1 /*
2 * Copyright (c) 2001, 2006, 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.
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23 */
24
25 # include "incls/_precompiled.incl"
26 # include "incls/_concurrentMarkSweepThread.cpp.incl"
27
28 // ======= Concurrent Mark Sweep Thread ========
29
30 // The CMS thread is created when Concurrent Mark Sweep is used in the
31 // older of two generations in a generational memory system.
32
33 ConcurrentMarkSweepThread*
34 ConcurrentMarkSweepThread::_cmst = NULL;
35 CMSCollector* ConcurrentMarkSweepThread::_collector = NULL;
36 bool ConcurrentMarkSweepThread::_should_terminate = false;
37 int ConcurrentMarkSweepThread::_CMS_flag = CMS_nil;
38
39 volatile jint ConcurrentMarkSweepThread::_pending_yields = 0;
40 volatile jint ConcurrentMarkSweepThread::_pending_decrements = 0;
41
42 volatile bool ConcurrentMarkSweepThread::_icms_enabled = false;
43 volatile bool ConcurrentMarkSweepThread::_should_run = false;
44 // When icms is enabled, the icms thread is stopped until explicitly
45 // started.
46 volatile bool ConcurrentMarkSweepThread::_should_stop = true;
47
48 SurrogateLockerThread*
49 ConcurrentMarkSweepThread::_slt = NULL;
50 SurrogateLockerThread::SLT_msg_type
51 ConcurrentMarkSweepThread::_sltBuffer = SurrogateLockerThread::empty;
52 Monitor*
53 ConcurrentMarkSweepThread::_sltMonitor = NULL;
54
55 ConcurrentMarkSweepThread::ConcurrentMarkSweepThread(CMSCollector* collector)
56 : ConcurrentGCThread() {
57 assert(UseConcMarkSweepGC, "UseConcMarkSweepGC should be set");
58 assert(_cmst == NULL, "CMS thread already created");
59 _cmst = this;
60 assert(_collector == NULL, "Collector already set");
61 _collector = collector;
62
63 set_name("Concurrent Mark-Sweep GC Thread");
64
65 if (os::create_thread(this, os::cgc_thread)) {
66 // XXX: need to set this to low priority
67 // unless "agressive mode" set; priority
68 // should be just less than that of VMThread.
69 os::set_priority(this, NearMaxPriority);
70 if (!DisableStartThread) {
71 os::start_thread(this);
72 }
73 }
74 _sltMonitor = SLT_lock;
75 set_icms_enabled(CMSIncrementalMode);
76 }
77
78 void ConcurrentMarkSweepThread::run() {
79 assert(this == cmst(), "just checking");
80
81 this->record_stack_base_and_size();
82 this->initialize_thread_local_storage();
83 this->set_active_handles(JNIHandleBlock::allocate_block());
84 // From this time Thread::current() should be working.
85 assert(this == Thread::current(), "just checking");
86 if (BindCMSThreadToCPU && !os::bind_to_processor(CPUForCMSThread)) {
87 warning("Couldn't bind CMS thread to processor %u", CPUForCMSThread);
88 }
89 // Wait until Universe::is_fully_initialized()
90 {
91 CMSLoopCountWarn loopX("CMS::run", "waiting for "
92 "Universe::is_fully_initialized()", 2);
93 MutexLockerEx x(CGC_lock, true);
94 set_CMS_flag(CMS_cms_wants_token);
95 // Wait until Universe is initialized and all initialization is completed.
96 while (!is_init_completed() && !Universe::is_fully_initialized() &&
97 !_should_terminate) {
98 CGC_lock->wait(true, 200);
99 loopX.tick();
100 }
101 // Wait until the surrogate locker thread that will do
102 // pending list locking on our behalf has been created.
103 // We cannot start the SLT thread ourselves since we need
104 // to be a JavaThread to do so.
105 CMSLoopCountWarn loopY("CMS::run", "waiting for SLT installation", 2);
106 while (_slt == NULL && !_should_terminate) {
107 CGC_lock->wait(true, 200);
108 loopY.tick();
109 }
110 clear_CMS_flag(CMS_cms_wants_token);
111 }
112
113 while (!_should_terminate) {
114 sleepBeforeNextCycle();
115 if (_should_terminate) break;
116 _collector->collect_in_background(false); // !clear_all_soft_refs
117 }
118 assert(_should_terminate, "just checking");
119 // Check that the state of any protocol for synchronization
120 // between background (CMS) and foreground collector is "clean"
121 // (i.e. will not potentially block the foreground collector,
122 // requiring action by us).
