1 /*
2 * Copyright (c) 2001, 2012, 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 %u", 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 _collector->collect_in_background(false); // !clear_all_soft_refs
144 }
145 assert(_should_terminate, "just checking");
146 // Check that the state of any protocol for synchronization
147 // between background (CMS) and foreground collector is "clean"
148 // (i.e. will not potentially block the foreground collector,
149 // requiring action by us).
150 verify_ok_to_terminate();
151 // Signal that it is terminated
152 {
153 MutexLockerEx mu(Terminator_lock,
154 Mutex::_no_safepoint_check_flag);
155 assert(_cmst == this, "Weird!");
156 _cmst = NULL;
157 Terminator_lock->notify();
158 }
159
160 // Thread destructor usually does this..
161 ThreadLocalStorage::set_thread(NULL);
162 }
163
164 #ifndef PRODUCT
165 void ConcurrentMarkSweepThread::verify_ok_to_terminate() const {
166 assert(!(CGC_lock->owned_by_self() || cms_thread_has_cms_token() ||
167 cms_thread_wants_cms_token()),
168 "Must renounce all worldly possessions and desires for nirvana");
169 _collector->verify_ok_to_terminate();
170 }
171 #endif
172
173 // create and start a new ConcurrentMarkSweep Thread for given CMS generation
174 ConcurrentMarkSweepThread* ConcurrentMarkSweepThread::start(CMSCollector* collector) {
175 if (!_should_terminate) {
176 assert(cmst() == NULL, "start() called twice?");
177 ConcurrentMarkSweepThread* th = new ConcurrentMarkSweepThread(collector);
178 assert(cmst() == th, "Where did the just-created CMS thread go?");
179 return th;
180 }
181 return NULL;
182 }
183
184 void ConcurrentMarkSweepThread::stop() {
185 if (CMSIncrementalMode) {
186 // Disable incremental mode and wake up the thread so it notices the change.
187 disable_icms();
188 start_icms();
189 }
190 // it is ok to take late safepoints here, if needed
191 {
192 MutexLockerEx x(Terminator_lock);
193 _should_terminate = true;
194 }
195 { // Now post a notify on CGC_lock so as to nudge
196 // CMS thread(s) that might be slumbering in
197 // sleepBeforeNextCycle.
198 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
199 CGC_lock->notify_all();
200 }
201 { // Now wait until (all) CMS thread(s) have exited
202 MutexLockerEx x(Terminator_lock);
203 while(cmst() != NULL) {
204 Terminator_lock->wait();
205 }
206 }
207 }
208
209 void ConcurrentMarkSweepThread::threads_do(ThreadClosure* tc) {
210 assert(tc != NULL, "Null ThreadClosure");
211 if (_cmst != NULL) {
212 tc->do_thread(_cmst);
213 }
214 assert(Universe::is_fully_initialized(),
215 "Called too early, make sure heap is fully initialized");
216 if (_collector != NULL) {
217 AbstractWorkGang* gang = _collector->conc_workers();
218 if (gang != NULL) {
219 gang->threads_do(tc);
220 }
221 }
222 }
223
224 void ConcurrentMarkSweepThread::print_on(outputStream* st) const {
225 st->print("\"%s\" ", name());
226 Thread::print_on(st);
227 st->cr();
228 }
229
230 void ConcurrentMarkSweepThread::print_all_on(outputStream* st) {
231 if (_cmst != NULL) {
232 _cmst->print_on(st);
233 st->cr();
234 }
235 if (_collector != NULL) {
236 AbstractWorkGang* gang = _collector->conc_workers();
237 if (gang != NULL) {
238 gang->print_worker_threads_on(st);
239 }
240 }
241 }
242
243 void ConcurrentMarkSweepThread::synchronize(bool is_cms_thread) {
244 assert(UseConcMarkSweepGC, "just checking");
245
246 MutexLockerEx x(CGC_lock,
247 Mutex::_no_safepoint_check_flag);
248 if (!is_cms_thread) {
249 assert(Thread::current()->is_VM_thread(), "Not a VM thread");
250 CMSSynchronousYieldRequest yr;
251 while (CMS_flag_is_set(CMS_cms_has_token)) {
252 // indicate that we want to get the token
253 set_CMS_flag(CMS_vm_wants_token);
254 CGC_lock->wait(true);
255 }
256 // claim the token and proceed
257 clear_CMS_flag(CMS_vm_wants_token);
258 set_CMS_flag(CMS_vm_has_token);
259 } else {
260 assert(Thread::current()->is_ConcurrentGC_thread(),
261 "Not a CMS thread");
262 // The following barrier assumes there's only one CMS thread.
