # of
1.618 - // uncontended locks. (We'd inflate during OSR, and then sync performance
1.619 - // would subsequently plummet because the thread would be forced thru the slow-path).
1.620 - // This problem has been made largely moot on IA32 by inlining the inflated fast-path
1.621 - // operations in Fast_Lock and Fast_Unlock in i486.ad.
1.622 - //
1.623 - // Note that there is a way to safely swing the object's markword from
1.624 - // one stack location to another. This avoids inflation. Obviously,
1.625 - // we need to ensure that both locations refer to the current thread's stack.
1.626 - // There are some subtle concurrency issues, however, and since the benefit is
1.627 - // is small (given the support for inflated fast-path locking in the fast_lock, etc)
1.628 - // we'll leave that optimization for another time.
1.629 +// Deprecated -- use FastHashCode() instead.
1.630
1.631 - if (displaced_header()->is_neutral()) {
1.632 - ObjectSynchronizer::inflate_helper(obj);
1.633 - // WARNING: We can not put check here, because the inflation
1.634 - // will not update the displaced header. Once BasicLock is inflated,
1.635 - // no one should ever look at its content.
1.636 - } else {
1.637 - // Typically the displaced header will be 0 (recursive stack lock) or
1.638 - // unused_mark. Naively we'd like to assert that the displaced mark
1.639 - // value is either 0, neutral, or 3. But with the advent of the
1.640 - // store-before-CAS avoidance in fast_lock/compiler_lock_object
1.641 - // we can find any flavor mark in the displaced mark.
1.642 - }
1.643 -// [RGV] The next line appears to do nothing!
1.644 - intptr_t dh = (intptr_t) displaced_header();
1.645 - dest->set_displaced_header(displaced_header());
1.646 +intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
1.647 + return FastHashCode (Thread::current(), obj()) ;
1.648 }
1.649
1.650 -// -----------------------------------------------------------------------------
1.651
1.652 -// standard constructor, allows locking failures
1.653 -ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) {
1.654 - _dolock = doLock;
1.655 - _thread = thread;
1.656 - debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);)
1.657 - _obj = obj;
1.658 +bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
1.659 + Handle h_obj) {
1.660 + if (UseBiasedLocking) {
1.661 + BiasedLocking::revoke_and_rebias(h_obj, false, thread);
1.662 + assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
1.663 + }
1.664
1.665 - if (_dolock) {
1.666 - TEVENT (ObjectLocker) ;
1.667 + assert(thread == JavaThread::current(), "Can only be called on current thread");
1.668 + oop obj = h_obj();
1.669
1.670 - ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
1.671 + markOop mark = ReadStableMark (obj) ;
1.672 +
1.673 + // Uncontended case, header points to stack
1.674 + if (mark->has_locker()) {
1.675 + return thread->is_lock_owned((address)mark->locker());
1.676 + }
1.677 + // Contended case, header points to ObjectMonitor (tagged pointer)
1.678 + if (mark->has_monitor()) {
1.679 + ObjectMonitor* monitor = mark->monitor();
1.680 + return monitor->is_entered(thread) != 0 ;
1.681 + }
1.682 + // Unlocked case, header in place
1.683 + assert(mark->is_neutral(), "sanity check");
1.684 + return false;
1.685 +}
1.686 +
1.687 +// Be aware of this method could revoke bias of the lock object.
1.688 +// This method querys the ownership of the lock handle specified by 'h_obj'.
1.689 +// If the current thread owns the lock, it returns owner_self. If no
1.690 +// thread owns the lock, it returns owner_none. Otherwise, it will return
1.691 +// ower_other.
1.692 +ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
1.693 +(JavaThread *self, Handle h_obj) {
1.694 + // The caller must beware this method can revoke bias, and
1.695 + // revocation can result in a safepoint.
1.696 + assert (!SafepointSynchronize::is_at_safepoint(), "invariant") ;
1.697 + assert (self->thread_state() != _thread_blocked , "invariant") ;
1.698 +
1.699 + // Possible mark states: neutral, biased, stack-locked, inflated
1.700 +
1.701 + if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) {
1.702 + // CASE: biased
1.703 + BiasedLocking::revoke_and_rebias(h_obj, false, self);
1.704 + assert(!h_obj->mark()->has_bias_pattern(),
1.705 + "biases should be revoked by now");
1.706 + }
1.707 +
1.708 + assert(self == JavaThread::current(), "Can only be called on current thread");
1.709 + oop obj = h_obj();
1.710 + markOop mark = ReadStableMark (obj) ;
1.711 +
1.712 + // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
1.713 + if (mark->has_locker()) {
1.714 + return self->is_lock_owned((address)mark->locker()) ?
1.715 + owner_self : owner_other;
1.716 + }
1.717 +
1.718 + // CASE: inflated. Mark (tagged pointer) points to an objectMonitor.
1.719 + // The Object:ObjectMonitor relationship is stable as long as we're
1.720 + // not at a safepoint.
1.721 + if (mark->has_monitor()) {
1.722 + void * owner = mark->monitor()->_owner ;
1.723 + if (owner == NULL) return owner_none ;
1.724 + return (owner == self ||
1.725 + self->is_lock_owned((address)owner)) ? owner_self : owner_other;
1.726 + }
1.727 +
1.728 + // CASE: neutral
1.729 + assert(mark->is_neutral(), "sanity check");
1.730 + return owner_none ; // it's unlocked
1.731 +}
1.732 +
1.733 +// FIXME: jvmti should call this
1.734 +JavaThread* ObjectSynchronizer::get_lock_owner(Handle h_obj, bool doLock) {
1.735 + if (UseBiasedLocking) {
1.736 + if (SafepointSynchronize::is_at_safepoint()) {
1.737 + BiasedLocking::revoke_at_safepoint(h_obj);
1.738 + } else {
1.739 + BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current());
1.740 + }
1.741 + assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
1.742 + }
1.743 +
1.744 + oop obj = h_obj();
1.745 + address owner = NULL;
1.746 +
1.747 + markOop mark = ReadStableMark (obj) ;
1.748 +
1.749 + // Uncontended case, header points to stack
1.750 + if (mark->has_locker()) {
1.751 + owner = (address) mark->locker();
1.752 + }
1.753 +
1.754 + // Contended case, header points to ObjectMonitor (tagged pointer)
1.755 + if (mark->has_monitor()) {
1.756 + ObjectMonitor* monitor = mark->monitor();
1.757 + assert(monitor != NULL, "monitor should be non-null");
1.758 + owner = (address) monitor->owner();
1.759 + }
1.760 +
1.761 + if (owner != NULL) {
1.762 + return Threads::owning_thread_from_monitor_owner(owner, doLock);
1.763 + }
1.764 +
1.765 + // Unlocked case, header in place
1.766 + // Cannot have assertion since this object may have been
1.767 + // locked by another thread when reaching here.
1.768 + // assert(mark->is_neutral(), "sanity check");
1.769 +
1.770 + return NULL;
1.771 +}
1.772 +// Visitors ...
1.773 +
1.774 +void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
1.775 + ObjectMonitor* block = gBlockList;
1.776 + ObjectMonitor* mid;
1.777 + while (block) {
1.778 + assert(block->object() == CHAINMARKER, "must be a block header");
1.779 + for (int i = _BLOCKSIZE - 1; i > 0; i--) {
1.780 + mid = block + i;
1.781 + oop object = (oop) mid->object();
1.782 + if (object != NULL) {
1.783 + closure->do_monitor(mid);
1.784 + }
1.785 + }
1.786 + block = (ObjectMonitor*) block->FreeNext;
1.787 }
1.788 }
1.789
1.790 -ObjectLocker::~ObjectLocker() {
1.791 - if (_dolock) {
1.792 - ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
1.793 - }
1.794 +// Get the next block in the block list.
1.795 +static inline ObjectMonitor* next(ObjectMonitor* block) {
1.796 + assert(block->object() == CHAINMARKER, "must be a block header");
1.797 + block = block->FreeNext ;
1.798 + assert(block == NULL || block->object() == CHAINMARKER, "must be a block header");
1.799 + return block;
1.800 }
1.801
1.802 -// -----------------------------------------------------------------------------
1.803
1.804 -
1.805 -PerfCounter * ObjectSynchronizer::_sync_Inflations = NULL ;
1.806 -PerfCounter * ObjectSynchronizer::_sync_Deflations = NULL ;
1.807 -PerfCounter * ObjectSynchronizer::_sync_ContendedLockAttempts = NULL ;
1.808 -PerfCounter * ObjectSynchronizer::_sync_FutileWakeups = NULL ;
1.809 -PerfCounter * ObjectSynchronizer::_sync_Parks = NULL ;
1.810 -PerfCounter * ObjectSynchronizer::_sync_EmptyNotifications = NULL ;
1.811 -PerfCounter * ObjectSynchronizer::_sync_Notifications = NULL ;
1.812 -PerfCounter * ObjectSynchronizer::_sync_PrivateA = NULL ;
1.813 -PerfCounter * ObjectSynchronizer::_sync_PrivateB = NULL ;
1.814 -PerfCounter * ObjectSynchronizer::_sync_SlowExit = NULL ;
1.815 -PerfCounter * ObjectSynchronizer::_sync_SlowEnter = NULL ;
1.816 -PerfCounter * ObjectSynchronizer::_sync_SlowNotify = NULL ;
1.817 -PerfCounter * ObjectSynchronizer::_sync_SlowNotifyAll = NULL ;
1.818 -PerfCounter * ObjectSynchronizer::_sync_FailedSpins = NULL ;
1.819 -PerfCounter * ObjectSynchronizer::_sync_SuccessfulSpins = NULL ;
1.820 -PerfCounter * ObjectSynchronizer::_sync_MonInCirculation = NULL ;
1.821 -PerfCounter * ObjectSynchronizer::_sync_MonScavenged = NULL ;
1.822 -PerfLongVariable * ObjectSynchronizer::_sync_MonExtant = NULL ;
1.823 -
1.824 -// One-shot global initialization for the sync subsystem.
1.825 -// We could also defer initialization and initialize on-demand
1.826 -// the first time we call inflate(). Initialization would
1.827 -// be protected - like so many things - by the MonitorCache_lock.
1.828 -
1.829 -void ObjectSynchronizer::Initialize () {
1.830 - static int InitializationCompleted = 0 ;
1.831 - assert (InitializationCompleted == 0, "invariant") ;
1.832 - InitializationCompleted = 1 ;
1.833 - if (UsePerfData) {
1.834 - EXCEPTION_MARK ;
1.835 - #define NEWPERFCOUNTER(n) {n = PerfDataManager::create_counter(SUN_RT, #n, PerfData::U_Events,CHECK); }
1.836 - #define NEWPERFVARIABLE(n) {n = PerfDataManager::create_variable(SUN_RT, #n, PerfData::U_Events,CHECK); }
1.837 - NEWPERFCOUNTER(_sync_Inflations) ;
1.838 - NEWPERFCOUNTER(_sync_Deflations) ;
1.839 - NEWPERFCOUNTER(_sync_ContendedLockAttempts) ;
1.840 - NEWPERFCOUNTER(_sync_FutileWakeups) ;
1.841 - NEWPERFCOUNTER(_sync_Parks) ;
1.842 - NEWPERFCOUNTER(_sync_EmptyNotifications) ;
1.843 - NEWPERFCOUNTER(_sync_Notifications) ;
1.844 - NEWPERFCOUNTER(_sync_SlowEnter) ;
1.845 - NEWPERFCOUNTER(_sync_SlowExit) ;
1.846 - NEWPERFCOUNTER(_sync_SlowNotify) ;
1.847 - NEWPERFCOUNTER(_sync_SlowNotifyAll) ;
1.848 - NEWPERFCOUNTER(_sync_FailedSpins) ;
1.849 - NEWPERFCOUNTER(_sync_SuccessfulSpins) ;
1.850 - NEWPERFCOUNTER(_sync_PrivateA) ;
1.851 - NEWPERFCOUNTER(_sync_PrivateB) ;
1.852 - NEWPERFCOUNTER(_sync_MonInCirculation) ;
1.853 - NEWPERFCOUNTER(_sync_MonScavenged) ;
1.854 - NEWPERFVARIABLE(_sync_MonExtant) ;
1.855 - #undef NEWPERFCOUNTER
1.856 - }
1.857 -}
1.858 -
1.859 -// Compile-time asserts
1.860 -// When possible, it's better to catch errors deterministically at
1.861 -// compile-time than at runtime. The down-side to using compile-time
1.862 -// asserts is that error message -- often something about negative array
1.863 -// indices -- is opaque.
1.864 -
1.865 -#define CTASSERT(x) { int tag[1-(2*!(x))]; printf ("Tag @" INTPTR_FORMAT "\n", (intptr_t)tag); }
1.866 -
1.867 -void ObjectMonitor::ctAsserts() {
1.868 - CTASSERT(offset_of (ObjectMonitor, _header) == 0);
1.869 -}
1.870 -
1.871 -static int Adjust (volatile int * adr, int dx) {
1.872 - int v ;
1.873 - for (v = *adr ; Atomic::cmpxchg (v + dx, adr, v) != v; v = *adr) ;
1.874 - return v ;
1.875 -}
1.876 -
1.877 -// Ad-hoc mutual exclusion primitives: SpinLock and Mux
1.878 -//
1.879 -// We employ SpinLocks _only for low-contention, fixed-length
1.880 -// short-duration critical sections where we're concerned
1.881 -// about native mutex_t or HotSpot Mutex:: latency.
1.882 -// The mux construct provides a spin-then-block mutual exclusion
1.883 -// mechanism.
1.884 -//
1.885 -// Testing has shown that contention on the ListLock guarding gFreeList
1.886 -// is common. If we implement ListLock as a simple SpinLock it's common
1.887 -// for the JVM to devolve to yielding with little progress. This is true
1.888 -// despite the fact that the critical sections protected by ListLock are
1.889 -// extremely short.
1.890 -//
1.891 -// TODO-FIXME: ListLock should be of type SpinLock.
1.892 -// We should make this a 1st-class type, integrated into the lock
1.893 -// hierarchy as leaf-locks. Critically, the SpinLock structure
1.894 -// should have sufficient padding to avoid false-sharing and excessive
1.895 -// cache-coherency traffic.
1.896 -
1.897 -
1.898 -typedef volatile int SpinLockT ;
1.899 -
1.900 -void Thread::SpinAcquire (volatile int * adr, const char * LockName) {
1.901 - if (Atomic::cmpxchg (1, adr, 0) == 0) {
1.902 - return ; // normal fast-path return
1.903 - }
1.904 -
1.905 - // Slow-path : We've encountered contention -- Spin/Yield/Block strategy.
1.906 - TEVENT (SpinAcquire - ctx) ;
1.907 - int ctr = 0 ;
1.908 - int Yields = 0 ;
1.909 - for (;;) {
1.910 - while (*adr != 0) {
1.911 - ++ctr ;
1.912 - if ((ctr & 0xFFF) == 0 || !os::is_MP()) {
1.913 - if (Yields > 5) {
1.914 - // Consider using a simple NakedSleep() instead.
1.915 - // Then SpinAcquire could be called by non-JVM threads
1.916 - Thread::current()->_ParkEvent->park(1) ;
1.917 - } else {
1.918 - os::NakedYield() ;
1.919 - ++Yields ;
1.920 - }
1.921 - } else {
1.922 - SpinPause() ;
1.923 - }
1.924 - }
1.925 - if (Atomic::cmpxchg (1, adr, 0) == 0) return ;
1.926 - }
1.927 -}
1.928 -
1.929 -void Thread::SpinRelease (volatile int * adr) {
1.930 - assert (*adr != 0, "invariant") ;
1.931 - OrderAccess::fence() ; // guarantee at least release consistency.
1.932 - // Roach-motel semantics.
1.933 - // It's safe if subsequent LDs and STs float "up" into the critical section,
1.934 - // but prior LDs and STs within the critical section can't be allowed
1.935 - // to reorder or float past the ST that releases the lock.
1.936 - *adr = 0 ;
1.937 -}
1.938 -
1.939 -// muxAcquire and muxRelease:
1.940 -//
1.941 -// * muxAcquire and muxRelease support a single-word lock-word construct.
1.942 -// The LSB of the word is set IFF the lock is held.
1.943 -// The remainder of the word points to the head of a singly-linked list
1.944 -// of threads blocked on the lock.
1.945 -//
1.946 -// * The current implementation of muxAcquire-muxRelease uses its own
1.947 -// dedicated Thread._MuxEvent instance. If we're interested in
1.948 -// minimizing the peak number of extant ParkEvent instances then
1.949 -// we could eliminate _MuxEvent and "borrow" _ParkEvent as long
1.950 -// as certain invariants were satisfied. Specifically, care would need
1.951 -// to be taken with regards to consuming unpark() "permits".
1.952 -// A safe rule of thumb is that a thread would never call muxAcquire()
1.953 -// if it's enqueued (cxq, EntryList, WaitList, etc) and will subsequently
1.954 -// park(). Otherwise the _ParkEvent park() operation in muxAcquire() could
1.955 -// consume an unpark() permit intended for monitorenter, for instance.
1.956 -// One way around this would be to widen the restricted-range semaphore
1.957 -// implemented in park(). Another alternative would be to provide
1.958 -// multiple instances of the PlatformEvent() for each thread. One
1.959 -// instance would be dedicated to muxAcquire-muxRelease, for instance.
1.960 -//
1.961 -// * Usage:
1.962 -// -- Only as leaf locks
1.963 -// -- for short-term locking only as muxAcquire does not perform
1.964 -// thread state transitions.
1.965 -//
1.966 -// Alternatives:
1.967 -// * We could implement muxAcquire and muxRelease with MCS or CLH locks
1.968 -// but with parking or spin-then-park instead of pure spinning.
1.969 -// * Use Taura-Oyama-Yonenzawa locks.
1.970 -// * It's possible to construct a 1-0 lock if we encode the lockword as
1.971 -// (List,LockByte). Acquire will CAS the full lockword while Release
1.972 -// will STB 0 into the LockByte. The 1-0 scheme admits stranding, so
1.973 -// acquiring threads use timers (ParkTimed) to detect and recover from
1.974 -// the stranding window. Thread/Node structures must be aligned on 256-byte
1.975 -// boundaries by using placement-new.
1.976 -// * Augment MCS with advisory back-link fields maintained with CAS().
1.977 -// Pictorially: LockWord -> T1 <-> T2 <-> T3 <-> ... <-> Tn <-> Owner.
1.978 -// The validity of the backlinks must be ratified before we trust the value.
1.979 -// If the backlinks are invalid the exiting thread must back-track through the
1.980 -// the forward links, which are always trustworthy.
1.981 -// * Add a successor indication. The LockWord is currently encoded as
1.982 -// (List, LOCKBIT:1). We could also add a SUCCBIT or an explicit _succ variable
1.983 -// to provide the usual futile-wakeup optimization.
1.984 -// See RTStt for details.
1.985 -// * Consider schedctl.sc_nopreempt to cover the critical section.
1.986 -//
1.987 -
1.988 -
1.989 -typedef volatile intptr_t MutexT ; // Mux Lock-word
1.990 -enum MuxBits { LOCKBIT = 1 } ;
1.991 -
1.992 -void Thread::muxAcquire (volatile intptr_t * Lock, const char * LockName) {
1.993 - intptr_t w = Atomic::cmpxchg_ptr (LOCKBIT, Lock, 0) ;
1.994 - if (w == 0) return ;
1.995 - if ((w & LOCKBIT) == 0 && Atomic::cmpxchg_ptr (w|LOCKBIT, Lock, w) == w) {
1.996 - return ;
1.997 - }
1.998 -
1.999 - TEVENT (muxAcquire - Contention) ;
1.1000 - ParkEvent * const Self = Thread::current()->_MuxEvent ;
1.1001 - assert ((intptr_t(Self) & LOCKBIT) == 0, "invariant") ;
1.1002 - for (;;) {
1.1003 - int its = (os::is_MP() ? 100 : 0) + 1 ;
1.1004 -
1.1005 - // Optional spin phase: spin-then-park strategy
1.1006 - while (--its >= 0) {
1.1007 - w = *Lock ;
1.1008 - if ((w & LOCKBIT) == 0 && Atomic::cmpxchg_ptr (w|LOCKBIT, Lock, w) == w) {
1.1009 - return ;
1.1010 - }
1.1011 - }
1.1012 -
1.1013 - Self->reset() ;
1.1014 - Self->OnList = intptr_t(Lock) ;
1.1015 - // The following fence() isn't _strictly necessary as the subsequent
1.1016 - // CAS() both serializes execution and ratifies the fetched *Lock value.
1.1017 - OrderAccess::fence();
1.1018 - for (;;) {
1.1019 - w = *Lock ;
1.1020 - if ((w & LOCKBIT) == 0) {
1.1021 - if (Atomic::cmpxchg_ptr (w|LOCKBIT, Lock, w) == w) {
1.1022 - Self->OnList = 0 ; // hygiene - allows stronger asserts
1.1023 - return ;
1.1024 - }
1.1025 - continue ; // Interference -- *Lock changed -- Just retry
1.1026 - }
1.1027 - assert (w & LOCKBIT, "invariant") ;
1.1028 - Self->ListNext = (ParkEvent *) (w & ~LOCKBIT );
1.1029 - if (Atomic::cmpxchg_ptr (intptr_t(Self)|LOCKBIT, Lock, w) == w) break ;
1.1030 - }
1.1031 -
1.1032 - while (Self->OnList != 0) {
1.1033 - Self->park() ;
1.1034 - }
1.1035 - }
1.1036 -}
1.1037 -
1.1038 -void Thread::muxAcquireW (volatile intptr_t * Lock, ParkEvent * ev) {
1.1039 - intptr_t w = Atomic::cmpxchg_ptr (LOCKBIT, Lock, 0) ;
1.1040 - if (w == 0) return ;
1.1041 - if ((w & LOCKBIT) == 0 && Atomic::cmpxchg_ptr (w|LOCKBIT, Lock, w) == w) {
1.1042 - return ;
1.1043 - }
1.1044 -
1.1045 - TEVENT (muxAcquire - Contention) ;
1.1046 - ParkEvent * ReleaseAfter = NULL ;
1.1047 - if (ev == NULL) {
1.1048 - ev = ReleaseAfter = ParkEvent::Allocate (NULL) ;
1.1049 - }
1.1050 - assert ((intptr_t(ev) & LOCKBIT) == 0, "invariant") ;
1.1051 - for (;;) {
1.1052 - guarantee (ev->OnList == 0, "invariant") ;
1.1053 - int its = (os::is_MP() ? 100 : 0) + 1 ;
1.1054 -
1.1055 - // Optional spin phase: spin-then-park strategy
1.1056 - while (--its >= 0) {
1.1057 - w = *Lock ;
1.1058 - if ((w & LOCKBIT) == 0 && Atomic::cmpxchg_ptr (w|LOCKBIT, Lock, w) == w) {
1.1059 - if (ReleaseAfter != NULL) {
1.1060 - ParkEvent::Release (ReleaseAfter) ;
1.1061 - }
1.1062 - return ;
1.1063 +void ObjectSynchronizer::oops_do(OopClosure* f) {
1.1064 + assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1.1065 + for (ObjectMonitor* block = gBlockList; block != NULL; block = next(block)) {
1.1066 + assert(block->object() == CHAINMARKER, "must be a block header");
1.1067 + for (int i = 1; i < _BLOCKSIZE; i++) {
1.1068 + ObjectMonitor* mid = &block[i];
1.1069 + if (mid->object() != NULL) {
1.1070 + f->do_oop((oop*)mid->object_addr());
1.1071 }
1.1072 }
1.1073 -
1.1074 - ev->reset() ;
1.1075 - ev->OnList = intptr_t(Lock) ;
1.1076 - // The following fence() isn't _strictly necessary as the subsequent
1.1077 - // CAS() both serializes execution and ratifies the fetched *Lock value.
1.1078 - OrderAccess::fence();
1.1079 - for (;;) {
1.1080 - w = *Lock ;
1.1081 - if ((w & LOCKBIT) == 0) {
1.1082 - if (Atomic::cmpxchg_ptr (w|LOCKBIT, Lock, w) == w) {
1.1083 - ev->OnList = 0 ;
1.1084 - // We call ::Release while holding the outer lock, thus
1.1085 - // artificially lengthening the critical section.
1.1086 - // Consider deferring the ::Release() until the subsequent unlock(),
1.1087 - // after we've dropped the outer lock.
1.1088 - if (ReleaseAfter != NULL) {
1.1089 - ParkEvent::Release (ReleaseAfter) ;
1.1090 - }
1.1091 - return ;
1.1092 - }
1.1093 - continue ; // Interference -- *Lock changed -- Just retry
1.1094 - }
1.1095 - assert (w & LOCKBIT, "invariant") ;
1.1096 - ev->ListNext = (ParkEvent *) (w & ~LOCKBIT );
1.1097 - if (Atomic::cmpxchg_ptr (intptr_t(ev)|LOCKBIT, Lock, w) == w) break ;
1.1098 - }
1.1099 -
1.1100 - while (ev->OnList != 0) {
1.1101 - ev->park() ;
1.1102 - }
1.1103 }
1.1104 }
1.1105
1.1106 -// Release() must extract a successor from the list and then wake that thread.
1.1107 -// It can "pop" the front of the list or use a detach-modify-reattach (DMR) scheme
1.1108 -// similar to that used by ParkEvent::Allocate() and ::Release(). DMR-based
1.1109 -// Release() would :
1.1110 -// (A) CAS() or swap() null to *Lock, releasing the lock and detaching the list.
1.1111 -// (B) Extract a successor from the private list "in-hand"
1.1112 -// (C) attempt to CAS() the residual back into *Lock over null.
1.1113 -// If there were any newly arrived threads and the CAS() would fail.
1.1114 -// In that case Release() would detach the RATs, re-merge the list in-hand
1.1115 -// with the RATs and repeat as needed. Alternately, Release() might
1.1116 -// detach and extract a successor, but then pass the residual list to the wakee.
1.1117 -// The wakee would be responsible for reattaching and remerging before it
1.1118 -// competed for the lock.
1.1119 -//
1.1120 -// Both "pop" and DMR are immune from ABA corruption -- there can be
1.1121 -// multiple concurrent pushers, but only one popper or detacher.
1.1122 -// This implementation pops from the head of the list. This is unfair,
1.1123 -// but tends to provide excellent throughput as hot threads remain hot.
1.1124 -// (We wake recently run threads first).
1.1125
1.1126 -void Thread::muxRelease (volatile intptr_t * Lock) {
1.1127 - for (;;) {
1.1128 - const intptr_t w = Atomic::cmpxchg_ptr (0, Lock, LOCKBIT) ;
1.1129 - assert (w & LOCKBIT, "invariant") ;
1.1130 - if (w == LOCKBIT) return ;
1.1131 - ParkEvent * List = (ParkEvent *) (w & ~LOCKBIT) ;
1.1132 - assert (List != NULL, "invariant") ;
1.1133 - assert (List->OnList == intptr_t(Lock), "invariant") ;
1.1134 - ParkEvent * nxt = List->ListNext ;
1.1135 -
1.1136 - // The following CAS() releases the lock and pops the head element.
1.1137 - if (Atomic::cmpxchg_ptr (intptr_t(nxt), Lock, w) != w) {
1.1138 - continue ;
1.1139 - }
1.1140 - List->OnList = 0 ;
1.1141 - OrderAccess::fence() ;
1.1142 - List->unpark () ;
1.1143 - return ;
1.1144 - }
1.1145 -}
1.1146 -
1.1147 +// -----------------------------------------------------------------------------
1.1148 // ObjectMonitor Lifecycle
1.1149 // -----------------------
1.1150 // Inflation unlinks monitors from the global gFreeList and
1.1151 @@ -718,41 +829,7 @@
1.1152 // -- assigned to an object. The object is inflated and the mark refers
1.1153 // to the objectmonitor.
