1 /*
2 * Copyright (c) 2001, 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 "classfile/systemDictionary.hpp"
27 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
28 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
29 #include "memory/genCollectedHeap.hpp"
30 #include "oops/instanceRefKlass.hpp"
31 #include "oops/oop.inline.hpp"
32 #include "runtime/init.hpp"
33 #include "runtime/interfaceSupport.hpp"
34 #include "runtime/java.hpp"
35 #include "runtime/javaCalls.hpp"
36 #include "runtime/mutexLocker.hpp"
37 #include "runtime/os.hpp"
38 #include "runtime/vmThread.hpp"
39
40 // ======= Concurrent Mark Sweep Thread ========
41
42 // The CMS thread is created when Concurrent Mark Sweep is used in the
43 // older of two generations in a generational memory system.
44
45 ConcurrentMarkSweepThread*
46 ConcurrentMarkSweepThread::_cmst = NULL;
47 CMSCollector* ConcurrentMarkSweepThread::_collector = NULL;
48 bool ConcurrentMarkSweepThread::_should_terminate = false;
49 int ConcurrentMarkSweepThread::_CMS_flag = CMS_nil;
50
51 volatile jint ConcurrentMarkSweepThread::_pending_yields = 0;
52 volatile jint ConcurrentMarkSweepThread::_pending_decrements = 0;
53
54 volatile jint ConcurrentMarkSweepThread::_icms_disabled = 0;
55 volatile bool ConcurrentMarkSweepThread::_should_run = false;
56 // When icms is enabled, the icms thread is stopped until explicitly
57 // started.
58 volatile bool ConcurrentMarkSweepThread::_should_stop = true;
59
60 SurrogateLockerThread*
61 ConcurrentMarkSweepThread::_slt = NULL;
62 SurrogateLockerThread::SLT_msg_type
63 ConcurrentMarkSweepThread::_sltBuffer = SurrogateLockerThread::empty;
64 Monitor*
65 ConcurrentMarkSweepThread::_sltMonitor = NULL;
66
67 ConcurrentMarkSweepThread::ConcurrentMarkSweepThread(CMSCollector* collector)
68 : ConcurrentGCThread() {
69 assert(UseConcMarkSweepGC, "UseConcMarkSweepGC should be set");
70 assert(_cmst == NULL, "CMS thread already created");
71 _cmst = this;
72 assert(_collector == NULL, "Collector already set");
73 _collector = collector;
74
75 set_name("Concurrent Mark-Sweep GC Thread");
76
77 if (os::create_thread(this, os::cgc_thread)) {
78 // An old comment here said: "Priority should be just less
79 // than that of VMThread". Since the VMThread runs at
80 // NearMaxPriority, the old comment was inaccurate, but
81 // changing the default priority to NearMaxPriority-1
82 // could change current behavior, so the default of
83 // NearMaxPriority stays in place.
84 //
85 // Note that there's a possibility of the VMThread
86 // starving if UseCriticalCMSThreadPriority is on.
87 // That won't happen on Solaris for various reasons,
88 // but may well happen on non-Solaris platforms.
89 int native_prio;
90 if (UseCriticalCMSThreadPriority) {
91 native_prio = os::java_to_os_priority[CriticalPriority];
92 } else {
93 native_prio = os::java_to_os_priority[NearMaxPriority];
94 }
95 os::set_native_priority(this, native_prio);
96
97 if (!DisableStartThread) {
98 os::start_thread(this);
99 }
100 }
101 _sltMonitor = SLT_lock;
102 assert(!CMSIncrementalMode || icms_is_enabled(), "Error");
103 }
104
105 void ConcurrentMarkSweepThread::run() {
106 assert(this == cmst(), "just checking");
107
108 this->record_stack_base_and_size();
109 this->initialize_thread_local_storage();
110 this->set_active_handles(JNIHandleBlock::allocate_block());
111 // From this time Thread::current() should be working.
112 assert(this == Thread::current(), "just checking");
113 if (BindCMSThreadToCPU && !os::bind_to_processor(CPUForCMSThread)) {
114 warning("Couldn't bind CMS thread to processor " UINTX_FORMAT, CPUForCMSThread);
115 }
116 // Wait until Universe::is_fully_initialized()
117 {
118 CMSLoopCountWarn loopX("CMS::run", "waiting for "
119 "Universe::is_fully_initialized()", 2);
120 MutexLockerEx x(CGC_lock, true);
121 set_CMS_flag(CMS_cms_wants_token);
122 // Wait until Universe is initialized and all initialization is completed.
