1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/src/share/vm/runtime/mutex.hpp Sat Dec 01 00:00:00 2007 +0000
1.3 @@ -0,0 +1,318 @@
1.4 +/*
1.5 + * Copyright 1998-2006 Sun Microsystems, Inc. All Rights Reserved.
1.6 + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
1.7 + *
1.8 + * This code is free software; you can redistribute it and/or modify it
1.9 + * under the terms of the GNU General Public License version 2 only, as
1.10 + * published by the Free Software Foundation.
1.11 + *
1.12 + * This code is distributed in the hope that it will be useful, but WITHOUT
1.13 + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
1.14 + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
1.15 + * version 2 for more details (a copy is included in the LICENSE file that
1.16 + * accompanied this code).
1.17 + *
1.18 + * You should have received a copy of the GNU General Public License version
1.19 + * 2 along with this work; if not, write to the Free Software Foundation,
1.20 + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
1.21 + *
1.22 + * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
1.23 + * CA 95054 USA or visit www.sun.com if you need additional information or
1.24 + * have any questions.
1.25 + *
1.26 + */
1.27 +
1.28 +// The SplitWord construct allows us to colocate the contention queue
1.29 +// (cxq) with the lock-byte. The queue elements are ParkEvents, which are
1.30 +// always aligned on 256-byte addresses - the least significant byte of
1.31 +// a ParkEvent is always 0. Colocating the lock-byte with the queue
1.32 +// allows us to easily avoid what would otherwise be a race in lock()
1.33 +// if we were to use two completely separate fields for the contention queue
1.34 +// and the lock indicator. Specifically, colocation renders us immune
1.35 +// from the race where a thread might enqueue itself in the lock() slow-path
1.36 +// immediately after the lock holder drops the outer lock in the unlock()
1.37 +// fast-path.
1.38 +//
1.39 +// Colocation allows us to use a fast-path unlock() form that uses
1.40 +// A MEMBAR instead of a CAS. MEMBAR has lower local latency than CAS
1.41 +// on many platforms.
1.42 +//
1.43 +// See:
1.44 +// + http://blogs.sun.com/dave/entry/biased_locking_in_hotspot
1.45 +// + http://blogs.sun.com/dave/resource/synchronization-public2.pdf
1.46 +//
1.47 +// Note that we're *not* using word-tearing the classic sense.
1.48 +// The lock() fast-path will CAS the lockword and the unlock()
1.49 +// fast-path will store into the lock-byte colocated within the lockword.
1.50 +// We depend on the fact that all our reference platforms have
1.51 +// coherent and atomic byte accesses. More precisely, byte stores
1.52 +// interoperate in a safe, sane, and expected manner with respect to
1.53 +// CAS, ST and LDs to the full-word containing the byte.
1.54 +// If you're porting HotSpot to a platform where that isn't the case
1.55 +// then you'll want change the unlock() fast path from:
1.56 +// STB;MEMBAR #storeload; LDN
1.57 +// to a full-word CAS of the lockword.
1.58 +
1.59 +
1.60 +union SplitWord { // full-word with separately addressable LSB
1.61 + volatile intptr_t FullWord ;
1.62 + volatile void * Address ;
1.63 + volatile jbyte Bytes [sizeof(intptr_t)] ;
1.64 +} ;
1.65 +
1.66 +// Endian-ness ... index of least-significant byte in SplitWord.Bytes[]
1.67 +#ifdef AMD64 // little
1.68 + #define _LSBINDEX 0
1.69 +#else
1.70 +#if IA32 // little
1.71 + #define _LSBINDEX 0
1.72 +#else
1.73 +#ifdef SPARC // big
1.74 + #define _LSBINDEX (sizeof(intptr_t)-1)
1.75 +#else
1.76 + #error "unknown architecture"
1.77 +#endif
1.78 +#endif
1.79 +#endif
1.80 +
1.81 +class ParkEvent ;
1.82 +
1.83 +// See orderAccess.hpp. We assume throughout the VM that mutex lock and
1.84 +// try_lock do fence-lock-acquire, and that unlock does a release-unlock,
1.85 +// *in that order*. If their implementations change such that these
1.86 +// assumptions are violated, a whole lot of code will break.
