1 /*
2 * Copyright (c) 2001, 2016, 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 int ConcurrentMarkSweepThread::_CMS_flag = CMS_nil;
46
47 volatile jint ConcurrentMarkSweepThread::_pending_yields = 0;
48
49 SurrogateLockerThread* ConcurrentMarkSweepThread::_slt = NULL;
50 SurrogateLockerThread::SLT_msg_type
51 ConcurrentMarkSweepThread::_sltBuffer = SurrogateLockerThread::empty;
52 Monitor* ConcurrentMarkSweepThread::_sltMonitor = NULL;
53
54 ConcurrentMarkSweepThread::ConcurrentMarkSweepThread(CMSCollector* collector)
55 : ConcurrentGCThread() {
56 assert(UseConcMarkSweepGC, "UseConcMarkSweepGC should be set");
57 assert(_cmst == NULL, "CMS thread already created");
58 _cmst = this;
59 assert(_collector == NULL, "Collector already set");
60 _collector = collector;
61
62 set_name("CMS Main Thread");
63
64 // An old comment here said: "Priority should be just less
65 // than that of VMThread". Since the VMThread runs at
66 // NearMaxPriority, the old comment was inaccurate, but
67 // changing the default priority to NearMaxPriority-1
68 // could change current behavior, so the default of
69 // NearMaxPriority stays in place.
70 //
71 // Note that there's a possibility of the VMThread
72 // starving if UseCriticalCMSThreadPriority is on.
73 // That won't happen on Solaris for various reasons,
74 // but may well happen on non-Solaris platforms.
75 create_and_start(UseCriticalCMSThreadPriority ? CriticalPriority : NearMaxPriority);
76
77 _sltMonitor = SLT_lock;
78 }
79
80 void ConcurrentMarkSweepThread::run_service() {
81 assert(this == cmst(), "just checking");
82
83 if (BindCMSThreadToCPU && !os::bind_to_processor(CPUForCMSThread)) {
84 warning("Couldn't bind CMS thread to processor " UINTX_FORMAT, CPUForCMSThread);
85 }
86
87 {
88 MutexLockerEx x(CGC_lock, true);
89 set_CMS_flag(CMS_cms_wants_token);
90 assert(is_init_completed() && Universe::is_fully_initialized(), "ConcurrentGCThread::run() should have waited for this.");
91
92 // Wait until the surrogate locker thread that will do
93 // pending list locking on our behalf has been created.
94 // We cannot start the SLT thread ourselves since we need
95 // to be a JavaThread to do so.
96 CMSLoopCountWarn loopY("CMS::run", "waiting for SLT installation", 2);
97 while (_slt == NULL && !should_terminate()) {
98 CGC_lock->wait(true, 200);
99 loopY.tick();
100 }
101 clear_CMS_flag(CMS_cms_wants_token);
102 }
103
104 while (!should_terminate()) {
105 sleepBeforeNextCycle();
106 if (should_terminate()) break;
107 GCIdMark gc_id_mark;
108 GCCause::Cause cause = _collector->_full_gc_requested ?
109 _collector->_full_gc_cause : GCCause::_cms_concurrent_mark;
110 _collector->collect_in_background(cause);
111 }
112
113 // Check that the state of any protocol for synchronization
114 // between background (CMS) and foreground collector is "clean"
115 // (i.e. will not potentially block the foreground collector,
116 // requiring action by us).
117 verify_ok_to_terminate();
118 }
119
120 #ifndef PRODUCT
121 void ConcurrentMarkSweepThread::verify_ok_to_terminate() const {
122 assert(!(CGC_lock->owned_by_self() || cms_thread_has_cms_token() ||
123 cms_thread_wants_cms_token()),
124 "Must renounce all worldly possessions and desires for nirvana");
125 _collector->verify_ok_to_terminate();
126 }
127 #endif
128
129 // create and start a new ConcurrentMarkSweep Thread for given CMS generation
130 ConcurrentMarkSweepThread* ConcurrentMarkSweepThread::start(CMSCollector* collector) {
131 guarantee(_cmst == NULL, "start() called twice!");
132 ConcurrentMarkSweepThread* th = new ConcurrentMarkSweepThread(collector);
133 assert(_cmst == th, "Where did the just-created CMS thread go?");
134 return th;
135 }
136
137 void ConcurrentMarkSweepThread::stop_service() {
138 // Now post a notify on CGC_lock so as to nudge
139 // CMS thread(s) that might be slumbering in
140 // sleepBeforeNextCycle.
