1 /*
2 * Copyright (c) 2001, 2015, 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/cms/concurrentMarkSweepGeneration.inline.hpp"
28 #include "gc/cms/concurrentMarkSweepThread.hpp"
29 #include "gc/shared/gcId.hpp"
30 #include "gc/shared/genCollectedHeap.hpp"
31 #include "oops/instanceRefKlass.hpp"
32 #include "oops/oop.inline.hpp"
33 #include "runtime/init.hpp"
34 #include "runtime/interfaceSupport.hpp"
35 #include "runtime/java.hpp"
36 #include "runtime/javaCalls.hpp"
37 #include "runtime/mutexLocker.hpp"
38 #include "runtime/os.hpp"
39 #include "runtime/vmThread.hpp"
40
41 // ======= Concurrent Mark Sweep Thread ========
42
43 ConcurrentMarkSweepThread* ConcurrentMarkSweepThread::_cmst = NULL;
44 CMSCollector* ConcurrentMarkSweepThread::_collector = NULL;
45 bool ConcurrentMarkSweepThread::_should_terminate = false;
46 int ConcurrentMarkSweepThread::_CMS_flag = CMS_nil;
47
48 volatile jint ConcurrentMarkSweepThread::_pending_yields = 0;
49
50 SurrogateLockerThread* ConcurrentMarkSweepThread::_slt = NULL;
51 SurrogateLockerThread::SLT_msg_type
52 ConcurrentMarkSweepThread::_sltBuffer = SurrogateLockerThread::empty;
53 Monitor* 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("CMS Main Thread");
64
65 if (os::create_thread(this, os::cgc_thread)) {
66 // An old comment here said: "Priority should be just less
67 // than that of VMThread". Since the VMThread runs at
68 // NearMaxPriority, the old comment was inaccurate, but
69 // changing the default priority to NearMaxPriority-1
70 // could change current behavior, so the default of
71 // NearMaxPriority stays in place.
72 //
73 // Note that there's a possibility of the VMThread
74 // starving if UseCriticalCMSThreadPriority is on.
75 // That won't happen on Solaris for various reasons,
76 // but may well happen on non-Solaris platforms.
77 int native_prio;
78 if (UseCriticalCMSThreadPriority) {
79 native_prio = os::java_to_os_priority[CriticalPriority];
80 } else {
81 native_prio = os::java_to_os_priority[NearMaxPriority];
82 }
83 os::set_native_priority(this, native_prio);
84
85 if (!DisableStartThread) {
86 os::start_thread(this);
87 }
88 }
89 _sltMonitor = SLT_lock;
90 }
91
92 void ConcurrentMarkSweepThread::run() {
93 assert(this == cmst(), "just checking");
94
95 initialize_in_thread();
96 // From this time Thread::current() should be working.
97 assert(this == Thread::current(), "just checking");
98 if (BindCMSThreadToCPU && !os::bind_to_processor(CPUForCMSThread)) {
99 warning("Couldn't bind CMS thread to processor " UINTX_FORMAT, CPUForCMSThread);
100 }
101 // Wait until Universe::is_fully_initialized()
102 {
103 CMSLoopCountWarn loopX("CMS::run", "waiting for "
104 "Universe::is_fully_initialized()", 2);
105 MutexLockerEx x(CGC_lock, true);
106 set_CMS_flag(CMS_cms_wants_token);
107 // Wait until Universe is initialized and all initialization is completed.
108 while (!is_init_completed() && !Universe::is_fully_initialized() &&
109 !_should_terminate) {
110 CGC_lock->wait(true, 200);
111 loopX.tick();
112 }
113 // Wait until the surrogate locker thread that will do
114 // pending list locking on our behalf has been created.
115 // We cannot start the SLT thread ourselves since we need
116 // to be a JavaThread to do so.
117 CMSLoopCountWarn loopY("CMS::run", "waiting for SLT installation", 2);
118 while (_slt == NULL && !_should_terminate) {
119 CGC_lock->wait(true, 200);
120 loopY.tick();
121 }
122 clear_CMS_flag(CMS_cms_wants_token);
123 }
124
125 while (!_should_terminate) {
126 sleepBeforeNextCycle();
127 if (_should_terminate) break;
128 GCIdMark gc_id_mark;
129 GCCause::Cause cause = _collector->_full_gc_requested ?
130 _collector->_full_gc_cause : GCCause::_cms_concurrent_mark;
131 _collector->collect_in_background(cause);
132 }
133 assert(_should_terminate, "just checking");
134 // Check that the state of any protocol for synchronization
135 // between background (CMS) and foreground collector is "clean"
136 // (i.e. will not potentially block the foreground collector,
137 // requiring action by us).
138 verify_ok_to_terminate();
139 // Signal that it is terminated
140 {
141 MutexLockerEx mu(Terminator_lock,
142 Mutex::_no_safepoint_check_flag);
143 assert(_cmst == this, "Weird!");
144 _cmst = NULL;
145 Terminator_lock->notify();
146 }
147
148 // Thread destructor usually does this..