1.87 +
1.88 +class Monitor : public CHeapObj {
1.89 +
1.90 + public:
1.91 + // A special lock: Is a lock where you are guaranteed not to block while you are
1.92 + // holding it, i.e., no vm operation can happen, taking other locks, etc.
1.93 + // NOTE: It is critical that the rank 'special' be the lowest (earliest)
1.94 + // (except for "event"?) for the deadlock dection to work correctly.
1.95 + // The rank native is only for use in Mutex's created by JVM_RawMonitorCreate,
1.96 + // which being external to the VM are not subject to deadlock detection.
1.97 + // The rank safepoint is used only for synchronization in reaching a
1.98 + // safepoint and leaving a safepoint. It is only used for the Safepoint_lock
1.99 + // currently. While at a safepoint no mutexes of rank safepoint are held
1.100 + // by any thread.
1.101 + // The rank named "leaf" is probably historical (and should
1.102 + // be changed) -- mutexes of this rank aren't really leaf mutexes
1.103 + // at all.
1.104 + enum lock_types {
1.105 + event,
1.106 + special,
1.107 + suspend_resume,
1.108 + leaf = suspend_resume + 2,
1.109 + safepoint = leaf + 10,
1.110 + barrier = safepoint + 1,
1.111 + nonleaf = barrier + 1,
1.112 + max_nonleaf = nonleaf + 900,
1.113 + native = max_nonleaf + 1
1.114 + };
1.115 +
1.116 + // The WaitSet and EntryList linked lists are composed of ParkEvents.
1.117 + // I use ParkEvent instead of threads as ParkEvents are immortal and
1.118 + // type-stable, meaning we can safely unpark() a possibly stale
1.119 + // list element in the unlock()-path.
1.120 +
1.121 + protected: // Monitor-Mutex metadata
1.122 + SplitWord _LockWord ; // Contention queue (cxq) colocated with Lock-byte
1.123 + enum LockWordBits { _LBIT=1 } ;
1.124 + Thread * volatile _owner; // The owner of the lock
1.125 + // Consider sequestering _owner on its own $line
1.126 + // to aid future synchronization mechanisms.
1.127 + ParkEvent * volatile _EntryList ; // List of threads waiting for entry
1.128 + ParkEvent * volatile _OnDeck ; // heir-presumptive
1.129 + volatile intptr_t _WaitLock [1] ; // Protects _WaitSet
1.130 + ParkEvent * volatile _WaitSet ; // LL of ParkEvents
1.131 + volatile bool _snuck; // Used for sneaky locking (evil).
1.132 + const char * _name; // Name of mutex
1.133 + int NotifyCount ; // diagnostic assist
1.134 + double pad [8] ; // avoid false sharing
1.135 +
1.136 + // Debugging fields for naming, deadlock detection, etc. (some only used in debug mode)
1.137 +#ifndef PRODUCT
1.138 + bool _allow_vm_block;
1.139 + debug_only(int _rank;) // rank (to avoid/detect potential deadlocks)
1.140 + debug_only(Monitor * _next;) // Used by a Thread to link up owned locks
1.141 + debug_only(Thread* _last_owner;) // the last thread to own the lock
1.142 + debug_only(static bool contains(Monitor * locks, Monitor * lock);)
1.143 + debug_only(static Monitor * get_least_ranked_lock(Monitor * locks);)
1.144 + debug_only(Monitor * get_least_ranked_lock_besides_this(Monitor * locks);)
1.145 +#endif
1.146 +
1.147 + void set_owner_implementation(Thread* owner) PRODUCT_RETURN;
1.148 + void check_prelock_state (Thread* thread) PRODUCT_RETURN;
1.149 + void check_block_state (Thread* thread) PRODUCT_RETURN;
1.150 +
1.151 + // platform-dependent support code can go here (in os_<os_family>.cpp)
1.152 + public:
1.153 + enum {
1.154 + _no_safepoint_check_flag = true,