123 while (!is_init_completed() && !Universe::is_fully_initialized() &&
124 !_should_terminate) {
125 CGC_lock->wait(true, 200);
126 loopX.tick();
127 }
128 // Wait until the surrogate locker thread that will do
129 // pending list locking on our behalf has been created.
130 // We cannot start the SLT thread ourselves since we need
131 // to be a JavaThread to do so.
132 CMSLoopCountWarn loopY("CMS::run", "waiting for SLT installation", 2);
133 while (_slt == NULL && !_should_terminate) {
134 CGC_lock->wait(true, 200);
135 loopY.tick();
136 }
137 clear_CMS_flag(CMS_cms_wants_token);
138 }
139
140 while (!_should_terminate) {
141 sleepBeforeNextCycle();
142 if (_should_terminate) break;
143 GCCause::Cause cause = _collector->_full_gc_requested ?
144 _collector->_full_gc_cause : GCCause::_cms_concurrent_mark;
145 _collector->collect_in_background(false, cause);
146 }
147 assert(_should_terminate, "just checking");
148 // Check that the state of any protocol for synchronization
149 // between background (CMS) and foreground collector is "clean"
150 // (i.e. will not potentially block the foreground collector,
151 // requiring action by us).
152 verify_ok_to_terminate();
153 // Signal that it is terminated
154 {
155 MutexLockerEx mu(Terminator_lock,
156 Mutex::_no_safepoint_check_flag);
157 assert(_cmst == this, "Weird!");
158 _cmst = NULL;
159 Terminator_lock->notify();
160 }
161
162 // Thread destructor usually does this..
163 ThreadLocalStorage::set_thread(NULL);
164 }
165
166 #ifndef PRODUCT
167 void ConcurrentMarkSweepThread::verify_ok_to_terminate() const {
168 assert(!(CGC_lock->owned_by_self() || cms_thread_has_cms_token() ||
169 cms_thread_wants_cms_token()),
170 "Must renounce all worldly possessions and desires for nirvana");
171 _collector->verify_ok_to_terminate();
172 }
173 #endif
174
175 // create and start a new ConcurrentMarkSweep Thread for given CMS generation
176 ConcurrentMarkSweepThread* ConcurrentMarkSweepThread::start(CMSCollector* collector) {
177 if (!_should_terminate) {
178 assert(cmst() == NULL, "start() called twice?");
179 ConcurrentMarkSweepThread* th = new ConcurrentMarkSweepThread(collector);
180 assert(cmst() == th, "Where did the just-created CMS thread go?");
181 return th;
182 }
183 return NULL;
184 }
185
186 void ConcurrentMarkSweepThread::stop() {
187 if (CMSIncrementalMode) {
188 // Disable incremental mode and wake up the thread so it notices the change.
189 disable_icms();
190 start_icms();
191 }
192 // it is ok to take late safepoints here, if needed
193 {
194 MutexLockerEx x(Terminator_lock);
195 _should_terminate = true;
196 }
197 { // Now post a notify on CGC_lock so as to nudge
198 // CMS thread(s) that might be slumbering in
199 // sleepBeforeNextCycle.
200 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
201 CGC_lock->notify_all();
202 }
203 { // Now wait until (all) CMS thread(s) have exited
204 MutexLockerEx x(Terminator_lock);
205 while(cmst() != NULL) {
206 Terminator_lock->wait();
207 }
208 }
209 }
210
211 void ConcurrentMarkSweepThread::threads_do(ThreadClosure* tc) {
212 assert(tc != NULL, "Null ThreadClosure");
213 if (_cmst != NULL) {
214 tc->do_thread(_cmst);
215 }
216 assert(Universe::is_fully_initialized(),
217 "Called too early, make sure heap is fully initialized");
218 if (_collector != NULL) {
219 AbstractWorkGang* gang = _collector->conc_workers();
220 if (gang != NULL) {
221 gang->threads_do(tc);
222 }
223 }
224 }
225
226 void ConcurrentMarkSweepThread::print_all_on(outputStream* st) {
227 if (_cmst != NULL) {
228 _cmst->print_on(st);
229 st->cr();
230 }
231 if (_collector != NULL) {
232 AbstractWorkGang* gang = _collector->conc_workers();
233 if (gang != NULL) {
234 gang->print_worker_threads_on(st);
235 }
236 }
237 }
238
239 void ConcurrentMarkSweepThread::synchronize(bool is_cms_thread) {
240 assert(UseConcMarkSweepGC, "just checking");
241
242 MutexLockerEx x(CGC_lock,
243 Mutex::_no_safepoint_check_flag);
244 if (!is_cms_thread) {
245 assert(Thread::current()->is_VM_thread(), "Not a VM thread");
246 CMSSynchronousYieldRequest yr;
247 while (CMS_flag_is_set(CMS_cms_has_token)) {
248 // indicate that we want to get the token
249 set_CMS_flag(CMS_vm_wants_token);
250 CGC_lock->wait(true);
251 }
252 // claim the token and proceed
253 clear_CMS_flag(CMS_vm_wants_token);
254 set_CMS_flag(CMS_vm_has_token);
255 } else {
256 assert(Thread::current()->is_ConcurrentGC_thread(),
257 "Not a CMS thread");
258 // The following barrier assumes there's only one CMS thread.
