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src/share/vm/memory/gcLocker.cpp@2c022e432e10 (annotated)

src/share/vm/memory/gcLocker.cpp

Fri, 20 Sep 2013 10:53:28 +0200

author

stefank

date

Fri, 20 Sep 2013 10:53:28 +0200

changeset 5769

2c022e432e10

parent 3571

09d00c18e323

child 6198

55fb97c4c58d

permissions

-rw-r--r--

8024974: Incorrect use of GC_locker::is_active()
Summary: SymbolTable and StringTable can make calls to GC_locker::is_active() outside a safepoint. This isn't safe because the GC_locker active state (lock count) is only updated at a safepoint and only remains valid as long as _needs_gc is true. However, outside a safepoint_needs_gc can change to false at any time, which makes it impossible to do a correct call to is_active() in that context. In this case these calls can just be removed since the input argument to basic_add() should never be on the heap and so there's no need to check the GC_locker state. This change also adjusts the assert() in is_active() to makes sure all calls to this function are always done under a safepoint.
Reviewed-by: brutisso, dcubed
Contributed-by: per.liden@oracle.com

duke@435	1	/*
never@3494	2	* Copyright (c) 1997, 2012, Oracle and/or its affiliates. All rights reserved.
duke@435	3	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
duke@435	4	*
duke@435	5	* This code is free software; you can redistribute it and/or modify it
duke@435	6	* under the terms of the GNU General Public License version 2 only, as
duke@435	7	* published by the Free Software Foundation.
duke@435	8	*
duke@435	9	* This code is distributed in the hope that it will be useful, but WITHOUT
duke@435	10	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
duke@435	11	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
duke@435	12	* version 2 for more details (a copy is included in the LICENSE file that
duke@435	13	* accompanied this code).
duke@435	14	*
duke@435	15	* You should have received a copy of the GNU General Public License version
duke@435	16	* 2 along with this work; if not, write to the Free Software Foundation,
duke@435	17	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
duke@435	18	*
trims@1907	19	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
trims@1907	20	* or visit www.oracle.com if you need additional information or have any
trims@1907	21	* questions.
duke@435	22	*
duke@435	23	*/
duke@435	24
stefank@2314	25	#include "precompiled.hpp"
stefank@2314	26	#include "memory/gcLocker.inline.hpp"
stefank@2314	27	#include "memory/resourceArea.hpp"
stefank@2314	28	#include "memory/sharedHeap.hpp"
duke@435	29
duke@435	30	volatile jint GC_locker::_jni_lock_count = 0;
duke@435	31	volatile jint GC_locker::_lock_count = 0;
duke@435	32	volatile bool GC_locker::_needs_gc = false;
duke@435	33	volatile bool GC_locker::_doing_gc = false;
never@3494	34
never@3494	35	#ifdef ASSERT
never@3494	36	volatile jint GC_locker::_debug_jni_lock_count = 0;
never@3494	37	#endif
never@3494	38
never@3494	39
never@3494	40	#ifdef ASSERT
never@3494	41	void GC_locker::verify_critical_count() {
never@3494	42	if (SafepointSynchronize::is_at_safepoint()) {
never@3494	43	assert(!needs_gc() || _debug_jni_lock_count == _jni_lock_count, "must agree");
never@3494	44	int count = 0;
never@3494	45	// Count the number of threads with critical operations in progress
never@3494	46	for (JavaThread* thr = Threads::first(); thr; thr = thr->next()) {
never@3494	47	if (thr->in_critical()) {
never@3494	48	count++;
never@3494	49	}
never@3494	50	}
never@3494	51	if (_jni_lock_count != count) {
never@3494	52	tty->print_cr("critical counts don't match: %d != %d", _jni_lock_count, count);
never@3494	53	for (JavaThread* thr = Threads::first(); thr; thr = thr->next()) {