1.155 + _allow_vm_block_flag = true,
1.156 + _as_suspend_equivalent_flag = true
1.157 + };
1.158 +
1.159 + enum WaitResults {
1.160 + CONDVAR_EVENT, // Wait returned because of condition variable notification
1.161 + INTERRUPT_EVENT, // Wait returned because waiting thread was interrupted
1.162 + NUMBER_WAIT_RESULTS
1.163 + };
1.164 +
1.165 + private:
1.166 + int TrySpin (Thread * Self) ;
1.167 + int TryLock () ;
1.168 + int TryFast () ;
1.169 + int AcquireOrPush (ParkEvent * ev) ;
1.170 + void IUnlock (bool RelaxAssert) ;
1.171 + void ILock (Thread * Self) ;
1.172 + int IWait (Thread * Self, jlong timo);
1.173 + int ILocked () ;
1.174 +
1.175 + protected:
1.176 + static void ClearMonitor (Monitor * m) ;
1.177 + Monitor() ;
1.178 +
1.179 + public:
1.180 + Monitor(int rank, const char *name, bool allow_vm_block=false);
1.181 + ~Monitor();
1.182 +
1.183 + // Wait until monitor is notified (or times out).
1.184 + // Defaults are to make safepoint checks, wait time is forever (i.e.,
1.185 + // zero), and not a suspend-equivalent condition. Returns true if wait
1.186 + // times out; otherwise returns false.
1.187 + bool wait(bool no_safepoint_check = !_no_safepoint_check_flag,
1.188 + long timeout = 0,
1.189 + bool as_suspend_equivalent = !_as_suspend_equivalent_flag);
1.190 + bool notify();
1.191 + bool notify_all();
1.192 +
1.193 +
1.194 + void lock(); // prints out warning if VM thread blocks
1.195 + void lock(Thread *thread); // overloaded with current thread
1.196 + void unlock();
1.197 + bool is_locked() const { return _owner != NULL; }
1.198 +
1.199 + bool try_lock(); // Like lock(), but unblocking. It returns false instead
1.200 +
1.201 + // Lock without safepoint check. Should ONLY be used by safepoint code and other code
1.202 + // that is guaranteed not to block while running inside the VM.
1.203 + void lock_without_safepoint_check();
1.204 + void lock_without_safepoint_check (Thread * Self) ;
1.205 +
1.206 + // Current owner - not not MT-safe. Can only be used to guarantee that
1.207 + // the current running thread owns the lock
1.208 + Thread* owner() const { return _owner; }
1.209 + bool owned_by_self() const;
1.210 +
1.211 + // Support for JVM_RawMonitorEnter & JVM_RawMonitorExit. These can be called by
1.212 + // non-Java thread. (We should really have a RawMonitor abstraction)
1.213 + void jvm_raw_lock();
1.214 + void jvm_raw_unlock();
1.215 + const char *name() const { return _name; }
1.216 +
1.217 + void print_on_error(outputStream* st) const;
1.218 +
1.219 + #ifndef PRODUCT
1.220 + void print_on(outputStream* st) const;
1.221 + void print() const { print_on(tty); }
1.222 + debug_only(int rank() const { return _rank; })
1.223 + bool allow_vm_block() { return _allow_vm_block; }
1.224 +
1.225 + debug_only(Monitor *next() const { return _next; })
1.226 + debug_only(void set_next(Monitor *next) { _next = next; })
1.227 + #endif
1.228 +
1.229 + void set_owner(Thread* owner) {
1.230 + #ifndef PRODUCT
1.231 + set_owner_implementation(owner);
1.232 + debug_only(void verify_Monitor(Thread* thr));
1.233 + #else
1.234 + _owner = owner;
1.235 + #endif
1.236 + }
1.237 +
1.238 +};
1.239 +
1.240 +// Normally we'd expect Monitor to extend Mutex in the sense that a monitor
1.241 +// constructed from pthreads primitives might extend a mutex by adding
1.242 +// a condvar and some extra metadata. In fact this was the case until J2SE7.