123 verify_ok_to_terminate();
124 // Signal that it is terminated
125 {
126 MutexLockerEx mu(Terminator_lock,
127 Mutex::_no_safepoint_check_flag);
128 assert(_cmst == this, "Weird!");
129 _cmst = NULL;
130 Terminator_lock->notify();
131 }
132
133 // Thread destructor usually does this..
134 ThreadLocalStorage::set_thread(NULL);
135 }
136
137 #ifndef PRODUCT
138 void ConcurrentMarkSweepThread::verify_ok_to_terminate() const {
139 assert(!(CGC_lock->owned_by_self() || cms_thread_has_cms_token() ||
140 cms_thread_wants_cms_token()),
141 "Must renounce all worldly possessions and desires for nirvana");
142 _collector->verify_ok_to_terminate();
143 }
144 #endif
145
146 // create and start a new ConcurrentMarkSweep Thread for given CMS generation
147 ConcurrentMarkSweepThread* ConcurrentMarkSweepThread::start(CMSCollector* collector) {
148 if (!_should_terminate) {
149 assert(cmst() == NULL, "start() called twice?");
150 ConcurrentMarkSweepThread* th = new ConcurrentMarkSweepThread(collector);
151 assert(cmst() == th, "Where did the just-created CMS thread go?");
152 return th;
153 }
154 return NULL;
155 }
156
157 void ConcurrentMarkSweepThread::stop() {
158 if (CMSIncrementalMode) {
159 // Disable incremental mode and wake up the thread so it notices the change.
160 disable_icms();
161 start_icms();
162 }
163 // it is ok to take late safepoints here, if needed
164 {
165 MutexLockerEx x(Terminator_lock);
166 _should_terminate = true;
167 }
168 { // Now post a notify on CGC_lock so as to nudge
169 // CMS thread(s) that might be slumbering in
170 // sleepBeforeNextCycle.
171 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
172 CGC_lock->notify_all();
173 }
174 { // Now wait until (all) CMS thread(s) have exited
175 MutexLockerEx x(Terminator_lock);
176 while(cmst() != NULL) {
177 Terminator_lock->wait();
178 }
179 }
180 }
181
182 void ConcurrentMarkSweepThread::threads_do(ThreadClosure* tc) {
183 assert(tc != NULL, "Null ThreadClosure");
184 if (_cmst != NULL) {
185 tc->do_thread(_cmst);
186 }
187 assert(Universe::is_fully_initialized(),
188 "Called too early, make sure heap is fully initialized");
189 if (_collector != NULL) {
190 AbstractWorkGang* gang = _collector->conc_workers();
191 if (gang != NULL) {
192 gang->threads_do(tc);
193 }
194 }
195 }
196
197 void ConcurrentMarkSweepThread::print_on(outputStream* st) const {
198 st->print("\"%s\" ", name());
199 Thread::print_on(st);
200 st->cr();
201 }
202
203 void ConcurrentMarkSweepThread::print_all_on(outputStream* st) {
204 if (_cmst != NULL) {
205 _cmst->print_on(st);
206 }
207 if (_collector != NULL) {
208 AbstractWorkGang* gang = _collector->conc_workers();
209 if (gang != NULL) {
210 gang->print_worker_threads_on(st);
211 }
212 }
213 }
214
215 void ConcurrentMarkSweepThread::synchronize(bool is_cms_thread) {
216 assert(UseConcMarkSweepGC, "just checking");
217
218 MutexLockerEx x(CGC_lock,
219 Mutex::_no_safepoint_check_flag);
220 if (!is_cms_thread) {
221 assert(Thread::current()->is_VM_thread(), "Not a VM thread");
222 CMSSynchronousYieldRequest yr;
223 while (CMS_flag_is_set(CMS_cms_has_token)) {
224 // indicate that we want to get the token
225 set_CMS_flag(CMS_vm_wants_token);
226 CGC_lock->wait(true);
227 }
228 // claim the token and proceed
229 clear_CMS_flag(CMS_vm_wants_token);
230 set_CMS_flag(CMS_vm_has_token);
231 } else {
232 assert(Thread::current()->is_ConcurrentGC_thread(),
233 "Not a CMS thread");
234 // The following barrier assumes there's only one CMS thread.
235 // This will need to be modified is there are more CMS threads than one.
