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