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