1.1154 //
1.1155 -// TODO-FIXME:
1.1156 -//
1.1157 -// * We currently protect the gFreeList with a simple lock.
1.1158 -// An alternate lock-free scheme would be to pop elements from the gFreeList
1.1159 -// with CAS. This would be safe from ABA corruption as long we only
1.1160 -// recycled previously appearing elements onto the list in deflate_idle_monitors()
1.1161 -// at STW-time. Completely new elements could always be pushed onto the gFreeList
1.1162 -// with CAS. Elements that appeared previously on the list could only
1.1163 -// be installed at STW-time.
1.1164 -//
1.1165 -// * For efficiency and to help reduce the store-before-CAS penalty
1.1166 -// the objectmonitors on gFreeList or local free lists should be ready to install
1.1167 -// with the exception of _header and _object. _object can be set after inflation.
1.1168 -// In particular, keep all objectMonitors on a thread's private list in ready-to-install
1.1169 -// state with m.Owner set properly.
1.1170 -//
1.1171 -// * We could all diffuse contention by using multiple global (FreeList, Lock)
1.1172 -// pairs -- threads could use trylock() and a cyclic-scan strategy to search for
1.1173 -// an unlocked free list.
1.1174 -//
1.1175 -// * Add lifecycle tags and assert()s.
1.1176 -//
1.1177 -// * Be more consistent about when we clear an objectmonitor's fields:
1.1178 -// A. After extracting the objectmonitor from a free list.
1.1179 -// B. After adding an objectmonitor to a free list.
1.1180 -//
1.1181
1.1182 -ObjectMonitor * ObjectSynchronizer::gBlockList = NULL ;
1.1183 -ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL ;
1.1184 -ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL ;
1.1185 -int ObjectSynchronizer::gOmInUseCount = 0;
1.1186 -static volatile intptr_t ListLock = 0 ; // protects global monitor free-list cache
1.1187 -static volatile int MonitorFreeCount = 0 ; // # on gFreeList
1.1188 -static volatile int MonitorPopulation = 0 ; // # Extant -- in circulation
1.1189 -#define CHAINMARKER ((oop)-1)
1.1190
1.1191 // Constraining monitor pool growth via MonitorBound ...
1.1192 //
1.1193 @@ -768,41 +845,8 @@
1.1194 // we'll incur more safepoints, which are harmful to performance.
1.1195 // See also: GuaranteedSafepointInterval
1.1196 //
1.1197 -// As noted elsewhere, the correct long-term solution is to deflate at
1.1198 -// monitorexit-time, in which case the number of inflated objects is bounded
1.1199 -// by the number of threads. That policy obviates the need for scavenging at
1.1200 -// STW safepoint time. As an aside, scavenging can be time-consuming when the
1.1201 -// # of extant monitors is large. Unfortunately there's a day-1 assumption baked
1.1202 -// into much HotSpot code that the object::monitor relationship, once established
1.1203 -// or observed, will remain stable except over potential safepoints.
1.1204 -//
1.1205 -// We can use either a blocking synchronous VM operation or an async VM operation.
1.1206 -// -- If we use a blocking VM operation :
1.1207 -// Calls to ScavengeCheck() should be inserted only into 'safe' locations in paths
1.1208 -// that lead to ::inflate() or ::omAlloc().
1.1209 -// Even though the safepoint will not directly induce GC, a GC might
1.1210 -// piggyback on the safepoint operation, so the caller should hold no naked oops.
1.1211 -// Furthermore, monitor::object relationships are NOT necessarily stable over this call
1.1212 -// unless the caller has made provisions to "pin" the object to the monitor, say
1.1213 -// by incrementing the monitor's _count field.
1.1214 -// -- If we use a non-blocking asynchronous VM operation :
1.1215 -// the constraints above don't apply. The safepoint will fire in the future
1.1216 -// at a more convenient time. On the other hand the latency between posting and
1.1217 -// running the safepoint introduces or admits "slop" or laxity during which the
1.1218 -// monitor population can climb further above the threshold. The monitor population,
1.1219 -// however, tends to converge asymptotically over time to a count that's slightly
1.1220 -// above the target value specified by MonitorBound. That is, we avoid unbounded
1.1221 -// growth, albeit with some imprecision.
1.1222 -//
1.1223 // The current implementation uses asynchronous VM operations.
1.1224 //
1.1225 -// Ideally we'd check if (MonitorPopulation > MonitorBound) in omAlloc()
1.1226 -// immediately before trying to grow the global list via allocation.
1.1227 -// If the predicate was true then we'd induce a synchronous safepoint, wait
1.1228 -// for the safepoint to complete, and then again to allocate from the global
1.1229 -// free list. This approach is much simpler and precise, admitting no "slop".
1.1230 -// Unfortunately we can't safely safepoint in the midst of omAlloc(), so
1.1231 -// instead we use asynchronous safepoints.
1.1232
1.1233 static void InduceScavenge (Thread * Self, const char * Whence) {
1.1234 // Induce STW safepoint to trim monitors
1.1235 @@ -812,7 +856,7 @@
1.1236 // TODO: assert thread state is reasonable
1.1237
1.1238 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
1.1239 - if (Knob_Verbose) {
1.1240 + if (ObjectMonitor::Knob_Verbose) {
1.1241 ::printf ("Monitor scavenge - Induced STW @%s (%d)\n", Whence, ForceMonitorScavenge) ;
1.1242 ::fflush(stdout) ;
1.1243 }
1.1244 @@ -822,7 +866,7 @@
1.1245 // The VMThread will delete the op when completed.
1.1246 VMThread::execute (new VM_ForceAsyncSafepoint()) ;
1.1247
1.1248 - if (Knob_Verbose) {
1.1249 + if (ObjectMonitor::Knob_Verbose) {
1.1250 ::printf ("Monitor scavenge - STW posted @%s (%d)\n", Whence, ForceMonitorScavenge) ;
1.1251 ::fflush(stdout) ;
1.1252 }
1.1253 @@ -844,7 +888,6 @@
1.1254 assert(freetally == Self->omFreeCount, "free count off");
1.1255 }
1.1256 */
1.1257 -
1.1258 ObjectMonitor * ATTR ObjectSynchronizer::omAlloc (Thread * Self) {
1.1259 // A large MAXPRIVATE value reduces both list lock contention
1.1260 // and list coherency traffic, but also tends to increase the
1.1261 @@ -974,12 +1017,6 @@
1.1262 // attempt failed. This doesn't allow unbounded #s of monitors to
1.1263 // accumulate on a thread's free list.
1.1264 //
1.1265 -// In the future the usage of omRelease() might change and monitors
1.1266 -// could migrate between free lists. In that case to avoid excessive
1.1267 -// accumulation we could limit omCount to (omProvision*2), otherwise return
1.1268 -// the objectMonitor to the global list. We should drain (return) in reasonable chunks.
1.1269 -// That is, *not* one-at-a-time.
1.1270 -
1.1271
1.1272 void ObjectSynchronizer::omRelease (Thread * Self, ObjectMonitor * m, bool fromPerThreadAlloc) {
1.1273 guarantee (m->object() == NULL, "invariant") ;
1.1274 @@ -1082,15 +1119,6 @@
1.1275 TEVENT (omFlush) ;
1.1276 }
1.1277
1.1278 -
1.1279 -// Get the next block in the block list.
1.1280 -static inline ObjectMonitor* next(ObjectMonitor* block) {
1.1281 - assert(block->object() == CHAINMARKER, "must be a block header");
1.1282 - block = block->FreeNext ;
1.1283 - assert(block == NULL || block->object() == CHAINMARKER, "must be a block header");
1.1284 - return block;
1.1285 -}
1.1286 -
1.1287 // Fast path code shared by multiple functions
1.1288 ObjectMonitor* ObjectSynchronizer::inflate_helper(oop obj) {
1.1289 markOop mark = obj->mark();
1.1290 @@ -1102,79 +1130,10 @@
1.1291 return ObjectSynchronizer::inflate(Thread::current(), obj);
1.1292 }
1.1293
1.1294 +
1.1295 // Note that we could encounter some performance loss through false-sharing as
1.1296 // multiple locks occupy the same $ line. Padding might be appropriate.
1.1297
1.1298 -#define NINFLATIONLOCKS 256
1.1299 -static volatile intptr_t InflationLocks [NINFLATIONLOCKS] ;
1.1300 -
1.1301 -static markOop ReadStableMark (oop obj) {
1.1302 - markOop mark = obj->mark() ;
1.1303 - if (!mark->is_being_inflated()) {
1.1304 - return mark ; // normal fast-path return
1.1305 - }
1.1306 -
1.1307 - int its = 0 ;
1.1308 - for (;;) {
1.1309 - markOop mark = obj->mark() ;
1.1310 - if (!mark->is_being_inflated()) {
1.1311 - return mark ; // normal fast-path return
1.1312 - }
1.1313 -
1.1314 - // The object is being inflated by some other thread.
1.1315 - // The caller of ReadStableMark() must wait for inflation to complete.
1.1316 - // Avoid live-lock
1.1317 - // TODO: consider calling SafepointSynchronize::do_call_back() while
1.1318 - // spinning to see if there's a safepoint pending. If so, immediately
1.1319 - // yielding or blocking would be appropriate. Avoid spinning while
1.1320 - // there is a safepoint pending.
1.1321 - // TODO: add inflation contention performance counters.
1.1322 - // TODO: restrict the aggregate number of spinners.
1.1323 -
1.1324 - ++its ;
1.1325 - if (its > 10000 || !os::is_MP()) {
1.1326 - if (its & 1) {
1.1327 - os::NakedYield() ;
1.1328 - TEVENT (Inflate: INFLATING - yield) ;
1.1329 - } else {
1.1330 - // Note that the following code attenuates the livelock problem but is not
1.1331 - // a complete remedy. A more complete solution would require that the inflating
1.1332 - // thread hold the associated inflation lock. The following code simply restricts
1.1333 - // the number of spinners to at most one. We'll have N-2 threads blocked
1.1334 - // on the inflationlock, 1 thread holding the inflation lock and using
1.1335 - // a yield/park strategy, and 1 thread in the midst of inflation.
1.1336 - // A more refined approach would be to change the encoding of INFLATING
1.1337 - // to allow encapsulation of a native thread pointer. Threads waiting for
1.1338 - // inflation to complete would use CAS to push themselves onto a singly linked
1.1339 - // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
1.1340 - // and calling park(). When inflation was complete the thread that accomplished inflation
1.1341 - // would detach the list and set the markword to inflated with a single CAS and
1.1342 - // then for each thread on the list, set the flag and unpark() the thread.
1.1343 - // This is conceptually similar to muxAcquire-muxRelease, except that muxRelease
1.1344 - // wakes at most one thread whereas we need to wake the entire list.
1.1345 - int ix = (intptr_t(obj) >> 5) & (NINFLATIONLOCKS-1) ;
1.1346 - int YieldThenBlock = 0 ;
1.1347 - assert (ix >= 0 && ix < NINFLATIONLOCKS, "invariant") ;
1.1348 - assert ((NINFLATIONLOCKS & (NINFLATIONLOCKS-1)) == 0, "invariant") ;
1.1349 - Thread::muxAcquire (InflationLocks + ix, "InflationLock") ;
1.1350 - while (obj->mark() == markOopDesc::INFLATING()) {
1.1351 - // Beware: NakedYield() is advisory and has almost no effect on some platforms
1.1352 - // so we periodically call Self->_ParkEvent->park(1).
1.1353 - // We use a mixed spin/yield/block mechanism.
1.1354 - if ((YieldThenBlock++) >= 16) {
1.1355 - Thread::current()->_ParkEvent->park(1) ;
1.1356 - } else {
1.1357 - os::NakedYield() ;
1.1358 - }
1.1359 - }
1.1360 - Thread::muxRelease (InflationLocks + ix ) ;
1.1361 - TEVENT (Inflate: INFLATING - yield/park) ;
1.1362 - }
1.1363 - } else {
1.1364 - SpinPause() ; // SMP-polite spinning
1.1365 - }
1.1366 - }
1.1367 -}
1.1368
1.1369 ObjectMonitor * ATTR ObjectSynchronizer::inflate (Thread * Self, oop object) {
1.1370 // Inflate mutates the heap ...
1.1371 @@ -1242,7 +1201,7 @@
1.1372 m->_Responsible = NULL ;
1.1373 m->OwnerIsThread = 0 ;
1.1374 m->_recursions = 0 ;
1.1375 - m->_SpinDuration = Knob_SpinLimit ; // Consider: maintain by type/class
1.1376 + m->_SpinDuration = ObjectMonitor::Knob_SpinLimit ; // Consider: maintain by type/class
1.1377
1.1378 markOop cmp = (markOop) Atomic::cmpxchg_ptr (markOopDesc::INFLATING(), object->mark_addr(), mark) ;
1.1379 if (cmp != mark) {
1.1380 @@ -1302,7 +1261,7 @@
1.1381
1.1382 // Hopefully the performance counters are allocated on distinct cache lines
1.1383 // to avoid false sharing on MP systems ...
1.1384 - if (_sync_Inflations != NULL) _sync_Inflations->inc() ;
1.1385 + if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc() ;
1.1386 TEVENT(Inflate: overwrite stacklock) ;
1.1387 if (TraceMonitorInflation) {
1.1388 if (object->is_instance()) {
1.1389 @@ -1335,7 +1294,7 @@
1.1390 m->OwnerIsThread = 1 ;
1.1391 m->_recursions = 0 ;
1.1392 m->_Responsible = NULL ;
1.1393 - m->_SpinDuration = Knob_SpinLimit ; // consider: keep metastats by type/class
1.1394 + m->_SpinDuration = ObjectMonitor::Knob_SpinLimit ; // consider: keep metastats by type/class
1.1395
1.1396 if (Atomic::cmpxchg_ptr (markOopDesc::encode(m), object->mark_addr(), mark) != mark) {
1.1397 m->set_object (NULL) ;
1.1398 @@ -1352,7 +1311,7 @@
1.1399
1.1400 // Hopefully the performance counters are allocated on distinct
1.1401 // cache lines to avoid false sharing on MP systems ...
1.1402 - if (_sync_Inflations != NULL) _sync_Inflations->inc() ;
1.1403 + if (ObjectMonitor::_sync_Inflations != NULL) ObjectMonitor::_sync_Inflations->inc() ;
1.1404 TEVENT(Inflate: overwrite neutral) ;
1.1405 if (TraceMonitorInflation) {
1.1406 if (object->is_instance()) {
1.1407 @@ -1366,547 +1325,9 @@
1.1408 }
1.1409 }
1.1410
1.1411 +// Note that we could encounter some performance loss through false-sharing as
1.1412 +// multiple locks occupy the same $ line. Padding might be appropriate.
1.1413
1.1414 -// This the fast monitor enter. The interpreter and compiler use
1.1415 -// some assembly copies of this code. Make sure update those code
1.1416 -// if the following function is changed. The implementation is
1.1417 -// extremely sensitive to race condition. Be careful.
1.1418 -
1.1419 -void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock, bool attempt_rebias, TRAPS) {
1.1420 - if (UseBiasedLocking) {
1.1421 - if (!SafepointSynchronize::is_at_safepoint()) {
1.1422 - BiasedLocking::Condition cond = BiasedLocking::revoke_and_rebias(obj, attempt_rebias, THREAD);
1.1423 - if (cond == BiasedLocking::BIAS_REVOKED_AND_REBIASED) {
1.1424 - return;
1.1425 - }
1.1426 - } else {
1.1427 - assert(!attempt_rebias, "can not rebias toward VM thread");
1.1428 - BiasedLocking::revoke_at_safepoint(obj);
1.1429 - }
1.1430 - assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
1.1431 - }
1.1432 -
1.1433 - slow_enter (obj, lock, THREAD) ;
1.1434 -}
1.1435 -
1.1436 -void ObjectSynchronizer::fast_exit(oop object, BasicLock* lock, TRAPS) {
1.1437 - assert(!object->mark()->has_bias_pattern(), "should not see bias pattern here");
1.1438 - // if displaced header is null, the previous enter is recursive enter, no-op
1.1439 - markOop dhw = lock->displaced_header();
1.1440 - markOop mark ;
1.1441 - if (dhw == NULL) {
1.1442 - // Recursive stack-lock.
1.1443 - // Diagnostics -- Could be: stack-locked, inflating, inflated.
1.1444 - mark = object->mark() ;
1.1445 - assert (!mark->is_neutral(), "invariant") ;
1.1446 - if (mark->has_locker() && mark != markOopDesc::INFLATING()) {
1.1447 - assert(THREAD->is_lock_owned((address)mark->locker()), "invariant") ;
1.1448 - }
1.1449 - if (mark->has_monitor()) {
1.1450 - ObjectMonitor * m = mark->monitor() ;
1.1451 - assert(((oop)(m->object()))->mark() == mark, "invariant") ;
1.1452 - assert(m->is_entered(THREAD), "invariant") ;
1.1453 - }
1.1454 - return ;
1.1455 - }
1.1456 -
1.1457 - mark = object->mark() ;
1.1458 -
1.1459 - // If the object is stack-locked by the current thread, try to
1.1460 - // swing the displaced header from the box back to the mark.
1.1461 - if (mark == (markOop) lock) {
1.1462 - assert (dhw->is_neutral(), "invariant") ;
1.1463 - if ((markOop) Atomic::cmpxchg_ptr (dhw, object->mark_addr(), mark) == mark) {
1.1464 - TEVENT (fast_exit: release stacklock) ;
1.1465 - return;
1.1466 - }
1.1467 - }
1.1468 -
1.1469 - ObjectSynchronizer::inflate(THREAD, object)->exit (THREAD) ;
1.1470 -}
1.1471 -
1.1472 -// This routine is used to handle interpreter/compiler slow case
1.1473 -// We don't need to use fast path here, because it must have been
1.1474 -// failed in the interpreter/compiler code.
1.1475 -void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) {
1.1476 - markOop mark = obj->mark();
1.1477 - assert(!mark->has_bias_pattern(), "should not see bias pattern here");
1.1478 -
1.1479 - if (mark->is_neutral()) {
1.1480 - // Anticipate successful CAS -- the ST of the displaced mark must
1.1481 - // be visible <= the ST performed by the CAS.
1.1482 - lock->set_displaced_header(mark);
1.1483 - if (mark == (markOop) Atomic::cmpxchg_ptr(lock, obj()->mark_addr(), mark)) {
1.1484 - TEVENT (slow_enter: release stacklock) ;
1.1485 - return ;
1.1486 - }
1.1487 - // Fall through to inflate() ...
1.1488 - } else
1.1489 - if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
1.1490 - assert(lock != mark->locker(), "must not re-lock the same lock");
1.1491 - assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock");
1.1492 - lock->set_displaced_header(NULL);
1.1493 - return;
1.1494 - }
1.1495 -
1.1496 -#if 0
1.1497 - // The following optimization isn't particularly useful.
1.1498 - if (mark->has_monitor() && mark->monitor()->is_entered(THREAD)) {
1.1499 - lock->set_displaced_header (NULL) ;
1.1500 - return ;
1.1501 - }
1.1502 -#endif
1.1503 -
1.1504 - // The object header will never be displaced to this lock,
1.1505 - // so it does not matter what the value is, except that it
1.1506 - // must be non-zero to avoid looking like a re-entrant lock,
1.1507 - // and must not look locked either.
1.1508 - lock->set_displaced_header(markOopDesc::unused_mark());
1.1509 - ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD);
1.1510 -}
1.1511 -
1.1512 -// This routine is used to handle interpreter/compiler slow case
1.1513 -// We don't need to use fast path here, because it must have
1.1514 -// failed in the interpreter/compiler code. Simply use the heavy
1.1515 -// weight monitor should be ok, unless someone find otherwise.
1.1516 -void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) {
1.1517 - fast_exit (object, lock, THREAD) ;
1.1518 -}
1.1519 -
1.1520 -// NOTE: must use heavy weight monitor to handle jni monitor enter
1.1521 -void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) { // possible entry from jni enter
1.1522 - // the current locking is from JNI instead of Java code
1.1523 - TEVENT (jni_enter) ;
1.1524 - if (UseBiasedLocking) {
1.1525 - BiasedLocking::revoke_and_rebias(obj, false, THREAD);
1.1526 - assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
1.1527 - }
1.1528 - THREAD->set_current_pending_monitor_is_from_java(false);
1.1529 - ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD);
1.1530 - THREAD->set_current_pending_monitor_is_from_java(true);
1.1531 -}
1.1532 -
1.1533 -// NOTE: must use heavy weight monitor to handle jni monitor enter
1.1534 -bool ObjectSynchronizer::jni_try_enter(Handle obj, Thread* THREAD) {
1.1535 - if (UseBiasedLocking) {
1.1536 - BiasedLocking::revoke_and_rebias(obj, false, THREAD);
1.1537 - assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
1.1538 - }
1.1539 -
1.1540 - ObjectMonitor* monitor = ObjectSynchronizer::inflate_helper(obj());
1.1541 - return monitor->try_enter(THREAD);
1.1542 -}
1.1543 -
1.1544 -
1.1545 -// NOTE: must use heavy weight monitor to handle jni monitor exit
1.1546 -void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
1.1547 - TEVENT (jni_exit) ;
1.1548 - if (UseBiasedLocking) {
1.1549 - BiasedLocking::revoke_and_rebias(obj, false, THREAD);
1.1550 - }
1.1551 - assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
1.1552 -
1.1553 - ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj);
1.1554 - // If this thread has locked the object, exit the monitor. Note: can't use
1.1555 - // monitor->check(CHECK); must exit even if an exception is pending.
1.1556 - if (monitor->check(THREAD)) {
1.1557 - monitor->exit(THREAD);
1.1558 - }
1.1559 -}
1.1560 -
1.1561 -// complete_exit()/reenter() are used to wait on a nested lock
1.1562 -// i.e. to give up an outer lock completely and then re-enter
1.1563 -// Used when holding nested locks - lock acquisition order: lock1 then lock2
1.1564 -// 1) complete_exit lock1 - saving recursion count
1.1565 -// 2) wait on lock2
1.1566 -// 3) when notified on lock2, unlock lock2
1.1567 -// 4) reenter lock1 with original recursion count
1.1568 -// 5) lock lock2
1.1569 -// NOTE: must use heavy weight monitor to handle complete_exit/reenter()
1.1570 -intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
1.1571 - TEVENT (complete_exit) ;
1.1572 - if (UseBiasedLocking) {
1.1573 - BiasedLocking::revoke_and_rebias(obj, false, THREAD);
1.1574 - assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
1.1575 - }
1.1576 -
1.1577 - ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
1.1578 -
1.1579 - return monitor->complete_exit(THREAD);
1.1580 -}
1.1581 -
1.1582 -// NOTE: must use heavy weight monitor to handle complete_exit/reenter()
1.1583 -void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) {
1.1584 - TEVENT (reenter) ;
1.1585 - if (UseBiasedLocking) {
1.1586 - BiasedLocking::revoke_and_rebias(obj, false, THREAD);
1.1587 - assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
1.1588 - }
1.1589 -
1.1590 - ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
1.1591 -
1.1592 - monitor->reenter(recursion, THREAD);
1.1593 -}
1.1594 -
1.1595 -// This exists only as a workaround of dtrace bug 6254741
1.1596 -int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
1.1597 - DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
1.1598 - return 0;
1.1599 -}
1.1600 -
1.1601 -// NOTE: must use heavy weight monitor to handle wait()
1.1602 -void ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
1.1603 - if (UseBiasedLocking) {
1.1604 - BiasedLocking::revoke_and_rebias(obj, false, THREAD);
1.1605 - assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
1.1606 - }
1.1607 - if (millis < 0) {
1.1608 - TEVENT (wait - throw IAX) ;
1.1609 - THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
1.1610 - }
1.1611 - ObjectMonitor* monitor = ObjectSynchronizer::inflate(THREAD, obj());
1.1612 - DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
1.1613 - monitor->wait(millis, true, THREAD);
1.1614 -
1.1615 - /* This dummy call is in place to get around dtrace bug 6254741. Once
1.1616 - that's fixed we can uncomment the following line and remove the call */
1.1617 - // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
1.1618 - dtrace_waited_probe(monitor, obj, THREAD);
1.1619 -}
1.1620 -
1.1621 -void ObjectSynchronizer::waitUninterruptibly (Handle obj, jlong millis, TRAPS) {
1.1622 - if (UseBiasedLocking) {
1.1623 - BiasedLocking::revoke_and_rebias(obj, false, THREAD);
1.1624 - assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
1.1625 - }
1.1626 - if (millis < 0) {
1.1627 - TEVENT (wait - throw IAX) ;
1.1628 - THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
1.1629 - }
1.1630 - ObjectSynchronizer::inflate(THREAD, obj()) -> wait(millis, false, THREAD) ;
1.1631 -}
1.1632 -
1.1633 -void ObjectSynchronizer::notify(Handle obj, TRAPS) {
1.1634 - if (UseBiasedLocking) {
1.1635 - BiasedLocking::revoke_and_rebias(obj, false, THREAD);
1.1636 - assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
1.1637 - }
1.1638 -
1.1639 - markOop mark = obj->mark();
1.1640 - if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
1.1641 - return;
1.1642 - }
1.1643 - ObjectSynchronizer::inflate(THREAD, obj())->notify(THREAD);
1.1644 -}
1.1645 -
1.1646 -// NOTE: see comment of notify()
1.1647 -void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
1.1648 - if (UseBiasedLocking) {
1.1649 - BiasedLocking::revoke_and_rebias(obj, false, THREAD);
1.1650 - assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
1.1651 - }
1.1652 -
1.1653 - markOop mark = obj->mark();
1.1654 - if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
1.1655 - return;
1.1656 - }
1.1657 - ObjectSynchronizer::inflate(THREAD, obj())->notifyAll(THREAD);
1.1658 -}
1.1659 -
1.1660 -intptr_t ObjectSynchronizer::FastHashCode (Thread * Self, oop obj) {
1.1661 - if (UseBiasedLocking) {
1.1662 - // NOTE: many places throughout the JVM do not expect a safepoint
1.1663 - // to be taken here, in particular most operations on perm gen
1.1664 - // objects. However, we only ever bias Java instances and all of
1.1665 - // the call sites of identity_hash that might revoke biases have
1.1666 - // been checked to make sure they can handle a safepoint. The
1.1667 - // added check of the bias pattern is to avoid useless calls to
1.1668 - // thread-local storage.
1.1669 - if (obj->mark()->has_bias_pattern()) {
1.1670 - // Box and unbox the raw reference just in case we cause a STW safepoint.
1.1671 - Handle hobj (Self, obj) ;
1.1672 - // Relaxing assertion for bug 6320749.
1.1673 - assert (Universe::verify_in_progress() ||
1.1674 - !SafepointSynchronize::is_at_safepoint(),
1.1675 - "biases should not be seen by VM thread here");
1.1676 - BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
1.1677 - obj = hobj() ;
1.1678 - assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
1.1679 - }
1.1680 - }
1.1681 -
1.1682 - // hashCode() is a heap mutator ...
1.1683 - // Relaxing assertion for bug 6320749.
