Mercurial > hg > graal-jvmci-8
diff src/share/vm/memory/gcLocker.hpp @ 0:a61af66fc99e jdk7-b24
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author | duke |
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date | Sat, 01 Dec 2007 00:00:00 +0000 |
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children | deb97b8ef02b |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/share/vm/memory/gcLocker.hpp Sat Dec 01 00:00:00 2007 +0000 @@ -0,0 +1,285 @@ +/* + * Copyright 1997-2007 Sun Microsystems, Inc. All Rights Reserved. + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. + * + * This code is free software; you can redistribute it and/or modify it + * under the terms of the GNU General Public License version 2 only, as + * published by the Free Software Foundation. + * + * This code is distributed in the hope that it will be useful, but WITHOUT + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License + * version 2 for more details (a copy is included in the LICENSE file that + * accompanied this code). + * + * You should have received a copy of the GNU General Public License version + * 2 along with this work; if not, write to the Free Software Foundation, + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. + * + * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, + * CA 95054 USA or visit www.sun.com if you need additional information or + * have any questions. + * + */ + +// The direct lock/unlock calls do not force a collection if an unlock +// decrements the count to zero. Avoid calling these if at all possible. + +class GC_locker: public AllStatic { + private: + static volatile jint _jni_lock_count; // number of jni active instances + static volatile jint _lock_count; // number of other active instances + static volatile bool _needs_gc; // heap is filling, we need a GC + // note: bool is typedef'd as jint + static volatile bool _doing_gc; // unlock_critical() is doing a GC + + // Accessors + static bool is_jni_active() { + return _jni_lock_count > 0; + } + + static void set_needs_gc() { + assert(SafepointSynchronize::is_at_safepoint(), + "needs_gc is only set at a safepoint"); + _needs_gc = true; + } + + static void clear_needs_gc() { + assert_lock_strong(JNICritical_lock); + _needs_gc = false; + } + + static void jni_lock() { + Atomic::inc(&_jni_lock_count); + CHECK_UNHANDLED_OOPS_ONLY( + if (CheckUnhandledOops) { Thread::current()->_gc_locked_out_count++; }) + assert(Universe::heap() == NULL || !Universe::heap()->is_gc_active(), + "locking failed"); + } + + static void jni_unlock() { + Atomic::dec(&_jni_lock_count); + CHECK_UNHANDLED_OOPS_ONLY( + if (CheckUnhandledOops) { Thread::current()->_gc_locked_out_count--; }) + } + + static void jni_lock_slow(); + static void jni_unlock_slow(); + + public: + // Accessors + static bool is_active(); + static bool needs_gc() { return _needs_gc; } + // Shorthand + static bool is_active_and_needs_gc() { return is_active() && needs_gc();} + + // Calls set_needs_gc() if is_active() is true. Returns is_active(). + static bool check_active_before_gc(); + + // Stalls the caller (who should not be in a jni critical section) + // until needs_gc() clears. Note however that needs_gc() may be + // set at a subsequent safepoint and/or cleared under the + // JNICritical_lock, so the caller may not safely assert upon + // return from this method that "!needs_gc()" since that is + // not a stable predicate. + static void stall_until_clear(); + + // Non-structured GC locking: currently needed for JNI. Use with care! + static void lock(); + static void unlock(); + + // The following two methods are used for JNI critical regions. + // If we find that we failed to perform a GC because the GC_locker + // was active, arrange for one as soon as possible by allowing + // all threads in critical regions to complete, but not allowing + // other critical regions to be entered. The reasons for that are: + // 1) a GC request won't be starved by overlapping JNI critical + // region activities, which can cause unnecessary OutOfMemory errors. + // 2) even if allocation requests can still be satisfied before GC locker + // becomes inactive, for example, in tenured generation possibly with + // heap expansion, those allocations can trigger lots of safepointing + // attempts (ineffective GC attempts) and require Heap_lock which + // slow down allocations tremendously. + // + // Note that critical regions can be nested in a single thread, so + // we must allow threads already in critical regions to continue. + // + // JNI critical regions are the only participants in this scheme + // because they are, by spec, well bounded while in a critical region. + // + // Each of the following two method is split into a fast path and a slow + // path. JNICritical_lock is only grabbed in the slow path. + // _needs_gc is initially false and every java thread will go + // through the fast path (which does the same thing as the slow path + // when _needs_gc is false). When GC happens at a safepoint, + // GC_locker::is_active() is checked. Since there is no safepoint in the + // fast path of lock_critical() and