never@3494	54	if (thr->in_critical()) {
never@3494	55	tty->print_cr(INTPTR_FORMAT " in_critical %d", thr, thr->in_critical());
never@3494	56	}
never@3494	57	}
never@3494	58	}
never@3494	59	assert(_jni_lock_count == count, "must be equal");
never@3494	60	}
never@3494	61	}
never@3494	62	#endif
never@3494	63
never@3494	64	bool GC_locker::check_active_before_gc() {
never@3494	65	assert(SafepointSynchronize::is_at_safepoint(), "only read at safepoint");
never@3494	66	if (is_active() && !_needs_gc) {
never@3494	67	verify_critical_count();
never@3494	68	_needs_gc = true;
never@3494	69	if (PrintJNIGCStalls && PrintGCDetails) {
never@3494	70	ResourceMark rm; // JavaThread::name() allocates to convert to UTF8
never@3571	71	gclog_or_tty->print_cr("%.3f: Setting _needs_gc. Thread \"%s\" %d locked.",
never@3571	72	gclog_or_tty->time_stamp().seconds(), Thread::current()->name(), _jni_lock_count);
never@3494	73	}
never@3494	74
never@3494	75	}
never@3494	76	return is_active();
never@3494	77	}
duke@435	78
duke@435	79	void GC_locker::stall_until_clear() {
duke@435	80	assert(!JavaThread::current()->in_critical(), "Would deadlock");
never@3494	81	MutexLocker ml(JNICritical_lock);
never@3494	82
never@3494	83	if (needs_gc()) {
never@3494	84	if (PrintJNIGCStalls && PrintGCDetails) {
never@3494	85	ResourceMark rm; // JavaThread::name() allocates to convert to UTF8
never@3571	86	gclog_or_tty->print_cr("%.3f: Allocation failed. Thread \"%s\" is stalled by JNI critical section, %d locked.",
never@3571	87	gclog_or_tty->time_stamp().seconds(), Thread::current()->name(), _jni_lock_count);
never@3494	88	}
apetrusenko@574	89	}
never@3494	90
duke@435	91	// Wait for _needs_gc to be cleared
never@3494	92	while (needs_gc()) {
duke@435	93	JNICritical_lock->wait();
duke@435	94	}
duke@435	95	}
duke@435	96
never@3494	97	void GC_locker::jni_lock(JavaThread* thread) {
never@3494	98	assert(!thread->in_critical(), "shouldn't currently be in a critical region");
duke@435	99	MutexLocker mu(JNICritical_lock);
duke@435	100	// Block entering threads if we know at least one thread is in a
duke@435	101	// JNI critical region and we need a GC.
duke@435	102	// We check that at least one thread is in a critical region before
duke@435	103	// blocking because blocked threads are woken up by a thread exiting
duke@435	104	// a JNI critical region.
never@3494	105	while ((needs_gc() && is_jni_active()) || _doing_gc) {
duke@435	106	JNICritical_lock->wait();
duke@435	107	}
never@3494	108	thread->enter_critical();
never@3494	109	_jni_lock_count++;
never@3494	110	increment_debug_jni_lock_count();
duke@435	111	}
duke@435	112
never@3494	113	void GC_locker::jni_unlock(JavaThread* thread) {
never@3494	114	assert(thread->in_last_critical(), "should be exiting critical region");
duke@435	115	MutexLocker mu(JNICritical_lock);
never@3494	116	_jni_lock_count--;
never@3494	117	decrement_debug_jni_lock_count();
never@3494	118	thread->exit_critical();
duke@435	119	if (needs_gc() && !is_jni_active()) {
duke@435	120	// We're the last thread out. Cause a GC to occur.
duke@435	121	// GC will also check is_active, so this check is not
duke@435	122	// strictly needed. It's added here to make it clear that
duke@435	123	// the GC will NOT be performed if any other caller
duke@435	124	// of GC_locker::lock() still needs GC locked.
stefank@5769	125	if (!is_active_internal()) {
duke@435	126	_doing_gc = true;
duke@435	127	{
duke@435	128	// Must give up the lock while at a safepoint
duke@435	129	MutexUnlocker munlock(JNICritical_lock);
never@3494	130	if (PrintJNIGCStalls && PrintGCDetails) {
never@3494	131	ResourceMark rm; // JavaThread::name() allocates to convert to UTF8
never@3571	132	gclog_or_tty->print_cr("%.3f: Thread \"%s\" is performing GC after exiting critical section, %d locked",