1.1684 - assert (Universe::verify_in_progress() ||
1.1685 - !SafepointSynchronize::is_at_safepoint(), "invariant") ;
1.1686 - assert (Universe::verify_in_progress() ||
1.1687 - Self->is_Java_thread() , "invariant") ;
1.1688 - assert (Universe::verify_in_progress() ||
1.1689 - ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant") ;
1.1690 -
1.1691 - ObjectMonitor* monitor = NULL;
1.1692 - markOop temp, test;
1.1693 - intptr_t hash;
1.1694 - markOop mark = ReadStableMark (obj);
1.1695 -
1.1696 - // object should remain ineligible for biased locking
1.1697 - assert (!mark->has_bias_pattern(), "invariant") ;
1.1698 -
1.1699 - if (mark->is_neutral()) {
1.1700 - hash = mark->hash(); // this is a normal header
1.1701 - if (hash) { // if it has hash, just return it
1.1702 - return hash;
1.1703 - }
1.1704 - hash = get_next_hash(Self, obj); // allocate a new hash code
1.1705 - temp = mark->copy_set_hash(hash); // merge the hash code into header
1.1706 - // use (machine word version) atomic operation to install the hash
1.1707 - test = (markOop) Atomic::cmpxchg_ptr(temp, obj->mark_addr(), mark);
1.1708 - if (test == mark) {
1.1709 - return hash;
1.1710 - }
1.1711 - // If atomic operation failed, we must inflate the header
1.1712 - // into heavy weight monitor. We could add more code here
1.1713 - // for fast path, but it does not worth the complexity.
1.1714 - } else if (mark->has_monitor()) {
1.1715 - monitor = mark->monitor();
1.1716 - temp = monitor->header();
1.1717 - assert (temp->is_neutral(), "invariant") ;
1.1718 - hash = temp->hash();
1.1719 - if (hash) {
1.1720 - return hash;
1.1721 - }
1.1722 - // Skip to the following code to reduce code size
1.1723 - } else if (Self->is_lock_owned((address)mark->locker())) {
1.1724 - temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned
1.1725 - assert (temp->is_neutral(), "invariant") ;
1.1726 - hash = temp->hash(); // by current thread, check if the displaced
1.1727 - if (hash) { // header contains hash code
1.1728 - return hash;
1.1729 - }
1.1730 - // WARNING:
1.1731 - // The displaced header is strictly immutable.
1.1732 - // It can NOT be changed in ANY cases. So we have
1.1733 - // to inflate the header into heavyweight monitor
1.1734 - // even the current thread owns the lock. The reason
1.1735 - // is the BasicLock (stack slot) will be asynchronously
1.1736 - // read by other threads during the inflate() function.
1.1737 - // Any change to stack may not propagate to other threads
1.1738 - // correctly.
1.1739 - }
1.1740 -
1.1741 - // Inflate the monitor to set hash code
1.1742 - monitor = ObjectSynchronizer::inflate(Self, obj);
1.1743 - // Load displaced header and check it has hash code
1.1744 - mark = monitor->header();
1.1745 - assert (mark->is_neutral(), "invariant") ;
1.1746 - hash = mark->hash();
1.1747 - if (hash == 0) {
1.1748 - hash = get_next_hash(Self, obj);
1.1749 - temp = mark->copy_set_hash(hash); // merge hash code into header
1.1750 - assert (temp->is_neutral(), "invariant") ;
1.1751 - test = (markOop) Atomic::cmpxchg_ptr(temp, monitor, mark);
1.1752 - if (test != mark) {
1.1753 - // The only update to the header in the monitor (outside GC)
1.1754 - // is install the hash code. If someone add new usage of
1.1755 - // displaced header, please update this code
1.1756 - hash = test->hash();
1.1757 - assert (test->is_neutral(), "invariant") ;
1.1758 - assert (hash != 0, "Trivial unexpected object/monitor header usage.");
1.1759 - }
1.1760 - }
1.1761 - // We finally get the hash
1.1762 - return hash;
1.1763 -}
1.1764 -
1.1765 -// Deprecated -- use FastHashCode() instead.
1.1766 -
1.1767 -intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
1.1768 - return FastHashCode (Thread::current(), obj()) ;
1.1769 -}
1.1770 -
1.1771 -bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
1.1772 - Handle h_obj) {
1.1773 - if (UseBiasedLocking) {
1.1774 - BiasedLocking::revoke_and_rebias(h_obj, false, thread);
1.1775 - assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
1.1776 - }
1.1777 -
1.1778 - assert(thread == JavaThread::current(), "Can only be called on current thread");
1.1779 - oop obj = h_obj();
1.1780 -
1.1781 - markOop mark = ReadStableMark (obj) ;
1.1782 -
1.1783 - // Uncontended case, header points to stack
1.1784 - if (mark->has_locker()) {
1.1785 - return thread->is_lock_owned((address)mark->locker());
1.1786 - }
1.1787 - // Contended case, header points to ObjectMonitor (tagged pointer)
1.1788 - if (mark->has_monitor()) {
1.1789 - ObjectMonitor* monitor = mark->monitor();
1.1790 - return monitor->is_entered(thread) != 0 ;
1.1791 - }
1.1792 - // Unlocked case, header in place
1.1793 - assert(mark->is_neutral(), "sanity check");
1.1794 - return false;
1.1795 -}
1.1796 -
1.1797 -// Be aware of this method could revoke bias of the lock object.
1.1798 -// This method querys the ownership of the lock handle specified by 'h_obj'.
1.1799 -// If the current thread owns the lock, it returns owner_self. If no
1.1800 -// thread owns the lock, it returns owner_none. Otherwise, it will return
1.1801 -// ower_other.
1.1802 -ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
1.1803 -(JavaThread *self, Handle h_obj) {
1.1804 - // The caller must beware this method can revoke bias, and
1.1805 - // revocation can result in a safepoint.
1.1806 - assert (!SafepointSynchronize::is_at_safepoint(), "invariant") ;
1.1807 - assert (self->thread_state() != _thread_blocked , "invariant") ;
1.1808 -
1.1809 - // Possible mark states: neutral, biased, stack-locked, inflated
1.1810 -
1.1811 - if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) {
1.1812 - // CASE: biased
1.1813 - BiasedLocking::revoke_and_rebias(h_obj, false, self);
1.1814 - assert(!h_obj->mark()->has_bias_pattern(),
1.1815 - "biases should be revoked by now");
1.1816 - }
1.1817 -
1.1818 - assert(self == JavaThread::current(), "Can only be called on current thread");
1.1819 - oop obj = h_obj();
1.1820 - markOop mark = ReadStableMark (obj) ;
1.1821 -
1.1822 - // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
1.1823 - if (mark->has_locker()) {
1.1824 - return self->is_lock_owned((address)mark->locker()) ?
1.1825 - owner_self : owner_other;
1.1826 - }
1.1827 -
1.1828 - // CASE: inflated. Mark (tagged pointer) points to an objectMonitor.
1.1829 - // The Object:ObjectMonitor relationship is stable as long as we're
1.1830 - // not at a safepoint.
1.1831 - if (mark->has_monitor()) {
1.1832 - void * owner = mark->monitor()->_owner ;
1.1833 - if (owner == NULL) return owner_none ;
1.1834 - return (owner == self ||
1.1835 - self->is_lock_owned((address)owner)) ? owner_self : owner_other;
1.1836 - }
1.1837 -
1.1838 - // CASE: neutral
1.1839 - assert(mark->is_neutral(), "sanity check");
1.1840 - return owner_none ; // it's unlocked
1.1841 -}
1.1842 -
1.1843 -// FIXME: jvmti should call this
1.1844 -JavaThread* ObjectSynchronizer::get_lock_owner(Handle h_obj, bool doLock) {
1.1845 - if (UseBiasedLocking) {
1.1846 - if (SafepointSynchronize::is_at_safepoint()) {
1.1847 - BiasedLocking::revoke_at_safepoint(h_obj);
1.1848 - } else {
1.1849 - BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current());
1.1850 - }
1.1851 - assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
1.1852 - }
1.1853 -
1.1854 - oop obj = h_obj();
1.1855 - address owner = NULL;
1.1856 -
1.1857 - markOop mark = ReadStableMark (obj) ;
1.1858 -
1.1859 - // Uncontended case, header points to stack
1.1860 - if (mark->has_locker()) {
1.1861 - owner = (address) mark->locker();
1.1862 - }
1.1863 -
1.1864 - // Contended case, header points to ObjectMonitor (tagged pointer)
1.1865 - if (mark->has_monitor()) {
1.1866 - ObjectMonitor* monitor = mark->monitor();
1.1867 - assert(monitor != NULL, "monitor should be non-null");
1.1868 - owner = (address) monitor->owner();
1.1869 - }
1.1870 -
1.1871 - if (owner != NULL) {
1.1872 - return Threads::owning_thread_from_monitor_owner(owner, doLock);
1.1873 - }
1.1874 -
1.1875 - // Unlocked case, header in place
1.1876 - // Cannot have assertion since this object may have been
1.1877 - // locked by another thread when reaching here.
1.1878 - // assert(mark->is_neutral(), "sanity check");
1.1879 -
1.1880 - return NULL;
1.1881 -}
1.1882 -
1.1883 -// Iterate through monitor cache and attempt to release thread's monitors
1.1884 -// Gives up on a particular monitor if an exception occurs, but continues
1.1885 -// the overall iteration, swallowing the exception.
1.1886 -class ReleaseJavaMonitorsClosure: public MonitorClosure {
1.1887 -private:
1.1888 - TRAPS;
1.1889 -
1.1890 -public:
1.1891 - ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
1.1892 - void do_monitor(ObjectMonitor* mid) {
1.1893 - if (mid->owner() == THREAD) {
1.1894 - (void)mid->complete_exit(CHECK);
1.1895 - }
1.1896 - }
1.1897 -};
1.1898 -
1.1899 -// Release all inflated monitors owned by THREAD. Lightweight monitors are
1.1900 -// ignored. This is meant to be called during JNI thread detach which assumes
1.1901 -// all remaining monitors are heavyweight. All exceptions are swallowed.
1.1902 -// Scanning the extant monitor list can be time consuming.
1.1903 -// A simple optimization is to add a per-thread flag that indicates a thread
1.1904 -// called jni_monitorenter() during its lifetime.
1.1905 -//
1.1906 -// Instead of No_Savepoint_Verifier it might be cheaper to
1.1907 -// use an idiom of the form:
1.1908 -// auto int tmp = SafepointSynchronize::_safepoint_counter ;
1.1909 -// <code that must not run at safepoint>
1.1910 -// guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1.1911 -// Since the tests are extremely cheap we could leave them enabled
1.1912 -// for normal product builds.
1.1913 -
1.1914 -void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
1.1915 - assert(THREAD == JavaThread::current(), "must be current Java thread");
1.1916 - No_Safepoint_Verifier nsv ;
1.1917 - ReleaseJavaMonitorsClosure rjmc(THREAD);
1.1918 - Thread::muxAcquire(&ListLock, "release_monitors_owned_by_thread");
1.1919 - ObjectSynchronizer::monitors_iterate(&rjmc);
1.1920 - Thread::muxRelease(&ListLock);
1.1921 - THREAD->clear_pending_exception();
1.1922 -}
1.1923 -
1.1924 -// Visitors ...
1.1925 -
1.1926 -void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
1.1927 - ObjectMonitor* block = gBlockList;
1.1928 - ObjectMonitor* mid;
1.1929 - while (block) {
1.1930 - assert(block->object() == CHAINMARKER, "must be a block header");
1.1931 - for (int i = _BLOCKSIZE - 1; i > 0; i--) {
1.1932 - mid = block + i;
1.1933 - oop object = (oop) mid->object();
1.1934 - if (object != NULL) {
1.1935 - closure->do_monitor(mid);
1.1936 - }
1.1937 - }
1.1938 - block = (ObjectMonitor*) block->FreeNext;
1.1939 - }
1.1940 -}
1.1941 -
1.1942 -void ObjectSynchronizer::oops_do(OopClosure* f) {
1.1943 - assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1.1944 - for (ObjectMonitor* block = gBlockList; block != NULL; block = next(block)) {
1.1945 - assert(block->object() == CHAINMARKER, "must be a block header");
1.1946 - for (int i = 1; i < _BLOCKSIZE; i++) {
1.1947 - ObjectMonitor* mid = &block[i];
1.1948 - if (mid->object() != NULL) {
1.1949 - f->do_oop((oop*)mid->object_addr());
1.1950 - }
1.1951 - }
1.1952 - }
1.1953 -}
1.1954
1.1955 // Deflate_idle_monitors() is called at all safepoints, immediately
1.1956 // after all mutators are stopped, but before any objects have moved.
1.1957 @@ -1936,12 +1357,11 @@
1.1958 // which in turn can mean large(r) numbers of objectmonitors in circulation.
1.1959 // This is an unfortunate aspect of this design.
1.1960 //
1.1961 -// Another refinement would be to refrain from calling deflate_idle_monitors()
1.1962 -// except at stop-the-world points associated with garbage collections.
1.1963 -//
1.1964 -// An even better solution would be to deflate on-the-fly, aggressively,
1.1965 -// at monitorexit-time as is done in EVM's metalock or Relaxed Locks.
1.1966
1.1967 +enum ManifestConstants {
1.1968 + ClearResponsibleAtSTW = 0,
1.1969 + MaximumRecheckInterval = 1000
1.1970 +} ;
1.1971
1.1972 // Deflate a single monitor if not in use
1.1973 // Return true if deflated, false if in use
1.1974 @@ -2088,7 +1508,7 @@
1.1975
1.1976 // Consider: audit gFreeList to ensure that MonitorFreeCount and list agree.
1.1977
1.1978 - if (Knob_Verbose) {
1.1979 + if (ObjectMonitor::Knob_Verbose) {
1.1980 ::printf ("Deflate: InCirc=%d InUse=%d Scavenged=%d ForceMonitorScavenge=%d : pop=%d free=%d\n",
1.1981 nInCirculation, nInuse, nScavenged, ForceMonitorScavenge,
1.1982 MonitorPopulation, MonitorFreeCount) ;
1.1983 @@ -2107,8 +1527,8 @@
1.1984 }
1.1985 Thread::muxRelease (&ListLock) ;
1.1986
1.1987 - if (_sync_Deflations != NULL) _sync_Deflations->inc(nScavenged) ;
1.1988 - if (_sync_MonExtant != NULL) _sync_MonExtant ->set_value(nInCirculation);
1.1989 + if (ObjectMonitor::_sync_Deflations != NULL) ObjectMonitor::_sync_Deflations->inc(nScavenged) ;
1.1990 + if (ObjectMonitor::_sync_MonExtant != NULL) ObjectMonitor::_sync_MonExtant ->set_value(nInCirculation);
1.1991
1.1992 // TODO: Add objectMonitor leak detection.
1.1993 // Audit/inventory the objectMonitors -- make sure they're all accounted for.
1.1994 @@ -2116,2810 +1536,49 @@
1.1995 GVars.stwCycle ++ ;
1.1996 }
1.1997
1.1998 -// A macro is used below because there may already be a pending
1.1999 -// exception which should not abort the execution of the routines
1.2000 -// which use this (which is why we don't put this into check_slow and
1.2001 -// call it with a CHECK argument).
1.2002 +// Monitor cleanup on JavaThread::exit
1.2003
1.2004 -#define CHECK_OWNER() \
1.2005 - do { \
1.2006 - if (THREAD != _owner) { \
1.2007 - if (THREAD->is_lock_owned((address) _owner)) { \
1.2008 - _owner = THREAD ; /* Convert from basiclock addr to Thread addr */ \
1.2009 - _recursions = 0; \
1.2010 - OwnerIsThread = 1 ; \
1.2011 - } else { \
1.2012 - TEVENT (Throw IMSX) ; \
1.2013 - THROW(vmSymbols::java_lang_IllegalMonitorStateException()); \
1.2014 - } \
1.2015 - } \
1.2016 - } while (false)
1.2017 +// Iterate through monitor cache and attempt to release thread's monitors
1.2018 +// Gives up on a particular monitor if an exception occurs, but continues
1.2019 +// the overall iteration, swallowing the exception.
1.2020 +class ReleaseJavaMonitorsClosure: public MonitorClosure {
1.2021 +private:
1.2022 + TRAPS;
1.2023
1.2024 -// TODO-FIXME: eliminate ObjectWaiters. Replace this visitor/enumerator
1.2025 -// interface with a simple FirstWaitingThread(), NextWaitingThread() interface.
1.2026 -
1.2027 -ObjectWaiter* ObjectMonitor::first_waiter() {
1.2028 - return _WaitSet;
1.2029 -}
1.2030 -
1.2031 -ObjectWaiter* ObjectMonitor::next_waiter(ObjectWaiter* o) {
1.2032 - return o->_next;
1.2033 -}
1.2034 -
1.2035 -Thread* ObjectMonitor::thread_of_waiter(ObjectWaiter* o) {
1.2036 - return o->_thread;
1.2037 -}
1.2038 -
1.2039 -// initialize the monitor, exception the semaphore, all other fields
1.2040 -// are simple integers or pointers
1.2041 -ObjectMonitor::ObjectMonitor() {
1.2042 - _header = NULL;
1.2043 - _count = 0;
1.2044 - _waiters = 0,
1.2045 - _recursions = 0;
1.2046 - _object = NULL;
1.2047 - _owner = NULL;
1.2048 - _WaitSet = NULL;
1.2049 - _WaitSetLock = 0 ;
1.2050 - _Responsible = NULL ;
1.2051 - _succ = NULL ;
1.2052 - _cxq = NULL ;
1.2053 - FreeNext = NULL ;
1.2054 - _EntryList = NULL ;
1.2055 - _SpinFreq = 0 ;
1.2056 - _SpinClock = 0 ;
1.2057 - OwnerIsThread = 0 ;
1.2058 -}
1.2059 -
1.2060 -ObjectMonitor::~ObjectMonitor() {
1.2061 - // TODO: Add asserts ...
1.2062 - // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0
1.2063 - // _count == 0 _EntryList == NULL etc
1.2064 -}
1.2065 -
1.2066 -intptr_t ObjectMonitor::is_busy() const {
1.2067 - // TODO-FIXME: merge _count and _waiters.
1.2068 - // TODO-FIXME: assert _owner == null implies _recursions = 0
1.2069 - // TODO-FIXME: assert _WaitSet != null implies _count > 0
1.2070 - return _count|_waiters|intptr_t(_owner)|intptr_t(_cxq)|intptr_t(_EntryList ) ;
1.2071 -}
1.2072 -
1.2073 -void ObjectMonitor::Recycle () {
1.2074 - // TODO: add stronger asserts ...
1.2075 - // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0
1.2076 - // _count == 0 EntryList == NULL
1.2077 - // _recursions == 0 _WaitSet == NULL
1.2078 - // TODO: assert (is_busy()|_recursions) == 0
1.2079 - _succ = NULL ;
1.2080 - _EntryList = NULL ;
1.2081 - _cxq = NULL ;
1.2082 - _WaitSet = NULL ;
1.2083 - _recursions = 0 ;
1.2084 - _SpinFreq = 0 ;
1.2085 - _SpinClock = 0 ;
1.2086 - OwnerIsThread = 0 ;
1.2087 -}
1.2088 -
1.2089 -// WaitSet management ...
1.2090 -
1.2091 -inline void ObjectMonitor::AddWaiter(ObjectWaiter* node) {
1.2092 - assert(node != NULL, "should not dequeue NULL node");
1.2093 - assert(node->_prev == NULL, "node already in list");
1.2094 - assert(node->_next == NULL, "node already in list");
1.2095 - // put node at end of queue (circular doubly linked list)
1.2096 - if (_WaitSet == NULL) {
1.2097 - _WaitSet = node;
1.2098 - node->_prev = node;
1.2099 - node->_next = node;
1.2100 - } else {
1.2101 - ObjectWaiter* head = _WaitSet ;
1.2102 - ObjectWaiter* tail = head->_prev;
1.2103 - assert(tail->_next == head, "invariant check");
1.2104 - tail->_next = node;
1.2105 - head->_prev = node;
1.2106 - node->_next = head;
1.2107 - node->_prev = tail;
1.2108 - }
1.2109 -}
1.2110 -
1.2111 -inline ObjectWaiter* ObjectMonitor::DequeueWaiter() {
1.2112 - // dequeue the very first waiter
1.2113 - ObjectWaiter* waiter = _WaitSet;
1.2114 - if (waiter) {
1.2115 - DequeueSpecificWaiter(waiter);
1.2116 - }
1.2117 - return waiter;
1.2118 -}
1.2119 -
1.2120 -inline void ObjectMonitor::DequeueSpecificWaiter(ObjectWaiter* node) {
1.2121 - assert(node != NULL, "should not dequeue NULL node");
1.2122 - assert(node->_prev != NULL, "node already removed from list");
1.2123 - assert(node->_next != NULL, "node already removed from list");
1.2124 - // when the waiter has woken up because of interrupt,
1.2125 - // timeout or other spurious wake-up, dequeue the
1.2126 - // waiter from waiting list
1.2127 - ObjectWaiter* next = node->_next;
1.2128 - if (next == node) {
1.2129 - assert(node->_prev == node, "invariant check");
1.2130 - _WaitSet = NULL;
1.2131 - } else {
1.2132 - ObjectWaiter* prev = node->_prev;
1.2133 - assert(prev->_next == node, "invariant check");
1.2134 - assert(next->_prev == node, "invariant check");
1.2135 - next->_prev = prev;
1.2136 - prev->_next = next;
1.2137 - if (_WaitSet == node) {
1.2138 - _WaitSet = next;
1.2139 +public:
1.2140 + ReleaseJavaMonitorsClosure(Thread* thread) : THREAD(thread) {}
1.2141 + void do_monitor(ObjectMonitor* mid) {
1.2142 + if (mid->owner() == THREAD) {
1.2143 + (void)mid->complete_exit(CHECK);
1.2144 }
1.2145 }
1.2146 - node->_next = NULL;
1.2147 - node->_prev = NULL;
1.2148 +};
1.2149 +
1.2150 +// Release all inflated monitors owned by THREAD. Lightweight monitors are
1.2151 +// ignored. This is meant to be called during JNI thread detach which assumes
1.2152 +// all remaining monitors are heavyweight. All exceptions are swallowed.
1.2153 +// Scanning the extant monitor list can be time consuming.
1.2154 +// A simple optimization is to add a per-thread flag that indicates a thread
1.2155 +// called jni_monitorenter() during its lifetime.
1.2156 +//
1.2157 +// Instead of No_Savepoint_Verifier it might be cheaper to
1.2158 +// use an idiom of the form:
1.2159 +// auto int tmp = SafepointSynchronize::_safepoint_counter ;
1.2160 +// <code that must not run at safepoint>
1.2161 +// guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1.2162 +// Since the tests are extremely cheap we could leave them enabled
1.2163 +// for normal product builds.
1.2164 +
1.2165 +void ObjectSynchronizer::release_monitors_owned_by_thread(TRAPS) {
1.2166 + assert(THREAD == JavaThread::current(), "must be current Java thread");
1.2167 + No_Safepoint_Verifier nsv ;
1.2168 + ReleaseJavaMonitorsClosure rjmc(THREAD);
1.2169 + Thread::muxAcquire(&ListLock, "release_monitors_owned_by_thread");
1.2170 + ObjectSynchronizer::monitors_iterate(&rjmc);
1.2171 + Thread::muxRelease(&ListLock);
1.2172 + THREAD->clear_pending_exception();
1.2173 }
1.2174
1.2175 -static char * kvGet (char * kvList, const char * Key) {
1.2176 - if (kvList == NULL) return NULL ;
1.2177 - size_t n = strlen (Key) ;
1.2178 - char * Search ;
1.2179 - for (Search = kvList ; *Search ; Search += strlen(Search) + 1) {
1.2180 - if (strncmp (Search, Key, n) == 0) {
1.2181 - if (Search[n] == '=') return Search + n + 1 ;
1.2182 - if (Search[n] == 0) return (char *) "1" ;
1.2183 - }
1.2184 - }
1.2185 - return NULL ;
1.2186 -}
1.2187 -
1.2188 -static int kvGetInt (char * kvList, const char * Key, int Default) {
1.2189 - char * v = kvGet (kvList, Key) ;
1.2190 - int rslt = v ? ::strtol (v, NULL, 0) : Default ;
1.2191 - if (Knob_ReportSettings && v != NULL) {
1.2192 - ::printf (" SyncKnob: %s %d(%d)\n", Key, rslt, Default) ;
1.2193 - ::fflush (stdout) ;
1.2194 - }
1.2195 - return rslt ;
1.2196 -}
1.2197 -
1.2198 -// By convention we unlink a contending thread from EntryList|cxq immediately
1.2199 -// after the thread acquires the lock in ::enter(). Equally, we could defer
1.2200 -// unlinking the thread until ::exit()-time.
1.2201 -
1.2202 -void ObjectMonitor::UnlinkAfterAcquire (Thread * Self, ObjectWaiter * SelfNode)
1.2203 -{
1.2204 - assert (_owner == Self, "invariant") ;
1.2205 - assert (SelfNode->_thread == Self, "invariant") ;
1.2206 -
1.2207 - if (SelfNode->TState == ObjectWaiter::TS_ENTER) {
1.2208 - // Normal case: remove Self from the DLL EntryList .
1.2209 - // This is a constant-time operation.
1.2210 - ObjectWaiter * nxt = SelfNode->_next ;
1.2211 - ObjectWaiter * prv = SelfNode->_prev ;
1.2212 - if (nxt != NULL) nxt->_prev = prv ;
1.2213 - if (prv != NULL) prv->_next = nxt ;
1.2214 - if (SelfNode == _EntryList ) _EntryList = nxt ;
1.2215 - assert (nxt == NULL || nxt->TState == ObjectWaiter::TS_ENTER, "invariant") ;
1.2216 - assert (prv == NULL || prv->TState == ObjectWaiter::TS_ENTER, "invariant") ;
1.2217 - TEVENT (Unlink from EntryList) ;
1.2218 - } else {
1.2219 - guarantee (SelfNode->TState == ObjectWaiter::TS_CXQ, "invariant") ;
1.2220 - // Inopportune interleaving -- Self is still on the cxq.
1.2221 - // This usually means the enqueue of self raced an exiting thread.
1.2222 - // Normally we'll find Self near the front of the cxq, so
1.2223 - // dequeueing is typically fast. If needbe we can accelerate
1.2224 - // this with some MCS/CHL-like bidirectional list hints and advisory
1.2225 - // back-links so dequeueing from the interior will normally operate
1.2226 - // in constant-time.
1.2227 - // Dequeue Self from either the head (with CAS) or from the interior
1.2228 - // with a linear-time scan and normal non-atomic memory operations.
1.2229 - // CONSIDER: if Self is on the cxq then simply drain cxq into EntryList
1.2230 - // and then unlink Self from EntryList. We have to drain eventually,
1.2231 - // so it might as well be now.
1.2232 -
1.2233 - ObjectWaiter * v = _cxq ;
1.2234 - assert (v != NULL, "invariant") ;
1.2235 - if (v != SelfNode || Atomic::cmpxchg_ptr (SelfNode->_next, &_cxq, v) != v) {
1.2236 - // The CAS above can fail from interference IFF a "RAT" arrived.
1.2237 - // In that case Self must be in the interior and can no longer be
1.2238 - // at the head of cxq.
