1 /*
2 * Copyright (c) 1997, 2013, 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 "memory/gcLocker.inline.hpp"
27 #include "memory/resourceArea.hpp"
28 #include "memory/sharedHeap.hpp"
29
30 volatile jint GC_locker::_jni_lock_count = 0;
31 volatile bool GC_locker::_needs_gc = false;
32 volatile bool GC_locker::_doing_gc = false;
33
34 #ifdef ASSERT
35 volatile jint GC_locker::_debug_jni_lock_count = 0;
36 #endif
37
38
39 #ifdef ASSERT
40 void GC_locker::verify_critical_count() {
41 if (SafepointSynchronize::is_at_safepoint()) {
42 assert(!needs_gc() || _debug_jni_lock_count == _jni_lock_count, "must agree");
43 int count = 0;
44 // Count the number of threads with critical operations in progress
45 for (JavaThread* thr = Threads::first(); thr; thr = thr->next()) {
46 if (thr->in_critical()) {
47 count++;
48 }
49 }
50 if (_jni_lock_count != count) {
51 tty->print_cr("critical counts don't match: %d != %d", _jni_lock_count, count);
52 for (JavaThread* thr = Threads::first(); thr; thr = thr->next()) {
53 if (thr->in_critical()) {
54 tty->print_cr(INTPTR_FORMAT " in_critical %d", thr, thr->in_critical());
55 }
56 }
57 }
58 assert(_jni_lock_count == count, "must be equal");
59 }
60 }
61 #endif
62
63 bool GC_locker::check_active_before_gc() {
64 assert(SafepointSynchronize::is_at_safepoint(), "only read at safepoint");
65 if (is_active() && !_needs_gc) {
66 verify_critical_count();
67 _needs_gc = true;
68 if (PrintJNIGCStalls && PrintGCDetails) {
69 ResourceMark rm; // JavaThread::name() allocates to convert to UTF8
70 gclog_or_tty->print_cr("%.3f: Setting _needs_gc. Thread \"%s\" %d locked.",
71 gclog_or_tty->time_stamp().seconds(), Thread::current()->name(), _jni_lock_count);
72 }
73
74 }
75 return is_active();
76 }
77
78 void GC_locker::stall_until_clear() {
79 assert(!JavaThread::current()->in_critical(), "Would deadlock");
80 MutexLocker ml(JNICritical_lock);
81
82 if (needs_gc()) {
83 if (PrintJNIGCStalls && PrintGCDetails) {
84 ResourceMark rm; // JavaThread::name() allocates to convert to UTF8
85 gclog_or_tty->print_cr("%.3f: Allocation failed. Thread \"%s\" is stalled by JNI critical section, %d locked.",
86 gclog_or_tty->time_stamp().seconds(), Thread::current()->name(), _jni_lock_count);
87 }
88 }
89
90 // Wait for _needs_gc to be cleared
91 while (needs_gc()) {
92 JNICritical_lock->wait();
93 }
94 }
95
96 void GC_locker::jni_lock(JavaThread* thread) {
97 assert(!thread->in_critical(), "shouldn't currently be in a critical region");
98 MutexLocker mu(JNICritical_lock);
99 // Block entering threads if we know at least one thread is in a
100 // JNI critical region and we need a GC.
101 // We check that at least one thread is in a critical region before
102 // blocking because blocked threads are woken up by a thread exiting
103 // a JNI critical region.
104 while (is_active_and_needs_gc() || _doing_gc) {
105 JNICritical_lock->wait();
106 }
107 thread->enter_critical();
108 _jni_lock_count++;
109 increment_debug_jni_lock_count();
110 }
111
112 void GC_locker::jni_unlock(JavaThread* thread) {
113 assert(thread->in_last_critical(), "should be exiting critical region");
114 MutexLocker mu(JNICritical_lock);
115 _jni_lock_count--;
116 decrement_debug_jni_lock_count();
117 thread->exit_critical();
118 if (needs_gc() && !is_active_internal()) {
119 // We're the last thread out. Cause a GC to occur.