1.243 +//
1.244 +// Currently, however, the base object is a monitor. Monitor contains all the
1.245 +// logic for wait(), notify(), etc. Mutex extends monitor and restricts the
1.246 +// visiblity of wait(), notify(), and notify_all().
1.247 +//
1.248 +// Another viable alternative would have been to have Monitor extend Mutex and
1.249 +// implement all the normal mutex and wait()-notify() logic in Mutex base class.
1.250 +// The wait()-notify() facility would be exposed via special protected member functions
1.251 +// (e.g., _Wait() and _Notify()) in Mutex. Monitor would extend Mutex and expose wait()
1.252 +// as a call to _Wait(). That is, the public wait() would be a wrapper for the protected
1.253 +// _Wait().
1.254 +//
1.255 +// An even better alternative is to simply eliminate Mutex:: and use Monitor:: instead.
1.256 +// After all, monitors are sufficient for Java-level synchronization. At one point in time
1.257 +// there may have been some benefit to having distinct mutexes and monitors, but that time
1.258 +// has past.
1.259 +//
1.260 +// The Mutex/Monitor design parallels that of Java-monitors, being based on
1.261 +// thread-specific park-unpark platform-specific primitives.
1.262 +
1.263 +
1.264 +class Mutex : public Monitor { // degenerate Monitor
1.265 + public:
1.266 + Mutex (int rank, const char *name, bool allow_vm_block=false);
1.267 + ~Mutex () ;
1.268 + private:
1.269 + bool notify () { ShouldNotReachHere(); return false; }
1.270 + bool notify_all() { ShouldNotReachHere(); return false; }
1.271 + bool wait (bool no_safepoint_check, long timeout, bool as_suspend_equivalent) {
1.272 + ShouldNotReachHere() ;
1.273 + return false ;
1.274 + }
1.275 +};
1.276 +
1.277 +/*
1.278 + * Per-thread blocking support for JSR166. See the Java-level
1.279 + * Documentation for rationale. Basically, park acts like wait, unpark
1.280 + * like notify.
1.281 + *
1.282 + * 6271289 --
1.283 + * To avoid errors where an os thread expires but the JavaThread still
1.284 + * exists, Parkers are immortal (type-stable) and are recycled across
1.285 + * new threads. This parallels the ParkEvent implementation.
1.286 + * Because park-unpark allow spurious wakeups it is harmless if an
1.287 + * unpark call unparks a new thread using the old Parker reference.
1.288 + *
1.289 + * In the future we'll want to think about eliminating Parker and using
1.290 + * ParkEvent instead. There's considerable duplication between the two
1.291 + * services.
1.292 + *
1.293 + */
1.294 +
1.295 +class Parker : public os::PlatformParker {
1.296 +private:
1.297 + volatile int _counter ;
1.298 + Parker * FreeNext ;
1.299 + JavaThread * AssociatedWith ; // Current association
1.300 +
1.301 +public:
1.302 + Parker() : PlatformParker() {
1.303 + _counter = 0 ;
1.304 + FreeNext = NULL ;
1.305 + AssociatedWith = NULL ;
1.306 + }
1.307 +protected:
1.308 + ~Parker() { ShouldNotReachHere(); }
1.309 +public:
1.310 + // For simplicity of interface with Java, all forms of park (indefinite,
1.311 + // relative, and absolute) are multiplexed into one call.
1.312 + void park(bool isAbsolute, jlong time);
1.313 + void unpark();
1.314 +
1.315 + // Lifecycle operators
1.316 + static Parker * Allocate (JavaThread * t) ;
1.317 + static void Release (Parker * e) ;
1.318 +private:
1.319 + static Parker * volatile FreeList ;
1.320 + static volatile int ListLock ;
1.321 +};