263 // This will need to be modified is there are more CMS threads than one.
264 while (CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token)) {
265 set_CMS_flag(CMS_cms_wants_token);
266 CGC_lock->wait(true);
267 }
268 // claim the token
269 clear_CMS_flag(CMS_cms_wants_token);
270 set_CMS_flag(CMS_cms_has_token);
271 }
272 }
273
274 void ConcurrentMarkSweepThread::desynchronize(bool is_cms_thread) {
275 assert(UseConcMarkSweepGC, "just checking");
276
277 MutexLockerEx x(CGC_lock,
278 Mutex::_no_safepoint_check_flag);
279 if (!is_cms_thread) {
280 assert(Thread::current()->is_VM_thread(), "Not a VM thread");
281 assert(CMS_flag_is_set(CMS_vm_has_token), "just checking");
282 clear_CMS_flag(CMS_vm_has_token);
283 if (CMS_flag_is_set(CMS_cms_wants_token)) {
284 // wake-up a waiting CMS thread
285 CGC_lock->notify();
286 }
287 assert(!CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token),
288 "Should have been cleared");
289 } else {
290 assert(Thread::current()->is_ConcurrentGC_thread(),
291 "Not a CMS thread");
292 assert(CMS_flag_is_set(CMS_cms_has_token), "just checking");
293 clear_CMS_flag(CMS_cms_has_token);
294 if (CMS_flag_is_set(CMS_vm_wants_token)) {
295 // wake-up a waiting VM thread
296 CGC_lock->notify();
297 }
298 assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
299 "Should have been cleared");
300 }
301 }
302
303 // Wait until the next synchronous GC, a concurrent full gc request,
304 // or a timeout, whichever is earlier.
305 void ConcurrentMarkSweepThread::wait_on_cms_lock(long t_millis) {
306 MutexLockerEx x(CGC_lock,
307 Mutex::_no_safepoint_check_flag);
308 if (_should_terminate || _collector->_full_gc_requested) {
309 return;
310 }
311 set_CMS_flag(CMS_cms_wants_token); // to provoke notifies
312 CGC_lock->wait(Mutex::_no_safepoint_check_flag, t_millis);
313 clear_CMS_flag(CMS_cms_wants_token);
314 assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
315 "Should not be set");
316 }
317
318 void ConcurrentMarkSweepThread::sleepBeforeNextCycle() {
319 while (!_should_terminate) {
320 if (CMSIncrementalMode) {
321 icms_wait();
322 return;
323 } else {
324 // Wait until the next synchronous GC, a concurrent full gc
325 // request or a timeout, whichever is earlier.
326 wait_on_cms_lock(CMSWaitDuration);
327 }
328 // Check if we should start a CMS collection cycle
329 if (_collector->shouldConcurrentCollect()) {
330 return;
331 }
332 // .. collection criterion not yet met, let's go back
333 // and wait some more
334 }
335 }
336
337 // Incremental CMS
338 void ConcurrentMarkSweepThread::start_icms() {
339 assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking");
340 MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag);
341 trace_state("start_icms");
342 _should_run = true;
343 iCMS_lock->notify_all();
344 }
345
346 void ConcurrentMarkSweepThread::stop_icms() {
347 assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking");
348 MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag);
349 if (!_should_stop) {
350 trace_state("stop_icms");
351 _should_stop = true;
352 _should_run = false;
353 asynchronous_yield_request();
354 iCMS_lock->notify_all();
355 }
356 }
357
358 void ConcurrentMarkSweepThread::icms_wait() {
359 assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking");
360 if (_should_stop && icms_is_enabled()) {
361 MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag);
362 trace_state("pause_icms");
363 _collector->stats().stop_cms_timer();
364 while(!_should_run && icms_is_enabled()) {
365 iCMS_lock->wait(Mutex::_no_safepoint_check_flag);
366 }
367 _collector->stats().start_cms_timer();
368 _should_stop = false;
369 trace_state("pause_icms end");
370 }
371 }
372
373 // Note: this method, although exported by the ConcurrentMarkSweepThread,
374 // which is a non-JavaThread, can only be called by a JavaThread.
375 // Currently this is done at vm creation time (post-vm-init) by the
376 // main/Primordial (Java)Thread.
377 // XXX Consider changing this in the future to allow the CMS thread
378 // itself to create this thread?
379 void ConcurrentMarkSweepThread::makeSurrogateLockerThread(TRAPS) {
380 assert(UseConcMarkSweepGC, "SLT thread needed only for CMS GC");
381 assert(_slt == NULL, "SLT already created");
382 _slt = SurrogateLockerThread::make(THREAD);
383 }