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src/share/vm/memory/gcLocker.cpp@9f28a4cac6d9 (annotated)

src/share/vm/memory/gcLocker.cpp

Wed, 31 Jul 2019 14:28:51 -0400

author

kbarrett

date

Wed, 31 Jul 2019 14:28:51 -0400

changeset 9787

9f28a4cac6d9

parent 6911

ce8f6bb717c9

child 9806

758c07667682

permissions

-rw-r--r--

8048556: Unnecessary GCLocker-initiated young GCs
Summary: Fixed recognition of unnecessary GCLocker collections.
Reviewed-by: pliden, tschatzl
Contributed-by: johnc@azul.com

duke@435	1	/*
drchase@6680	2	* Copyright (c) 1997, 2014, 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"
goetz@6911	29	#include "runtime/thread.inline.hpp"
duke@435	30
duke@435	31	volatile jint GC_locker::_jni_lock_count = 0;
duke@435	32	volatile bool GC_locker::_needs_gc = false;
duke@435	33	volatile bool GC_locker::_doing_gc = false;
kbarrett@9787	34	unsigned int GC_locker::_total_collections = 0;
never@3494	35
never@3494	36	#ifdef ASSERT
never@3494	37	volatile jint GC_locker::_debug_jni_lock_count = 0;
never@3494	38	#endif
never@3494	39
never@3494	40
never@3494	41	#ifdef ASSERT
never@3494	42	void GC_locker::verify_critical_count() {
never@3494	43	if (SafepointSynchronize::is_at_safepoint()) {
never@3494	44	assert(!needs_gc() || _debug_jni_lock_count == _jni_lock_count, "must agree");
never@3494	45	int count = 0;
never@3494	46	// Count the number of threads with critical operations in progress
never@3494	47	for (JavaThread* thr = Threads::first(); thr; thr = thr->next()) {
never@3494	48	if (thr->in_critical()) {
never@3494	49	count++;
never@3494	50	}
never@3494	51	}
never@3494	52	if (_jni_lock_count != count) {
never@3494	53	tty->print_cr("critical counts don't match: %d != %d", _jni_lock_count, count);
never@3494	54	for (JavaThread* thr = Threads::first(); thr; thr = thr->next()) {
never@3494	55	if (thr->in_critical()) {
drchase@6680	56	tty->print_cr(INTPTR_FORMAT " in_critical %d", p2i(thr), thr->in_critical());
never@3494	57	}
never@3494	58	}
never@3494	59	}
never@3494	60	assert(_jni_lock_count == count, "must be equal");
never@3494	61	}
never@3494	62	}
never@3494	63	#endif
never@3494	64
never@3494	65	bool GC_locker::check_active_before_gc() {
never@3494	66	assert(SafepointSynchronize::is_at_safepoint(), "only read at safepoint");
never@3494	67	if (is_active() && !_needs_gc) {
never@3494	68	verify_critical_count();
never@3494	69	_needs_gc = true;
never@3494	70	if (PrintJNIGCStalls && PrintGCDetails) {
never@3494	71	ResourceMark rm; // JavaThread::name() allocates to convert to UTF8
never@3571	72	gclog_or_tty->print_cr("%.3f: Setting _needs_gc. Thread \"%s\" %d locked.",
never@3571	73	gclog_or_tty->time_stamp().seconds(), Thread::current()->name(), _jni_lock_count);
never@3494	74	}
never@3494	75
never@3494	76	}
never@3494	77	return is_active();
never@3494	78	}
duke@435	79
duke@435	80	void GC_locker::stall_until_clear() {
duke@435	81	assert(!JavaThread::current()->in_critical(), "Would deadlock");
never@3494	82	MutexLocker ml(JNICritical_lock);
never@3494	83
never@3494	84	if (needs_gc()) {
never@3494	85	if (PrintJNIGCStalls && PrintGCDetails) {
never@3494	86	ResourceMark rm; // JavaThread::name() allocates to convert to UTF8
