/* * Copyright (c) 1997, 2013, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. * */ #ifndef SHARE_VM_MEMORY_GCLOCKER_HPP #define SHARE_VM_MEMORY_GCLOCKER_HPP #include "gc_interface/collectedHeap.hpp" #include "memory/genCollectedHeap.hpp" #include "memory/universe.hpp" #include "oops/oop.hpp" #include "runtime/thread.inline.hpp" #ifdef TARGET_OS_FAMILY_linux # include "os_linux.inline.hpp" #endif #ifdef TARGET_OS_FAMILY_solaris # include "os_solaris.inline.hpp" #endif #ifdef TARGET_OS_FAMILY_windows # include "os_windows.inline.hpp" #endif #ifdef TARGET_OS_FAMILY_bsd # include "os_bsd.inline.hpp" #endif // 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: // The _jni_lock_count keeps track of the number of threads that are // currently in a critical region. It's only kept up to date when // _needs_gc is true. The current value is computed during // safepointing and decremented during the slow path of GC_locker // unlocking. static volatile jint _jni_lock_count; // number of jni 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 #ifdef ASSERT // This lock count is updated for all operations and is used to // validate the jni_lock_count that is computed during safepoints. static volatile jint _debug_jni_lock_count; #endif // At a safepoint, visit all threads and count the number of active // critical sections. This is used to ensure that all active // critical sections are exited before a new one is started. static void verify_critical_count() NOT_DEBUG_RETURN; static void jni_lock(JavaThread* thread); static void jni_unlock(JavaThread* thread); static bool is_active_internal() { verify_critical_count(); return _jni_lock_count > 0; } public: // Accessors static bool is_active() { assert(SafepointSynchronize::is_at_safepoint(), "only read at safepoint"); return is_active_internal(); } static bool needs_gc() { return _needs_gc; } // Shorthand static bool is_active_and_needs_gc() { // Use is_active_internal since _needs_gc can change from true to // false outside of a safepoint, triggering the assert in // is_active. return needs_gc() && is_active_internal(); } // In debug mode track the locking state at all times static void increment_debug_jni_lock_count() { #ifdef ASSERT assert(_debug_jni_lock_count >= 0, "bad value"); Atomic::inc(&_debug_jni_lock_count); #endif } static void decrement_debug_jni_lock_count() { #ifdef ASSERT assert(_debug_jni_lock_count > 0, "bad value"); Atomic::dec(&_debug_jni_lock_count); #endif } // Set the current lock count static void set_jni_lock_count(int count) { _jni_lock_count = count; verify_critical_count(); } // Sets _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(); // 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 simply increments or decrements the // current thread's critical count. 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); static address needs_gc_address() { return (address) &_needs_gc; } }; // 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), _activated(activated) { _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 }; // A SkipGCALot object is used to elide the usual effect of gc-a-lot // over a section of execution by a thread. Currently, it's used only to // prevent re-entrant calls to GC. class SkipGCALot : public StackObj { private: bool _saved; Thread* _t; public: #ifdef ASSERT SkipGCALot(Thread* t) : _t(t) { _saved = _t->skip_gcalot(); _t->set_skip_gcalot(true); } ~SkipGCALot() { assert(_t->skip_gcalot(), "Save-restore protocol invariant"); _t->set_skip_gcalot(_saved); } #else SkipGCALot(Thread* t) { } ~SkipGCALot() { } #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 }; #endif // SHARE_VM_MEMORY_GCLOCKER_HPP