236 while (CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token)) {
237 set_CMS_flag(CMS_cms_wants_token);
238 CGC_lock->wait(true);
239 }
240 // claim the token
241 clear_CMS_flag(CMS_cms_wants_token);
242 set_CMS_flag(CMS_cms_has_token);
243 }
244 }
245
246 void ConcurrentMarkSweepThread::desynchronize(bool is_cms_thread) {
247 assert(UseConcMarkSweepGC, "just checking");
248
249 MutexLockerEx x(CGC_lock,
250 Mutex::_no_safepoint_check_flag);
251 if (!is_cms_thread) {
252 assert(Thread::current()->is_VM_thread(), "Not a VM thread");
253 assert(CMS_flag_is_set(CMS_vm_has_token), "just checking");
254 clear_CMS_flag(CMS_vm_has_token);
255 if (CMS_flag_is_set(CMS_cms_wants_token)) {
256 // wake-up a waiting CMS thread
257 CGC_lock->notify();
258 }
259 assert(!CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token),
260 "Should have been cleared");
261 } else {
262 assert(Thread::current()->is_ConcurrentGC_thread(),
263 "Not a CMS thread");
264 assert(CMS_flag_is_set(CMS_cms_has_token), "just checking");
265 clear_CMS_flag(CMS_cms_has_token);
266 if (CMS_flag_is_set(CMS_vm_wants_token)) {
267 // wake-up a waiting VM thread
268 CGC_lock->notify();
269 }
270 assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
271 "Should have been cleared");
272 }
273 }
274
275 // Wait until the next synchronous GC or a timeout, whichever is earlier.
276 void ConcurrentMarkSweepThread::wait_on_cms_lock(long t) {
277 MutexLockerEx x(CGC_lock,
278 Mutex::_no_safepoint_check_flag);
279 set_CMS_flag(CMS_cms_wants_token); // to provoke notifies
280 CGC_lock->wait(Mutex::_no_safepoint_check_flag, t);
281 clear_CMS_flag(CMS_cms_wants_token);
282 assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
283 "Should not be set");
284 }
285
286 void ConcurrentMarkSweepThread::sleepBeforeNextCycle() {
287 while (!_should_terminate) {
288 if (CMSIncrementalMode) {
289 icms_wait();
290 return;
291 } else {
292 // Wait until the next synchronous GC or a timeout, whichever is earlier
293 wait_on_cms_lock(CMSWaitDuration);
294 }
295 // Check if we should start a CMS collection cycle
296 if (_collector->shouldConcurrentCollect()) {
297 return;
298 }
299 // .. collection criterion not yet met, let's go back
300 // and wait some more
301 }
302 }
303
304 // Incremental CMS
305 void ConcurrentMarkSweepThread::start_icms() {
306 assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking");
307 MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag);
308 trace_state("start_icms");
309 _should_run = true;
310 iCMS_lock->notify_all();
311 }
312
313 void ConcurrentMarkSweepThread::stop_icms() {
314 assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking");
315 MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag);
316 if (!_should_stop) {
317 trace_state("stop_icms");
318 _should_stop = true;
319 _should_run = false;
320 asynchronous_yield_request();
321 iCMS_lock->notify_all();
322 }
323 }
324
325 void ConcurrentMarkSweepThread::icms_wait() {
326 assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking");
327 if (_should_stop && icms_enabled()) {
328 MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag);
329 trace_state("pause_icms");
330 _collector->stats().stop_cms_timer();
331 while(!_should_run && icms_enabled()) {
332 iCMS_lock->wait(Mutex::_no_safepoint_check_flag);
333 }
334 _collector->stats().start_cms_timer();
335 _should_stop = false;
336 trace_state("pause_icms end");
337 }
338 }
339
340 // Note: this method, although exported by the ConcurrentMarkSweepThread,
341 // which is a non-JavaThread, can only be called by a JavaThread.
342 // Currently this is done at vm creation time (post-vm-init) by the
343 // main/Primordial (Java)Thread.
344 // XXX Consider changing this in the future to allow the CMS thread
345 // itself to create this thread?
346 void ConcurrentMarkSweepThread::makeSurrogateLockerThread(TRAPS) {
347 assert(UseConcMarkSweepGC, "SLT thread needed only for CMS GC");
348 assert(_slt == NULL, "SLT already created");
349 _slt = SurrogateLockerThread::make(THREAD);
350 }