1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
|
/*
* Copyright (c) 1997, 2014, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*
*/
#include "precompiled.hpp"
#include "memory/gcLocker.inline.hpp"
#include "memory/resourceArea.hpp"
#include "memory/sharedHeap.hpp"
#include "runtime/thread.inline.hpp"
volatile jint GC_locker::_jni_lock_count = 0;
volatile bool GC_locker::_needs_gc = false;
volatile bool GC_locker::_doing_gc = false;
unsigned int GC_locker::_total_collections = 0;
#ifdef ASSERT
volatile jint GC_locker::_debug_jni_lock_count = 0;
#endif
#ifdef ASSERT
void GC_locker::verify_critical_count() {
if (SafepointSynchronize::is_at_safepoint()) {
assert(!needs_gc() || _debug_jni_lock_count == _jni_lock_count, "must agree");
int count = 0;
// Count the number of threads with critical operations in progress
for (JavaThread* thr = Threads::first(); thr; thr = thr->next()) {
if (thr->in_critical()) {
count++;
}
}
if (_jni_lock_count != count) {
tty->print_cr("critical counts don't match: %d != %d", _jni_lock_count, count);
for (JavaThread* thr = Threads::first(); thr; thr = thr->next()) {
if (thr->in_critical()) {
tty->print_cr(INTPTR_FORMAT " in_critical %d", p2i(thr), thr->in_critical());
}
}
}
assert(_jni_lock_count == count, "must be equal");
}
}
#endif
bool GC_locker::check_active_before_gc() {
assert(SafepointSynchronize::is_at_safepoint(), "only read at safepoint");
if (is_active() && !_needs_gc) {
verify_critical_count();
_needs_gc = true;
if (PrintJNIGCStalls && PrintGCDetails) {
ResourceMark rm; // JavaThread::name() allocates to convert to UTF8
gclog_or_tty->print_cr("%.3f: Setting _needs_gc. Thread \"%s\" %d locked.",
gclog_or_tty->time_stamp().seconds(), Thread::current()->name(), _jni_lock_count);
}
}
return is_active();
}
void GC_locker::stall_until_clear() {
assert(!JavaThread::current()->in_critical(), "Would deadlock");
MutexLocker ml(JNICritical_lock);
if (needs_gc()) {
if (PrintJNIGCStalls && PrintGCDetails) {
ResourceMark rm; // JavaThread::name() allocates to convert to UTF8
gclog_or_tty->print_cr("%.3f: Allocation failed. Thread \"%s\" is stalled by JNI critical section, %d locked.",
gclog_or_tty->time_stamp().seconds(), Thread::current()->name(), _jni_lock_count);
}
}
// Wait for _needs_gc to be cleared
while (needs_gc()) {
JNICritical_lock->wait();
}
}
bool GC_locker::should_discard(GCCause::Cause cause, uint total_collections) {
return (cause == GCCause::_gc_locker) &&
(_total_collections != total_collections);
}
void GC_locker::jni_lock(JavaThread* thread) {
assert(!thread->in_critical(), "shouldn't currently be in a critical region");
MutexLocker mu(JNICritical_lock);
// Block entering threads if we know at least one thread is in a
// JNI critical region and we need a GC.
// We check that at least one thread is in a critical region before
// blocking because blocked threads are woken up by a thread exiting
// a JNI critical region.
while (is_active_and_needs_gc() || _doing_gc) {
JNICritical_lock->wait();
}
thread->enter_critical();
_jni_lock_count++;
increment_debug_jni_lock_count();
}
void GC_locker::jni_unlock(JavaThread* thread) {
assert(thread->in_last_critical(), "should be exiting critical region");
MutexLocker mu(JNICritical_lock);
_jni_lock_count--;
decrement_debug_jni_lock_count();
thread->exit_critical();
if (needs_gc() && !is_active_internal()) {
// We're the last thread out. Request a GC.
// Capture the current total collections, to allow detection of
// other collections that make this one unnecessary. The value of
// total_collections() is only changed at a safepoint, so there
// must not be a safepoint between the lock becoming inactive and
// getting the count, else there may be unnecessary GCLocker GCs.
_total_collections = Universe::heap()->total_collections();
_doing_gc = true;
{
// Must give up the lock while at a safepoint
MutexUnlocker munlock(JNICritical_lock);
if (PrintJNIGCStalls && PrintGCDetails) {
ResourceMark rm; // JavaThread::name() allocates to convert to UTF8
gclog_or_tty->print_cr("%.3f: Thread \"%s\" is performing GC after exiting critical section, %d locked",
gclog_or_tty->time_stamp().seconds(), Thread::current()->name(), _jni_lock_count);
}
Universe::heap()->collect(GCCause::_gc_locker);
}
_doing_gc = false;
_needs_gc = false;
JNICritical_lock->notify_all();
}
}
// Implementation of No_GC_Verifier
#ifdef ASSERT
No_GC_Verifier::No_GC_Verifier(bool verifygc) {
_verifygc = verifygc;
if (_verifygc) {
CollectedHeap* h = Universe::heap();
assert(!h->is_gc_active(), "GC active during No_GC_Verifier");
_old_invocations = h->total_collections();
}
}
No_GC_Verifier::~No_GC_Verifier() {
if (_verifygc) {
CollectedHeap* h = Universe::heap();
assert(!h->is_gc_active(), "GC active during No_GC_Verifier");
if (_old_invocations != h->total_collections()) {
fatal("collection in a No_GC_Verifier secured function");
}
}
}
Pause_No_GC_Verifier::Pause_No_GC_Verifier(No_GC_Verifier * ngcv) {
_ngcv = ngcv;
if (_ngcv->_verifygc) {
// if we were verifying, then make sure that nothing is
// wrong before we "pause" verification
CollectedHeap* h = Universe::heap();
assert(!h->is_gc_active(), "GC active during No_GC_Verifier");
if (_ngcv->_old_invocations != h->total_collections()) {
fatal("collection in a No_GC_Verifier secured function");
}
}
}
Pause_No_GC_Verifier::~Pause_No_GC_Verifier() {
if (_ngcv->_verifygc) {
// if we were verifying before, then reenable verification
CollectedHeap* h = Universe::heap();
assert(!h->is_gc_active(), "GC active during No_GC_Verifier");
_ngcv->_old_invocations = h->total_collections();
}
}
// JRT_LEAF rules:
// A JRT_LEAF method may not interfere with safepointing by
// 1) acquiring or blocking on a Mutex or JavaLock - checked
// 2) allocating heap memory - checked
// 3) executing a VM operation - checked
// 4) executing a system call (including malloc) that could block or grab a lock
// 5) invoking GC
// 6) reaching a safepoint
// 7) running too long
// Nor may any method it calls.
JRT_Leaf_Verifier::JRT_Leaf_Verifier()
: No_Safepoint_Verifier(true, JRT_Leaf_Verifier::should_verify_GC())
{
}
JRT_Leaf_Verifier::~JRT_Leaf_Verifier()
{
}
bool JRT_Leaf_Verifier::should_verify_GC() {
switch (JavaThread::current()->thread_state()) {
case _thread_in_Java:
// is in a leaf routine, there must be no safepoint.
return true;
case _thread_in_native:
// A native thread is not subject to safepoints.
// Even while it is in a leaf routine, GC is ok
return false;
default:
// Leaf routines cannot be called from other contexts.
ShouldNotReachHere();
return false;
}
}
#endif
|