259 // This will need to be modified is there are more CMS threads than one.
260 while (CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token)) {
261 set_CMS_flag(CMS_cms_wants_token);
262 CGC_lock->wait(true);
263 }
264 // claim the token
265 clear_CMS_flag(CMS_cms_wants_token);
266 set_CMS_flag(CMS_cms_has_token);
267 }
268 }
269
270 void ConcurrentMarkSweepThread::desynchronize(bool is_cms_thread) {
271 assert(UseConcMarkSweepGC, "just checking");
272
273 MutexLockerEx x(CGC_lock,
274 Mutex::_no_safepoint_check_flag);
275 if (!is_cms_thread) {
276 assert(Thread::current()->is_VM_thread(), "Not a VM thread");
277 assert(CMS_flag_is_set(CMS_vm_has_token), "just checking");
278 clear_CMS_flag(CMS_vm_has_token);
279 if (CMS_flag_is_set(CMS_cms_wants_token)) {
280 // wake-up a waiting CMS thread
281 CGC_lock->notify();
282 }
283 assert(!CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token),
284 "Should have been cleared");
285 } else {
286 assert(Thread::current()->is_ConcurrentGC_thread(),
287 "Not a CMS thread");
288 assert(CMS_flag_is_set(CMS_cms_has_token), "just checking");
289 clear_CMS_flag(CMS_cms_has_token);
290 if (CMS_flag_is_set(CMS_vm_wants_token)) {
291 // wake-up a waiting VM thread
292 CGC_lock->notify();
293 }
294 assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
295 "Should have been cleared");
296 }
297 }
298
299 // Wait until any cms_lock event
300 void ConcurrentMarkSweepThread::wait_on_cms_lock(long t_millis) {
301 MutexLockerEx x(CGC_lock,
302 Mutex::_no_safepoint_check_flag);
303 if (_should_terminate || _collector->_full_gc_requested) {
304 return;
305 }
306 set_CMS_flag(CMS_cms_wants_token); // to provoke notifies
307 CGC_lock->wait(Mutex::_no_safepoint_check_flag, t_millis);
308 clear_CMS_flag(CMS_cms_wants_token);
309 assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
310 "Should not be set");
311 }
312
313 // Wait until the next synchronous GC, a concurrent full gc request,
314 // or a timeout, whichever is earlier.