never@3571	87	gclog_or_tty->print_cr("%.3f: Allocation failed. Thread \"%s\" is stalled by JNI critical section, %d locked.",
never@3571	88	gclog_or_tty->time_stamp().seconds(), Thread::current()->name(), _jni_lock_count);
never@3494	89	}
apetrusenko@574	90	}
never@3494	91
duke@435	92	// Wait for _needs_gc to be cleared
never@3494	93	while (needs_gc()) {
duke@435	94	JNICritical_lock->wait();
duke@435	95	}
duke@435	96	}
duke@435	97
kbarrett@9787	98	bool GC_locker::should_discard(GCCause::Cause cause, uint total_collections) {
kbarrett@9787	99	return (cause == GCCause::_gc_locker) &&
kbarrett@9787	100	(_total_collections != total_collections);
kbarrett@9787	101	}
kbarrett@9787	102
never@3494	103	void GC_locker::jni_lock(JavaThread* thread) {
never@3494	104	assert(!thread->in_critical(), "shouldn't currently be in a critical region");
duke@435	105	MutexLocker mu(JNICritical_lock);
duke@435	106	// Block entering threads if we know at least one thread is in a
duke@435	107	// JNI critical region and we need a GC.
duke@435	108	// We check that at least one thread is in a critical region before
duke@435	109	// blocking because blocked threads are woken up by a thread exiting
duke@435	110	// a JNI critical region.
sjohanss@6619	111	while (is_active_and_needs_gc() || _doing_gc) {
duke@435	112	JNICritical_lock->wait();
duke@435	113	}
never@3494	114	thread->enter_critical();
never@3494	115	_jni_lock_count++;
never@3494	116	increment_debug_jni_lock_count();
duke@435	117	}
duke@435	118
never@3494	119	void GC_locker::jni_unlock(JavaThread* thread) {
never@3494	120	assert(thread->in_last_critical(), "should be exiting critical region");
duke@435	121	MutexLocker mu(JNICritical_lock);
never@3494	122	_jni_lock_count--;
never@3494	123	decrement_debug_jni_lock_count();
never@3494	124	thread->exit_critical();
sjohanss@6619	125	if (needs_gc() && !is_active_internal()) {
kbarrett@9787	126	// We're the last thread out. Request a GC.
kbarrett@9787	127	// Capture the current total collections, to allow detection of
kbarrett@9787	128	// other collections that make this one unnecessary. The value of
kbarrett@9787	129	// total_collections() is only changed at a safepoint, so there
kbarrett@9787	130	// must not be a safepoint between the lock becoming inactive and
kbarrett@9787	131	// getting the count, else there may be unnecessary GCLocker GCs.
kbarrett@9787	132	_total_collections = Universe::heap()->total_collections();
sjohanss@6619	133	_doing_gc = true;
sjohanss@6619	134	{
sjohanss@6619	135	// Must give up the lock while at a safepoint
sjohanss@6619	136	MutexUnlocker munlock(JNICritical_lock);
sjohanss@6619	137	if (PrintJNIGCStalls && PrintGCDetails) {
sjohanss@6619	138	ResourceMark rm; // JavaThread::name() allocates to convert to UTF8
sjohanss@6619	139	gclog_or_tty->print_cr("%.3f: Thread \"%s\" is performing GC after exiting critical section, %d locked",
sjohanss@6619	140	gclog_or_tty->time_stamp().seconds(), Thread::current()->name(), _jni_lock_count);
duke@435	141	}
sjohanss@6619	142	Universe::heap()->collect(GCCause::_gc_locker);
duke@435	143	}
sjohanss@6619	144	_doing_gc = false;
never@3494	145	_needs_gc = false;
duke@435	146	JNICritical_lock->notify_all();
duke@435	147	}
duke@435	148	}
duke@435	149
duke@435	150	// Implementation of No_GC_Verifier
duke@435	151