149 ThreadLocalStorage::set_thread(NULL);
150 }
151
152 #ifndef PRODUCT
153 void ConcurrentMarkSweepThread::verify_ok_to_terminate() const {
154 assert(!(CGC_lock->owned_by_self() || cms_thread_has_cms_token() ||
155 cms_thread_wants_cms_token()),
156 "Must renounce all worldly possessions and desires for nirvana");
157 _collector->verify_ok_to_terminate();
158 }
159 #endif
160
161 // create and start a new ConcurrentMarkSweep Thread for given CMS generation
162 ConcurrentMarkSweepThread* ConcurrentMarkSweepThread::start(CMSCollector* collector) {
163 if (!_should_terminate) {
164 assert(cmst() == NULL, "start() called twice?");
165 ConcurrentMarkSweepThread* th = new ConcurrentMarkSweepThread(collector);
166 assert(cmst() == th, "Where did the just-created CMS thread go?");
167 return th;
168 }
169 return NULL;
170 }
171
172 void ConcurrentMarkSweepThread::stop() {
173 // it is ok to take late safepoints here, if needed
174 {
175 MutexLockerEx x(Terminator_lock);
176 _should_terminate = true;
177 }
178 { // Now post a notify on CGC_lock so as to nudge
179 // CMS thread(s) that might be slumbering in
180 // sleepBeforeNextCycle.
181 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
182 CGC_lock->notify_all();
183 }
184 { // Now wait until (all) CMS thread(s) have exited
185 MutexLockerEx x(Terminator_lock);
186 while(cmst() != NULL) {
187 Terminator_lock->wait();
188 }
189 }
190 }
191
192 void ConcurrentMarkSweepThread::threads_do(ThreadClosure* tc) {
193 assert(tc != NULL, "Null ThreadClosure");
194 if (_cmst != NULL) {
195 tc->do_thread(_cmst);
196 }
197 assert(Universe::is_fully_initialized(),
198 "Called too early, make sure heap is fully initialized");
199 if (_collector != NULL) {
200 AbstractWorkGang* gang = _collector->conc_workers();
201 if (gang != NULL) {
202 gang->threads_do(tc);
203 }
204 }
205 }
206
207 void ConcurrentMarkSweepThread::print_all_on(outputStream* st) {
208 if (_cmst != NULL) {
209 _cmst->print_on(st);
210 st->cr();
211 }
212 if (_collector != NULL) {
213 AbstractWorkGang* gang = _collector->conc_workers();
214 if (gang != NULL) {
215 gang->print_worker_threads_on(st);
216 }
217 }
218 }
219
220 void ConcurrentMarkSweepThread::synchronize(bool is_cms_thread) {
221 assert(UseConcMarkSweepGC, "just checking");
222
223 MutexLockerEx x(CGC_lock,
224 Mutex::_no_safepoint_check_flag);
225 if (!is_cms_thread) {
226 assert(Thread::current()->is_VM_thread(), "Not a VM thread");
227 CMSSynchronousYieldRequest yr;
228 while (CMS_flag_is_set(CMS_cms_has_token)) {
229 // indicate that we want to get the token
230 set_CMS_flag(CMS_vm_wants_token);
231 CGC_lock->wait(true);
232 }
233 // claim the token and proceed
234 clear_CMS_flag(CMS_vm_wants_token);
235 set_CMS_flag(CMS_vm_has_token);
236 } else {
237 assert(Thread::current()->is_ConcurrentGC_thread(),
238 "Not a CMS thread");
239 // The following barrier assumes there's only one CMS thread.
240 // This will need to be modified is there are more CMS threads than one.
241 while (CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token)) {
242 set_CMS_flag(CMS_cms_wants_token);
243 CGC_lock->wait(true);
244 }
245 // claim the token
246 clear_CMS_flag(CMS_cms_wants_token);
247 set_CMS_flag(CMS_cms_has_token);
248 }
249 }
250
251 void ConcurrentMarkSweepThread::desynchronize(bool is_cms_thread) {
252 assert(UseConcMarkSweepGC, "just checking");
253
254 MutexLockerEx x(CGC_lock,
255 Mutex::_no_safepoint_check_flag);
256 if (!is_cms_thread) {
257 assert(Thread::current()->is_VM_thread(), "Not a VM thread");
258 assert(CMS_flag_is_set(CMS_vm_has_token), "just checking");
259 clear_CMS_flag(CMS_vm_has_token);
260 if (CMS_flag_is_set(CMS_cms_wants_token)) {
261 // wake-up a waiting CMS thread
262 CGC_lock->notify();
263 }
264 assert(!CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token),
265 "Should have been cleared");
266 } else {
267 assert(Thread::current()->is_ConcurrentGC_thread(),
268 "Not a CMS thread");
269 assert(CMS_flag_is_set(CMS_cms_has_token), "just checking");
270 clear_CMS_flag(CMS_cms_has_token);
271 if (CMS_flag_is_set(CMS_vm_wants_token)) {
272 // wake-up a waiting VM thread
273 CGC_lock->notify();
274 }
275 assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
276 "Should have been cleared");
277 }
278 }
279
280 // Wait until any cms_lock event
281 void ConcurrentMarkSweepThread::wait_on_cms_lock(long t_millis) {
282 MutexLockerEx x(CGC_lock,
283 Mutex::_no_safepoint_check_flag);
284 if (_should_terminate || _collector->_full_gc_requested) {
285 return;
286 }
287 set_CMS_flag(CMS_cms_wants_token); // to provoke notifies
288 CGC_lock->wait(Mutex::_no_safepoint_check_flag, t_millis);
289 clear_CMS_flag(CMS_cms_wants_token);
290 assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
291 "Should not be set");
292 }
293
294 // Wait until the next synchronous GC, a concurrent full gc request,
295 // or a timeout, whichever is earlier.