1.2239 - if (v == SelfNode) {
1.2240 - assert (_cxq != v, "invariant") ;
1.2241 - v = _cxq ; // CAS above failed - start scan at head of list
1.2242 - }
1.2243 - ObjectWaiter * p ;
1.2244 - ObjectWaiter * q = NULL ;
1.2245 - for (p = v ; p != NULL && p != SelfNode; p = p->_next) {
1.2246 - q = p ;
1.2247 - assert (p->TState == ObjectWaiter::TS_CXQ, "invariant") ;
1.2248 - }
1.2249 - assert (v != SelfNode, "invariant") ;
1.2250 - assert (p == SelfNode, "Node not found on cxq") ;
1.2251 - assert (p != _cxq, "invariant") ;
1.2252 - assert (q != NULL, "invariant") ;
1.2253 - assert (q->_next == p, "invariant") ;
1.2254 - q->_next = p->_next ;
1.2255 - }
1.2256 - TEVENT (Unlink from cxq) ;
1.2257 - }
1.2258 -
1.2259 - // Diagnostic hygiene ...
1.2260 - SelfNode->_prev = (ObjectWaiter *) 0xBAD ;
1.2261 - SelfNode->_next = (ObjectWaiter *) 0xBAD ;
1.2262 - SelfNode->TState = ObjectWaiter::TS_RUN ;
1.2263 -}
1.2264 -
1.2265 -// Caveat: TryLock() is not necessarily serializing if it returns failure.
1.2266 -// Callers must compensate as needed.
1.2267 -
1.2268 -int ObjectMonitor::TryLock (Thread * Self) {
1.2269 - for (;;) {
1.2270 - void * own = _owner ;
1.2271 - if (own != NULL) return 0 ;
1.2272 - if (Atomic::cmpxchg_ptr (Self, &_owner, NULL) == NULL) {
1.2273 - // Either guarantee _recursions == 0 or set _recursions = 0.
1.2274 - assert (_recursions == 0, "invariant") ;
1.2275 - assert (_owner == Self, "invariant") ;
1.2276 - // CONSIDER: set or assert that OwnerIsThread == 1
1.2277 - return 1 ;
1.2278 - }
1.2279 - // The lock had been free momentarily, but we lost the race to the lock.
1.2280 - // Interference -- the CAS failed.
1.2281 - // We can either return -1 or retry.
1.2282 - // Retry doesn't make as much sense because the lock was just acquired.
1.2283 - if (true) return -1 ;
1.2284 - }
1.2285 -}
1.2286 -
1.2287 -// NotRunnable() -- informed spinning
1.2288 -//
1.2289 -// Don't bother spinning if the owner is not eligible to drop the lock.
1.2290 -// Peek at the owner's schedctl.sc_state and Thread._thread_values and
1.2291 -// spin only if the owner thread is _thread_in_Java or _thread_in_vm.
1.2292 -// The thread must be runnable in order to drop the lock in timely fashion.
1.2293 -// If the _owner is not runnable then spinning will not likely be
1.2294 -// successful (profitable).
1.2295 -//
1.2296 -// Beware -- the thread referenced by _owner could have died
1.2297 -// so a simply fetch from _owner->_thread_state might trap.
1.2298 -// Instead, we use SafeFetchXX() to safely LD _owner->_thread_state.
1.2299 -// Because of the lifecycle issues the schedctl and _thread_state values
1.2300 -// observed by NotRunnable() might be garbage. NotRunnable must
1.2301 -// tolerate this and consider the observed _thread_state value
1.2302 -// as advisory.
1.2303 -//
1.2304 -// Beware too, that _owner is sometimes a BasicLock address and sometimes
1.2305 -// a thread pointer. We differentiate the two cases with OwnerIsThread.
1.2306 -// Alternately, we might tag the type (thread pointer vs basiclock pointer)
1.2307 -// with the LSB of _owner. Another option would be to probablistically probe
1.2308 -// the putative _owner->TypeTag value.
1.2309 -//
1.2310 -// Checking _thread_state isn't perfect. Even if the thread is
1.2311 -// in_java it might be blocked on a page-fault or have been preempted
1.2312 -// and sitting on a ready/dispatch queue. _thread state in conjunction
1.2313 -// with schedctl.sc_state gives us a good picture of what the
1.2314 -// thread is doing, however.
1.2315 -//
1.2316 -// TODO: check schedctl.sc_state.
1.2317 -// We'll need to use SafeFetch32() to read from the schedctl block.
1.2318 -// See RFE #5004247 and http://sac.sfbay.sun.com/Archives/CaseLog/arc/PSARC/2005/351/
1.2319 -//
1.2320 -// The return value from NotRunnable() is *advisory* -- the
1.2321 -// result is based on sampling and is not necessarily coherent.
1.2322 -// The caller must tolerate false-negative and false-positive errors.
1.2323 -// Spinning, in general, is probabilistic anyway.
1.2324 -
1.2325 -
1.2326 -int ObjectMonitor::NotRunnable (Thread * Self, Thread * ox) {
1.2327 - // Check either OwnerIsThread or ox->TypeTag == 2BAD.
1.2328 - if (!OwnerIsThread) return 0 ;
1.2329 -
1.2330 - if (ox == NULL) return 0 ;
1.2331 -
1.2332 - // Avoid transitive spinning ...
1.2333 - // Say T1 spins or blocks trying to acquire L. T1._Stalled is set to L.
1.2334 - // Immediately after T1 acquires L it's possible that T2, also
1.2335 - // spinning on L, will see L.Owner=T1 and T1._Stalled=L.
1.2336 - // This occurs transiently after T1 acquired L but before
1.2337 - // T1 managed to clear T1.Stalled. T2 does not need to abort
1.2338 - // its spin in this circumstance.
1.2339 - intptr_t BlockedOn = SafeFetchN ((intptr_t *) &ox->_Stalled, intptr_t(1)) ;
1.2340 -
1.2341 - if (BlockedOn == 1) return 1 ;
1.2342 - if (BlockedOn != 0) {
1.2343 - return BlockedOn != intptr_t(this) && _owner == ox ;
1.2344 - }
1.2345 -
1.2346 - assert (sizeof(((JavaThread *)ox)->_thread_state == sizeof(int)), "invariant") ;
1.2347 - int jst = SafeFetch32 ((int *) &((JavaThread *) ox)->_thread_state, -1) ; ;
1.2348 - // consider also: jst != _thread_in_Java -- but that's overspecific.
1.2349 - return jst == _thread_blocked || jst == _thread_in_native ;
1.2350 -}
1.2351 -
1.2352 -
1.2353 -// Adaptive spin-then-block - rational spinning
1.2354 -//
1.2355 -// Note that we spin "globally" on _owner with a classic SMP-polite TATAS
1.2356 -// algorithm. On high order SMP systems it would be better to start with
1.2357 -// a brief global spin and then revert to spinning locally. In the spirit of MCS/CLH,
1.2358 -// a contending thread could enqueue itself on the cxq and then spin locally
1.2359 -// on a thread-specific variable such as its ParkEvent._Event flag.
1.2360 -// That's left as an exercise for the reader. Note that global spinning is
1.2361 -// not problematic on Niagara, as the L2$ serves the interconnect and has both
1.2362 -// low latency and massive bandwidth.
1.2363 -//
1.2364 -// Broadly, we can fix the spin frequency -- that is, the % of contended lock
1.2365 -// acquisition attempts where we opt to spin -- at 100% and vary the spin count
1.2366 -// (duration) or we can fix the count at approximately the duration of
1.2367 -// a context switch and vary the frequency. Of course we could also
1.2368 -// vary both satisfying K == Frequency * Duration, where K is adaptive by monitor.
1.2369 -// See http://j2se.east/~dice/PERSIST/040824-AdaptiveSpinning.html.
1.2370 -//
1.2371 -// This implementation varies the duration "D", where D varies with
1.2372 -// the success rate of recent spin attempts. (D is capped at approximately
1.2373 -// length of a round-trip context switch). The success rate for recent
1.2374 -// spin attempts is a good predictor of the success rate of future spin
1.2375 -// attempts. The mechanism adapts automatically to varying critical
1.2376 -// section length (lock modality), system load and degree of parallelism.
1.2377 -// D is maintained per-monitor in _SpinDuration and is initialized
1.2378 -// optimistically. Spin frequency is fixed at 100%.
1.2379 -//
1.2380 -// Note that _SpinDuration is volatile, but we update it without locks
1.2381 -// or atomics. The code is designed so that _SpinDuration stays within
1.2382 -// a reasonable range even in the presence of races. The arithmetic
1.2383 -// operations on _SpinDuration are closed over the domain of legal values,
1.2384 -// so at worst a race will install and older but still legal value.
1.2385 -// At the very worst this introduces some apparent non-determinism.
1.2386 -// We might spin when we shouldn't or vice-versa, but since the spin
1.2387 -// count are relatively short, even in the worst case, the effect is harmless.
1.2388 -//
1.2389 -// Care must be taken that a low "D" value does not become an
1.2390 -// an absorbing state. Transient spinning failures -- when spinning
1.2391 -// is overall profitable -- should not cause the system to converge
1.2392 -// on low "D" values. We want spinning to be stable and predictable
1.2393 -// and fairly responsive to change and at the same time we don't want
1.2394 -// it to oscillate, become metastable, be "too" non-deterministic,
1.2395 -// or converge on or enter undesirable stable absorbing states.
1.2396 -//
1.2397 -// We implement a feedback-based control system -- using past behavior
1.2398 -// to predict future behavior. We face two issues: (a) if the
1.2399 -// input signal is random then the spin predictor won't provide optimal
1.2400 -// results, and (b) if the signal frequency is too high then the control
1.2401 -// system, which has some natural response lag, will "chase" the signal.
1.2402 -// (b) can arise from multimodal lock hold times. Transient preemption
1.2403 -// can also result in apparent bimodal lock hold times.
1.2404 -// Although sub-optimal, neither condition is particularly harmful, as
1.2405 -// in the worst-case we'll spin when we shouldn't or vice-versa.
1.2406 -// The maximum spin duration is rather short so the failure modes aren't bad.
1.2407 -// To be conservative, I've tuned the gain in system to bias toward
1.2408 -// _not spinning. Relatedly, the system can sometimes enter a mode where it
1.2409 -// "rings" or oscillates between spinning and not spinning. This happens
1.2410 -// when spinning is just on the cusp of profitability, however, so the
1.2411 -// situation is not dire. The state is benign -- there's no need to add
1.2412 -// hysteresis control to damp the transition rate between spinning and
1.2413 -// not spinning.
1.2414 -//
1.2415 -// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
1.2416 -//
1.2417 -// Spin-then-block strategies ...
1.2418 -//
1.2419 -// Thoughts on ways to improve spinning :
1.2420 -//
1.2421 -// * Periodically call {psr_}getloadavg() while spinning, and
1.2422 -// permit unbounded spinning if the load average is <
1.2423 -// the number of processors. Beware, however, that getloadavg()
1.2424 -// is exceptionally fast on solaris (about 1/10 the cost of a full
1.2425 -// spin cycle, but quite expensive on linux. Beware also, that
1.2426 -// multiple JVMs could "ring" or oscillate in a feedback loop.
1.2427 -// Sufficient damping would solve that problem.
1.2428 -//
1.2429 -// * We currently use spin loops with iteration counters to approximate
1.2430 -// spinning for some interval. Given the availability of high-precision
1.2431 -// time sources such as gethrtime(), %TICK, %STICK, RDTSC, etc., we should
1.2432 -// someday reimplement the spin loops to duration-based instead of iteration-based.
1.2433 -//
1.2434 -// * Don't spin if there are more than N = (CPUs/2) threads
1.2435 -// currently spinning on the monitor (or globally).
1.2436 -// That is, limit the number of concurrent spinners.
1.2437 -// We might also limit the # of spinners in the JVM, globally.
1.2438 -//
1.2439 -// * If a spinning thread observes _owner change hands it should
1.2440 -// abort the spin (and park immediately) or at least debit
1.2441 -// the spin counter by a large "penalty".
1.2442 -//
1.2443 -// * Classically, the spin count is either K*(CPUs-1) or is a
1.2444 -// simple constant that approximates the length of a context switch.
1.2445 -// We currently use a value -- computed by a special utility -- that
1.2446 -// approximates round-trip context switch times.
1.2447 -//
1.2448 -// * Normally schedctl_start()/_stop() is used to advise the kernel
1.2449 -// to avoid preempting threads that are running in short, bounded
1.2450 -// critical sections. We could use the schedctl hooks in an inverted
1.2451 -// sense -- spinners would set the nopreempt flag, but poll the preempt
1.2452 -// pending flag. If a spinner observed a pending preemption it'd immediately
1.2453 -// abort the spin and park. As such, the schedctl service acts as
1.2454 -// a preemption warning mechanism.
1.2455 -//
1.2456 -// * In lieu of spinning, if the system is running below saturation
1.2457 -// (that is, loadavg() << #cpus), we can instead suppress futile
1.2458 -// wakeup throttling, or even wake more than one successor at exit-time.
1.2459 -// The net effect is largely equivalent to spinning. In both cases,
1.2460 -// contending threads go ONPROC and opportunistically attempt to acquire
1.2461 -// the lock, decreasing lock handover latency at the expense of wasted
1.2462 -// cycles and context switching.
1.2463 -//
1.2464 -// * We might to spin less after we've parked as the thread will
1.2465 -// have less $ and TLB affinity with the processor.
1.2466 -// Likewise, we might spin less if we come ONPROC on a different
1.2467 -// processor or after a long period (>> rechose_interval).
1.2468 -//
1.2469 -// * A table-driven state machine similar to Solaris' dispadmin scheduling
1.2470 -// tables might be a better design. Instead of encoding information in
1.2471 -// _SpinDuration, _SpinFreq and _SpinClock we'd just use explicit,
1.2472 -// discrete states. Success or failure during a spin would drive
1.2473 -// state transitions, and each state node would contain a spin count.
1.2474 -//
1.2475 -// * If the processor is operating in a mode intended to conserve power
1.2476 -// (such as Intel's SpeedStep) or to reduce thermal output (thermal
1.2477 -// step-down mode) then the Java synchronization subsystem should
1.2478 -// forgo spinning.
1.2479 -//
1.2480 -// * The minimum spin duration should be approximately the worst-case
1.2481 -// store propagation latency on the platform. That is, the time
1.2482 -// it takes a store on CPU A to become visible on CPU B, where A and
1.2483 -// B are "distant".
1.2484 -//
1.2485 -// * We might want to factor a thread's priority in the spin policy.
1.2486 -// Threads with a higher priority might spin for slightly longer.
1.2487 -// Similarly, if we use back-off in the TATAS loop, lower priority
1.2488 -// threads might back-off longer. We don't currently use a
1.2489 -// thread's priority when placing it on the entry queue. We may
1.2490 -// want to consider doing so in future releases.
1.2491 -//
1.2492 -// * We might transiently drop a thread's scheduling priority while it spins.
1.2493 -// SCHED_BATCH on linux and FX scheduling class at priority=0 on Solaris
1.2494 -// would suffice. We could even consider letting the thread spin indefinitely at
1.2495 -// a depressed or "idle" priority. This brings up fairness issues, however --
1.2496 -// in a saturated system a thread would with a reduced priority could languish
1.2497 -// for extended periods on the ready queue.
1.2498 -//
1.2499 -// * While spinning try to use the otherwise wasted time to help the VM make
1.2500 -// progress:
1.2501 -//
1.2502 -// -- YieldTo() the owner, if the owner is OFFPROC but ready
1.2503 -// Done our remaining quantum directly to the ready thread.
1.2504 -// This helps "push" the lock owner through the critical section.
1.2505 -// It also tends to improve affinity/locality as the lock
1.2506 -// "migrates" less frequently between CPUs.
1.2507 -// -- Walk our own stack in anticipation of blocking. Memoize the roots.
1.2508 -// -- Perform strand checking for other thread. Unpark potential strandees.
1.2509 -// -- Help GC: trace or mark -- this would need to be a bounded unit of work.
1.2510 -// Unfortunately this will pollute our $ and TLBs. Recall that we
1.2511 -// spin to avoid context switching -- context switching has an
1.2512 -// immediate cost in latency, a disruptive cost to other strands on a CMT
1.2513 -// processor, and an amortized cost because of the D$ and TLB cache
1.2514 -// reload transient when the thread comes back ONPROC and repopulates
1.2515 -// $s and TLBs.
1.2516 -// -- call getloadavg() to see if the system is saturated. It'd probably
1.2517 -// make sense to call getloadavg() half way through the spin.
1.2518 -// If the system isn't at full capacity the we'd simply reset
1.2519 -// the spin counter to and extend the spin attempt.
1.2520 -// -- Doug points out that we should use the same "helping" policy
1.2521 -// in thread.yield().
1.2522 -//
1.2523 -// * Try MONITOR-MWAIT on systems that support those instructions.
1.2524 -//
1.2525 -// * The spin statistics that drive spin decisions & frequency are
1.2526 -// maintained in the objectmonitor structure so if we deflate and reinflate
1.2527 -// we lose spin state. In practice this is not usually a concern
1.2528 -// as the default spin state after inflation is aggressive (optimistic)
1.2529 -// and tends toward spinning. So in the worst case for a lock where
1.2530 -// spinning is not profitable we may spin unnecessarily for a brief
1.2531 -// period. But then again, if a lock is contended it'll tend not to deflate
1.2532 -// in the first place.
1.2533 -
1.2534 -
1.2535 -intptr_t ObjectMonitor::SpinCallbackArgument = 0 ;
1.2536 -int (*ObjectMonitor::SpinCallbackFunction)(intptr_t, int) = NULL ;
1.2537 -
1.2538 -// Spinning: Fixed frequency (100%), vary duration
1.2539 -
1.2540 -int ObjectMonitor::TrySpin_VaryDuration (Thread * Self) {
1.2541 -
1.2542 - // Dumb, brutal spin. Good for comparative measurements against adaptive spinning.
1.2543 - int ctr = Knob_FixedSpin ;
1.2544 - if (ctr != 0) {
1.2545 - while (--ctr >= 0) {
1.2546 - if (TryLock (Self) > 0) return 1 ;
1.2547 - SpinPause () ;
1.2548 - }
1.2549 - return 0 ;
1.2550 - }
1.2551 -
1.2552 - for (ctr = Knob_PreSpin + 1; --ctr >= 0 ; ) {
1.2553 - if (TryLock(Self) > 0) {
1.2554 - // Increase _SpinDuration ...
1.2555 - // Note that we don't clamp SpinDuration precisely at SpinLimit.
1.2556 - // Raising _SpurDuration to the poverty line is key.
1.2557 - int x = _SpinDuration ;
1.2558 - if (x < Knob_SpinLimit) {
1.2559 - if (x < Knob_Poverty) x = Knob_Poverty ;
1.2560 - _SpinDuration = x + Knob_BonusB ;
1.2561 - }
1.2562 - return 1 ;
1.2563 - }
1.2564 - SpinPause () ;
1.2565 - }
1.2566 -
1.2567 - // Admission control - verify preconditions for spinning
1.2568 - //
1.2569 - // We always spin a little bit, just to prevent _SpinDuration == 0 from
1.2570 - // becoming an absorbing state. Put another way, we spin briefly to
1.2571 - // sample, just in case the system load, parallelism, contention, or lock
1.2572 - // modality changed.
1.2573 - //
1.2574 - // Consider the following alternative:
1.2575 - // Periodically set _SpinDuration = _SpinLimit and try a long/full
1.2576 - // spin attempt. "Periodically" might mean after a tally of
1.2577 - // the # of failed spin attempts (or iterations) reaches some threshold.
1.2578 - // This takes us into the realm of 1-out-of-N spinning, where we
1.2579 - // hold the duration constant but vary the frequency.
1.2580 -
1.2581 - ctr = _SpinDuration ;
1.2582 - if (ctr < Knob_SpinBase) ctr = Knob_SpinBase ;
1.2583 - if (ctr <= 0) return 0 ;
1.2584 -
1.2585 - if (Knob_SuccRestrict && _succ != NULL) return 0 ;
1.2586 - if (Knob_OState && NotRunnable (Self, (Thread *) _owner)) {
1.2587 - TEVENT (Spin abort - notrunnable [TOP]);
1.2588 - return 0 ;
1.2589 - }
1.2590 -
1.2591 - int MaxSpin = Knob_MaxSpinners ;
1.2592 - if (MaxSpin >= 0) {
1.2593 - if (_Spinner > MaxSpin) {
1.2594 - TEVENT (Spin abort -- too many spinners) ;
1.2595 - return 0 ;
1.2596 - }
1.2597 - // Slighty racy, but benign ...
1.2598 - Adjust (&_Spinner, 1) ;
1.2599 - }
1.2600 -
1.2601 - // We're good to spin ... spin ingress.
1.2602 - // CONSIDER: use Prefetch::write() to avoid RTS->RTO upgrades
1.2603 - // when preparing to LD...CAS _owner, etc and the CAS is likely
1.2604 - // to succeed.
1.2605 - int hits = 0 ;
1.2606 - int msk = 0 ;
1.2607 - int caspty = Knob_CASPenalty ;
1.2608 - int oxpty = Knob_OXPenalty ;
1.2609 - int sss = Knob_SpinSetSucc ;
1.2610 - if (sss && _succ == NULL ) _succ = Self ;
1.2611 - Thread * prv = NULL ;
1.2612 -
1.2613 - // There are three ways to exit the following loop:
1.2614 - // 1. A successful spin where this thread has acquired the lock.
1.2615 - // 2. Spin failure with prejudice
1.2616 - // 3. Spin failure without prejudice
1.2617 -
1.2618 - while (--ctr >= 0) {
1.2619 -
1.2620 - // Periodic polling -- Check for pending GC
1.2621 - // Threads may spin while they're unsafe.
1.2622 - // We don't want spinning threads to delay the JVM from reaching
1.2623 - // a stop-the-world safepoint or to steal cycles from GC.
1.2624 - // If we detect a pending safepoint we abort in order that
1.2625 - // (a) this thread, if unsafe, doesn't delay the safepoint, and (b)
1.2626 - // this thread, if safe, doesn't steal cycles from GC.
1.2627 - // This is in keeping with the "no loitering in runtime" rule.
1.2628 - // We periodically check to see if there's a safepoint pending.
1.2629 - if ((ctr & 0xFF) == 0) {
1.2630 - if (SafepointSynchronize::do_call_back()) {
1.2631 - TEVENT (Spin: safepoint) ;
1.2632 - goto Abort ; // abrupt spin egress
1.2633 - }
1.2634 - if (Knob_UsePause & 1) SpinPause () ;
1.2635 -
1.2636 - int (*scb)(intptr_t,int) = SpinCallbackFunction ;
1.2637 - if (hits > 50 && scb != NULL) {
1.2638 - int abend = (*scb)(SpinCallbackArgument, 0) ;
1.2639 - }
1.2640 - }
1.2641 -
1.2642 - if (Knob_UsePause & 2) SpinPause() ;
1.2643 -
1.2644 - // Exponential back-off ... Stay off the bus to reduce coherency traffic.
1.2645 - // This is useful on classic SMP systems, but is of less utility on
1.2646 - // N1-style CMT platforms.
1.2647 - //
1.2648 - // Trade-off: lock acquisition latency vs coherency bandwidth.
1.2649 - // Lock hold times are typically short. A histogram
1.2650 - // of successful spin attempts shows that we usually acquire
1.2651 - // the lock early in the spin. That suggests we want to
1.2652 - // sample _owner frequently in the early phase of the spin,
1.2653 - // but then back-off and sample less frequently as the spin
1.2654 - // progresses. The back-off makes a good citizen on SMP big
1.2655 - // SMP systems. Oversampling _owner can consume excessive
1.2656 - // coherency bandwidth. Relatedly, if we _oversample _owner we
1.2657 - // can inadvertently interfere with the the ST m->owner=null.
1.2658 - // executed by the lock owner.
1.2659 - if (ctr & msk) continue ;
1.2660 - ++hits ;
1.2661 - if ((hits & 0xF) == 0) {
1.2662 - // The 0xF, above, corresponds to the exponent.
1.2663 - // Consider: (msk+1)|msk
1.2664 - msk = ((msk << 2)|3) & BackOffMask ;
1.2665 - }
1.2666 -
1.2667 - // Probe _owner with TATAS
1.2668 - // If this thread observes the monitor transition or flicker
1.2669 - // from locked to unlocked to locked, then the odds that this
1.2670 - // thread will acquire the lock in this spin attempt go down
1.2671 - // considerably. The same argument applies if the CAS fails
1.2672 - // or if we observe _owner change from one non-null value to
1.2673 - // another non-null value. In such cases we might abort
1.2674 - // the spin without prejudice or apply a "penalty" to the
1.2675 - // spin count-down variable "ctr", reducing it by 100, say.
1.2676 -
1.2677 - Thread * ox = (Thread *) _owner ;
1.2678 - if (ox == NULL) {
1.2679 - ox = (Thread *) Atomic::cmpxchg_ptr (Self, &_owner, NULL) ;
1.2680 - if (ox == NULL) {
1.2681 - // The CAS succeeded -- this thread acquired ownership
1.2682 - // Take care of some bookkeeping to exit spin state.
1.2683 - if (sss && _succ == Self) {
1.2684 - _succ = NULL ;
1.2685 - }
1.2686 - if (MaxSpin > 0) Adjust (&_Spinner, -1) ;
1.2687 -
1.2688 - // Increase _SpinDuration :
1.2689 - // The spin was successful (profitable) so we tend toward
1.2690 - // longer spin attempts in the future.
1.2691 - // CONSIDER: factor "ctr" into the _SpinDuration adjustment.
1.2692 - // If we acquired the lock early in the spin cycle it
1.2693 - // makes sense to increase _SpinDuration proportionally.
1.2694 - // Note that we don't clamp SpinDuration precisely at SpinLimit.
1.2695 - int x = _SpinDuration ;
1.2696 - if (x < Knob_SpinLimit) {
1.2697 - if (x < Knob_Poverty) x = Knob_Poverty ;
1.2698 - _SpinDuration = x + Knob_Bonus ;
1.2699 - }
1.2700 - return 1 ;
1.2701 - }
1.2702 -
1.2703 - // The CAS failed ... we can take any of the following actions:
1.2704 - // * penalize: ctr -= Knob_CASPenalty
1.2705 - // * exit spin with prejudice -- goto Abort;
1.2706 - // * exit spin without prejudice.
1.2707 - // * Since CAS is high-latency, retry again immediately.
1.2708 - prv = ox ;
1.2709 - TEVENT (Spin: cas failed) ;
1.2710 - if (caspty == -2) break ;
1.2711 - if (caspty == -1) goto Abort ;
1.2712 - ctr -= caspty ;
1.2713 - continue ;
1.2714 - }
1.2715 -
1.2716 - // Did lock ownership change hands ?
1.2717 - if (ox != prv && prv != NULL ) {
1.2718 - TEVENT (spin: Owner changed)
1.2719 - if (oxpty == -2) break ;
1.2720 - if (oxpty == -1) goto Abort ;
1.2721 - ctr -= oxpty ;
1.2722 - }
1.2723 - prv = ox ;
1.2724 -
1.2725 - // Abort the spin if the owner is not executing.
1.2726 - // The owner must be executing in order to drop the lock.
1.2727 - // Spinning while the owner is OFFPROC is idiocy.
1.2728 - // Consider: ctr -= RunnablePenalty ;
1.2729 - if (Knob_OState && NotRunnable (Self, ox)) {
1.2730 - TEVENT (Spin abort - notrunnable);
1.2731 - goto Abort ;
1.2732 - }
1.2733 - if (sss && _succ == NULL ) _succ = Self ;
1.2734 - }
1.2735 -
1.2736 - // Spin failed with prejudice -- reduce _SpinDuration.
