1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/src/share/vm/memory/gcLocker.hpp Sat Dec 01 00:00:00 2007 +0000
1.3 @@ -0,0 +1,285 @@
1.4 +/*
1.5 + * Copyright 1997-2007 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 direct lock/unlock calls do not force a collection if an unlock
1.29 +// decrements the count to zero. Avoid calling these if at all possible.
1.30 +
1.31 +class GC_locker: public AllStatic {
1.32 + private:
1.33 + static volatile jint _jni_lock_count; // number of jni active instances
1.34 + static volatile jint _lock_count; // number of other active instances
1.35 + static volatile bool _needs_gc; // heap is filling, we need a GC
1.36 + // note: bool is typedef'd as jint
1.37 + static volatile bool _doing_gc; // unlock_critical() is doing a GC
1.38 +
1.39 + // Accessors
1.40 + static bool is_jni_active() {
1.41 + return _jni_lock_count > 0;
1.42 + }
1.43 +
1.44 + static void set_needs_gc() {
1.45 + assert(SafepointSynchronize::is_at_safepoint(),
1.46 + "needs_gc is only set at a safepoint");
1.47 + _needs_gc = true;
1.48 + }
1.49 +
1.50 + static void clear_needs_gc() {
1.51 + assert_lock_strong(JNICritical_lock);
1.52 + _needs_gc = false;
1.53 + }
1.54 +
1.55 + static void jni_lock() {
1.56 + Atomic::inc(&_jni_lock_count);
1.57 + CHECK_UNHANDLED_OOPS_ONLY(
1.58 + if (CheckUnhandledOops) { Thread::current()->_gc_locked_out_count++; })
1.59 + assert(Universe::heap() == NULL || !Universe::heap()->is_gc_active(),
1.60 + "locking failed");
1.61 + }
1.62 +
1.63 + static void jni_unlock() {
1.64 + Atomic::dec(&_jni_lock_count);
1.65 + CHECK_UNHANDLED_OOPS_ONLY(
1.66 + if (CheckUnhandledOops) { Thread::current()->_gc_locked_out_count--; })
1.67 + }
1.68 +
1.69 + static void jni_lock_slow();
1.70 + static void jni_unlock_slow();
1.71 +
1.72 + public:
1.73 + // Accessors
1.74 + static bool is_active();
1.75 + static bool needs_gc() { return _needs_gc; }
1.76 + // Shorthand
1.77 + static bool is_active_and_needs_gc() { return is_active() && needs_gc();}
1.78 +
1.79 + // Calls set_needs_gc() if is_active() is true. Returns is_active().
1.80 + static bool check_active_before_gc();
1.81 +
1.82 + // Stalls the caller (who should not be in a jni critical section)
1.83 + // until needs_gc() clears. Note however that needs_gc() may be
1.84 + // set at a subsequent safepoint and/or cleared under the
1.85 + // JNICritical_lock, so the caller may not safely assert upon
1.86 + // return from this method that "!needs_gc()" since that is
1.87 + // not a stable predicate.
1.88 + static void stall_until_clear();
1.89 +
1.90 + // Non-structured GC locking: currently needed for JNI. Use with care!
1.91 + static void lock();
1.92 + static void unlock();
1.93 +
1.94 + // The following two methods are used for JNI critical regions.
1.95 + // If we find that we failed to perform a GC because the GC_locker
1.96 + // was active, arrange for one as soon as possible by allowing
1.97 + // all threads in critical regions to complete, but not allowing
1.98 + // other critical regions to be entered. The reasons for that are:
1.99 + // 1) a GC request won't be starved by overlapping JNI critical
1.100 + // region activities, which can cause unnecessary OutOfMemory errors.
1.101 + // 2) even if allocation requests can still be satisfied before GC locker
1.102 + // becomes inactive, for example, in tenured generation possibly with
1.103 + // heap expansion, those allocations can trigger lots of safepointing
1.104 + // attempts (ineffective GC attempts) and require Heap_lock which
1.105 + // slow down allocations tremendously.
1.106 + //
1.107 + // Note that critical regions can be nested in a single thread, so
1.108 + // we must allow threads already in critical regions to continue.