141 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
142 CGC_lock->notify_all();
143 }
144
145 void ConcurrentMarkSweepThread::threads_do(ThreadClosure* tc) {
146 assert(tc != NULL, "Null ThreadClosure");
147 if (cmst() != NULL && !cmst()->has_terminated()) {
148 tc->do_thread(cmst());
149 }
150 assert(Universe::is_fully_initialized(),
151 "Called too early, make sure heap is fully initialized");
152 if (_collector != NULL) {
153 AbstractWorkGang* gang = _collector->conc_workers();
154 if (gang != NULL) {
155 gang->threads_do(tc);
156 }
157 }
158 }
159
160 void ConcurrentMarkSweepThread::print_all_on(outputStream* st) {
161 if (cmst() != NULL && !cmst()->has_terminated()) {
162 cmst()->print_on(st);
163 st->cr();
164 }
165 if (_collector != NULL) {
166 AbstractWorkGang* gang = _collector->conc_workers();
167 if (gang != NULL) {
168 gang->print_worker_threads_on(st);
169 }
170 }
171 }
172
173 void ConcurrentMarkSweepThread::synchronize(bool is_cms_thread) {
174 assert(UseConcMarkSweepGC, "just checking");
175
176 MutexLockerEx x(CGC_lock,
177 Mutex::_no_safepoint_check_flag);
178 if (!is_cms_thread) {
179 assert(Thread::current()->is_VM_thread(), "Not a VM thread");
180 CMSSynchronousYieldRequest yr;
181 while (CMS_flag_is_set(CMS_cms_has_token)) {
182 // indicate that we want to get the token
183 set_CMS_flag(CMS_vm_wants_token);
184 CGC_lock->wait(true);
185 }
186 // claim the token and proceed
187 clear_CMS_flag(CMS_vm_wants_token);
188 set_CMS_flag(CMS_vm_has_token);
189 } else {
190 assert(Thread::current()->is_ConcurrentGC_thread(),
191 "Not a CMS thread");
192 // The following barrier assumes there's only one CMS thread.
193 // This will need to be modified is there are more CMS threads than one.
194 while (CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token)) {
195 set_CMS_flag(CMS_cms_wants_token);
196 CGC_lock->wait(true);
197 }
198 // claim the token
199 clear_CMS_flag(CMS_cms_wants_token);
200 set_CMS_flag(CMS_cms_has_token);
201 }
202 }
203
204 void ConcurrentMarkSweepThread::desynchronize(bool is_cms_thread) {
205 assert(UseConcMarkSweepGC, "just checking");
206
207 MutexLockerEx x(CGC_lock,
208 Mutex::_no_safepoint_check_flag);
209 if (!is_cms_thread) {
210 assert(Thread::current()->is_VM_thread(), "Not a VM thread");
211 assert(CMS_flag_is_set(CMS_vm_has_token), "just checking");
212 clear_CMS_flag(CMS_vm_has_token);
213 if (CMS_flag_is_set(CMS_cms_wants_token)) {
214 // wake-up a waiting CMS thread
215 CGC_lock->notify();
216 }
217 assert(!CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token),
218 "Should have been cleared");
219 } else {
220 assert(Thread::current()->is_ConcurrentGC_thread(),
221 "Not a CMS thread");
222 assert(CMS_flag_is_set(CMS_cms_has_token), "just checking");
223 clear_CMS_flag(CMS_cms_has_token);
224 if (CMS_flag_is_set(CMS_vm_wants_token)) {
225 // wake-up a waiting VM thread
226 CGC_lock->notify();
227 }
228 assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
229 "Should have been cleared");
230 }
231 }
232
233 // Wait until any cms_lock event
234 void ConcurrentMarkSweepThread::wait_on_cms_lock(long t_millis) {
235 MutexLockerEx x(CGC_lock,
236 Mutex::_no_safepoint_check_flag);
237 if (should_terminate() || _collector->_full_gc_requested) {
238 return;
239 }
240 set_CMS_flag(CMS_cms_wants_token); // to provoke notifies
241 CGC_lock->wait(Mutex::_no_safepoint_check_flag, t_millis);
242 clear_CMS_flag(CMS_cms_wants_token);
243 assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
244 "Should not be set");
245 }
246
247 // Wait until the next synchronous GC, a concurrent full gc request,
248 // or a timeout, whichever is earlier.