1.2737 - // TODO: Use an AIMD-like policy to adjust _SpinDuration.
1.2738 - // AIMD is globally stable.
1.2739 - TEVENT (Spin failure) ;
1.2740 - {
1.2741 - int x = _SpinDuration ;
1.2742 - if (x > 0) {
1.2743 - // Consider an AIMD scheme like: x -= (x >> 3) + 100
1.2744 - // This is globally sample and tends to damp the response.
1.2745 - x -= Knob_Penalty ;
1.2746 - if (x < 0) x = 0 ;
1.2747 - _SpinDuration = x ;
1.2748 - }
1.2749 - }
1.2750 -
1.2751 - Abort:
1.2752 - if (MaxSpin >= 0) Adjust (&_Spinner, -1) ;
1.2753 - if (sss && _succ == Self) {
1.2754 - _succ = NULL ;
1.2755 - // Invariant: after setting succ=null a contending thread
1.2756 - // must recheck-retry _owner before parking. This usually happens
1.2757 - // in the normal usage of TrySpin(), but it's safest
1.2758 - // to make TrySpin() as foolproof as possible.
1.2759 - OrderAccess::fence() ;
1.2760 - if (TryLock(Self) > 0) return 1 ;
1.2761 - }
1.2762 - return 0 ;
1.2763 -}
1.2764 -
1.2765 -#define TrySpin TrySpin_VaryDuration
1.2766 -
1.2767 -static void DeferredInitialize () {
1.2768 - if (InitDone > 0) return ;
1.2769 - if (Atomic::cmpxchg (-1, &InitDone, 0) != 0) {
1.2770 - while (InitDone != 1) ;
1.2771 - return ;
1.2772 - }
1.2773 -
1.2774 - // One-shot global initialization ...
1.2775 - // The initialization is idempotent, so we don't need locks.
1.2776 - // In the future consider doing this via os::init_2().
1.2777 - // SyncKnobs consist of <Key>=<Value> pairs in the style
1.2778 - // of environment variables. Start by converting ':' to NUL.
1.2779 -
1.2780 - if (SyncKnobs == NULL) SyncKnobs = "" ;
1.2781 -
1.2782 - size_t sz = strlen (SyncKnobs) ;
1.2783 - char * knobs = (char *) malloc (sz + 2) ;
1.2784 - if (knobs == NULL) {
1.2785 - vm_exit_out_of_memory (sz + 2, "Parse SyncKnobs") ;
1.2786 - guarantee (0, "invariant") ;
1.2787 - }
1.2788 - strcpy (knobs, SyncKnobs) ;
1.2789 - knobs[sz+1] = 0 ;
1.2790 - for (char * p = knobs ; *p ; p++) {
1.2791 - if (*p == ':') *p = 0 ;
1.2792 - }
1.2793 -
1.2794 - #define SETKNOB(x) { Knob_##x = kvGetInt (knobs, #x, Knob_##x); }
1.2795 - SETKNOB(ReportSettings) ;
1.2796 - SETKNOB(Verbose) ;
1.2797 - SETKNOB(FixedSpin) ;
1.2798 - SETKNOB(SpinLimit) ;
1.2799 - SETKNOB(SpinBase) ;
1.2800 - SETKNOB(SpinBackOff);
1.2801 - SETKNOB(CASPenalty) ;
1.2802 - SETKNOB(OXPenalty) ;
1.2803 - SETKNOB(LogSpins) ;
1.2804 - SETKNOB(SpinSetSucc) ;
1.2805 - SETKNOB(SuccEnabled) ;
1.2806 - SETKNOB(SuccRestrict) ;
1.2807 - SETKNOB(Penalty) ;
1.2808 - SETKNOB(Bonus) ;
1.2809 - SETKNOB(BonusB) ;
1.2810 - SETKNOB(Poverty) ;
1.2811 - SETKNOB(SpinAfterFutile) ;
1.2812 - SETKNOB(UsePause) ;
1.2813 - SETKNOB(SpinEarly) ;
1.2814 - SETKNOB(OState) ;
1.2815 - SETKNOB(MaxSpinners) ;
1.2816 - SETKNOB(PreSpin) ;
1.2817 - SETKNOB(ExitPolicy) ;
1.2818 - SETKNOB(QMode);
1.2819 - SETKNOB(ResetEvent) ;
1.2820 - SETKNOB(MoveNotifyee) ;
1.2821 - SETKNOB(FastHSSEC) ;
1.2822 - #undef SETKNOB
1.2823 -
1.2824 - if (os::is_MP()) {
1.2825 - BackOffMask = (1 << Knob_SpinBackOff) - 1 ;
1.2826 - if (Knob_ReportSettings) ::printf ("BackOffMask=%X\n", BackOffMask) ;
1.2827 - // CONSIDER: BackOffMask = ROUNDUP_NEXT_POWER2 (ncpus-1)
1.2828 - } else {
1.2829 - Knob_SpinLimit = 0 ;
1.2830 - Knob_SpinBase = 0 ;
1.2831 - Knob_PreSpin = 0 ;
1.2832 - Knob_FixedSpin = -1 ;
1.2833 - }
1.2834 -
1.2835 - if (Knob_LogSpins == 0) {
1.2836 - ObjectSynchronizer::_sync_FailedSpins = NULL ;
1.2837 - }
1.2838 -
1.2839 - free (knobs) ;
1.2840 - OrderAccess::fence() ;
1.2841 - InitDone = 1 ;
1.2842 -}
1.2843 -
1.2844 -// Theory of operations -- Monitors lists, thread residency, etc:
1.2845 -//
1.2846 -// * A thread acquires ownership of a monitor by successfully
1.2847 -// CAS()ing the _owner field from null to non-null.
1.2848 -//
1.2849 -// * Invariant: A thread appears on at most one monitor list --
1.2850 -// cxq, EntryList or WaitSet -- at any one time.
1.2851 -//
1.2852 -// * Contending threads "push" themselves onto the cxq with CAS
1.2853 -// and then spin/park.
1.2854 -//
1.2855 -// * After a contending thread eventually acquires the lock it must
1.2856 -// dequeue itself from either the EntryList or the cxq.
1.2857 -//
1.2858 -// * The exiting thread identifies and unparks an "heir presumptive"
1.2859 -// tentative successor thread on the EntryList. Critically, the
1.2860 -// exiting thread doesn't unlink the successor thread from the EntryList.
1.2861 -// After having been unparked, the wakee will recontend for ownership of
1.2862 -// the monitor. The successor (wakee) will either acquire the lock or
1.2863 -// re-park itself.
1.2864 -//
1.2865 -// Succession is provided for by a policy of competitive handoff.
1.2866 -// The exiting thread does _not_ grant or pass ownership to the
1.2867 -// successor thread. (This is also referred to as "handoff" succession").
1.2868 -// Instead the exiting thread releases ownership and possibly wakes
1.2869 -// a successor, so the successor can (re)compete for ownership of the lock.
1.2870 -// If the EntryList is empty but the cxq is populated the exiting
1.2871 -// thread will drain the cxq into the EntryList. It does so by
1.2872 -// by detaching the cxq (installing null with CAS) and folding
1.2873 -// the threads from the cxq into the EntryList. The EntryList is
1.2874 -// doubly linked, while the cxq is singly linked because of the
1.2875 -// CAS-based "push" used to enqueue recently arrived threads (RATs).
1.2876 -//
1.2877 -// * Concurrency invariants:
1.2878 -//
1.2879 -// -- only the monitor owner may access or mutate the EntryList.
1.2880 -// The mutex property of the monitor itself protects the EntryList
1.2881 -// from concurrent interference.
1.2882 -// -- Only the monitor owner may detach the cxq.
1.2883 -//
1.2884 -// * The monitor entry list operations avoid locks, but strictly speaking
1.2885 -// they're not lock-free. Enter is lock-free, exit is not.
1.2886 -// See http://j2se.east/~dice/PERSIST/040825-LockFreeQueues.html
1.2887 -//
1.2888 -// * The cxq can have multiple concurrent "pushers" but only one concurrent
1.2889 -// detaching thread. This mechanism is immune from the ABA corruption.
1.2890 -// More precisely, the CAS-based "push" onto cxq is ABA-oblivious.
1.2891 -//
1.2892 -// * Taken together, the cxq and the EntryList constitute or form a
1.2893 -// single logical queue of threads stalled trying to acquire the lock.
1.2894 -// We use two distinct lists to improve the odds of a constant-time
1.2895 -// dequeue operation after acquisition (in the ::enter() epilog) and
1.2896 -// to reduce heat on the list ends. (c.f. Michael Scott's "2Q" algorithm).
1.2897 -// A key desideratum is to minimize queue & monitor metadata manipulation
1.2898 -// that occurs while holding the monitor lock -- that is, we want to
1.2899 -// minimize monitor lock holds times. Note that even a small amount of
1.2900 -// fixed spinning will greatly reduce the # of enqueue-dequeue operations
1.2901 -// on EntryList|cxq. That is, spinning relieves contention on the "inner"
1.2902 -// locks and monitor metadata.
1.2903 -//
1.2904 -// Cxq points to the the set of Recently Arrived Threads attempting entry.
1.2905 -// Because we push threads onto _cxq with CAS, the RATs must take the form of
1.2906 -// a singly-linked LIFO. We drain _cxq into EntryList at unlock-time when
1.2907 -// the unlocking thread notices that EntryList is null but _cxq is != null.
1.2908 -//
1.2909 -// The EntryList is ordered by the prevailing queue discipline and
1.2910 -// can be organized in any convenient fashion, such as a doubly-linked list or
1.2911 -// a circular doubly-linked list. Critically, we want insert and delete operations
1.2912 -// to operate in constant-time. If we need a priority queue then something akin
1.2913 -// to Solaris' sleepq would work nicely. Viz.,
1.2914 -// http://agg.eng/ws/on10_nightly/source/usr/src/uts/common/os/sleepq.c.
1.2915 -// Queue discipline is enforced at ::exit() time, when the unlocking thread
1.2916 -// drains the cxq into the EntryList, and orders or reorders the threads on the
1.2917 -// EntryList accordingly.
1.2918 -//
1.2919 -// Barring "lock barging", this mechanism provides fair cyclic ordering,
1.2920 -// somewhat similar to an elevator-scan.
1.2921 -//
1.2922 -// * The monitor synchronization subsystem avoids the use of native
1.2923 -// synchronization primitives except for the narrow platform-specific
1.2924 -// park-unpark abstraction. See the comments in os_solaris.cpp regarding
1.2925 -// the semantics of park-unpark. Put another way, this monitor implementation
1.2926 -// depends only on atomic operations and park-unpark. The monitor subsystem
1.2927 -// manages all RUNNING->BLOCKED and BLOCKED->READY transitions while the
1.2928 -// underlying OS manages the READY<->RUN transitions.
1.2929 -//
1.2930 -// * Waiting threads reside on the WaitSet list -- wait() puts
1.2931 -// the caller onto the WaitSet.
1.2932 -//
1.2933 -// * notify() or notifyAll() simply transfers threads from the WaitSet to
1.2934 -// either the EntryList or cxq. Subsequent exit() operations will
1.2935 -// unpark the notifyee. Unparking a notifee in notify() is inefficient -
1.2936 -// it's likely the notifyee would simply impale itself on the lock held
1.2937 -// by the notifier.
1.2938 -//
1.2939 -// * An interesting alternative is to encode cxq as (List,LockByte) where
1.2940 -// the LockByte is 0 iff the monitor is owned. _owner is simply an auxiliary
1.2941 -// variable, like _recursions, in the scheme. The threads or Events that form
1.2942 -// the list would have to be aligned in 256-byte addresses. A thread would
1.2943 -// try to acquire the lock or enqueue itself with CAS, but exiting threads
1.2944 -// could use a 1-0 protocol and simply STB to set the LockByte to 0.
1.2945 -// Note that is is *not* word-tearing, but it does presume that full-word
1.2946 -// CAS operations are coherent with intermix with STB operations. That's true
1.2947 -// on most common processors.
1.2948 -//
1.2949 -// * See also http://blogs.sun.com/dave
1.2950 -
1.2951 -
1.2952 -void ATTR ObjectMonitor::EnterI (TRAPS) {
1.2953 - Thread * Self = THREAD ;
1.2954 - assert (Self->is_Java_thread(), "invariant") ;
1.2955 - assert (((JavaThread *) Self)->thread_state() == _thread_blocked , "invariant") ;
1.2956 -
1.2957 - // Try the lock - TATAS
1.2958 - if (TryLock (Self) > 0) {
1.2959 - assert (_succ != Self , "invariant") ;
1.2960 - assert (_owner == Self , "invariant") ;
1.2961 - assert (_Responsible != Self , "invariant") ;
1.2962 - return ;
1.2963 - }
1.2964 -
1.2965 - DeferredInitialize () ;
1.2966 -
1.2967 - // We try one round of spinning *before* enqueueing Self.
1.2968 - //
1.2969 - // If the _owner is ready but OFFPROC we could use a YieldTo()
1.2970 - // operation to donate the remainder of this thread's quantum
1.2971 - // to the owner. This has subtle but beneficial affinity
1.2972 - // effects.
1.2973 -
1.2974 - if (TrySpin (Self) > 0) {
1.2975 - assert (_owner == Self , "invariant") ;
1.2976 - assert (_succ != Self , "invariant") ;
1.2977 - assert (_Responsible != Self , "invariant") ;
1.2978 - return ;
1.2979 - }
1.2980 -
1.2981 - // The Spin failed -- Enqueue and park the thread ...
1.2982 - assert (_succ != Self , "invariant") ;
1.2983 - assert (_owner != Self , "invariant") ;
1.2984 - assert (_Responsible != Self , "invariant") ;
1.2985 -
1.2986 - // Enqueue "Self" on ObjectMonitor's _cxq.
1.2987 - //
1.2988 - // Node acts as a proxy for Self.
1.2989 - // As an aside, if were to ever rewrite the synchronization code mostly
1.2990 - // in Java, WaitNodes, ObjectMonitors, and Events would become 1st-class
1.2991 - // Java objects. This would avoid awkward lifecycle and liveness issues,
1.2992 - // as well as eliminate a subset of ABA issues.
1.2993 - // TODO: eliminate ObjectWaiter and enqueue either Threads or Events.
1.2994 - //
1.2995 -
1.2996 - ObjectWaiter node(Self) ;
1.2997 - Self->_ParkEvent->reset() ;
1.2998 - node._prev = (ObjectWaiter *) 0xBAD ;
1.2999 - node.TState = ObjectWaiter::TS_CXQ ;
1.3000 -
1.3001 - // Push "Self" onto the front of the _cxq.
1.3002 - // Once on cxq/EntryList, Self stays on-queue until it acquires the lock.
1.3003 - // Note that spinning tends to reduce the rate at which threads
1.3004 - // enqueue and dequeue on EntryList|cxq.
1.3005 - ObjectWaiter * nxt ;
1.3006 - for (;;) {
1.3007 - node._next = nxt = _cxq ;
1.3008 - if (Atomic::cmpxchg_ptr (&node, &_cxq, nxt) == nxt) break ;
1.3009 -
1.3010 - // Interference - the CAS failed because _cxq changed. Just retry.
1.3011 - // As an optional optimization we retry the lock.
1.3012 - if (TryLock (Self) > 0) {
1.3013 - assert (_succ != Self , "invariant") ;
1.3014 - assert (_owner == Self , "invariant") ;
1.3015 - assert (_Responsible != Self , "invariant") ;
1.3016 - return ;
1.3017 - }
1.3018 - }
1.3019 -
1.3020 - // Check for cxq|EntryList edge transition to non-null. This indicates
1.3021 - // the onset of contention. While contention persists exiting threads
1.3022 - // will use a ST:MEMBAR:LD 1-1 exit protocol. When contention abates exit
1.3023 - // operations revert to the faster 1-0 mode. This enter operation may interleave
1.3024 - // (race) a concurrent 1-0 exit operation, resulting in stranding, so we
1.3025 - // arrange for one of the contending thread to use a timed park() operations
1.3026 - // to detect and recover from the race. (Stranding is form of progress failure
1.3027 - // where the monitor is unlocked but all the contending threads remain parked).
1.3028 - // That is, at least one of the contended threads will periodically poll _owner.
1.3029 - // One of the contending threads will become the designated "Responsible" thread.
1.3030 - // The Responsible thread uses a timed park instead of a normal indefinite park
1.3031 - // operation -- it periodically wakes and checks for and recovers from potential
1.3032 - // strandings admitted by 1-0 exit operations. We need at most one Responsible
1.3033 - // thread per-monitor at any given moment. Only threads on cxq|EntryList may
1.3034 - // be responsible for a monitor.
1.3035 - //
1.3036 - // Currently, one of the contended threads takes on the added role of "Responsible".
1.3037 - // A viable alternative would be to use a dedicated "stranding checker" thread
1.3038 - // that periodically iterated over all the threads (or active monitors) and unparked
1.3039 - // successors where there was risk of stranding. This would help eliminate the
1.3040 - // timer scalability issues we see on some platforms as we'd only have one thread
1.3041 - // -- the checker -- parked on a timer.
1.3042 -
1.3043 - if ((SyncFlags & 16) == 0 && nxt == NULL && _EntryList == NULL) {
1.3044 - // Try to assume the role of responsible thread for the monitor.
1.3045 - // CONSIDER: ST vs CAS vs { if (Responsible==null) Responsible=Self }
1.3046 - Atomic::cmpxchg_ptr (Self, &_Responsible, NULL) ;
1.3047 - }
1.3048 -
1.3049 - // The lock have been released while this thread was occupied queueing
1.3050 - // itself onto _cxq. To close the race and avoid "stranding" and
1.3051 - // progress-liveness failure we must resample-retry _owner before parking.
1.3052 - // Note the Dekker/Lamport duality: ST cxq; MEMBAR; LD Owner.
1.3053 - // In this case the ST-MEMBAR is accomplished with CAS().
1.3054 - //
1.3055 - // TODO: Defer all thread state transitions until park-time.
1.3056 - // Since state transitions are heavy and inefficient we'd like
1.3057 - // to defer the state transitions until absolutely necessary,
1.3058 - // and in doing so avoid some transitions ...
1.3059 -
1.3060 - TEVENT (Inflated enter - Contention) ;
1.3061 - int nWakeups = 0 ;
1.3062 - int RecheckInterval = 1 ;
1.3063 -
1.3064 - for (;;) {
1.3065 -
1.3066 - if (TryLock (Self) > 0) break ;
1.3067 - assert (_owner != Self, "invariant") ;
1.3068 -
1.3069 - if ((SyncFlags & 2) && _Responsible == NULL) {
1.3070 - Atomic::cmpxchg_ptr (Self, &_Responsible, NULL) ;
1.3071 - }
1.3072 -
1.3073 - // park self
1.3074 - if (_Responsible == Self || (SyncFlags & 1)) {
1.3075 - TEVENT (Inflated enter - park TIMED) ;
1.3076 - Self->_ParkEvent->park ((jlong) RecheckInterval) ;
1.3077 - // Increase the RecheckInterval, but clamp the value.
1.3078 - RecheckInterval *= 8 ;
1.3079 - if (RecheckInterval > 1000) RecheckInterval = 1000 ;
1.3080 - } else {
1.3081 - TEVENT (Inflated enter - park UNTIMED) ;
1.3082 - Self->_ParkEvent->park() ;
1.3083 - }
1.3084 -
1.3085 - if (TryLock(Self) > 0) break ;
1.3086 -
1.3087 - // The lock is still contested.
1.3088 - // Keep a tally of the # of futile wakeups.
1.3089 - // Note that the counter is not protected by a lock or updated by atomics.
1.3090 - // That is by design - we trade "lossy" counters which are exposed to
1.3091 - // races during updates for a lower probe effect.
1.3092 - TEVENT (Inflated enter - Futile wakeup) ;
1.3093 - if (ObjectSynchronizer::_sync_FutileWakeups != NULL) {
1.3094 - ObjectSynchronizer::_sync_FutileWakeups->inc() ;
1.3095 - }
1.3096 - ++ nWakeups ;
1.3097 -
1.3098 - // Assuming this is not a spurious wakeup we'll normally find _succ == Self.
1.3099 - // We can defer clearing _succ until after the spin completes
1.3100 - // TrySpin() must tolerate being called with _succ == Self.
1.3101 - // Try yet another round of adaptive spinning.
1.3102 - if ((Knob_SpinAfterFutile & 1) && TrySpin (Self) > 0) break ;
1.3103 -
1.3104 - // We can find that we were unpark()ed and redesignated _succ while
1.3105 - // we were spinning. That's harmless. If we iterate and call park(),
1.3106 - // park() will consume the event and return immediately and we'll
1.3107 - // just spin again. This pattern can repeat, leaving _succ to simply
1.3108 - // spin on a CPU. Enable Knob_ResetEvent to clear pending unparks().
1.3109 - // Alternately, we can sample fired() here, and if set, forgo spinning
1.3110 - // in the next iteration.
1.3111 -
1.3112 - if ((Knob_ResetEvent & 1) && Self->_ParkEvent->fired()) {
1.3113 - Self->_ParkEvent->reset() ;
1.3114 - OrderAccess::fence() ;
1.3115 - }
1.3116 - if (_succ == Self) _succ = NULL ;
1.3117 -
1.3118 - // Invariant: after clearing _succ a thread *must* retry _owner before parking.
1.3119 - OrderAccess::fence() ;
1.3120 - }
1.3121 -
1.3122 - // Egress :
1.3123 - // Self has acquired the lock -- Unlink Self from the cxq or EntryList.
1.3124 - // Normally we'll find Self on the EntryList .
1.3125 - // From the perspective of the lock owner (this thread), the
1.3126 - // EntryList is stable and cxq is prepend-only.
1.3127 - // The head of cxq is volatile but the interior is stable.
1.3128 - // In addition, Self.TState is stable.
1.3129 -
1.3130 - assert (_owner == Self , "invariant") ;
1.3131 - assert (object() != NULL , "invariant") ;
1.3132 - // I'd like to write:
1.3133 - // guarantee (((oop)(object()))->mark() == markOopDesc::encode(this), "invariant") ;
1.3134 - // but as we're at a safepoint that's not safe.
1.3135 -
1.3136 - UnlinkAfterAcquire (Self, &node) ;
1.3137 - if (_succ == Self) _succ = NULL ;
1.3138 -
1.3139 - assert (_succ != Self, "invariant") ;
1.3140 - if (_Responsible == Self) {
1.3141 - _Responsible = NULL ;
1.3142 - // Dekker pivot-point.
1.3143 - // Consider OrderAccess::storeload() here
1.3144 -
1.3145 - // We may leave threads on cxq|EntryList without a designated
1.3146 - // "Responsible" thread. This is benign. When this thread subsequently
1.3147 - // exits the monitor it can "see" such preexisting "old" threads --
1.3148 - // threads that arrived on the cxq|EntryList before the fence, above --
1.3149 - // by LDing cxq|EntryList. Newly arrived threads -- that is, threads
1.3150 - // that arrive on cxq after the ST:MEMBAR, above -- will set Responsible
1.3151 - // non-null and elect a new "Responsible" timer thread.
1.3152 - //
1.3153 - // This thread executes:
1.3154 - // ST Responsible=null; MEMBAR (in enter epilog - here)
1.3155 - // LD cxq|EntryList (in subsequent exit)
1.3156 - //
1.3157 - // Entering threads in the slow/contended path execute:
1.3158 - // ST cxq=nonnull; MEMBAR; LD Responsible (in enter prolog)
1.3159 - // The (ST cxq; MEMBAR) is accomplished with CAS().
1.3160 - //
1.3161 - // The MEMBAR, above, prevents the LD of cxq|EntryList in the subsequent
1.3162 - // exit operation from floating above the ST Responsible=null.
1.3163 - //
1.3164 - // In *practice* however, EnterI() is always followed by some atomic
1.3165 - // operation such as the decrement of _count in ::enter(). Those atomics
1.3166 - // obviate the need for the explicit MEMBAR, above.
1.3167 - }
1.3168 -
1.3169 - // We've acquired ownership with CAS().
1.3170 - // CAS is serializing -- it has MEMBAR/FENCE-equivalent semantics.
1.3171 - // But since the CAS() this thread may have also stored into _succ,
1.3172 - // EntryList, cxq or Responsible. These meta-data updates must be
1.3173 - // visible __before this thread subsequently drops the lock.
1.3174 - // Consider what could occur if we didn't enforce this constraint --
1.3175 - // STs to monitor meta-data and user-data could reorder with (become
1.3176 - // visible after) the ST in exit that drops ownership of the lock.
1.3177 - // Some other thread could then acquire the lock, but observe inconsistent
1.3178 - // or old monitor meta-data and heap data. That violates the JMM.
1.3179 - // To that end, the 1-0 exit() operation must have at least STST|LDST
1.3180 - // "release" barrier semantics. Specifically, there must be at least a
1.3181 - // STST|LDST barrier in exit() before the ST of null into _owner that drops
1.3182 - // the lock. The barrier ensures that changes to monitor meta-data and data
1.3183 - // protected by the lock will be visible before we release the lock, and
1.3184 - // therefore before some other thread (CPU) has a chance to acquire the lock.
1.3185 - // See also: http://gee.cs.oswego.edu/dl/jmm/cookbook.html.
1.3186 - //
1.3187 - // Critically, any prior STs to _succ or EntryList must be visible before
1.3188 - // the ST of null into _owner in the *subsequent* (following) corresponding
1.3189 - // monitorexit. Recall too, that in 1-0 mode monitorexit does not necessarily
1.3190 - // execute a serializing instruction.
1.3191 -
1.3192 - if (SyncFlags & 8) {
1.3193 - OrderAccess::fence() ;
1.3194 - }
1.3195 - return ;
1.3196 -}
1.3197 -
1.3198 -// ExitSuspendEquivalent:
1.3199 -// A faster alternate to handle_special_suspend_equivalent_condition()
1.3200 -//
1.3201 -// handle_special_suspend_equivalent_condition() unconditionally
1.3202 -// acquires the SR_lock. On some platforms uncontended MutexLocker()
1.3203 -// operations have high latency. Note that in ::enter() we call HSSEC
1.3204 -// while holding the monitor, so we effectively lengthen the critical sections.
1.3205 -//
1.3206 -// There are a number of possible solutions:
1.3207 -//
1.3208 -// A. To ameliorate the problem we might also defer state transitions
1.3209 -// to as late as possible -- just prior to parking.
1.3210 -// Given that, we'd call HSSEC after having returned from park(),
1.3211 -// but before attempting to acquire the monitor. This is only a
1.3212 -// partial solution. It avoids calling HSSEC while holding the
1.3213 -// monitor (good), but it still increases successor reacquisition latency --
1.3214 -// the interval between unparking a successor and the time the successor
1.3215 -// resumes and retries the lock. See ReenterI(), which defers state transitions.
1.3216 -// If we use this technique we can also avoid EnterI()-exit() loop
1.3217 -// in ::enter() where we iteratively drop the lock and then attempt
1.3218 -// to reacquire it after suspending.
1.3219 -//
1.3220 -// B. In the future we might fold all the suspend bits into a
1.3221 -// composite per-thread suspend flag and then update it with CAS().
