1 /*
2 * Copyright (c) 1997, 2012, 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 jint GC_locker::_lock_count = 0;
32 volatile bool GC_locker::_needs_gc = false;
33 volatile bool GC_locker::_doing_gc = false;
34 jlong GC_locker::_wait_begin = 0;
35
36 #ifdef ASSERT
37 volatile jint GC_locker::_debug_jni_lock_count = 0;
38 #endif
39
40
41 #ifdef ASSERT
42 void GC_locker::verify_critical_count() {
43 if (SafepointSynchronize::is_at_safepoint()) {
44 assert(!needs_gc() || _debug_jni_lock_count == _jni_lock_count, "must agree");
45 int count = 0;
46 // Count the number of threads with critical operations in progress
47 for (JavaThread* thr = Threads::first(); thr; thr = thr->next()) {
48 if (thr->in_critical()) {
49 count++;
50 }
51 }
52 if (_jni_lock_count != count) {
53 tty->print_cr("critical counts don't match: %d != %d", _jni_lock_count, count);
54 for (JavaThread* thr = Threads::first(); thr; thr = thr->next()) {
55 if (thr->in_critical()) {
56 tty->print_cr(INTPTR_FORMAT " in_critical %d", thr, thr->in_critical());
57 }
58 }
59 }
60 assert(_jni_lock_count == count, "must be equal");
61 }
62 }
63 #endif
64
65 bool GC_locker::check_active_before_gc() {
66 assert(SafepointSynchronize::is_at_safepoint(), "only read at safepoint");
67 if (is_active() && !_needs_gc) {
68 verify_critical_count();
69 _needs_gc = true;
70 if (PrintJNIGCStalls && PrintGCDetails) {
71 ResourceMark rm; // JavaThread::name() allocates to convert to UTF8
72 _wait_begin = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
73 gclog_or_tty->print_cr(INT64_FORMAT ": Setting _needs_gc. Thread \"%s\" %d locked.",
74 _wait_begin, Thread::current()->name(), _jni_lock_count);
75 }
76
77 }
78 return is_active();
79 }
80
81 void GC_locker::stall_until_clear() {
82 assert(!JavaThread::current()->in_critical(), "Would deadlock");
83 MutexLocker ml(JNICritical_lock);
84
85 if (needs_gc()) {
86 if (PrintJNIGCStalls && PrintGCDetails) {
87 ResourceMark rm; // JavaThread::name() allocates to convert to UTF8
88 gclog_or_tty->print_cr(INT64_FORMAT ": Allocation failed. Thread \"%s\" is stalled by JNI critical section, %d locked.",
89 (os::javaTimeNanos() / NANOSECS_PER_MILLISEC) - _wait_begin, Thread::current()->name(), _jni_lock_count);
90 }
91 }
92
93 // Wait for _needs_gc to be cleared
94 while (needs_gc()) {
95 JNICritical_lock->wait();
96 }
97 }
98
99 void GC_locker::jni_lock(JavaThread* thread) {
100 assert(!thread->in_critical(), "shouldn't currently be in a critical region");
101 MutexLocker mu(JNICritical_lock);
102 // Block entering threads if we know at least one thread is in a
103 // JNI critical region and we need a GC.
104 // We check that at least one thread is in a critical region before
105 // blocking because blocked threads are woken up by a thread exiting
106 // a JNI critical region.
107 while ((needs_gc() && is_jni_active()) || _doing_gc) {
108 JNICritical_lock->wait();
109 }
110 thread->enter_critical();
111 _jni_lock_count++;
112 increment_debug_jni_lock_count();
113 }
114
115 void GC_locker::jni_unlock(JavaThread* thread) {
116 assert(thread->in_last_critical(), "should be exiting critical region");
117 MutexLocker mu(JNICritical_lock);
118 _jni_lock_count--;
119 decrement_debug_jni_lock_count();
120 thread->exit_critical();
121 if (needs_gc() && !is_jni_active()) {
122 // We're the last thread out. Cause a GC to occur.
