1/*
2 * Copyright (c) 1997, 2019, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25#include "precompiled.hpp"
26#include "gc/shared/collectedHeap.hpp"
27#include "gc/shared/gcLocker.hpp"
28#include "memory/resourceArea.hpp"
29#include "memory/universe.hpp"
30#include "logging/log.hpp"
31#include "runtime/atomic.hpp"
32#include "runtime/safepoint.hpp"
33#include "runtime/thread.inline.hpp"
34#include "runtime/threadSMR.hpp"
35
36volatile jint GCLocker::_jni_lock_count = 0;
37volatile bool GCLocker::_needs_gc = false;
38volatile bool GCLocker::_doing_gc = false;
39
40#ifdef ASSERT
41volatile jint GCLocker::_debug_jni_lock_count = 0;
42#endif
43
44
45#ifdef ASSERT
46void GCLocker::verify_critical_count() {
47 if (SafepointSynchronize::is_at_safepoint()) {
48 assert(!needs_gc() || _debug_jni_lock_count == _jni_lock_count, "must agree");
49 int count = 0;
50 // Count the number of threads with critical operations in progress
51 JavaThreadIteratorWithHandle jtiwh;
52 for (; JavaThread *thr = jtiwh.next(); ) {
53 if (thr->in_critical()) {
54 count++;
55 }
56 }
57 if (_jni_lock_count != count) {
58 log_error(gc, verify)("critical counts don't match: %d != %d", _jni_lock_count, count);
59 jtiwh.rewind();
60 for (; JavaThread *thr = jtiwh.next(); ) {
61 if (thr->in_critical()) {
62 log_error(gc, verify)(INTPTR_FORMAT " in_critical %d", p2i(thr), thr->in_critical());
63 }
64 }
65 }
66 assert(_jni_lock_count == count, "must be equal");
67 }
68}
69
70// In debug mode track the locking state at all times
71void GCLocker::increment_debug_jni_lock_count() {
72 assert(_debug_jni_lock_count >= 0, "bad value");
73 Atomic::inc(&_debug_jni_lock_count);
74}
75
76void GCLocker::decrement_debug_jni_lock_count() {
77 assert(_debug_jni_lock_count > 0, "bad value");
78 Atomic::dec(&_debug_jni_lock_count);
79}
80#endif
81
82void GCLocker::log_debug_jni(const char* msg) {
83 Log(gc, jni) log;
84 if (log.is_debug()) {
85 ResourceMark rm; // JavaThread::name() allocates to convert to UTF8
86 log.debug("%s Thread \"%s\" %d locked.", msg, Thread::current()->name(), _jni_lock_count);
87 }
88}
89
90bool GCLocker::is_at_safepoint() {
91 return SafepointSynchronize::is_at_safepoint();
92}
93
94bool GCLocker::check_active_before_gc() {
95 assert(SafepointSynchronize::is_at_safepoint(), "only read at safepoint");
96 if (is_active() && !_needs_gc) {
97 verify_critical_count();
98 _needs_gc = true;
99 log_debug_jni("Setting _needs_gc.");
100 }
101 return is_active();
102}
103
104void GCLocker::stall_until_clear() {
105 assert(!JavaThread::current()->in_critical(), "Would deadlock");
106 MonitorLocker ml(JNICritical_lock);
107
108 if (needs_gc()) {
109 log_debug_jni("Allocation failed. Thread stalled by JNI critical section.");
110 }
111
112 // Wait for _needs_gc to be cleared
113 while (needs_gc()) {
114 ml.wait();
115 }
116}
117
118void GCLocker::jni_lock(JavaThread* thread) {
119 assert(!thread->in_critical(), "shouldn't currently be in a critical region");
120 MonitorLocker ml(JNICritical_lock);
121 // Block entering threads if we know at least one thread is in a
122 // JNI critical region and we need a GC.
123 // We check that at least one thread is in a critical region before
124 // blocking because blocked threads are woken up by a thread exiting
125 // a JNI critical region.
126 while (is_active_and_needs_gc() || _doing_gc) {
127 ml.wait();
128 }
129 thread->enter_critical();
130 _jni_lock_count++;
131 increment_debug_jni_lock_count();
132}
133
134void GCLocker::jni_unlock(JavaThread* thread) {
135 assert(thread->in_last_critical(), "should be exiting critical region");
136 MutexLocker mu(JNICritical_lock);
137 _jni_lock_count--;
138 decrement_debug_jni_lock_count();
139 thread->exit_critical();
140 if (needs_gc() && !is_active_internal()) {
141 // We're the last thread out. Cause a GC to occur.
142 _doing_gc = true;
143 {
144 // Must give up the lock while at a safepoint
145 MutexUnlocker munlock(JNICritical_lock);
146 log_debug_jni("Performing GC after exiting critical section.");
147 Universe::heap()->collect(GCCause::_gc_locker);
148 }
149 _doing_gc = false;
150 _needs_gc = false;
151 JNICritical_lock->notify_all();
152 }
153}
154