315 void ConcurrentMarkSweepThread::wait_on_cms_lock_for_scavenge(long t_millis) {
316 // Wait time in millis or 0 value representing infinite wait for a scavenge
317 assert(t_millis >= 0, "Wait time for scavenge should be 0 or positive");
318
319 GenCollectedHeap* gch = GenCollectedHeap::heap();
320 double start_time_secs = os::elapsedTime();
321 double end_time_secs = start_time_secs + (t_millis / ((double) MILLIUNITS));
322
323 // Total collections count before waiting loop
324 unsigned int before_count;
325 {
326 MutexLockerEx hl(Heap_lock, Mutex::_no_safepoint_check_flag);
327 before_count = gch->total_collections();
328 }
329
330 unsigned int loop_count = 0;
331
332 while(!_should_terminate) {
333 double now_time = os::elapsedTime();
334 long wait_time_millis;
335
336 if(t_millis != 0) {
337 // New wait limit
338 wait_time_millis = (long) ((end_time_secs - now_time) * MILLIUNITS);
339 if(wait_time_millis <= 0) {
340 // Wait time is over
341 break;
342 }
343 } else {
344 // No wait limit, wait if necessary forever
345 wait_time_millis = 0;
346 }
347
348 // Wait until the next event or the remaining timeout
349 {
350 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
351
352 if (_should_terminate || _collector->_full_gc_requested) {
353 return;
354 }
355 set_CMS_flag(CMS_cms_wants_token); // to provoke notifies
356 assert(t_millis == 0 || wait_time_millis > 0, "Sanity");
357 CGC_lock->wait(Mutex::_no_safepoint_check_flag, wait_time_millis);
358 clear_CMS_flag(CMS_cms_wants_token);
359 assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
360 "Should not be set");
361 }
362
363 // Extra wait time check before entering the heap lock to get the collection count
364 if(t_millis != 0 && os::elapsedTime() >= end_time_secs) {
365 // Wait time is over
366 break;
367 }
368
369 // Total collections count after the event
370 unsigned int after_count;
371 {
372 MutexLockerEx hl(Heap_lock, Mutex::_no_safepoint_check_flag);
373 after_count = gch->total_collections();
374 }
375
376 if(before_count != after_count) {
377 // There was a collection - success
378 break;
379 }
380
381 // Too many loops warning
382 if(++loop_count == 0) {
383 warning("wait_on_cms_lock_for_scavenge() has looped %u times", loop_count - 1);
384 }
385 }
386 }
387
388 void ConcurrentMarkSweepThread::sleepBeforeNextCycle() {
389 while (!_should_terminate) {
390 if (CMSIncrementalMode) {
391 icms_wait();
392 if(CMSWaitDuration >= 0) {
393 // Wait until the next synchronous GC, a concurrent full gc
394 // request or a timeout, whichever is earlier.
395 wait_on_cms_lock_for_scavenge(CMSWaitDuration);
396 }
397 return;
398 } else {
399 if(CMSWaitDuration >= 0) {
400 // Wait until the next synchronous GC, a concurrent full gc
401 // request or a timeout, whichever is earlier.
402 wait_on_cms_lock_for_scavenge(CMSWaitDuration);
403 } else {
404 // Wait until any cms_lock event or check interval not to call shouldConcurrentCollect permanently
405 wait_on_cms_lock(CMSCheckInterval);
406 }
407 }
408 // Check if we should start a CMS collection cycle
409 if (_collector->shouldConcurrentCollect()) {
410 return;
411 }
412 // .. collection criterion not yet met, let's go back
413 // and wait some more
414 }
415 }
416
417 // Incremental CMS
418 void ConcurrentMarkSweepThread::start_icms() {
419 assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking");
420 MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag);
421 trace_state("start_icms");
422 _should_run = true;
423 iCMS_lock->notify_all();
424 }
425
426 void ConcurrentMarkSweepThread::stop_icms() {
427 assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking");
428 MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag);
429 if (!_should_stop) {
430 trace_state("stop_icms");
431 _should_stop = true;
432 _should_run = false;
433 asynchronous_yield_request();
434 iCMS_lock->notify_all();
435 }
436 }
437
438 void ConcurrentMarkSweepThread::icms_wait() {
439 assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking");
440 if (_should_stop && icms_is_enabled()) {
441 MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag);
442 trace_state("pause_icms");
443 _collector->stats().stop_cms_timer();
444 while(!_should_run && icms_is_enabled()) {
445 iCMS_lock->wait(Mutex::_no_safepoint_check_flag);
446 }
447 _collector->stats().start_cms_timer();
448 _should_stop = false;
449 trace_state("pause_icms end");
450 }
451 }
452
453 // Note: this method, although exported by the ConcurrentMarkSweepThread,
454 // which is a non-JavaThread, can only be called by a JavaThread.
455 // Currently this is done at vm creation time (post-vm-init) by the
456 // main/Primordial (Java)Thread.
457 // XXX Consider changing this in the future to allow the CMS thread
458 // itself to create this thread?
459 void ConcurrentMarkSweepThread::makeSurrogateLockerThread(TRAPS) {
460 assert(UseConcMarkSweepGC, "SLT thread needed only for CMS GC");
461 assert(_slt == NULL, "SLT already created");
462 _slt = SurrogateLockerThread::make(THREAD);
463 }