1.109 + //
1.110 + // JNI critical regions are the only participants in this scheme
1.111 + // because they are, by spec, well bounded while in a critical region.
1.112 + //
1.113 + // Each of the following two method is split into a fast path and a slow
1.114 + // path. JNICritical_lock is only grabbed in the slow path.
1.115 + // _needs_gc is initially false and every java thread will go
1.116 + // through the fast path (which does the same thing as the slow path
1.117 + // when _needs_gc is false). When GC happens at a safepoint,
1.118 + // GC_locker::is_active() is checked. Since there is no safepoint in the
1.119 + // fast path of lock_critical() and unlock_critical(), there is no race
1.120 + // condition between the fast path and GC. After _needs_gc is set at a
1.121 + // safepoint, every thread will go through the slow path after the safepoint.
1.122 + // Since after a safepoint, each of the following two methods is either
1.123 + // entered from the method entry and falls into the slow path, or is
1.124 + // resumed from the safepoints in the method, which only exist in the slow
1.125 + // path. So when _needs_gc is set, the slow path is always taken, till
1.126 + // _needs_gc is cleared.
1.127 + static void lock_critical(JavaThread* thread);
1.128 + static void unlock_critical(JavaThread* thread);
1.129 +};
1.130 +
1.131 +
1.132 +// A No_GC_Verifier object can be placed in methods where one assumes that
1.133 +// no garbage collection will occur. The destructor will verify this property
1.134 +// unless the constructor is called with argument false (not verifygc).
1.135 +//
1.136 +// The check will only be done in debug mode and if verifygc true.
1.137 +
1.138 +class No_GC_Verifier: public StackObj {
1.139 + friend class Pause_No_GC_Verifier;
1.140 +
1.141 + protected:
1.142 + bool _verifygc;
1.143 + unsigned int _old_invocations;
1.144 +
1.145 + public:
1.146 +#ifdef ASSERT
1.147 + No_GC_Verifier(bool verifygc = true);
1.148 + ~No_GC_Verifier();
1.149 +#else
1.150 + No_GC_Verifier(bool verifygc = true) {}
1.151 + ~No_GC_Verifier() {}
1.152 +#endif
1.153 +};
1.154 +
1.155 +// A Pause_No_GC_Verifier is used to temporarily pause the behavior
1.156 +// of a No_GC_Verifier object. If we are not in debug mode or if the
1.157 +// No_GC_Verifier object has a _verifygc value of false, then there
1.158 +// is nothing to do.
1.159 +
1.160 +class Pause_No_GC_Verifier: public StackObj {
1.161 + private:
1.162 + No_GC_Verifier * _ngcv;
1.163 +
1.164 + public:
1.165 +#ifdef ASSERT
1.166 + Pause_No_GC_Verifier(No_GC_Verifier * ngcv);
1.167 + ~Pause_No_GC_Verifier();
1.168 +#else
1.169 + Pause_No_GC_Verifier(No_GC_Verifier * ngcv) {}
1.170 + ~Pause_No_GC_Verifier() {}
1.171 +#endif
1.172 +};
1.173 +
1.174 +
1.175 +// A No_Safepoint_Verifier object will throw an assertion failure if
1.176 +// the current thread passes a possible safepoint while this object is
1.177 +// instantiated. A safepoint, will either be: an oop allocation, blocking
1.178 +// on a Mutex or JavaLock, or executing a VM operation.