1.3222 -// Alternately, a Dekker-like mechanism with multiple variables
1.3223 -// would suffice:
1.3224 -// ST Self->_suspend_equivalent = false
1.3225 -// MEMBAR
1.3226 -// LD Self_>_suspend_flags
1.3227 -//
1.3228 -
1.3229 -
1.3230 -bool ObjectMonitor::ExitSuspendEquivalent (JavaThread * jSelf) {
1.3231 - int Mode = Knob_FastHSSEC ;
1.3232 - if (Mode && !jSelf->is_external_suspend()) {
1.3233 - assert (jSelf->is_suspend_equivalent(), "invariant") ;
1.3234 - jSelf->clear_suspend_equivalent() ;
1.3235 - if (2 == Mode) OrderAccess::storeload() ;
1.3236 - if (!jSelf->is_external_suspend()) return false ;
1.3237 - // We raced a suspension -- fall thru into the slow path
1.3238 - TEVENT (ExitSuspendEquivalent - raced) ;
1.3239 - jSelf->set_suspend_equivalent() ;
1.3240 - }
1.3241 - return jSelf->handle_special_suspend_equivalent_condition() ;
1.3242 -}
1.3243 -
1.3244 -
1.3245 -// ReenterI() is a specialized inline form of the latter half of the
1.3246 -// contended slow-path from EnterI(). We use ReenterI() only for
1.3247 -// monitor reentry in wait().
1.3248 -//
1.3249 -// In the future we should reconcile EnterI() and ReenterI(), adding
1.3250 -// Knob_Reset and Knob_SpinAfterFutile support and restructuring the
1.3251 -// loop accordingly.
1.3252 -
1.3253 -void ATTR ObjectMonitor::ReenterI (Thread * Self, ObjectWaiter * SelfNode) {
1.3254 - assert (Self != NULL , "invariant") ;
1.3255 - assert (SelfNode != NULL , "invariant") ;
1.3256 - assert (SelfNode->_thread == Self , "invariant") ;
1.3257 - assert (_waiters > 0 , "invariant") ;
1.3258 - assert (((oop)(object()))->mark() == markOopDesc::encode(this) , "invariant") ;
1.3259 - assert (((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant") ;
1.3260 - JavaThread * jt = (JavaThread *) Self ;
1.3261 -
1.3262 - int nWakeups = 0 ;
1.3263 - for (;;) {
1.3264 - ObjectWaiter::TStates v = SelfNode->TState ;
1.3265 - guarantee (v == ObjectWaiter::TS_ENTER || v == ObjectWaiter::TS_CXQ, "invariant") ;
1.3266 - assert (_owner != Self, "invariant") ;
1.3267 -
1.3268 - if (TryLock (Self) > 0) break ;
1.3269 - if (TrySpin (Self) > 0) break ;
1.3270 -
1.3271 - TEVENT (Wait Reentry - parking) ;
1.3272 -
1.3273 - // State transition wrappers around park() ...
1.3274 - // ReenterI() wisely defers state transitions until
1.3275 - // it's clear we must park the thread.
1.3276 - {
1.3277 - OSThreadContendState osts(Self->osthread());
1.3278 - ThreadBlockInVM tbivm(jt);
1.3279 -
1.3280 - // cleared by handle_special_suspend_equivalent_condition()
1.3281 - // or java_suspend_self()
1.3282 - jt->set_suspend_equivalent();
1.3283 - if (SyncFlags & 1) {
1.3284 - Self->_ParkEvent->park ((jlong)1000) ;
1.3285 - } else {
1.3286 - Self->_ParkEvent->park () ;
1.3287 - }
1.3288 -
1.3289 - // were we externally suspended while we were waiting?
1.3290 - for (;;) {
1.3291 - if (!ExitSuspendEquivalent (jt)) break ;
1.3292 - if (_succ == Self) { _succ = NULL; OrderAccess::fence(); }
1.3293 - jt->java_suspend_self();
1.3294 - jt->set_suspend_equivalent();
1.3295 - }
1.3296 - }
1.3297 -
1.3298 - // Try again, but just so we distinguish between futile wakeups and
1.3299 - // successful wakeups. The following test isn't algorithmically
1.3300 - // necessary, but it helps us maintain sensible statistics.
1.3301 - if (TryLock(Self) > 0) break ;
1.3302 -
1.3303 - // The lock is still contested.
1.3304 - // Keep a tally of the # of futile wakeups.
1.3305 - // Note that the counter is not protected by a lock or updated by atomics.
1.3306 - // That is by design - we trade "lossy" counters which are exposed to
1.3307 - // races during updates for a lower probe effect.
1.3308 - TEVENT (Wait Reentry - futile wakeup) ;
1.3309 - ++ nWakeups ;
1.3310 -
1.3311 - // Assuming this is not a spurious wakeup we'll normally
1.3312 - // find that _succ == Self.
1.3313 - if (_succ == Self) _succ = NULL ;
1.3314 -
1.3315 - // Invariant: after clearing _succ a contending thread
1.3316 - // *must* retry _owner before parking.
1.3317 - OrderAccess::fence() ;
1.3318 -
1.3319 - if (ObjectSynchronizer::_sync_FutileWakeups != NULL) {
1.3320 - ObjectSynchronizer::_sync_FutileWakeups->inc() ;
1.3321 - }
1.3322 - }
1.3323 -
1.3324 - // Self has acquired the lock -- Unlink Self from the cxq or EntryList .
1.3325 - // Normally we'll find Self on the EntryList.
1.3326 - // Unlinking from the EntryList is constant-time and atomic-free.
1.3327 - // From the perspective of the lock owner (this thread), the
1.3328 - // EntryList is stable and cxq is prepend-only.
1.3329 - // The head of cxq is volatile but the interior is stable.
1.3330 - // In addition, Self.TState is stable.
1.3331 -
1.3332 - assert (_owner == Self, "invariant") ;
1.3333 - assert (((oop)(object()))->mark() == markOopDesc::encode(this), "invariant") ;
1.3334 - UnlinkAfterAcquire (Self, SelfNode) ;
1.3335 - if (_succ == Self) _succ = NULL ;
1.3336 - assert (_succ != Self, "invariant") ;
1.3337 - SelfNode->TState = ObjectWaiter::TS_RUN ;
1.3338 - OrderAccess::fence() ; // see comments at the end of EnterI()
1.3339 -}
1.3340 -
1.3341 -bool ObjectMonitor::try_enter(Thread* THREAD) {
1.3342 - if (THREAD != _owner) {
1.3343 - if (THREAD->is_lock_owned ((address)_owner)) {
1.3344 - assert(_recursions == 0, "internal state error");
1.3345 - _owner = THREAD ;
1.3346 - _recursions = 1 ;
1.3347 - OwnerIsThread = 1 ;
1.3348 - return true;
1.3349 - }
1.3350 - if (Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) != NULL) {
1.3351 - return false;
1.3352 - }
1.3353 - return true;
1.3354 - } else {
1.3355 - _recursions++;
1.3356 - return true;
1.3357 - }
1.3358 -}
1.3359 -
1.3360 -void ATTR ObjectMonitor::enter(TRAPS) {
1.3361 - // The following code is ordered to check the most common cases first
1.3362 - // and to reduce RTS->RTO cache line upgrades on SPARC and IA32 processors.
1.3363 - Thread * const Self = THREAD ;
1.3364 - void * cur ;
1.3365 -
1.3366 - cur = Atomic::cmpxchg_ptr (Self, &_owner, NULL) ;
1.3367 - if (cur == NULL) {
1.3368 - // Either ASSERT _recursions == 0 or explicitly set _recursions = 0.
1.3369 - assert (_recursions == 0 , "invariant") ;
1.3370 - assert (_owner == Self, "invariant") ;
1.3371 - // CONSIDER: set or assert OwnerIsThread == 1
1.3372 - return ;
1.3373 - }
1.3374 -
1.3375 - if (cur == Self) {
1.3376 - // TODO-FIXME: check for integer overflow! BUGID 6557169.
1.3377 - _recursions ++ ;
1.3378 - return ;
1.3379 - }
1.3380 -
1.3381 - if (Self->is_lock_owned ((address)cur)) {
1.3382 - assert (_recursions == 0, "internal state error");
1.3383 - _recursions = 1 ;
1.3384 - // Commute owner from a thread-specific on-stack BasicLockObject address to
1.3385 - // a full-fledged "Thread *".
1.3386 - _owner = Self ;
1.3387 - OwnerIsThread = 1 ;
1.3388 - return ;
1.3389 - }
1.3390 -
1.3391 - // We've encountered genuine contention.
1.3392 - assert (Self->_Stalled == 0, "invariant") ;
1.3393 - Self->_Stalled = intptr_t(this) ;
1.3394 -
1.3395 - // Try one round of spinning *before* enqueueing Self
1.3396 - // and before going through the awkward and expensive state
1.3397 - // transitions. The following spin is strictly optional ...
1.3398 - // Note that if we acquire the monitor from an initial spin
1.3399 - // we forgo posting JVMTI events and firing DTRACE probes.
1.3400 - if (Knob_SpinEarly && TrySpin (Self) > 0) {
1.3401 - assert (_owner == Self , "invariant") ;
1.3402 - assert (_recursions == 0 , "invariant") ;
1.3403 - assert (((oop)(object()))->mark() == markOopDesc::encode(this), "invariant") ;
1.3404 - Self->_Stalled = 0 ;
1.3405 - return ;
1.3406 - }
1.3407 -
1.3408 - assert (_owner != Self , "invariant") ;
1.3409 - assert (_succ != Self , "invariant") ;
1.3410 - assert (Self->is_Java_thread() , "invariant") ;
1.3411 - JavaThread * jt = (JavaThread *) Self ;
1.3412 - assert (!SafepointSynchronize::is_at_safepoint(), "invariant") ;
1.3413 - assert (jt->thread_state() != _thread_blocked , "invariant") ;
1.3414 - assert (this->object() != NULL , "invariant") ;
1.3415 - assert (_count >= 0, "invariant") ;
1.3416 -
1.3417 - // Prevent deflation at STW-time. See deflate_idle_monitors() and is_busy().
1.3418 - // Ensure the object-monitor relationship remains stable while there's contention.
1.3419 - Atomic::inc_ptr(&_count);
1.3420 -
1.3421 - { // Change java thread status to indicate blocked on monitor enter.
1.3422 - JavaThreadBlockedOnMonitorEnterState jtbmes(jt, this);
1.3423 -
1.3424 - DTRACE_MONITOR_PROBE(contended__enter, this, object(), jt);
1.3425 - if (JvmtiExport::should_post_monitor_contended_enter()) {
1.3426 - JvmtiExport::post_monitor_contended_enter(jt, this);
1.3427 - }
1.3428 -
1.3429 - OSThreadContendState osts(Self->osthread());
1.3430 - ThreadBlockInVM tbivm(jt);
1.3431 -
1.3432 - Self->set_current_pending_monitor(this);
1.3433 -
1.3434 - // TODO-FIXME: change the following for(;;) loop to straight-line code.
1.3435 - for (;;) {
1.3436 - jt->set_suspend_equivalent();
1.3437 - // cleared by handle_special_suspend_equivalent_condition()
1.3438 - // or java_suspend_self()
1.3439 -
1.3440 - EnterI (THREAD) ;
1.3441 -
1.3442 - if (!ExitSuspendEquivalent(jt)) break ;
1.3443 -
1.3444 - //
1.3445 - // We have acquired the contended monitor, but while we were
1.3446 - // waiting another thread suspended us. We don't want to enter
1.3447 - // the monitor while suspended because that would surprise the
1.3448 - // thread that suspended us.
1.3449 - //
1.3450 - _recursions = 0 ;
1.3451 - _succ = NULL ;
1.3452 - exit (Self) ;
1.3453 -
1.3454 - jt->java_suspend_self();
1.3455 - }
1.3456 - Self->set_current_pending_monitor(NULL);
1.3457 - }
1.3458 -
1.3459 - Atomic::dec_ptr(&_count);
1.3460 - assert (_count >= 0, "invariant") ;
1.3461 - Self->_Stalled = 0 ;
1.3462 -
1.3463 - // Must either set _recursions = 0 or ASSERT _recursions == 0.
1.3464 - assert (_recursions == 0 , "invariant") ;
1.3465 - assert (_owner == Self , "invariant") ;
1.3466 - assert (_succ != Self , "invariant") ;
1.3467 - assert (((oop)(object()))->mark() == markOopDesc::encode(this), "invariant") ;
1.3468 -
1.3469 - // The thread -- now the owner -- is back in vm mode.
1.3470 - // Report the glorious news via TI,DTrace and jvmstat.
1.3471 - // The probe effect is non-trivial. All the reportage occurs
1.3472 - // while we hold the monitor, increasing the length of the critical
1.3473 - // section. Amdahl's parallel speedup law comes vividly into play.
1.3474 - //
1.3475 - // Another option might be to aggregate the events (thread local or
1.3476 - // per-monitor aggregation) and defer reporting until a more opportune
1.3477 - // time -- such as next time some thread encounters contention but has
1.3478 - // yet to acquire the lock. While spinning that thread could
1.3479 - // spinning we could increment JVMStat counters, etc.
1.3480 -
1.3481 - DTRACE_MONITOR_PROBE(contended__entered, this, object(), jt);
1.3482 - if (JvmtiExport::should_post_monitor_contended_entered()) {
1.3483 - JvmtiExport::post_monitor_contended_entered(jt, this);
1.3484 - }
1.3485 - if (ObjectSynchronizer::_sync_ContendedLockAttempts != NULL) {
1.3486 - ObjectSynchronizer::_sync_ContendedLockAttempts->inc() ;
1.3487 - }
1.3488 -}
1.3489 -
1.3490 -void ObjectMonitor::ExitEpilog (Thread * Self, ObjectWaiter * Wakee) {
1.3491 - assert (_owner == Self, "invariant") ;
1.3492 -
1.3493 - // Exit protocol:
1.3494 - // 1. ST _succ = wakee
1.3495 - // 2. membar #loadstore|#storestore;
1.3496 - // 2. ST _owner = NULL
1.3497 - // 3. unpark(wakee)
1.3498 -
1.3499 - _succ = Knob_SuccEnabled ? Wakee->_thread : NULL ;
1.3500 - ParkEvent * Trigger = Wakee->_event ;
1.3501 -
1.3502 - // Hygiene -- once we've set _owner = NULL we can't safely dereference Wakee again.
1.3503 - // The thread associated with Wakee may have grabbed the lock and "Wakee" may be
1.3504 - // out-of-scope (non-extant).
1.3505 - Wakee = NULL ;
1.3506 -
1.3507 - // Drop the lock
1.3508 - OrderAccess::release_store_ptr (&_owner, NULL) ;
1.3509 - OrderAccess::fence() ; // ST _owner vs LD in unpark()
1.3510 -
1.3511 - // TODO-FIXME:
1.3512 - // If there's a safepoint pending the best policy would be to
1.3513 - // get _this thread to a safepoint and only wake the successor
1.3514 - // after the safepoint completed. monitorexit uses a "leaf"
1.3515 - // state transition, however, so this thread can't become
1.3516 - // safe at this point in time. (Its stack isn't walkable).
1.3517 - // The next best thing is to defer waking the successor by
1.3518 - // adding to a list of thread to be unparked after at the
1.3519 - // end of the forthcoming STW).
1.3520 - if (SafepointSynchronize::do_call_back()) {
1.3521 - TEVENT (unpark before SAFEPOINT) ;
1.3522 - }
1.3523 -
1.3524 - // Possible optimizations ...
1.3525 - //
1.3526 - // * Consider: set Wakee->UnparkTime = timeNow()
1.3527 - // When the thread wakes up it'll compute (timeNow() - Self->UnparkTime()).
1.3528 - // By measuring recent ONPROC latency we can approximate the
1.3529 - // system load. In turn, we can feed that information back
1.3530 - // into the spinning & succession policies.
1.3531 - // (ONPROC latency correlates strongly with load).
1.3532 - //
1.3533 - // * Pull affinity:
1.3534 - // If the wakee is cold then transiently setting it's affinity
1.3535 - // to the current CPU is a good idea.
1.3536 - // See http://j2se.east/~dice/PERSIST/050624-PullAffinity.txt
1.3537 - DTRACE_MONITOR_PROBE(contended__exit, this, object(), Self);
1.3538 - Trigger->unpark() ;
1.3539 -
1.3540 - // Maintain stats and report events to JVMTI
1.3541 - if (ObjectSynchronizer::_sync_Parks != NULL) {
1.3542 - ObjectSynchronizer::_sync_Parks->inc() ;
1.3543 - }
1.3544 -}
1.3545 -
1.3546 -
1.3547 -// exit()
1.3548 -// ~~~~~~
1.3549 -// Note that the collector can't reclaim the objectMonitor or deflate
1.3550 -// the object out from underneath the thread calling ::exit() as the
1.3551 -// thread calling ::exit() never transitions to a stable state.
1.3552 -// This inhibits GC, which in turn inhibits asynchronous (and
1.3553 -// inopportune) reclamation of "this".
1.3554 -//
1.3555 -// We'd like to assert that: (THREAD->thread_state() != _thread_blocked) ;
1.3556 -// There's one exception to the claim above, however. EnterI() can call
1.3557 -// exit() to drop a lock if the acquirer has been externally suspended.
1.3558 -// In that case exit() is called with _thread_state as _thread_blocked,
1.3559 -// but the monitor's _count field is > 0, which inhibits reclamation.
1.3560 -//
1.3561 -// 1-0 exit
1.3562 -// ~~~~~~~~
1.3563 -// ::exit() uses a canonical 1-1 idiom with a MEMBAR although some of
1.3564 -// the fast-path operators have been optimized so the common ::exit()
1.3565 -// operation is 1-0. See i486.ad fast_unlock(), for instance.
1.3566 -// The code emitted by fast_unlock() elides the usual MEMBAR. This
1.3567 -// greatly improves latency -- MEMBAR and CAS having considerable local
1.3568 -// latency on modern processors -- but at the cost of "stranding". Absent the
1.3569 -// MEMBAR, a thread in fast_unlock() can race a thread in the slow
1.3570 -// ::enter() path, resulting in the entering thread being stranding
1.3571 -// and a progress-liveness failure. Stranding is extremely rare.
1.3572 -// We use timers (timed park operations) & periodic polling to detect
1.3573 -// and recover from stranding. Potentially stranded threads periodically
1.3574 -// wake up and poll the lock. See the usage of the _Responsible variable.
1.3575 -//
1.3576 -// The CAS() in enter provides for safety and exclusion, while the CAS or
1.3577 -// MEMBAR in exit provides for progress and avoids stranding. 1-0 locking
1.3578 -// eliminates the CAS/MEMBAR from the exist path, but it admits stranding.
1.3579 -// We detect and recover from stranding with timers.
1.3580 -//
1.3581 -// If a thread transiently strands it'll park until (a) another
1.3582 -// thread acquires the lock and then drops the lock, at which time the
1.3583 -// exiting thread will notice and unpark the stranded thread, or, (b)
1.3584 -// the timer expires. If the lock is high traffic then the stranding latency
1.3585 -// will be low due to (a). If the lock is low traffic then the odds of
1.3586 -// stranding are lower, although the worst-case stranding latency
1.3587 -// is longer. Critically, we don't want to put excessive load in the
1.3588 -// platform's timer subsystem. We want to minimize both the timer injection
1.3589 -// rate (timers created/sec) as well as the number of timers active at
1.3590 -// any one time. (more precisely, we want to minimize timer-seconds, which is
1.3591 -// the integral of the # of active timers at any instant over time).
1.3592 -// Both impinge on OS scalability. Given that, at most one thread parked on
1.3593 -// a monitor will use a timer.
1.3594 -
1.3595 -void ATTR ObjectMonitor::exit(TRAPS) {
1.3596 - Thread * Self = THREAD ;
1.3597 - if (THREAD != _owner) {
1.3598 - if (THREAD->is_lock_owned((address) _owner)) {
1.3599 - // Transmute _owner from a BasicLock pointer to a Thread address.
1.3600 - // We don't need to hold _mutex for this transition.
1.3601 - // Non-null to Non-null is safe as long as all readers can
1.3602 - // tolerate either flavor.
1.3603 - assert (_recursions == 0, "invariant") ;
1.3604 - _owner = THREAD ;
1.3605 - _recursions = 0 ;
1.3606 - OwnerIsThread = 1 ;
1.3607 - } else {
1.3608 - // NOTE: we need to handle unbalanced monitor enter/exit
1.3609 - // in native code by throwing an exception.
1.3610 - // TODO: Throw an IllegalMonitorStateException ?
1.3611 - TEVENT (Exit - Throw IMSX) ;
1.3612 - assert(false, "Non-balanced monitor enter/exit!");
1.3613 - if (false) {
1.3614 - THROW(vmSymbols::java_lang_IllegalMonitorStateException());
1.3615 - }
1.3616 - return;
1.3617 - }
1.3618 - }
1.3619 -
1.3620 - if (_recursions != 0) {
1.3621 - _recursions--; // this is simple recursive enter
1.3622 - TEVENT (Inflated exit - recursive) ;
1.3623 - return ;
1.3624 - }
1.3625 -
1.3626 - // Invariant: after setting Responsible=null an thread must execute
1.3627 - // a MEMBAR or other serializing instruction before fetching EntryList|cxq.
1.3628 - if ((SyncFlags & 4) == 0) {
1.3629 - _Responsible = NULL ;
1.3630 - }
1.3631 -
1.3632 - for (;;) {
1.3633 - assert (THREAD == _owner, "invariant") ;
1.3634 -
1.3635 - // Fast-path monitor exit:
1.3636 - //
1.3637 - // Observe the Dekker/Lamport duality:
1.3638 - // A thread in ::exit() executes:
1.3639 - // ST Owner=null; MEMBAR; LD EntryList|cxq.
1.3640 - // A thread in the contended ::enter() path executes the complementary:
1.3641 - // ST EntryList|cxq = nonnull; MEMBAR; LD Owner.
1.3642 - //
1.3643 - // Note that there's a benign race in the exit path. We can drop the
1.3644 - // lock, another thread can reacquire the lock immediately, and we can
1.3645 - // then wake a thread unnecessarily (yet another flavor of futile wakeup).
1.3646 - // This is benign, and we've structured the code so the windows are short
1.3647 - // and the frequency of such futile wakeups is low.
1.3648 - //
1.3649 - // We could eliminate the race by encoding both the "LOCKED" state and
1.3650 - // the queue head in a single word. Exit would then use either CAS to
1.3651 - // clear the LOCKED bit/byte. This precludes the desirable 1-0 optimization,
1.3652 - // however.
1.3653 - //
1.3654 - // Possible fast-path ::exit() optimization:
1.3655 - // The current fast-path exit implementation fetches both cxq and EntryList.
1.3656 - // See also i486.ad fast_unlock(). Testing has shown that two LDs
1.3657 - // isn't measurably slower than a single LD on any platforms.
1.3658 - // Still, we could reduce the 2 LDs to one or zero by one of the following:
1.3659 - //
1.3660 - // - Use _count instead of cxq|EntryList
1.3661 - // We intend to eliminate _count, however, when we switch
1.3662 - // to on-the-fly deflation in ::exit() as is used in
1.3663 - // Metalocks and RelaxedLocks.
1.3664 - //
1.3665 - // - Establish the invariant that cxq == null implies EntryList == null.
1.3666 - // set cxq == EMPTY (1) to encode the state where cxq is empty
1.3667 - // by EntryList != null. EMPTY is a distinguished value.
1.3668 - // The fast-path exit() would fetch cxq but not EntryList.
1.3669 - //
1.3670 - // - Encode succ as follows:
1.3671 - // succ = t : Thread t is the successor -- t is ready or is spinning.
1.3672 - // Exiting thread does not need to wake a successor.
1.3673 - // succ = 0 : No successor required -> (EntryList|cxq) == null
1.3674 - // Exiting thread does not need to wake a successor
1.3675 - // succ = 1 : Successor required -> (EntryList|cxq) != null and
1.3676 - // logically succ == null.
1.3677 - // Exiting thread must wake a successor.
1.3678 - //
1.3679 - // The 1-1 fast-exit path would appear as :
1.3680 - // _owner = null ; membar ;
1.3681 - // if (_succ == 1 && CAS (&_owner, null, Self) == null) goto SlowPath
1.3682 - // goto FastPathDone ;
1.3683 - //
1.3684 - // and the 1-0 fast-exit path would appear as:
1.3685 - // if (_succ == 1) goto SlowPath
1.3686 - // Owner = null ;
1.3687 - // goto FastPathDone
1.3688 - //
1.3689 - // - Encode the LSB of _owner as 1 to indicate that exit()
1.3690 - // must use the slow-path and make a successor ready.
1.3691 - // (_owner & 1) == 0 IFF succ != null || (EntryList|cxq) == null
1.3692 - // (_owner & 1) == 0 IFF succ == null && (EntryList|cxq) != null (obviously)
1.3693 - // The 1-0 fast exit path would read:
1.3694 - // if (_owner != Self) goto SlowPath
1.3695 - // _owner = null
1.3696 - // goto FastPathDone
1.3697 -
1.3698 - if (Knob_ExitPolicy == 0) {
1.3699 - // release semantics: prior loads and stores from within the critical section
1.3700 - // must not float (reorder) past the following store that drops the lock.
1.3701 - // On SPARC that requires MEMBAR #loadstore|#storestore.
1.3702 - // But of course in TSO #loadstore|#storestore is not required.
1.3703 - // I'd like to write one of the following:
1.3704 - // A. OrderAccess::release() ; _owner = NULL
1.3705 - // B. OrderAccess::loadstore(); OrderAccess::storestore(); _owner = NULL;
1.3706 - // Unfortunately OrderAccess::release() and OrderAccess::loadstore() both
1.3707 - // store into a _dummy variable. That store is not needed, but can result
1.3708 - // in massive wasteful coherency traffic on classic SMP systems.
1.3709 - // Instead, I use release_store(), which is implemented as just a simple
1.3710 - // ST on x64, x86 and SPARC.
1.3711 - OrderAccess::release_store_ptr (&_owner, NULL) ; // drop the lock
1.3712 - OrderAccess::storeload() ; // See if we need to wake a successor
1.3713 - if ((intptr_t(_EntryList)|intptr_t(_cxq)) == 0 || _succ != NULL) {
1.3714 - TEVENT (Inflated exit - simple egress) ;
1.3715 - return ;
1.3716 - }
1.3717 - TEVENT (Inflated exit - complex egress) ;
1.3718 -
1.3719 - // Normally the exiting thread is responsible for ensuring succession,
1.3720 - // but if other successors are ready or other entering threads are spinning
1.3721 - // then this thread can simply store NULL into _owner and exit without
1.3722 - // waking a successor. The existence of spinners or ready successors
1.3723 - // guarantees proper succession (liveness). Responsibility passes to the
1.3724 - // ready or running successors. The exiting thread delegates the duty.
1.3725 - // More precisely, if a successor already exists this thread is absolved
1.3726 - // of the responsibility of waking (unparking) one.
1.3727 - //
1.3728 - // The _succ variable is critical to reducing futile wakeup frequency.
1.3729 - // _succ identifies the "heir presumptive" thread that has been made
1.3730 - // ready (unparked) but that has not yet run. We need only one such
1.3731 - // successor thread to guarantee progress.
1.3732 - // See http://www.usenix.org/events/jvm01/full_papers/dice/dice.pdf
1.3733 - // section 3.3 "Futile Wakeup Throttling" for details.
1.3734 - //
1.3735 - // Note that spinners in Enter() also set _succ non-null.
1.3736 - // In the current implementation spinners opportunistically set
1.3737 - // _succ so that exiting threads might avoid waking a successor.