never@3571	133	gclog_or_tty->time_stamp().seconds(), Thread::current()->name(), _jni_lock_count);
never@3494	134	}
duke@435	135	Universe::heap()->collect(GCCause::_gc_locker);
duke@435	136	}
duke@435	137	_doing_gc = false;
duke@435	138	}
never@3494	139
never@3494	140	_needs_gc = false;
duke@435	141	JNICritical_lock->notify_all();
duke@435	142	}
duke@435	143	}
duke@435	144
duke@435	145	// Implementation of No_GC_Verifier
duke@435	146
duke@435	147	#ifdef ASSERT
duke@435	148
duke@435	149	No_GC_Verifier::No_GC_Verifier(bool verifygc) {
duke@435	150	_verifygc = verifygc;
duke@435	151	if (_verifygc) {
duke@435	152	CollectedHeap* h = Universe::heap();
duke@435	153	assert(!h->is_gc_active(), "GC active during No_GC_Verifier");
duke@435	154	_old_invocations = h->total_collections();
duke@435	155	}
duke@435	156	}
duke@435	157
duke@435	158
duke@435	159	No_GC_Verifier::~No_GC_Verifier() {
duke@435	160	if (_verifygc) {
duke@435	161	CollectedHeap* h = Universe::heap();
duke@435	162	assert(!h->is_gc_active(), "GC active during No_GC_Verifier");
duke@435	163	if (_old_invocations != h->total_collections()) {
duke@435	164	fatal("collection in a No_GC_Verifier secured function");
duke@435	165	}
duke@435	166	}
duke@435	167	}
duke@435	168
duke@435	169	Pause_No_GC_Verifier::Pause_No_GC_Verifier(No_GC_Verifier * ngcv) {
duke@435	170	_ngcv = ngcv;
duke@435	171	if (_ngcv->_verifygc) {
duke@435	172	// if we were verifying, then make sure that nothing is
duke@435	173	// wrong before we "pause" verification
duke@435	174	CollectedHeap* h = Universe::heap();
duke@435	175	assert(!h->is_gc_active(), "GC active during No_GC_Verifier");
duke@435	176	if (_ngcv->_old_invocations != h->total_collections()) {
duke@435	177	fatal("collection in a No_GC_Verifier secured function");
duke@435	178	}
duke@435	179	}
duke@435	180	}
duke@435	181
duke@435	182
duke@435	183	Pause_No_GC_Verifier::~Pause_No_GC_Verifier() {
duke@435	184	if (_ngcv->_verifygc) {
duke@435	185	// if we were verifying before, then reenable verification
duke@435	186	CollectedHeap* h = Universe::heap();
duke@435	187	assert(!h->is_gc_active(), "GC active during No_GC_Verifier");
duke@435	188	_ngcv->_old_invocations = h->total_collections();
duke@435	189	}
duke@435	190	}
duke@435	191
duke@435	192
duke@435	193	// JRT_LEAF rules:
duke@435	194	// A JRT_LEAF method may not interfere with safepointing by
duke@435	195	// 1) acquiring or blocking on a Mutex or JavaLock - checked
duke@435	196	// 2) allocating heap memory - checked
duke@435	197	// 3) executing a VM operation - checked
duke@435	198	// 4) executing a system call (including malloc) that could block or grab a lock
duke@435	199	// 5) invoking GC
duke@435	200	// 6) reaching a safepoint
duke@435	201	// 7) running too long
duke@435	202	// Nor may any method it calls.
duke@435	203	JRT_Leaf_Verifier::JRT_Leaf_Verifier()
duke@435	204	: No_Safepoint_Verifier(true, JRT_Leaf_Verifier::should_verify_GC())
duke@435	205	{
duke@435	206	}
duke@435	207
duke@435	208	JRT_Leaf_Verifier::~JRT_Leaf_Verifier()
duke@435	209	{
duke@435	210	}
duke@435	211
duke@435	212	bool JRT_Leaf_Verifier::should_verify_GC() {
duke@435	213	switch (JavaThread::current()->thread_state()) {
duke@435	214	case _thread_in_Java:
duke@435	215	// is in a leaf routine, there must be no safepoint.
duke@435	216	return true;
duke@435	217	case _thread_in_native:
duke@435	218	// A native thread is not subject to safepoints.
duke@435	219	// Even while it is in a leaf routine, GC is ok
duke@435	220	return false;
duke@435	221	default:
duke@435	222	// Leaf routines cannot be called from other contexts.
duke@435	223	ShouldNotReachHere();
duke@435	224	return false;
duke@435	225	}
duke@435	226	}
duke@435	227	#endif