unlock_critical(), there is no race + // condition between the fast path and GC. After _needs_gc is set at a + // safepoint, every thread will go through the slow path after the safepoint. + // Since after a safepoint, each of the following two methods is either + // entered from the method entry and falls into the slow path, or is + // resumed from the safepoints in the method, which only exist in the slow + // path. So when _needs_gc is set, the slow path is always taken, till + // _needs_gc is cleared. + static void lock_critical(JavaThread* thread); + static void unlock_critical(JavaThread* thread); +}; + + +// A No_GC_Verifier object can be placed in methods where one assumes that +// no garbage collection will occur. The destructor will verify this property +// unless the constructor is called with argument false (not verifygc). +// +// The check will only be done in debug mode and if verifygc true. + +class No_GC_Verifier: public StackObj { + friend class Pause_No_GC_Verifier; + + protected: + bool _verifygc; + unsigned int _old_invocations; + + public: +#ifdef ASSERT + No_GC_Verifier(bool verifygc = true); + ~No_GC_Verifier(); +#else + No_GC_Verifier(bool verifygc = true) {} + ~No_GC_Verifier() {} +#endif +}; + +// A Pause_No_GC_Verifier is used to temporarily pause the behavior +// of a No_GC_Verifier object. If we are not in debug mode or if the +// No_GC_Verifier object has a _verifygc value of false, then there +// is nothing to do. + +class Pause_No_GC_Verifier: public StackObj { + private: + No_GC_Verifier * _ngcv; + + public: +#ifdef ASSERT + Pause_No_GC_Verifier(No_GC_Verifier * ngcv); + ~Pause_No_GC_Verifier(); +#else + Pause_No_GC_Verifier(No_GC_Verifier * ngcv) {} + ~Pause_No_GC_Verifier() {} +#endif +}; + + +// A No_Safepoint_Verifier object will throw an assertion failure if +// the current thread passes a possible safepoint while this object is +// instantiated. A safepoint, will either be: an oop allocation, blocking +// on a Mutex or JavaLock, or executing a VM operation. +// +// If StrictSafepointChecks is turned off, it degrades into a No_GC_Verifier +// +class No_Safepoint_Verifier : public No_GC_Verifier { + friend class Pause_No_Safepoint_Verifier; + + private: + bool _activated; + Thread *_thread; + public: +#ifdef ASSERT + No_Safepoint_Verifier(bool activated = true, bool verifygc = true ) : No_GC_Verifier(verifygc) { + _thread = Thread::current(); + if (_activated) { + _thread->_allow_allocation_count++; + _thread->_allow_safepoint_count++; + } + } + + ~No_Safepoint_Verifier() { + if (_activated) { + _thread->_allow_allocation_count--; + _thread->_allow_safepoint_count--; + } + } +#else + No_Safepoint_Verifier(bool activated = true, bool verifygc = true) : No_GC_Verifier(verifygc){} + ~No_Safepoint_Verifier() {} +#endif +}; + +// A Pause_No_Safepoint_Verifier is used to temporarily pause the +// behavior of a No_Safepoint_Verifier object. If we are not in debug +// mode then there is nothing to do. If the No_Safepoint_Verifier +// object has an _activated value of false, then there is nothing to +// do for safepoint and allocation checking, but there may still be +// something to do for the underlying No_GC_Verifier object. + +class Pause_No_Safepoint_Verifier : public Pause_No_GC_Verifier { + private: + No_Safepoint_Verifier * _nsv; + + public: +#ifdef ASSERT + Pause_No_Safepoint_Verifier(No_Safepoint_Verifier * nsv) + : Pause_No_GC_Verifier(nsv) { + + _nsv = nsv; + if (_nsv->_activated) { + _nsv->_thread->_allow_allocation_count--; + _nsv->_thread->_allow_safepoint_count--; + } + } + + ~Pause_No_Safepoint_Verifier() { + if (_nsv->_activated) { + _nsv->_thread->_allow_allocation_count++; + _nsv->_thread->_allow_safepoint_count++; + } + } +#else + Pause_No_Safepoint_Verifier(No_Safepoint_Verifier * nsv) + : Pause_No_GC_Verifier(nsv) {} + ~Pause_No_Safepoint_Verifier() {} +#endif +}; + +// JRT_LEAF currently can be called from either _thread_in_Java or +// _thread_in_native mode. In _thread_in_native, it is ok +// for another thread to trigger GC. The rest of the JRT_LEAF +// rules apply. +class JRT_Leaf_Verifier : public No_Safepoint_Verifier { + static bool should_verify_GC(); + public: +#ifdef ASSERT + JRT_Leaf_Verifier(); + ~JRT_Leaf_Verifier(); +#else + JRT_Leaf_Verifier() {} + ~JRT_Leaf_Verifier() {} +#endif +}; + +// A No_Alloc_Verifier object can be placed in methods where one assumes that +// no allocation will occur. The destructor will verify this property +// unless the constructor is called with argument false (not activated). +// +// The check will only be done in debug mode and if activated. +// Note: this only makes sense at safepoints (otherwise, other threads may +// allocate concurrently.) + +class No_Alloc_Verifier : public StackObj { + private: + bool _activated; + + public: +#ifdef ASSERT + No_Alloc_Verifier(bool activated = true) { + _activated = activated; + if (_activated) Thread::current()->_allow_allocation_count++; + } + + ~No_Alloc_Verifier() { + if (_activated) Thread::current()->_allow_allocation_count--; + } +#else + No_Alloc_Verifier(bool activated = true) {} + ~No_Alloc_Verifier() {} +#endif +};