1.179 +//
1.180 +// If StrictSafepointChecks is turned off, it degrades into a No_GC_Verifier
1.181 +//
1.182 +class No_Safepoint_Verifier : public No_GC_Verifier {
1.183 + friend class Pause_No_Safepoint_Verifier;
1.184 +
1.185 + private:
1.186 + bool _activated;
1.187 + Thread *_thread;
1.188 + public:
1.189 +#ifdef ASSERT
1.190 + No_Safepoint_Verifier(bool activated = true, bool verifygc = true ) : No_GC_Verifier(verifygc) {
1.191 + _thread = Thread::current();
1.192 + if (_activated) {
1.193 + _thread->_allow_allocation_count++;
1.194 + _thread->_allow_safepoint_count++;
1.195 + }
1.196 + }
1.197 +
1.198 + ~No_Safepoint_Verifier() {
1.199 + if (_activated) {
1.200 + _thread->_allow_allocation_count--;
1.201 + _thread->_allow_safepoint_count--;
1.202 + }
1.203 + }
1.204 +#else
1.205 + No_Safepoint_Verifier(bool activated = true, bool verifygc = true) : No_GC_Verifier(verifygc){}
1.206 + ~No_Safepoint_Verifier() {}
1.207 +#endif
1.208 +};
1.209 +
1.210 +// A Pause_No_Safepoint_Verifier is used to temporarily pause the
1.211 +// behavior of a No_Safepoint_Verifier object. If we are not in debug
1.212 +// mode then there is nothing to do. If the No_Safepoint_Verifier
1.213 +// object has an _activated value of false, then there is nothing to
1.214 +// do for safepoint and allocation checking, but there may still be
1.215 +// something to do for the underlying No_GC_Verifier object.
1.216 +
1.217 +class Pause_No_Safepoint_Verifier : public Pause_No_GC_Verifier {
1.218 + private:
1.219 + No_Safepoint_Verifier * _nsv;
1.220 +
1.221 + public:
1.222 +#ifdef ASSERT
1.223 + Pause_No_Safepoint_Verifier(No_Safepoint_Verifier * nsv)
1.224 + : Pause_No_GC_Verifier(nsv) {
1.225 +
1.226 + _nsv = nsv;
1.227 + if (_nsv->_activated) {
1.228 + _nsv->_thread->_allow_allocation_count--;
1.229 + _nsv->_thread->_allow_safepoint_count--;
1.230 + }
1.231 + }
1.232 +
1.233 + ~Pause_No_Safepoint_Verifier() {
1.234 + if (_nsv->_activated) {
1.235 + _nsv->_thread->_allow_allocation_count++;
1.236 + _nsv->_thread->_allow_safepoint_count++;
1.237 + }
1.238 + }
1.239 +#else
1.240 + Pause_No_Safepoint_Verifier(No_Safepoint_Verifier * nsv)
1.241 + : Pause_No_GC_Verifier(nsv) {}
1.242 + ~Pause_No_Safepoint_Verifier() {}
1.243 +#endif
1.244 +};
1.245 +
1.246 +// JRT_LEAF currently can be called from either _thread_in_Java or
1.247 +// _thread_in_native mode. In _thread_in_native, it is ok
1.248 +// for another thread to trigger GC. The rest of the JRT_LEAF
1.249 +// rules apply.
1.250 +class JRT_Leaf_Verifier : public No_Safepoint_Verifier {
1.251 + static bool should_verify_GC();
1.252 + public:
1.253 +#ifdef ASSERT
1.254 + JRT_Leaf_Verifier();
1.255 + ~JRT_Leaf_Verifier();
1.256 +#else
1.257 + JRT_Leaf_Verifier() {}
1.258 + ~JRT_Leaf_Verifier() {}
1.259 +#endif
1.260 +};
1.261 +
1.262 +// A No_Alloc_Verifier object can be placed in methods where one assumes that
1.263 +// no allocation will occur. The destructor will verify this property
1.264 +// unless the constructor is called with argument false (not activated).
1.265 +//
1.266 +// The check will only be done in debug mode and if activated.
1.267 +// Note: this only makes sense at safepoints (otherwise, other threads may
1.268 +// allocate concurrently.)
1.269 +
1.270 +class No_Alloc_Verifier : public StackObj {
1.271 + private:
1.272 + bool _activated;
1.273 +
1.274 + public:
1.275 +#ifdef ASSERT
1.276 + No_Alloc_Verifier(bool activated = true) {
1.277 + _activated = activated;
1.278 + if (_activated) Thread::current()->_allow_allocation_count++;
1.279 + }
1.280 +
1.281 + ~No_Alloc_Verifier() {
1.282 + if (_activated) Thread::current()->_allow_allocation_count--;
1.283 + }
1.284 +#else
1.285 + No_Alloc_Verifier(bool activated = true) {}
1.286 + ~No_Alloc_Verifier() {}
1.287 +#endif
1.288 +};