120 _doing_gc = true;
121 {
122 // Must give up the lock while at a safepoint
123 MutexUnlocker munlock(JNICritical_lock);
124 if (PrintJNIGCStalls && PrintGCDetails) {
125 ResourceMark rm; // JavaThread::name() allocates to convert to UTF8
126 gclog_or_tty->print_cr("%.3f: Thread \"%s\" is performing GC after exiting critical section, %d locked",
127 gclog_or_tty->time_stamp().seconds(), Thread::current()->name(), _jni_lock_count);
128 }
129 Universe::heap()->collect(GCCause::_gc_locker);
130 }
131 _doing_gc = false;
132 _needs_gc = false;
133 JNICritical_lock->notify_all();
134 }
135 }
136
137 // Implementation of No_GC_Verifier
138
139 #ifdef ASSERT
140
141 No_GC_Verifier::No_GC_Verifier(bool verifygc) {
142 _verifygc = verifygc;
143 if (_verifygc) {
144 CollectedHeap* h = Universe::heap();
145 assert(!h->is_gc_active(), "GC active during No_GC_Verifier");
146 _old_invocations = h->total_collections();
147 }
148 }
149
150
151 No_GC_Verifier::~No_GC_Verifier() {
152 if (_verifygc) {
153 CollectedHeap* h = Universe::heap();
154 assert(!h->is_gc_active(), "GC active during No_GC_Verifier");
155 if (_old_invocations != h->total_collections()) {
156 fatal("collection in a No_GC_Verifier secured function");
157 }
158 }
159 }
160
161 Pause_No_GC_Verifier::Pause_No_GC_Verifier(No_GC_Verifier * ngcv) {
162 _ngcv = ngcv;
163 if (_ngcv->_verifygc) {
164 // if we were verifying, then make sure that nothing is
165 // wrong before we "pause" verification
166 CollectedHeap* h = Universe::heap();
167 assert(!h->is_gc_active(), "GC active during No_GC_Verifier");
168 if (_ngcv->_old_invocations != h->total_collections()) {
169 fatal("collection in a No_GC_Verifier secured function");
170 }
171 }
172 }
173
174
175 Pause_No_GC_Verifier::~Pause_No_GC_Verifier() {
176 if (_ngcv->_verifygc) {
177 // if we were verifying before, then reenable verification
178 CollectedHeap* h = Universe::heap();
179 assert(!h->is_gc_active(), "GC active during No_GC_Verifier");
180 _ngcv->_old_invocations = h->total_collections();
181 }
182 }
183
184
185 // JRT_LEAF rules:
186 // A JRT_LEAF method may not interfere with safepointing by
187 // 1) acquiring or blocking on a Mutex or JavaLock - checked
188 // 2) allocating heap memory - checked
189 // 3) executing a VM operation - checked
190 // 4) executing a system call (including malloc) that could block or grab a lock
191 // 5) invoking GC
192 // 6) reaching a safepoint
193 // 7) running too long
194 // Nor may any method it calls.
195 JRT_Leaf_Verifier::JRT_Leaf_Verifier()
196 : No_Safepoint_Verifier(true, JRT_Leaf_Verifier::should_verify_GC())
197 {
198 }
199
200 JRT_Leaf_Verifier::~JRT_Leaf_Verifier()
201 {
202 }
203
204 bool JRT_Leaf_Verifier::should_verify_GC() {
205 switch (JavaThread::current()->thread_state()) {
206 case _thread_in_Java:
207 // is in a leaf routine, there must be no safepoint.
208 return true;
209 case _thread_in_native:
210 // A native thread is not subject to safepoints.
211 // Even while it is in a leaf routine, GC is ok
212 return false;
213 default:
214 // Leaf routines cannot be called from other contexts.
215 ShouldNotReachHere();
216 return false;
217 }
218 }
219 #endif