123 // GC will also check is_active, so this check is not
124 // strictly needed. It's added here to make it clear that
125 // the GC will NOT be performed if any other caller
126 // of GC_locker::lock() still needs GC locked.
127 if (!is_active()) {
128 _doing_gc = true;
129 {
130 // Must give up the lock while at a safepoint
131 MutexUnlocker munlock(JNICritical_lock);
132 if (PrintJNIGCStalls && PrintGCDetails) {
133 ResourceMark rm; // JavaThread::name() allocates to convert to UTF8
134 gclog_or_tty->print_cr(INT64_FORMAT ": Thread \"%s\" is performing GC after exiting critical section, %d locked",
135 (os::javaTimeNanos() / NANOSECS_PER_MILLISEC) - _wait_begin, Thread::current()->name(), _jni_lock_count);
136 }
137 Universe::heap()->collect(GCCause::_gc_locker);
138 }
139 _doing_gc = false;
140 }
141
142 _needs_gc = false;
143 JNICritical_lock->notify_all();
144 }
145 }
146
147 // Implementation of No_GC_Verifier
148
149 #ifdef ASSERT
150
151 No_GC_Verifier::No_GC_Verifier(bool verifygc) {
152 _verifygc = verifygc;
153 if (_verifygc) {
154 CollectedHeap* h = Universe::heap();
155 assert(!h->is_gc_active(), "GC active during No_GC_Verifier");
156 _old_invocations = h->total_collections();
157 }
158 }
159
160
161 No_GC_Verifier::~No_GC_Verifier() {
162 if (_verifygc) {
163 CollectedHeap* h = Universe::heap();
164 assert(!h->is_gc_active(), "GC active during No_GC_Verifier");
165 if (_old_invocations != h->total_collections()) {
166 fatal("collection in a No_GC_Verifier secured function");
167 }
168 }
169 }
170
171 Pause_No_GC_Verifier::Pause_No_GC_Verifier(No_GC_Verifier * ngcv) {
172 _ngcv = ngcv;
173 if (_ngcv->_verifygc) {
174 // if we were verifying, then make sure that nothing is
175 // wrong before we "pause" verification
176 CollectedHeap* h = Universe::heap();
177 assert(!h->is_gc_active(), "GC active during No_GC_Verifier");
178 if (_ngcv->_old_invocations != h->total_collections()) {
179 fatal("collection in a No_GC_Verifier secured function");
180 }
181 }
182 }
183
184
185 Pause_No_GC_Verifier::~Pause_No_GC_Verifier() {
186 if (_ngcv->_verifygc) {
187 // if we were verifying before, then reenable verification
188 CollectedHeap* h = Universe::heap();
189 assert(!h->is_gc_active(), "GC active during No_GC_Verifier");
190 _ngcv->_old_invocations = h->total_collections();
191 }
192 }
193
194
195 // JRT_LEAF rules:
196 // A JRT_LEAF method may not interfere with safepointing by
197 // 1) acquiring or blocking on a Mutex or JavaLock - checked
198 // 2) allocating heap memory - checked
199 // 3) executing a VM operation - checked
200 // 4) executing a system call (including malloc) that could block or grab a lock
201 // 5) invoking GC
202 // 6) reaching a safepoint
203 // 7) running too long
204 // Nor may any method it calls.
205 JRT_Leaf_Verifier::JRT_Leaf_Verifier()
206 : No_Safepoint_Verifier(true, JRT_Leaf_Verifier::should_verify_GC())
207 {
208 }
209
210 JRT_Leaf_Verifier::~JRT_Leaf_Verifier()
211 {
212 }
213
214 bool JRT_Leaf_Verifier::should_verify_GC() {
215 switch (JavaThread::current()->thread_state()) {
216 case _thread_in_Java:
217 // is in a leaf routine, there must be no safepoint.
218 return true;
219 case _thread_in_native:
220 // A native thread is not subject to safepoints.
221 // Even while it is in a leaf routine, GC is ok
222 return false;
223 default:
224 // Leaf routines cannot be called from other contexts.
225 ShouldNotReachHere();
226 return false;
227 }
228 }
229 #endif