1 /*
2 * Copyright (c) 1997, 2014, 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 #include "runtime/thread.inline.hpp"
30
31 volatile jint GC_locker::_jni_lock_count = 0;
32 volatile bool GC_locker::_needs_gc = false;
33 volatile bool GC_locker::_doing_gc = false;
34
35 #ifdef ASSERT
36 volatile jint GC_locker::_debug_jni_lock_count = 0;
37 #endif
38
39
40 #ifdef ASSERT
41 void GC_locker::verify_critical_count() {
42 if (SafepointSynchronize::is_at_safepoint()) {
43 assert(!needs_gc() || _debug_jni_lock_count == _jni_lock_count, "must agree");
44 int count = 0;
45 // Count the number of threads with critical operations in progress
46 for (JavaThread* thr = Threads::first(); thr; thr = thr->next()) {
47 if (thr->in_critical()) {
48 count++;
49 }
50 }
51 if (_jni_lock_count != count) {
52 tty->print_cr("critical counts don't match: %d != %d", _jni_lock_count, count);
53 for (JavaThread* thr = Threads::first(); thr; thr = thr->next()) {
54 if (thr->in_critical()) {
55 tty->print_cr(INTPTR_FORMAT " in_critical %d", p2i(thr), thr->in_critical());
56 }
57 }
58 }
59 assert(_jni_lock_count == count, "must be equal");
60 }
61 }
62 #endif
63
64 bool GC_locker::check_active_before_gc() {
65 assert(SafepointSynchronize::is_at_safepoint(), "only read at safepoint");
66 if (is_active() && !_needs_gc) {
67 verify_critical_count();
68 _needs_gc = true;
69 if (PrintJNIGCStalls && PrintGCDetails) {
70 ResourceMark rm; // JavaThread::name() allocates to convert to UTF8
71 gclog_or_tty->print_cr("%.3f: Setting _needs_gc. Thread \"%s\" %d locked.",
72 gclog_or_tty->time_stamp().seconds(), Thread::current()->name(), _jni_lock_count);
73 }
74
75 }
76 return is_active();
77 }
78
79 void GC_locker::stall_until_clear() {
80 assert(!JavaThread::current()->in_critical(), "Would deadlock");
81 MutexLocker ml(JNICritical_lock);
82
83 if (needs_gc()) {
84 if (PrintJNIGCStalls && PrintGCDetails) {
85 ResourceMark rm; // JavaThread::name() allocates to convert to UTF8
86 gclog_or_tty->print_cr("%.3f: Allocation failed. Thread \"%s\" is stalled by JNI critical section, %d locked.",
87 gclog_or_tty->time_stamp().seconds(), Thread::current()->name(), _jni_lock_count);
88 }
89 }
90
91 // Wait for _needs_gc to be cleared
92 while (needs_gc()) {
93 JNICritical_lock->wait();
94 }
95 }
96
97 void GC_locker::jni_lock(JavaThread* thread) {
98 assert(!thread->in_critical(), "shouldn't currently be in a critical region");
99 MutexLocker mu(JNICritical_lock);
100 // Block entering threads if we know at least one thread is in a
101 // JNI critical region and we need a GC.
102 // We check that at least one thread is in a critical region before
103 // blocking because blocked threads are woken up by a thread exiting
104 // a JNI critical region.
105 while (is_active_and_needs_gc() || _doing_gc) {
106 JNICritical_lock->wait();
107 }
108 thread->enter_critical();
109 _jni_lock_count++;
110 increment_debug_jni_lock_count();
111 }
112
113 void GC_locker::jni_unlock(JavaThread* thread) {
114 assert(thread->in_last_critical(), "should be exiting critical region");
115 MutexLocker mu(JNICritical_lock);
116 _jni_lock_count--;
117 decrement_debug_jni_lock_count();
118 thread->exit_critical();
119 if (needs_gc() && !is_active_internal()) {
120 // We're the last thread out. Cause a GC to occur.