1.3738 - // Another less appealing alternative would be for the exiting thread
1.3739 - // to drop the lock and then spin briefly to see if a spinner managed
1.3740 - // to acquire the lock. If so, the exiting thread could exit
1.3741 - // immediately without waking a successor, otherwise the exiting
1.3742 - // thread would need to dequeue and wake a successor.
1.3743 - // (Note that we'd need to make the post-drop spin short, but no
1.3744 - // shorter than the worst-case round-trip cache-line migration time.
1.3745 - // The dropped lock needs to become visible to the spinner, and then
1.3746 - // the acquisition of the lock by the spinner must become visible to
1.3747 - // the exiting thread).
1.3748 - //
1.3749 -
1.3750 - // It appears that an heir-presumptive (successor) must be made ready.
1.3751 - // Only the current lock owner can manipulate the EntryList or
1.3752 - // drain _cxq, so we need to reacquire the lock. If we fail
1.3753 - // to reacquire the lock the responsibility for ensuring succession
1.3754 - // falls to the new owner.
1.3755 - //
1.3756 - if (Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) != NULL) {
1.3757 - return ;
1.3758 - }
1.3759 - TEVENT (Exit - Reacquired) ;
1.3760 - } else {
1.3761 - if ((intptr_t(_EntryList)|intptr_t(_cxq)) == 0 || _succ != NULL) {
1.3762 - OrderAccess::release_store_ptr (&_owner, NULL) ; // drop the lock
1.3763 - OrderAccess::storeload() ;
1.3764 - // Ratify the previously observed values.
1.3765 - if (_cxq == NULL || _succ != NULL) {
1.3766 - TEVENT (Inflated exit - simple egress) ;
1.3767 - return ;
1.3768 - }
1.3769 -
1.3770 - // inopportune interleaving -- the exiting thread (this thread)
1.3771 - // in the fast-exit path raced an entering thread in the slow-enter
1.3772 - // path.
1.3773 - // We have two choices:
1.3774 - // A. Try to reacquire the lock.
1.3775 - // If the CAS() fails return immediately, otherwise
1.3776 - // we either restart/rerun the exit operation, or simply
1.3777 - // fall-through into the code below which wakes a successor.
1.3778 - // B. If the elements forming the EntryList|cxq are TSM
1.3779 - // we could simply unpark() the lead thread and return
1.3780 - // without having set _succ.
1.3781 - if (Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) != NULL) {
1.3782 - TEVENT (Inflated exit - reacquired succeeded) ;
1.3783 - return ;
1.3784 - }
1.3785 - TEVENT (Inflated exit - reacquired failed) ;
1.3786 - } else {
1.3787 - TEVENT (Inflated exit - complex egress) ;
1.3788 - }
1.3789 - }
1.3790 -
1.3791 - guarantee (_owner == THREAD, "invariant") ;
1.3792 -
1.3793 - // Select an appropriate successor ("heir presumptive") from the EntryList
1.3794 - // and make it ready. Generally we just wake the head of EntryList .
1.3795 - // There's no algorithmic constraint that we use the head - it's just
1.3796 - // a policy decision. Note that the thread at head of the EntryList
1.3797 - // remains at the head until it acquires the lock. This means we'll
1.3798 - // repeatedly wake the same thread until it manages to grab the lock.
1.3799 - // This is generally a good policy - if we're seeing lots of futile wakeups
1.3800 - // at least we're waking/rewaking a thread that's like to be hot or warm
1.3801 - // (have residual D$ and TLB affinity).
1.3802 - //
1.3803 - // "Wakeup locality" optimization:
1.3804 - // http://j2se.east/~dice/PERSIST/040825-WakeLocality.txt
1.3805 - // In the future we'll try to bias the selection mechanism
1.3806 - // to preferentially pick a thread that recently ran on
1.3807 - // a processor element that shares cache with the CPU on which
1.3808 - // the exiting thread is running. We need access to Solaris'
1.3809 - // schedctl.sc_cpu to make that work.
1.3810 - //
1.3811 - ObjectWaiter * w = NULL ;
1.3812 - int QMode = Knob_QMode ;
1.3813 -
1.3814 - if (QMode == 2 && _cxq != NULL) {
1.3815 - // QMode == 2 : cxq has precedence over EntryList.
1.3816 - // Try to directly wake a successor from the cxq.
1.3817 - // If successful, the successor will need to unlink itself from cxq.
1.3818 - w = _cxq ;
1.3819 - assert (w != NULL, "invariant") ;
1.3820 - assert (w->TState == ObjectWaiter::TS_CXQ, "Invariant") ;
1.3821 - ExitEpilog (Self, w) ;
1.3822 - return ;
1.3823 - }
1.3824 -
1.3825 - if (QMode == 3 && _cxq != NULL) {
1.3826 - // Aggressively drain cxq into EntryList at the first opportunity.
1.3827 - // This policy ensure that recently-run threads live at the head of EntryList.
1.3828 - // Drain _cxq into EntryList - bulk transfer.
1.3829 - // First, detach _cxq.
1.3830 - // The following loop is tantamount to: w = swap (&cxq, NULL)
1.3831 - w = _cxq ;
1.3832 - for (;;) {
1.3833 - assert (w != NULL, "Invariant") ;
1.3834 - ObjectWaiter * u = (ObjectWaiter *) Atomic::cmpxchg_ptr (NULL, &_cxq, w) ;
1.3835 - if (u == w) break ;
1.3836 - w = u ;
1.3837 - }
1.3838 - assert (w != NULL , "invariant") ;
1.3839 -
1.3840 - ObjectWaiter * q = NULL ;
1.3841 - ObjectWaiter * p ;
1.3842 - for (p = w ; p != NULL ; p = p->_next) {
1.3843 - guarantee (p->TState == ObjectWaiter::TS_CXQ, "Invariant") ;
1.3844 - p->TState = ObjectWaiter::TS_ENTER ;
1.3845 - p->_prev = q ;
1.3846 - q = p ;
1.3847 - }
1.3848 -
1.3849 - // Append the RATs to the EntryList
1.3850 - // TODO: organize EntryList as a CDLL so we can locate the tail in constant-time.
1.3851 - ObjectWaiter * Tail ;
1.3852 - for (Tail = _EntryList ; Tail != NULL && Tail->_next != NULL ; Tail = Tail->_next) ;
1.3853 - if (Tail == NULL) {
1.3854 - _EntryList = w ;
1.3855 - } else {
1.3856 - Tail->_next = w ;
1.3857 - w->_prev = Tail ;
1.3858 - }
1.3859 -
1.3860 - // Fall thru into code that tries to wake a successor from EntryList
1.3861 - }
1.3862 -
1.3863 - if (QMode == 4 && _cxq != NULL) {
1.3864 - // Aggressively drain cxq into EntryList at the first opportunity.
1.3865 - // This policy ensure that recently-run threads live at the head of EntryList.
1.3866 -
1.3867 - // Drain _cxq into EntryList - bulk transfer.
1.3868 - // First, detach _cxq.
1.3869 - // The following loop is tantamount to: w = swap (&cxq, NULL)
1.3870 - w = _cxq ;
1.3871 - for (;;) {
1.3872 - assert (w != NULL, "Invariant") ;
1.3873 - ObjectWaiter * u = (ObjectWaiter *) Atomic::cmpxchg_ptr (NULL, &_cxq, w) ;
1.3874 - if (u == w) break ;
1.3875 - w = u ;
1.3876 - }
1.3877 - assert (w != NULL , "invariant") ;
1.3878 -
1.3879 - ObjectWaiter * q = NULL ;
1.3880 - ObjectWaiter * p ;
1.3881 - for (p = w ; p != NULL ; p = p->_next) {
1.3882 - guarantee (p->TState == ObjectWaiter::TS_CXQ, "Invariant") ;
1.3883 - p->TState = ObjectWaiter::TS_ENTER ;
1.3884 - p->_prev = q ;
1.3885 - q = p ;
1.3886 - }
1.3887 -
1.3888 - // Prepend the RATs to the EntryList
1.3889 - if (_EntryList != NULL) {
1.3890 - q->_next = _EntryList ;
1.3891 - _EntryList->_prev = q ;
1.3892 - }
1.3893 - _EntryList = w ;
1.3894 -
1.3895 - // Fall thru into code that tries to wake a successor from EntryList
1.3896 - }
1.3897 -
1.3898 - w = _EntryList ;
1.3899 - if (w != NULL) {
1.3900 - // I'd like to write: guarantee (w->_thread != Self).
1.3901 - // But in practice an exiting thread may find itself on the EntryList.
1.3902 - // Lets say thread T1 calls O.wait(). Wait() enqueues T1 on O's waitset and
1.3903 - // then calls exit(). Exit release the lock by setting O._owner to NULL.
1.3904 - // Lets say T1 then stalls. T2 acquires O and calls O.notify(). The
1.3905 - // notify() operation moves T1 from O's waitset to O's EntryList. T2 then
1.3906 - // release the lock "O". T2 resumes immediately after the ST of null into
1.3907 - // _owner, above. T2 notices that the EntryList is populated, so it
1.3908 - // reacquires the lock and then finds itself on the EntryList.
1.3909 - // Given all that, we have to tolerate the circumstance where "w" is
1.3910 - // associated with Self.
1.3911 - assert (w->TState == ObjectWaiter::TS_ENTER, "invariant") ;
1.3912 - ExitEpilog (Self, w) ;
1.3913 - return ;
1.3914 - }
1.3915 -
1.3916 - // If we find that both _cxq and EntryList are null then just
1.3917 - // re-run the exit protocol from the top.
1.3918 - w = _cxq ;
1.3919 - if (w == NULL) continue ;
1.3920 -
1.3921 - // Drain _cxq into EntryList - bulk transfer.
1.3922 - // First, detach _cxq.
1.3923 - // The following loop is tantamount to: w = swap (&cxq, NULL)
1.3924 - for (;;) {
1.3925 - assert (w != NULL, "Invariant") ;
1.3926 - ObjectWaiter * u = (ObjectWaiter *) Atomic::cmpxchg_ptr (NULL, &_cxq, w) ;
1.3927 - if (u == w) break ;
1.3928 - w = u ;
1.3929 - }
1.3930 - TEVENT (Inflated exit - drain cxq into EntryList) ;
1.3931 -
1.3932 - assert (w != NULL , "invariant") ;
1.3933 - assert (_EntryList == NULL , "invariant") ;
1.3934 -
1.3935 - // Convert the LIFO SLL anchored by _cxq into a DLL.
1.3936 - // The list reorganization step operates in O(LENGTH(w)) time.
1.3937 - // It's critical that this step operate quickly as
1.3938 - // "Self" still holds the outer-lock, restricting parallelism
1.3939 - // and effectively lengthening the critical section.
1.3940 - // Invariant: s chases t chases u.
1.3941 - // TODO-FIXME: consider changing EntryList from a DLL to a CDLL so
1.3942 - // we have faster access to the tail.
1.3943 -
1.3944 - if (QMode == 1) {
1.3945 - // QMode == 1 : drain cxq to EntryList, reversing order
1.3946 - // We also reverse the order of the list.
1.3947 - ObjectWaiter * s = NULL ;
1.3948 - ObjectWaiter * t = w ;
1.3949 - ObjectWaiter * u = NULL ;
1.3950 - while (t != NULL) {
1.3951 - guarantee (t->TState == ObjectWaiter::TS_CXQ, "invariant") ;
1.3952 - t->TState = ObjectWaiter::TS_ENTER ;
1.3953 - u = t->_next ;
1.3954 - t->_prev = u ;
1.3955 - t->_next = s ;
1.3956 - s = t;
1.3957 - t = u ;
1.3958 - }
1.3959 - _EntryList = s ;
1.3960 - assert (s != NULL, "invariant") ;
1.3961 - } else {
1.3962 - // QMode == 0 or QMode == 2
1.3963 - _EntryList = w ;
1.3964 - ObjectWaiter * q = NULL ;
1.3965 - ObjectWaiter * p ;
1.3966 - for (p = w ; p != NULL ; p = p->_next) {
1.3967 - guarantee (p->TState == ObjectWaiter::TS_CXQ, "Invariant") ;
1.3968 - p->TState = ObjectWaiter::TS_ENTER ;
1.3969 - p->_prev = q ;
1.3970 - q = p ;
1.3971 - }
1.3972 - }
1.3973 -
1.3974 - // In 1-0 mode we need: ST EntryList; MEMBAR #storestore; ST _owner = NULL
1.3975 - // The MEMBAR is satisfied by the release_store() operation in ExitEpilog().
1.3976 -
1.3977 - // See if we can abdicate to a spinner instead of waking a thread.
1.3978 - // A primary goal of the implementation is to reduce the
1.3979 - // context-switch rate.
1.3980 - if (_succ != NULL) continue;
1.3981 -
1.3982 - w = _EntryList ;
1.3983 - if (w != NULL) {
1.3984 - guarantee (w->TState == ObjectWaiter::TS_ENTER, "invariant") ;
1.3985 - ExitEpilog (Self, w) ;
1.3986 - return ;
1.3987 - }
1.3988 - }
1.3989 -}
1.3990 -// complete_exit exits a lock returning recursion count
1.3991 -// complete_exit/reenter operate as a wait without waiting
1.3992 -// complete_exit requires an inflated monitor
1.3993 -// The _owner field is not always the Thread addr even with an
1.3994 -// inflated monitor, e.g. the monitor can be inflated by a non-owning
1.3995 -// thread due to contention.
1.3996 -intptr_t ObjectMonitor::complete_exit(TRAPS) {
1.3997 - Thread * const Self = THREAD;
1.3998 - assert(Self->is_Java_thread(), "Must be Java thread!");
1.3999 - JavaThread *jt = (JavaThread *)THREAD;
1.4000 -
1.4001 - DeferredInitialize();
1.4002 -
1.4003 - if (THREAD != _owner) {
1.4004 - if (THREAD->is_lock_owned ((address)_owner)) {
1.4005 - assert(_recursions == 0, "internal state error");
1.4006 - _owner = THREAD ; /* Convert from basiclock addr to Thread addr */
1.4007 - _recursions = 0 ;
1.4008 - OwnerIsThread = 1 ;
1.4009 - }
1.4010 - }
1.4011 -
1.4012 - guarantee(Self == _owner, "complete_exit not owner");
1.4013 - intptr_t save = _recursions; // record the old recursion count
1.4014 - _recursions = 0; // set the recursion level to be 0
1.4015 - exit (Self) ; // exit the monitor
1.4016 - guarantee (_owner != Self, "invariant");
1.4017 - return save;
1.4018 -}
1.4019 -
1.4020 -// reenter() enters a lock and sets recursion count
1.4021 -// complete_exit/reenter operate as a wait without waiting
1.4022 -void ObjectMonitor::reenter(intptr_t recursions, TRAPS) {
1.4023 - Thread * const Self = THREAD;
1.4024 - assert(Self->is_Java_thread(), "Must be Java thread!");
1.4025 - JavaThread *jt = (JavaThread *)THREAD;
1.4026 -
1.4027 - guarantee(_owner != Self, "reenter already owner");
1.4028 - enter (THREAD); // enter the monitor
1.4029 - guarantee (_recursions == 0, "reenter recursion");
1.4030 - _recursions = recursions;
1.4031 - return;
1.4032 -}
1.4033 -
1.4034 -// Note: a subset of changes to ObjectMonitor::wait()
1.4035 -// will need to be replicated in complete_exit above
1.4036 -void ObjectMonitor::wait(jlong millis, bool interruptible, TRAPS) {
1.4037 - Thread * const Self = THREAD ;
1.4038 - assert(Self->is_Java_thread(), "Must be Java thread!");
1.4039 - JavaThread *jt = (JavaThread *)THREAD;
1.4040 -
1.4041 - DeferredInitialize () ;
1.4042 -
1.4043 - // Throw IMSX or IEX.
1.4044 - CHECK_OWNER();
1.4045 -
1.4046 - // check for a pending interrupt
1.4047 - if (interruptible && Thread::is_interrupted(Self, true) && !HAS_PENDING_EXCEPTION) {
1.4048 - // post monitor waited event. Note that this is past-tense, we are done waiting.
1.4049 - if (JvmtiExport::should_post_monitor_waited()) {
1.4050 - // Note: 'false' parameter is passed here because the
1.4051 - // wait was not timed out due to thread interrupt.
1.4052 - JvmtiExport::post_monitor_waited(jt, this, false);
1.4053 - }
1.4054 - TEVENT (Wait - Throw IEX) ;
1.4055 - THROW(vmSymbols::java_lang_InterruptedException());
1.4056 - return ;
1.4057 - }
1.4058 - TEVENT (Wait) ;
1.4059 -
1.4060 - assert (Self->_Stalled == 0, "invariant") ;
1.4061 - Self->_Stalled = intptr_t(this) ;
1.4062 - jt->set_current_waiting_monitor(this);
1.4063 -
1.4064 - // create a node to be put into the queue
1.4065 - // Critically, after we reset() the event but prior to park(), we must check
1.4066 - // for a pending interrupt.
1.4067 - ObjectWaiter node(Self);
1.4068 - node.TState = ObjectWaiter::TS_WAIT ;
1.4069 - Self->_ParkEvent->reset() ;
1.4070 - OrderAccess::fence(); // ST into Event; membar ; LD interrupted-flag
1.4071 -
1.4072 - // Enter the waiting queue, which is a circular doubly linked list in this case
1.4073 - // but it could be a priority queue or any data structure.
1.4074 - // _WaitSetLock protects the wait queue. Normally the wait queue is accessed only
1.4075 - // by the the owner of the monitor *except* in the case where park()
1.4076 - // returns because of a timeout of interrupt. Contention is exceptionally rare
1.4077 - // so we use a simple spin-lock instead of a heavier-weight blocking lock.
1.4078 -
1.4079 - Thread::SpinAcquire (&_WaitSetLock, "WaitSet - add") ;
1.4080 - AddWaiter (&node) ;
1.4081 - Thread::SpinRelease (&_WaitSetLock) ;
1.4082 -
1.4083 - if ((SyncFlags & 4) == 0) {
1.4084 - _Responsible = NULL ;
1.4085 - }
1.4086 - intptr_t save = _recursions; // record the old recursion count
1.4087 - _waiters++; // increment the number of waiters
1.4088 - _recursions = 0; // set the recursion level to be 1
1.4089 - exit (Self) ; // exit the monitor
1.4090 - guarantee (_owner != Self, "invariant") ;
1.4091 -
1.4092 - // As soon as the ObjectMonitor's ownership is dropped in the exit()
1.4093 - // call above, another thread can enter() the ObjectMonitor, do the
1.4094 - // notify(), and exit() the ObjectMonitor. If the other thread's
1.4095 - // exit() call chooses this thread as the successor and the unpark()
1.4096 - // call happens to occur while this thread is posting a
1.4097 - // MONITOR_CONTENDED_EXIT event, then we run the risk of the event
1.4098 - // handler using RawMonitors and consuming the unpark().
1.4099 - //
1.4100 - // To avoid the problem, we re-post the event. This does no harm
1.4101 - // even if the original unpark() was not consumed because we are the
1.4102 - // chosen successor for this monitor.
1.4103 - if (node._notified != 0 && _succ == Self) {
1.4104 - node._event->unpark();
1.4105 - }
1.4106 -
1.4107 - // The thread is on the WaitSet list - now park() it.
1.4108 - // On MP systems it's conceivable that a brief spin before we park
1.4109 - // could be profitable.
1.4110 - //
1.4111 - // TODO-FIXME: change the following logic to a loop of the form
1.4112 - // while (!timeout && !interrupted && _notified == 0) park()
1.4113 -
1.4114 - int ret = OS_OK ;
1.4115 - int WasNotified = 0 ;
1.4116 - { // State transition wrappers
1.4117 - OSThread* osthread = Self->osthread();
1.4118 - OSThreadWaitState osts(osthread, true);
1.4119 - {
1.4120 - ThreadBlockInVM tbivm(jt);
1.4121 - // Thread is in thread_blocked state and oop access is unsafe.
1.4122 - jt->set_suspend_equivalent();
1.4123 -
1.4124 - if (interruptible && (Thread::is_interrupted(THREAD, false) || HAS_PENDING_EXCEPTION)) {
1.4125 - // Intentionally empty
1.4126 - } else
1.4127 - if (node._notified == 0) {
1.4128 - if (millis <= 0) {
1.4129 - Self->_ParkEvent->park () ;
1.4130 - } else {
1.4131 - ret = Self->_ParkEvent->park (millis) ;
1.4132 - }
1.4133 - }
1.4134 -
1.4135 - // were we externally suspended while we were waiting?
1.4136 - if (ExitSuspendEquivalent (jt)) {
1.4137 - // TODO-FIXME: add -- if succ == Self then succ = null.
1.4138 - jt->java_suspend_self();
1.4139 - }
1.4140 -
1.4141 - } // Exit thread safepoint: transition _thread_blocked -> _thread_in_vm
1.4142 -
1.4143 -
1.4144 - // Node may be on the WaitSet, the EntryList (or cxq), or in transition
1.4145 - // from the WaitSet to the EntryList.
1.4146 - // See if we need to remove Node from the WaitSet.
1.4147 - // We use double-checked locking to avoid grabbing _WaitSetLock
1.4148 - // if the thread is not on the wait queue.
1.4149 - //
1.4150 - // Note that we don't need a fence before the fetch of TState.
1.4151 - // In the worst case we'll fetch a old-stale value of TS_WAIT previously
1.4152 - // written by the is thread. (perhaps the fetch might even be satisfied
1.4153 - // by a look-aside into the processor's own store buffer, although given
1.4154 - // the length of the code path between the prior ST and this load that's
1.4155 - // highly unlikely). If the following LD fetches a stale TS_WAIT value
1.4156 - // then we'll acquire the lock and then re-fetch a fresh TState value.
1.4157 - // That is, we fail toward safety.
1.4158 -
1.4159 - if (node.TState == ObjectWaiter::TS_WAIT) {
1.4160 - Thread::SpinAcquire (&_WaitSetLock, "WaitSet - unlink") ;
1.4161 - if (node.TState == ObjectWaiter::TS_WAIT) {
1.4162 - DequeueSpecificWaiter (&node) ; // unlink from WaitSet
1.4163 - assert(node._notified == 0, "invariant");
1.4164 - node.TState = ObjectWaiter::TS_RUN ;
1.4165 - }
1.4166 - Thread::SpinRelease (&_WaitSetLock) ;
1.4167 - }
1.4168 -
1.4169 - // The thread is now either on off-list (TS_RUN),
1.4170 - // on the EntryList (TS_ENTER), or on the cxq (TS_CXQ).
1.4171 - // The Node's TState variable is stable from the perspective of this thread.
1.4172 - // No other threads will asynchronously modify TState.
1.4173 - guarantee (node.TState != ObjectWaiter::TS_WAIT, "invariant") ;
1.4174 - OrderAccess::loadload() ;
1.4175 - if (_succ == Self) _succ = NULL ;
1.4176 - WasNotified = node._notified ;
1.4177 -
1.4178 - // Reentry phase -- reacquire the monitor.
1.4179 - // re-enter contended monitor after object.wait().
1.4180 - // retain OBJECT_WAIT state until re-enter successfully completes
1.4181 - // Thread state is thread_in_vm and oop access is again safe,
1.4182 - // although the raw address of the object may have changed.
1.4183 - // (Don't cache naked oops over safepoints, of course).
1.4184 -
1.4185 - // post monitor waited event. Note that this is past-tense, we are done waiting.
1.4186 - if (JvmtiExport::should_post_monitor_waited()) {
1.4187 - JvmtiExport::post_monitor_waited(jt, this, ret == OS_TIMEOUT);
1.4188 - }
1.4189 - OrderAccess::fence() ;
1.4190 -
1.4191 - assert (Self->_Stalled != 0, "invariant") ;
1.4192 - Self->_Stalled = 0 ;
1.4193 -
1.4194 - assert (_owner != Self, "invariant") ;
1.4195 - ObjectWaiter::TStates v = node.TState ;
1.4196 - if (v == ObjectWaiter::TS_RUN) {
1.4197 - enter (Self) ;
1.4198 - } else {
1.4199 - guarantee (v == ObjectWaiter::TS_ENTER || v == ObjectWaiter::TS_CXQ, "invariant") ;
1.4200 - ReenterI (Self, &node) ;
1.4201 - node.wait_reenter_end(this);
1.4202 - }
1.4203 -
1.4204 - // Self has reacquired the lock.
1.4205 - // Lifecycle - the node representing Self must not appear on any queues.
1.4206 - // Node is about to go out-of-scope, but even if it were immortal we wouldn't
1.4207 - // want residual elements associated with this thread left on any lists.
1.4208 - guarantee (node.TState == ObjectWaiter::TS_RUN, "invariant") ;
1.4209 - assert (_owner == Self, "invariant") ;
1.4210 - assert (_succ != Self , "invariant") ;
1.4211 - } // OSThreadWaitState()
1.4212 -
1.4213 - jt->set_current_waiting_monitor(NULL);
1.4214 -
1.4215 - guarantee (_recursions == 0, "invariant") ;
1.4216 - _recursions = save; // restore the old recursion count
1.4217 - _waiters--; // decrement the number of waiters
1.4218 -
1.4219 - // Verify a few postconditions
1.4220 - assert (_owner == Self , "invariant") ;
1.4221 - assert (_succ != Self , "invariant") ;
1.4222 - assert (((oop)(object()))->mark() == markOopDesc::encode(this), "invariant") ;
1.4223 -
1.4224 - if (SyncFlags & 32) {
1.4225 - OrderAccess::fence() ;
1.4226 - }
1.4227 -
1.4228 - // check if the notification happened
1.4229 - if (!WasNotified) {
1.4230 - // no, it could be timeout or Thread.interrupt() or both
1.4231 - // check for interrupt event, otherwise it is timeout
1.4232 - if (interruptible && Thread::is_interrupted(Self, true) && !HAS_PENDING_EXCEPTION) {
1.4233 - TEVENT (Wait - throw IEX from epilog) ;
1.4234 - THROW(vmSymbols::java_lang_InterruptedException());
1.4235 - }
1.4236 - }
1.4237 -
1.4238 - // NOTE: Spurious wake up will be consider as timeout.
1.4239 - // Monitor notify has precedence over thread interrupt.
1.4240 -}
1.4241 -
1.4242 -
1.4243 -// Consider:
1.4244 -// If the lock is cool (cxq == null && succ == null) and we're on an MP system
1.4245 -// then instead of transferring a thread from the WaitSet to the EntryList
1.4246 -// we might just dequeue a thread from the WaitSet and directly unpark() it.
1.4247 -
1.4248 -void ObjectMonitor::notify(TRAPS) {
1.4249 - CHECK_OWNER();
1.4250 - if (_WaitSet == NULL) {
1.4251 - TEVENT (Empty-Notify) ;
1.4252 - return ;
1.4253 - }
1.4254 - DTRACE_MONITOR_PROBE(notify, this, object(), THREAD);
1.4255 -
1.4256 - int Policy = Knob_MoveNotifyee ;
1.4257 -
1.4258 - Thread::SpinAcquire (&_WaitSetLock, "WaitSet - notify") ;
1.4259 - ObjectWaiter * iterator = DequeueWaiter() ;
1.4260 - if (iterator != NULL) {
1.4261 - TEVENT (Notify1 - Transfer) ;
1.4262 - guarantee (iterator->TState == ObjectWaiter::TS_WAIT, "invariant") ;
1.4263 - guarantee (iterator->_notified == 0, "invariant") ;
1.4264 - // Disposition - what might we do with iterator ?
1.4265 - // a. add it directly to the EntryList - either tail or head.
1.4266 - // b. push it onto the front of the _cxq.
1.4267 - // For now we use (a).