296 void ConcurrentMarkSweepThread::wait_on_cms_lock_for_scavenge(long t_millis) {
297 // Wait time in millis or 0 value representing infinite wait for a scavenge
298 assert(t_millis >= 0, "Wait time for scavenge should be 0 or positive");
299
300 GenCollectedHeap* gch = GenCollectedHeap::heap();
301 double start_time_secs = os::elapsedTime();
302 double end_time_secs = start_time_secs + (t_millis / ((double) MILLIUNITS));
303
304 // Total collections count before waiting loop
305 unsigned int before_count;
306 {
307 MutexLockerEx hl(Heap_lock, Mutex::_no_safepoint_check_flag);
308 before_count = gch->total_collections();
309 }
310
311 unsigned int loop_count = 0;
312
313 while(!_should_terminate) {
314 double now_time = os::elapsedTime();
315 long wait_time_millis;
316
317 if(t_millis != 0) {
318 // New wait limit
319 wait_time_millis = (long) ((end_time_secs - now_time) * MILLIUNITS);
320 if(wait_time_millis <= 0) {
321 // Wait time is over
322 break;
323 }
324 } else {
325 // No wait limit, wait if necessary forever
326 wait_time_millis = 0;
327 }
328
329 // Wait until the next event or the remaining timeout
330 {
331 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
332
333 if (_should_terminate || _collector->_full_gc_requested) {
334 return;
335 }
336 set_CMS_flag(CMS_cms_wants_token); // to provoke notifies
337 assert(t_millis == 0 || wait_time_millis > 0, "Sanity");
338 CGC_lock->wait(Mutex::_no_safepoint_check_flag, wait_time_millis);
339 clear_CMS_flag(CMS_cms_wants_token);
340 assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
341 "Should not be set");
342 }
343
344 // Extra wait time check before entering the heap lock to get the collection count
345 if(t_millis != 0 && os::elapsedTime() >= end_time_secs) {
346 // Wait time is over
347 break;
348 }
349
350 // Total collections count after the event
351 unsigned int after_count;
352 {
353 MutexLockerEx hl(Heap_lock, Mutex::_no_safepoint_check_flag);
354 after_count = gch->total_collections();
355 }
356
357 if(before_count != after_count) {
358 // There was a collection - success
359 break;
360 }
361
362 // Too many loops warning
363 if(++loop_count == 0) {
364 warning("wait_on_cms_lock_for_scavenge() has looped %u times", loop_count - 1);
365 }
366 }
367 }
368
369 void ConcurrentMarkSweepThread::sleepBeforeNextCycle() {
370 while (!_should_terminate) {
371 if(CMSWaitDuration >= 0) {
372 // Wait until the next synchronous GC, a concurrent full gc
373 // request or a timeout, whichever is earlier.
374 wait_on_cms_lock_for_scavenge(CMSWaitDuration);
375 } else {
376 // Wait until any cms_lock event or check interval not to call shouldConcurrentCollect permanently
377 wait_on_cms_lock(CMSCheckInterval);
378 }
379 // Check if we should start a CMS collection cycle
380 if (_collector->shouldConcurrentCollect()) {
381 return;
382 }
383 // .. collection criterion not yet met, let's go back
384 // and wait some more
385 }
386 }
387
388 // Note: this method, although exported by the ConcurrentMarkSweepThread,
389 // which is a non-JavaThread, can only be called by a JavaThread.
390 // Currently this is done at vm creation time (post-vm-init) by the
391 // main/Primordial (Java)Thread.
392 // XXX Consider changing this in the future to allow the CMS thread
393 // itself to create this thread?
394 void ConcurrentMarkSweepThread::makeSurrogateLockerThread(TRAPS) {
395 assert(UseConcMarkSweepGC, "SLT thread needed only for CMS GC");
396 assert(_slt == NULL, "SLT already created");
397 _slt = SurrogateLockerThread::make(THREAD);
398 }