duke@435	152	#ifdef ASSERT
duke@435	153
duke@435	154	No_GC_Verifier::No_GC_Verifier(bool verifygc) {
duke@435	155	_verifygc = verifygc;
duke@435	156	if (_verifygc) {
duke@435	157	CollectedHeap* h = Universe::heap();
duke@435	158	assert(!h->is_gc_active(), "GC active during No_GC_Verifier");
duke@435	159	_old_invocations = h->total_collections();
duke@435	160	}
duke@435	161	}
duke@435	162
duke@435	163
duke@435	164	No_GC_Verifier::~No_GC_Verifier() {
duke@435	165	if (_verifygc) {
duke@435	166	CollectedHeap* h = Universe::heap();
duke@435	167	assert(!h->is_gc_active(), "GC active during No_GC_Verifier");
duke@435	168	if (_old_invocations != h->total_collections()) {
duke@435	169	fatal("collection in a No_GC_Verifier secured function");
duke@435	170	}
duke@435	171	}
duke@435	172	}
duke@435	173
duke@435	174	Pause_No_GC_Verifier::Pause_No_GC_Verifier(No_GC_Verifier * ngcv) {
duke@435	175	_ngcv = ngcv;
duke@435	176	if (_ngcv->_verifygc) {
duke@435	177	// if we were verifying, then make sure that nothing is
duke@435	178	// wrong before we "pause" verification
duke@435	179	CollectedHeap* h = Universe::heap();
duke@435	180	assert(!h->is_gc_active(), "GC active during No_GC_Verifier");
duke@435	181	if (_ngcv->_old_invocations != h->total_collections()) {
duke@435	182	fatal("collection in a No_GC_Verifier secured function");
duke@435	183	}
duke@435	184	}
duke@435	185	}
duke@435	186
duke@435	187
duke@435	188	Pause_No_GC_Verifier::~Pause_No_GC_Verifier() {
duke@435	189	if (_ngcv->_verifygc) {
duke@435	190	// if we were verifying before, then reenable verification
duke@435	191	CollectedHeap* h = Universe::heap();
duke@435	192	assert(!h->is_gc_active(), "GC active during No_GC_Verifier");
duke@435	193	_ngcv->_old_invocations = h->total_collections();
duke@435	194	}
duke@435	195	}
duke@435	196
duke@435	197
duke@435	198	// JRT_LEAF rules:
duke@435	199	// A JRT_LEAF method may not interfere with safepointing by
duke@435	200	// 1) acquiring or blocking on a Mutex or JavaLock - checked
duke@435	201	// 2) allocating heap memory - checked
duke@435	202	// 3) executing a VM operation - checked
duke@435	203	// 4) executing a system call (including malloc) that could block or grab a lock
duke@435	204	// 5) invoking GC
duke@435	205	// 6) reaching a safepoint
duke@435	206	// 7) running too long
duke@435	207	// Nor may any method it calls.
duke@435	208	JRT_Leaf_Verifier::JRT_Leaf_Verifier()
duke@435	209	: No_Safepoint_Verifier(true, JRT_Leaf_Verifier::should_verify_GC())
duke@435	210	{
duke@435	211	}
duke@435	212
duke@435	213	JRT_Leaf_Verifier::~JRT_Leaf_Verifier()
duke@435	214	{
duke@435	215	}
duke@435	216
duke@435	217	bool JRT_Leaf_Verifier::should_verify_GC() {
duke@435	218	switch (JavaThread::current()->thread_state()) {
duke@435	219	case _thread_in_Java:
duke@435	220	// is in a leaf routine, there must be no safepoint.
duke@435	221	return true;
duke@435	222	case _thread_in_native:
duke@435	223	// A native thread is not subject to safepoints.
duke@435	224	// Even while it is in a leaf routine, GC is ok
duke@435	225	return false;
duke@435	226	default:
duke@435	227	// Leaf routines cannot be called from other contexts.
duke@435	228	ShouldNotReachHere();
duke@435	229	return false;
duke@435	230	}
duke@435	231	}
duke@435	232	#endif