249 void ConcurrentMarkSweepThread::wait_on_cms_lock_for_scavenge(long t_millis) {
250 // Wait time in millis or 0 value representing infinite wait for a scavenge
251 assert(t_millis >= 0, "Wait time for scavenge should be 0 or positive");
252
253 GenCollectedHeap* gch = GenCollectedHeap::heap();
254 double start_time_secs = os::elapsedTime();
255 double end_time_secs = start_time_secs + (t_millis / ((double) MILLIUNITS));
256
257 // Total collections count before waiting loop
258 unsigned int before_count;
259 {
260 MutexLockerEx hl(Heap_lock, Mutex::_no_safepoint_check_flag);
261 before_count = gch->total_collections();
262 }
263
264 unsigned int loop_count = 0;
265
266 while(!should_terminate()) {
267 double now_time = os::elapsedTime();
268 long wait_time_millis;
269
270 if(t_millis != 0) {
271 // New wait limit
272 wait_time_millis = (long) ((end_time_secs - now_time) * MILLIUNITS);
273 if(wait_time_millis <= 0) {
274 // Wait time is over
275 break;
276 }
277 } else {
278 // No wait limit, wait if necessary forever
279 wait_time_millis = 0;
280 }
281
282 // Wait until the next event or the remaining timeout
283 {
284 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
285
286 if (should_terminate() || _collector->_full_gc_requested) {
287 return;
288 }
289 set_CMS_flag(CMS_cms_wants_token); // to provoke notifies
290 assert(t_millis == 0 || wait_time_millis > 0, "Sanity");
291 CGC_lock->wait(Mutex::_no_safepoint_check_flag, wait_time_millis);
292 clear_CMS_flag(CMS_cms_wants_token);
293 assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
294 "Should not be set");
295 }
296
297 // Extra wait time check before entering the heap lock to get the collection count
298 if(t_millis != 0 && os::elapsedTime() >= end_time_secs) {
299 // Wait time is over
300 break;
301 }
302
303 // Total collections count after the event
304 unsigned int after_count;
305 {
306 MutexLockerEx hl(Heap_lock, Mutex::_no_safepoint_check_flag);
307 after_count = gch->total_collections();
308 }
309
310 if(before_count != after_count) {
311 // There was a collection - success
312 break;
313 }
314
315 // Too many loops warning
316 if(++loop_count == 0) {
317 warning("wait_on_cms_lock_for_scavenge() has looped %u times", loop_count - 1);
318 }
319 }
320 }
321
322 void ConcurrentMarkSweepThread::sleepBeforeNextCycle() {
323 while (!should_terminate()) {
324 if(CMSWaitDuration >= 0) {
325 // Wait until the next synchronous GC, a concurrent full gc
326 // request or a timeout, whichever is earlier.
327 wait_on_cms_lock_for_scavenge(CMSWaitDuration);
328 } else {
329 // Wait until any cms_lock event or check interval not to call shouldConcurrentCollect permanently
330 wait_on_cms_lock(CMSCheckInterval);
331 }
332 // Check if we should start a CMS collection cycle
333 if (_collector->shouldConcurrentCollect()) {
334 return;
335 }
336 // .. collection criterion not yet met, let's go back
337 // and wait some more
338 }
339 }
340
341 // Note: this method, although exported by the ConcurrentMarkSweepThread,
342 // which is a non-JavaThread, can only be called by a JavaThread.
343 // Currently this is done at vm creation time (post-vm-init) by the
344 // main/Primordial (Java)Thread.
345 // XXX Consider changing this in the future to allow the CMS thread
346 // itself to create this thread?
347 void ConcurrentMarkSweepThread::makeSurrogateLockerThread(TRAPS) {
348 assert(UseConcMarkSweepGC, "SLT thread needed only for CMS GC");
349 assert(_slt == NULL, "SLT already created");
350 _slt = SurrogateLockerThread::make(THREAD);
351 }