121 _doing_gc = true;
122 {
123 // Must give up the lock while at a safepoint
124 MutexUnlocker munlock(JNICritical_lock);
125 if (PrintJNIGCStalls && PrintGCDetails) {
126 ResourceMark rm; // JavaThread::name() allocates to convert to UTF8
127 gclog_or_tty->print_cr("%.3f: Thread \"%s\" is performing GC after exiting critical section, %d locked",
128 gclog_or_tty->time_stamp().seconds(), Thread::current()->name(), _jni_lock_count);
129 }
130 Universe::heap()->collect(GCCause::_gc_locker);
131 }
132 _doing_gc = false;
133 _needs_gc = false;
134 JNICritical_lock->notify_all();
135 }
136 }
137
138 // Implementation of No_GC_Verifier
139
140 #ifdef ASSERT
141
142 No_GC_Verifier::No_GC_Verifier(bool verifygc) {
143 _verifygc = verifygc;
144 if (_verifygc) {
145 CollectedHeap* h = Universe::heap();
146 assert(!h->is_gc_active(), "GC active during No_GC_Verifier");
147 _old_invocations = h->total_collections();
148 }
149 }
150
151
152 No_GC_Verifier::~No_GC_Verifier() {
153 if (_verifygc) {
154 CollectedHeap* h = Universe::heap();
155 assert(!h->is_gc_active(), "GC active during No_GC_Verifier");
156 if (_old_invocations != h->total_collections()) {
157 fatal("collection in a No_GC_Verifier secured function");
158 }
159 }
160 }
161
162 Pause_No_GC_Verifier::Pause_No_GC_Verifier(No_GC_Verifier * ngcv) {
163 _ngcv = ngcv;
164 if (_ngcv->_verifygc) {
165 // if we were verifying, then make sure that nothing is
166 // wrong before we "pause" verification
167 CollectedHeap* h = Universe::heap();
168 assert(!h->is_gc_active(), "GC active during No_GC_Verifier");
169 if (_ngcv->_old_invocations != h->total_collections()) {
170 fatal("collection in a No_GC_Verifier secured function");
171 }
172 }
173 }
174
175
176 Pause_No_GC_Verifier::~Pause_No_GC_Verifier() {
177 if (_ngcv->_verifygc) {
178 // if we were verifying before, then reenable verification
179 CollectedHeap* h = Universe::heap();
180 assert(!h->is_gc_active(), "GC active during No_GC_Verifier");
181 _ngcv->_old_invocations = h->total_collections();
182 }
183 }
184
185
186 // JRT_LEAF rules:
187 // A JRT_LEAF method may not interfere with safepointing by
188 // 1) acquiring or blocking on a Mutex or JavaLock - checked
189 // 2) allocating heap memory - checked
190 // 3) executing a VM operation - checked
191 // 4) executing a system call (including malloc) that could block or grab a lock
192 // 5) invoking GC
193 // 6) reaching a safepoint
194 // 7) running too long
195 // Nor may any method it calls.
196 JRT_Leaf_Verifier::JRT_Leaf_Verifier()
197 : No_Safepoint_Verifier(true, JRT_Leaf_Verifier::should_verify_GC())
198 {
199 }
200
201 JRT_Leaf_Verifier::~JRT_Leaf_Verifier()
202 {
203 }
204
205 bool JRT_Leaf_Verifier::should_verify_GC() {
206 switch (JavaThread::current()->thread_state()) {
207 case _thread_in_Java:
208 // is in a leaf routine, there must be no safepoint.
209 return true;
210 case _thread_in_native:
211 // A native thread is not subject to safepoints.
212 // Even while it is in a leaf routine, GC is ok
213 return false;
214 default:
215 // Leaf routines cannot be called from other contexts.
216 ShouldNotReachHere();
217 return false;
218 }
219 }
220 #endif