1.4268 - if (Policy != 4) {
1.4269 - iterator->TState = ObjectWaiter::TS_ENTER ;
1.4270 - }
1.4271 - iterator->_notified = 1 ;
1.4272 -
1.4273 - ObjectWaiter * List = _EntryList ;
1.4274 - if (List != NULL) {
1.4275 - assert (List->_prev == NULL, "invariant") ;
1.4276 - assert (List->TState == ObjectWaiter::TS_ENTER, "invariant") ;
1.4277 - assert (List != iterator, "invariant") ;
1.4278 - }
1.4279 -
1.4280 - if (Policy == 0) { // prepend to EntryList
1.4281 - if (List == NULL) {
1.4282 - iterator->_next = iterator->_prev = NULL ;
1.4283 - _EntryList = iterator ;
1.4284 - } else {
1.4285 - List->_prev = iterator ;
1.4286 - iterator->_next = List ;
1.4287 - iterator->_prev = NULL ;
1.4288 - _EntryList = iterator ;
1.4289 - }
1.4290 - } else
1.4291 - if (Policy == 1) { // append to EntryList
1.4292 - if (List == NULL) {
1.4293 - iterator->_next = iterator->_prev = NULL ;
1.4294 - _EntryList = iterator ;
1.4295 - } else {
1.4296 - // CONSIDER: finding the tail currently requires a linear-time walk of
1.4297 - // the EntryList. We can make tail access constant-time by converting to
1.4298 - // a CDLL instead of using our current DLL.
1.4299 - ObjectWaiter * Tail ;
1.4300 - for (Tail = List ; Tail->_next != NULL ; Tail = Tail->_next) ;
1.4301 - assert (Tail != NULL && Tail->_next == NULL, "invariant") ;
1.4302 - Tail->_next = iterator ;
1.4303 - iterator->_prev = Tail ;
1.4304 - iterator->_next = NULL ;
1.4305 - }
1.4306 - } else
1.4307 - if (Policy == 2) { // prepend to cxq
1.4308 - // prepend to cxq
1.4309 - if (List == NULL) {
1.4310 - iterator->_next = iterator->_prev = NULL ;
1.4311 - _EntryList = iterator ;
1.4312 - } else {
1.4313 - iterator->TState = ObjectWaiter::TS_CXQ ;
1.4314 - for (;;) {
1.4315 - ObjectWaiter * Front = _cxq ;
1.4316 - iterator->_next = Front ;
1.4317 - if (Atomic::cmpxchg_ptr (iterator, &_cxq, Front) == Front) {
1.4318 - break ;
1.4319 - }
1.4320 - }
1.4321 - }
1.4322 - } else
1.4323 - if (Policy == 3) { // append to cxq
1.4324 - iterator->TState = ObjectWaiter::TS_CXQ ;
1.4325 - for (;;) {
1.4326 - ObjectWaiter * Tail ;
1.4327 - Tail = _cxq ;
1.4328 - if (Tail == NULL) {
1.4329 - iterator->_next = NULL ;
1.4330 - if (Atomic::cmpxchg_ptr (iterator, &_cxq, NULL) == NULL) {
1.4331 - break ;
1.4332 - }
1.4333 - } else {
1.4334 - while (Tail->_next != NULL) Tail = Tail->_next ;
1.4335 - Tail->_next = iterator ;
1.4336 - iterator->_prev = Tail ;
1.4337 - iterator->_next = NULL ;
1.4338 - break ;
1.4339 - }
1.4340 - }
1.4341 - } else {
1.4342 - ParkEvent * ev = iterator->_event ;
1.4343 - iterator->TState = ObjectWaiter::TS_RUN ;
1.4344 - OrderAccess::fence() ;
1.4345 - ev->unpark() ;
1.4346 - }
1.4347 -
1.4348 - if (Policy < 4) {
1.4349 - iterator->wait_reenter_begin(this);
1.4350 - }
1.4351 -
1.4352 - // _WaitSetLock protects the wait queue, not the EntryList. We could
1.4353 - // move the add-to-EntryList operation, above, outside the critical section
1.4354 - // protected by _WaitSetLock. In practice that's not useful. With the
1.4355 - // exception of wait() timeouts and interrupts the monitor owner
1.4356 - // is the only thread that grabs _WaitSetLock. There's almost no contention
1.4357 - // on _WaitSetLock so it's not profitable to reduce the length of the
1.4358 - // critical section.
1.4359 - }
1.4360 -
1.4361 - Thread::SpinRelease (&_WaitSetLock) ;
1.4362 -
1.4363 - if (iterator != NULL && ObjectSynchronizer::_sync_Notifications != NULL) {
1.4364 - ObjectSynchronizer::_sync_Notifications->inc() ;
1.4365 - }
1.4366 -}
1.4367 -
1.4368 -
1.4369 -void ObjectMonitor::notifyAll(TRAPS) {
1.4370 - CHECK_OWNER();
1.4371 - ObjectWaiter* iterator;
1.4372 - if (_WaitSet == NULL) {
1.4373 - TEVENT (Empty-NotifyAll) ;
1.4374 - return ;
1.4375 - }
1.4376 - DTRACE_MONITOR_PROBE(notifyAll, this, object(), THREAD);
1.4377 -
1.4378 - int Policy = Knob_MoveNotifyee ;
1.4379 - int Tally = 0 ;
1.4380 - Thread::SpinAcquire (&_WaitSetLock, "WaitSet - notifyall") ;
1.4381 -
1.4382 - for (;;) {
1.4383 - iterator = DequeueWaiter () ;
1.4384 - if (iterator == NULL) break ;
1.4385 - TEVENT (NotifyAll - Transfer1) ;
1.4386 - ++Tally ;
1.4387 -
1.4388 - // Disposition - what might we do with iterator ?
1.4389 - // a. add it directly to the EntryList - either tail or head.
1.4390 - // b. push it onto the front of the _cxq.
1.4391 - // For now we use (a).
1.4392 - //
1.4393 - // TODO-FIXME: currently notifyAll() transfers the waiters one-at-a-time from the waitset
1.4394 - // to the EntryList. This could be done more efficiently with a single bulk transfer,
1.4395 - // but in practice it's not time-critical. Beware too, that in prepend-mode we invert the
1.4396 - // order of the waiters. Lets say that the waitset is "ABCD" and the EntryList is "XYZ".
1.4397 - // After a notifyAll() in prepend mode the waitset will be empty and the EntryList will
1.4398 - // be "DCBAXYZ".
1.4399 -
1.4400 - guarantee (iterator->TState == ObjectWaiter::TS_WAIT, "invariant") ;
1.4401 - guarantee (iterator->_notified == 0, "invariant") ;
1.4402 - iterator->_notified = 1 ;
1.4403 - if (Policy != 4) {
1.4404 - iterator->TState = ObjectWaiter::TS_ENTER ;
1.4405 - }
1.4406 -
1.4407 - ObjectWaiter * List = _EntryList ;
1.4408 - if (List != NULL) {
1.4409 - assert (List->_prev == NULL, "invariant") ;
1.4410 - assert (List->TState == ObjectWaiter::TS_ENTER, "invariant") ;
1.4411 - assert (List != iterator, "invariant") ;
1.4412 - }
1.4413 -
1.4414 - if (Policy == 0) { // prepend to EntryList
1.4415 - if (List == NULL) {
1.4416 - iterator->_next = iterator->_prev = NULL ;
1.4417 - _EntryList = iterator ;
1.4418 - } else {
1.4419 - List->_prev = iterator ;
1.4420 - iterator->_next = List ;
1.4421 - iterator->_prev = NULL ;
1.4422 - _EntryList = iterator ;
1.4423 - }
1.4424 - } else
1.4425 - if (Policy == 1) { // append to EntryList
1.4426 - if (List == NULL) {
1.4427 - iterator->_next = iterator->_prev = NULL ;
1.4428 - _EntryList = iterator ;
1.4429 - } else {
1.4430 - // CONSIDER: finding the tail currently requires a linear-time walk of
1.4431 - // the EntryList. We can make tail access constant-time by converting to
1.4432 - // a CDLL instead of using our current DLL.
1.4433 - ObjectWaiter * Tail ;
1.4434 - for (Tail = List ; Tail->_next != NULL ; Tail = Tail->_next) ;
1.4435 - assert (Tail != NULL && Tail->_next == NULL, "invariant") ;
1.4436 - Tail->_next = iterator ;
1.4437 - iterator->_prev = Tail ;
1.4438 - iterator->_next = NULL ;
1.4439 - }
1.4440 - } else
1.4441 - if (Policy == 2) { // prepend to cxq
1.4442 - // prepend to cxq
1.4443 - iterator->TState = ObjectWaiter::TS_CXQ ;
1.4444 - for (;;) {
1.4445 - ObjectWaiter * Front = _cxq ;
1.4446 - iterator->_next = Front ;
1.4447 - if (Atomic::cmpxchg_ptr (iterator, &_cxq, Front) == Front) {
1.4448 - break ;
1.4449 - }
1.4450 - }
1.4451 - } else
1.4452 - if (Policy == 3) { // append to cxq
1.4453 - iterator->TState = ObjectWaiter::TS_CXQ ;
1.4454 - for (;;) {
1.4455 - ObjectWaiter * Tail ;
1.4456 - Tail = _cxq ;
1.4457 - if (Tail == NULL) {
1.4458 - iterator->_next = NULL ;
1.4459 - if (Atomic::cmpxchg_ptr (iterator, &_cxq, NULL) == NULL) {
1.4460 - break ;
1.4461 - }
1.4462 - } else {
1.4463 - while (Tail->_next != NULL) Tail = Tail->_next ;
1.4464 - Tail->_next = iterator ;
1.4465 - iterator->_prev = Tail ;
1.4466 - iterator->_next = NULL ;
1.4467 - break ;
1.4468 - }
1.4469 - }
1.4470 - } else {
1.4471 - ParkEvent * ev = iterator->_event ;
1.4472 - iterator->TState = ObjectWaiter::TS_RUN ;
1.4473 - OrderAccess::fence() ;
1.4474 - ev->unpark() ;
1.4475 - }
1.4476 -
1.4477 - if (Policy < 4) {
1.4478 - iterator->wait_reenter_begin(this);
1.4479 - }
1.4480 -
1.4481 - // _WaitSetLock protects the wait queue, not the EntryList. We could
1.4482 - // move the add-to-EntryList operation, above, outside the critical section
1.4483 - // protected by _WaitSetLock. In practice that's not useful. With the
1.4484 - // exception of wait() timeouts and interrupts the monitor owner
1.4485 - // is the only thread that grabs _WaitSetLock. There's almost no contention
1.4486 - // on _WaitSetLock so it's not profitable to reduce the length of the
1.4487 - // critical section.
1.4488 - }
1.4489 -
1.4490 - Thread::SpinRelease (&_WaitSetLock) ;
1.4491 -
1.4492 - if (Tally != 0 && ObjectSynchronizer::_sync_Notifications != NULL) {
1.4493 - ObjectSynchronizer::_sync_Notifications->inc(Tally) ;
1.4494 - }
1.4495 -}
1.4496 -
1.4497 -// check_slow() is a misnomer. It's called to simply to throw an IMSX exception.
1.4498 -// TODO-FIXME: remove check_slow() -- it's likely dead.
1.4499 -
1.4500 -void ObjectMonitor::check_slow(TRAPS) {
1.4501 - TEVENT (check_slow - throw IMSX) ;
1.4502 - assert(THREAD != _owner && !THREAD->is_lock_owned((address) _owner), "must not be owner");
1.4503 - THROW_MSG(vmSymbols::java_lang_IllegalMonitorStateException(), "current thread not owner");
1.4504 -}
1.4505 -
1.4506 -
1.4507 -// -------------------------------------------------------------------------
1.4508 -// The raw monitor subsystem is entirely distinct from normal
1.4509 -// java-synchronization or jni-synchronization. raw monitors are not
1.4510 -// associated with objects. They can be implemented in any manner
1.4511 -// that makes sense. The original implementors decided to piggy-back
1.4512 -// the raw-monitor implementation on the existing Java objectMonitor mechanism.
1.4513 -// This flaw needs to fixed. We should reimplement raw monitors as sui-generis.
1.4514 -// Specifically, we should not implement raw monitors via java monitors.
1.4515 -// Time permitting, we should disentangle and deconvolve the two implementations
1.4516 -// and move the resulting raw monitor implementation over to the JVMTI directories.
1.4517 -// Ideally, the raw monitor implementation would be built on top of
1.4518 -// park-unpark and nothing else.
1.4519 -//
1.4520 -// raw monitors are used mainly by JVMTI
1.4521 -// The raw monitor implementation borrows the ObjectMonitor structure,
1.4522 -// but the operators are degenerate and extremely simple.
1.4523 -//
1.4524 -// Mixed use of a single objectMonitor instance -- as both a raw monitor
1.4525 -// and a normal java monitor -- is not permissible.
1.4526 -//
1.4527 -// Note that we use the single RawMonitor_lock to protect queue operations for
1.4528 -// _all_ raw monitors. This is a scalability impediment, but since raw monitor usage
1.4529 -// is deprecated and rare, this is not of concern. The RawMonitor_lock can not
1.4530 -// be held indefinitely. The critical sections must be short and bounded.
1.4531 -//
1.4532 -// -------------------------------------------------------------------------
1.4533 -
1.4534 -int ObjectMonitor::SimpleEnter (Thread * Self) {
1.4535 - for (;;) {
1.4536 - if (Atomic::cmpxchg_ptr (Self, &_owner, NULL) == NULL) {
1.4537 - return OS_OK ;
1.4538 - }
1.4539 -
1.4540 - ObjectWaiter Node (Self) ;
1.4541 - Self->_ParkEvent->reset() ; // strictly optional
1.4542 - Node.TState = ObjectWaiter::TS_ENTER ;
1.4543 -
1.4544 - RawMonitor_lock->lock_without_safepoint_check() ;
1.4545 - Node._next = _EntryList ;
1.4546 - _EntryList = &Node ;
1.4547 - OrderAccess::fence() ;
1.4548 - if (_owner == NULL && Atomic::cmpxchg_ptr (Self, &_owner, NULL) == NULL) {
1.4549 - _EntryList = Node._next ;
1.4550 - RawMonitor_lock->unlock() ;
1.4551 - return OS_OK ;
1.4552 - }
1.4553 - RawMonitor_lock->unlock() ;
1.4554 - while (Node.TState == ObjectWaiter::TS_ENTER) {
1.4555 - Self->_ParkEvent->park() ;
1.4556 - }
1.4557 - }
1.4558 -}
1.4559 -
1.4560 -int ObjectMonitor::SimpleExit (Thread * Self) {
1.4561 - guarantee (_owner == Self, "invariant") ;
1.4562 - OrderAccess::release_store_ptr (&_owner, NULL) ;
1.4563 - OrderAccess::fence() ;
1.4564 - if (_EntryList == NULL) return OS_OK ;
1.4565 - ObjectWaiter * w ;
1.4566 -
1.4567 - RawMonitor_lock->lock_without_safepoint_check() ;
1.4568 - w = _EntryList ;
1.4569 - if (w != NULL) {
1.4570 - _EntryList = w->_next ;
1.4571 - }
1.4572 - RawMonitor_lock->unlock() ;
1.4573 - if (w != NULL) {
1.4574 - guarantee (w ->TState == ObjectWaiter::TS_ENTER, "invariant") ;
1.4575 - ParkEvent * ev = w->_event ;
1.4576 - w->TState = ObjectWaiter::TS_RUN ;
1.4577 - OrderAccess::fence() ;
1.4578 - ev->unpark() ;
1.4579 - }
1.4580 - return OS_OK ;
1.4581 -}
1.4582 -
1.4583 -int ObjectMonitor::SimpleWait (Thread * Self, jlong millis) {
1.4584 - guarantee (_owner == Self , "invariant") ;
1.4585 - guarantee (_recursions == 0, "invariant") ;
1.4586 -
1.4587 - ObjectWaiter Node (Self) ;
1.4588 - Node._notified = 0 ;
1.4589 - Node.TState = ObjectWaiter::TS_WAIT ;
1.4590 -
1.4591 - RawMonitor_lock->lock_without_safepoint_check() ;
1.4592 - Node._next = _WaitSet ;
1.4593 - _WaitSet = &Node ;
1.4594 - RawMonitor_lock->unlock() ;
1.4595 -
1.4596 - SimpleExit (Self) ;
1.4597 - guarantee (_owner != Self, "invariant") ;
1.4598 -
1.4599 - int ret = OS_OK ;
1.4600 - if (millis <= 0) {
1.4601 - Self->_ParkEvent->park();
1.4602 - } else {
1.4603 - ret = Self->_ParkEvent->park(millis);
1.4604 - }
1.4605 -
1.4606 - // If thread still resides on the waitset then unlink it.
1.4607 - // Double-checked locking -- the usage is safe in this context
1.4608 - // as we TState is volatile and the lock-unlock operators are
1.4609 - // serializing (barrier-equivalent).
1.4610 -
1.4611 - if (Node.TState == ObjectWaiter::TS_WAIT) {
1.4612 - RawMonitor_lock->lock_without_safepoint_check() ;
1.4613 - if (Node.TState == ObjectWaiter::TS_WAIT) {
1.4614 - // Simple O(n) unlink, but performance isn't critical here.
1.4615 - ObjectWaiter * p ;
1.4616 - ObjectWaiter * q = NULL ;
1.4617 - for (p = _WaitSet ; p != &Node; p = p->_next) {
1.4618 - q = p ;
1.4619 - }
1.4620 - guarantee (p == &Node, "invariant") ;
1.4621 - if (q == NULL) {
1.4622 - guarantee (p == _WaitSet, "invariant") ;
1.4623 - _WaitSet = p->_next ;
1.4624 - } else {
1.4625 - guarantee (p == q->_next, "invariant") ;
1.4626 - q->_next = p->_next ;
1.4627 - }
1.4628 - Node.TState = ObjectWaiter::TS_RUN ;
1.4629 - }
1.4630 - RawMonitor_lock->unlock() ;
1.4631 - }
1.4632 -
1.4633 - guarantee (Node.TState == ObjectWaiter::TS_RUN, "invariant") ;
1.4634 - SimpleEnter (Self) ;
1.4635 -
1.4636 - guarantee (_owner == Self, "invariant") ;
1.4637 - guarantee (_recursions == 0, "invariant") ;
1.4638 - return ret ;
1.4639 -}
1.4640 -
1.4641 -int ObjectMonitor::SimpleNotify (Thread * Self, bool All) {
1.4642 - guarantee (_owner == Self, "invariant") ;
1.4643 - if (_WaitSet == NULL) return OS_OK ;
1.4644 -
1.4645 - // We have two options:
1.4646 - // A. Transfer the threads from the WaitSet to the EntryList
1.4647 - // B. Remove the thread from the WaitSet and unpark() it.
1.4648 - //
1.4649 - // We use (B), which is crude and results in lots of futile
1.4650 - // context switching. In particular (B) induces lots of contention.
1.4651 -
1.4652 - ParkEvent * ev = NULL ; // consider using a small auto array ...
1.4653 - RawMonitor_lock->lock_without_safepoint_check() ;
1.4654 - for (;;) {
1.4655 - ObjectWaiter * w = _WaitSet ;
1.4656 - if (w == NULL) break ;
1.4657 - _WaitSet = w->_next ;
1.4658 - if (ev != NULL) { ev->unpark(); ev = NULL; }
1.4659 - ev = w->_event ;
1.4660 - OrderAccess::loadstore() ;
1.4661 - w->TState = ObjectWaiter::TS_RUN ;
1.4662 - OrderAccess::storeload();
1.4663 - if (!All) break ;
1.4664 - }
1.4665 - RawMonitor_lock->unlock() ;
1.4666 - if (ev != NULL) ev->unpark();
1.4667 - return OS_OK ;
1.4668 -}
1.4669 -
1.4670 -// Any JavaThread will enter here with state _thread_blocked
1.4671 -int ObjectMonitor::raw_enter(TRAPS) {
1.4672 - TEVENT (raw_enter) ;
1.4673 - void * Contended ;
1.4674 -
1.4675 - // don't enter raw monitor if thread is being externally suspended, it will
1.4676 - // surprise the suspender if a "suspended" thread can still enter monitor
1.4677 - JavaThread * jt = (JavaThread *)THREAD;
1.4678 - if (THREAD->is_Java_thread()) {
1.4679 - jt->SR_lock()->lock_without_safepoint_check();
1.4680 - while (jt->is_external_suspend()) {
1.4681 - jt->SR_lock()->unlock();
1.4682 - jt->java_suspend_self();
1.4683 - jt->SR_lock()->lock_without_safepoint_check();
1.4684 - }
1.4685 - // guarded by SR_lock to avoid racing with new external suspend requests.
1.4686 - Contended = Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) ;
1.4687 - jt->SR_lock()->unlock();
1.4688 - } else {
1.4689 - Contended = Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) ;
1.4690 - }
1.4691 -
1.4692 - if (Contended == THREAD) {
1.4693 - _recursions ++ ;
1.4694 - return OM_OK ;
1.4695 - }
1.4696 -
1.4697 - if (Contended == NULL) {
1.4698 - guarantee (_owner == THREAD, "invariant") ;
1.4699 - guarantee (_recursions == 0, "invariant") ;
1.4700 - return OM_OK ;
1.4701 - }
1.4702 -
1.4703 - THREAD->set_current_pending_monitor(this);
1.4704 -
1.4705 - if (!THREAD->is_Java_thread()) {
1.4706 - // No other non-Java threads besides VM thread would acquire
1.4707 - // a raw monitor.
1.4708 - assert(THREAD->is_VM_thread(), "must be VM thread");
1.4709 - SimpleEnter (THREAD) ;
1.4710 - } else {
1.4711 - guarantee (jt->thread_state() == _thread_blocked, "invariant") ;
1.4712 - for (;;) {
1.4713 - jt->set_suspend_equivalent();
1.4714 - // cleared by handle_special_suspend_equivalent_condition() or
1.4715 - // java_suspend_self()
1.4716 - SimpleEnter (THREAD) ;
1.4717 -
1.4718 - // were we externally suspended while we were waiting?
1.4719 - if (!jt->handle_special_suspend_equivalent_condition()) break ;
1.4720 -
1.4721 - // This thread was externally suspended
1.4722 - //
1.4723 - // This logic isn't needed for JVMTI raw monitors,
1.4724 - // but doesn't hurt just in case the suspend rules change. This
1.4725 - // logic is needed for the ObjectMonitor.wait() reentry phase.
1.4726 - // We have reentered the contended monitor, but while we were
1.4727 - // waiting another thread suspended us. We don't want to reenter
1.4728 - // the monitor while suspended because that would surprise the
1.4729 - // thread that suspended us.
1.4730 - //
1.4731 - // Drop the lock -
1.4732 - SimpleExit (THREAD) ;
1.4733 -
1.4734 - jt->java_suspend_self();
1.4735 - }
1.4736 -
1.4737 - assert(_owner == THREAD, "Fatal error with monitor owner!");
1.4738 - assert(_recursions == 0, "Fatal error with monitor recursions!");
1.4739 - }
1.4740 -
1.4741 - THREAD->set_current_pending_monitor(NULL);
1.4742 - guarantee (_recursions == 0, "invariant") ;
1.4743 - return OM_OK;
1.4744 -}
1.4745 -
1.4746 -// Used mainly for JVMTI raw monitor implementation
1.4747 -// Also used for ObjectMonitor::wait().
1.4748 -int ObjectMonitor::raw_exit(TRAPS) {
1.4749 - TEVENT (raw_exit) ;
1.4750 - if (THREAD != _owner) {
1.4751 - return OM_ILLEGAL_MONITOR_STATE;
1.4752 - }
1.4753 - if (_recursions > 0) {
1.4754 - --_recursions ;
1.4755 - return OM_OK ;
1.4756 - }
1.4757 -
1.4758 - void * List = _EntryList ;
1.4759 - SimpleExit (THREAD) ;
1.4760 -
1.4761 - return OM_OK;
1.4762 -}
1.4763 -
1.4764 -// Used for JVMTI raw monitor implementation.
1.4765 -// All JavaThreads will enter here with state _thread_blocked
1.4766 -
1.4767 -int ObjectMonitor::raw_wait(jlong millis, bool interruptible, TRAPS) {
1.4768 - TEVENT (raw_wait) ;
1.4769 - if (THREAD != _owner) {
1.4770 - return OM_ILLEGAL_MONITOR_STATE;
1.4771 - }
1.4772 -
1.4773 - // To avoid spurious wakeups we reset the parkevent -- This is strictly optional.
1.4774 - // The caller must be able to tolerate spurious returns from raw_wait().
1.4775 - THREAD->_ParkEvent->reset() ;
1.4776 - OrderAccess::fence() ;
1.4777 -
1.4778 - // check interrupt event
1.4779 - if (interruptible && Thread::is_interrupted(THREAD, true)) {
1.4780 - return OM_INTERRUPTED;
1.4781 - }
1.4782 -
1.4783 - intptr_t save = _recursions ;
1.4784 - _recursions = 0 ;
1.4785 - _waiters ++ ;
1.4786 - if (THREAD->is_Java_thread()) {
1.4787 - guarantee (((JavaThread *) THREAD)->thread_state() == _thread_blocked, "invariant") ;
1.4788 - ((JavaThread *)THREAD)->set_suspend_equivalent();
1.4789 - }
1.4790 - int rv = SimpleWait (THREAD, millis) ;
1.4791 - _recursions = save ;
1.4792 - _waiters -- ;
1.4793 -
1.4794 - guarantee (THREAD == _owner, "invariant") ;
1.4795 - if (THREAD->is_Java_thread()) {
1.4796 - JavaThread * jSelf = (JavaThread *) THREAD ;
1.4797 - for (;;) {
1.4798 - if (!jSelf->handle_special_suspend_equivalent_condition()) break ;
1.4799 - SimpleExit (THREAD) ;
1.4800 - jSelf->java_suspend_self();
1.4801 - SimpleEnter (THREAD) ;
1.4802 - jSelf->set_suspend_equivalent() ;
1.4803 - }
1.4804 - }
1.4805 - guarantee (THREAD == _owner, "invariant") ;
1.4806 -
1.4807 - if (interruptible && Thread::is_interrupted(THREAD, true)) {
1.4808 - return OM_INTERRUPTED;
1.4809 - }
1.4810 - return OM_OK ;
1.4811 -}
1.4812 -
1.4813 -int ObjectMonitor::raw_notify(TRAPS) {
1.4814 - TEVENT (raw_notify) ;
1.4815 - if (THREAD != _owner) {
1.4816 - return OM_ILLEGAL_MONITOR_STATE;
1.4817 - }
1.4818 - SimpleNotify (THREAD, false) ;
1.4819 - return OM_OK;
1.4820 -}
1.4821 -
1.4822 -int ObjectMonitor::raw_notifyAll(TRAPS) {
1.4823 - TEVENT (raw_notifyAll) ;
1.4824 - if (THREAD != _owner) {
1.4825 - return OM_ILLEGAL_MONITOR_STATE;
1.4826 - }
1.4827 - SimpleNotify (THREAD, true) ;
1.4828 - return OM_OK;
1.4829 -}
1.4830 -
1.4831 -#ifndef PRODUCT
1.4832 -void ObjectMonitor::verify() {
1.4833 -}
1.4834 -
1.4835 -void ObjectMonitor::print() {
1.4836 -}
1.4837 -#endif
1.4838 -
1.4839 //------------------------------------------------------------------------------
1.4840 // Non-product code
1.4841
