1 /*
2 * Copyright (c) 1997, 2017, 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 "logging/log.hpp"
30 #include "runtime/atomic.hpp"
31 #include "runtime/thread.inline.hpp"
32 #include "runtime/threadSMR.hpp"
33
34 volatile jint GCLocker::_jni_lock_count = 0;
35 volatile bool GCLocker::_needs_gc = false;
36 volatile bool GCLocker::_doing_gc = false;
37
38 #ifdef ASSERT
39 volatile jint GCLocker::_debug_jni_lock_count = 0;
40 #endif
41
42
43 #ifdef ASSERT
44 void GCLocker::verify_critical_count() {
45 if (SafepointSynchronize::is_at_safepoint()) {
46 assert(!needs_gc() || _debug_jni_lock_count == _jni_lock_count, "must agree");
47 int count = 0;
48 // Count the number of threads with critical operations in progress
49 JavaThreadIteratorWithHandle jtiwh;
50 for (; JavaThread *thr = jtiwh.next(); ) {
51 if (thr->in_critical()) {
52 count++;
53 }
54 }
55 if (_jni_lock_count != count) {
56 log_error(gc, verify)("critical counts don't match: %d != %d", _jni_lock_count, count);
57 jtiwh.rewind();
58 for (; JavaThread *thr = jtiwh.next(); ) {
59 if (thr->in_critical()) {
60 log_error(gc, verify)(INTPTR_FORMAT " in_critical %d", p2i(thr), thr->in_critical());
61 }
62 }
63 }
64 assert(_jni_lock_count == count, "must be equal");
65 }
66 }
67
68 // In debug mode track the locking state at all times
69 void GCLocker::increment_debug_jni_lock_count() {
70 assert(_debug_jni_lock_count >= 0, "bad value");
71 Atomic::inc(&_debug_jni_lock_count);
72 }
73
74 void GCLocker::decrement_debug_jni_lock_count() {
75 assert(_debug_jni_lock_count > 0, "bad value");
76 Atomic::dec(&_debug_jni_lock_count);
77 }
78 #endif
79
80 void GCLocker::log_debug_jni(const char* msg) {
81 Log(gc, jni) log;
82 if (log.is_debug()) {
83 ResourceMark rm; // JavaThread::name() allocates to convert to UTF8
84 log.debug("%s Thread \"%s\" %d locked.", msg, Thread::current()->name(), _jni_lock_count);
85 }
86 }
87
88 bool GCLocker::is_at_safepoint() {
89 return SafepointSynchronize::is_at_safepoint();
90 }
91
92 bool GCLocker::check_active_before_gc() {
93 assert(SafepointSynchronize::is_at_safepoint(), "only read at safepoint");
94 if (is_active() && !_needs_gc) {
95 verify_critical_count();
96 _needs_gc = true;
97 log_debug_jni("Setting _needs_gc.");
98 }
99 return is_active();
100 }
101
102 void GCLocker::stall_until_clear() {
103 assert(!JavaThread::current()->in_critical(), "Would deadlock");
104 MutexLocker ml(JNICritical_lock);
105
106 if (needs_gc()) {
107 log_debug_jni("Allocation failed. Thread stalled by JNI critical section.");
108 }
109
110 // Wait for _needs_gc to be cleared
111 while (needs_gc()) {
112 JNICritical_lock->wait();
113 }
114 }
115
116 void GCLocker::jni_lock(JavaThread* thread) {
117 assert(!thread->in_critical(), "shouldn't currently be in a critical region");
118 MutexLocker mu(JNICritical_lock);
119 // Block entering threads if we know at least one thread is in a
120 // JNI critical region and we need a GC.
121 // We check that at least one thread is in a critical region before
122 // blocking because blocked threads are woken up by a thread exiting
123 // a JNI critical region.
124 while (is_active_and_needs_gc() || _doing_gc) {
125 JNICritical_lock->wait();
126 }
127 thread->enter_critical();
128 _jni_lock_count++;
129 increment_debug_jni_lock_count();
130 }
131
132 void GCLocker::jni_unlock(JavaThread* thread) {
133 assert(thread->in_last_critical(), "should be exiting critical region");
134 MutexLocker mu(JNICritical_lock);
135 _jni_lock_count--;
136 decrement_debug_jni_lock_count();
137 thread->exit_critical();
138 if (needs_gc() && !is_active_internal()) {
139 // We're the last thread out. Cause a GC to occur.
140 _doing_gc = true;
141 {
142 // Must give up the lock while at a safepoint
143 MutexUnlocker munlock(JNICritical_lock);
144 log_debug_jni("Performing GC after exiting critical section.");
145 Universe::heap()->collect(GCCause::_gc_locker);
146 }
147 _doing_gc = false;
148 _needs_gc = false;
149 JNICritical_lock->notify_all();
150 }
151 }