1 /*
2 * Copyright (c) 2001, 2017, 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/cmsHeap.hpp"
28 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
29 #include "gc/cms/concurrentMarkSweepThread.hpp"
30 #include "gc/shared/gcId.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 ConcurrentMarkSweepThread* ConcurrentMarkSweepThread::_cmst = NULL;
43 CMSCollector* ConcurrentMarkSweepThread::_collector = NULL;
44 int ConcurrentMarkSweepThread::_CMS_flag = CMS_nil;
45
46 volatile jint ConcurrentMarkSweepThread::_pending_yields = 0;
47
48 ConcurrentMarkSweepThread::ConcurrentMarkSweepThread(CMSCollector* collector)
49 : ConcurrentGCThread() {
50 assert(UseConcMarkSweepGC, "UseConcMarkSweepGC should be set");
51 assert(_cmst == NULL, "CMS thread already created");
52 _cmst = this;
53 assert(_collector == NULL, "Collector already set");
54 _collector = collector;
55
56 set_name("CMS Main Thread");
57
58 // An old comment here said: "Priority should be just less
59 // than that of VMThread". Since the VMThread runs at
60 // NearMaxPriority, the old comment was inaccurate, but
61 // changing the default priority to NearMaxPriority-1
62 // could change current behavior, so the default of
63 // NearMaxPriority stays in place.
64 //
65 // Note that there's a possibility of the VMThread
66 // starving if UseCriticalCMSThreadPriority is on.
67 // That won't happen on Solaris for various reasons,
68 // but may well happen on non-Solaris platforms.
69 create_and_start(UseCriticalCMSThreadPriority ? CriticalPriority : NearMaxPriority);
70 }
71
72 void ConcurrentMarkSweepThread::run_service() {
73 assert(this == cmst(), "just checking");
74
75 if (BindCMSThreadToCPU && !os::bind_to_processor(CPUForCMSThread)) {
76 log_warning(gc)("Couldn't bind CMS thread to processor " UINTX_FORMAT, CPUForCMSThread);
77 }
78
79 while (!should_terminate()) {
80 sleepBeforeNextCycle();
81 if (should_terminate()) break;
82 GCIdMark gc_id_mark;
83 GCCause::Cause cause = _collector->_full_gc_requested ?
84 _collector->_full_gc_cause : GCCause::_cms_concurrent_mark;
85 _collector->collect_in_background(cause);
86 }
87
88 // Check that the state of any protocol for synchronization
89 // between background (CMS) and foreground collector is "clean"
90 // (i.e. will not potentially block the foreground collector,
91 // requiring action by us).
92 verify_ok_to_terminate();
93 }
94
95 #ifndef PRODUCT
96 void ConcurrentMarkSweepThread::verify_ok_to_terminate() const {
97 assert(!(CGC_lock->owned_by_self() || cms_thread_has_cms_token() ||
98 cms_thread_wants_cms_token()),
99 "Must renounce all worldly possessions and desires for nirvana");
100 _collector->verify_ok_to_terminate();
101 }
102 #endif
103
104 // create and start a new ConcurrentMarkSweep Thread for given CMS generation
105 ConcurrentMarkSweepThread* ConcurrentMarkSweepThread::start(CMSCollector* collector) {
106 guarantee(_cmst == NULL, "start() called twice!");
107 ConcurrentMarkSweepThread* th = new ConcurrentMarkSweepThread(collector);
108 assert(_cmst == th, "Where did the just-created CMS thread go?");
109 return th;
110 }
111
112 void ConcurrentMarkSweepThread::stop_service() {
113 // Now post a notify on CGC_lock so as to nudge
114 // CMS thread(s) that might be slumbering in
115 // sleepBeforeNextCycle.
116 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
117 CGC_lock->notify_all();
118 }
119
120 void ConcurrentMarkSweepThread::threads_do(ThreadClosure* tc) {
121 assert(tc != NULL, "Null ThreadClosure");
122 if (cmst() != NULL && !cmst()->has_terminated()) {
123 tc->do_thread(cmst());
124 }
125 assert(Universe::is_fully_initialized(),
126 "Called too early, make sure heap is fully initialized");
127 if (_collector != NULL) {
128 AbstractWorkGang* gang = _collector->conc_workers();
129 if (gang != NULL) {
130 gang->threads_do(tc);
131 }
132 }
133 }
134
135 void ConcurrentMarkSweepThread::print_all_on(outputStream* st) {
136 if (cmst() != NULL && !cmst()->has_terminated()) {
137 cmst()->print_on(st);
138 st->cr();
139 }
140 if (_collector != NULL) {
141 AbstractWorkGang* gang = _collector->conc_workers();
142 if (gang != NULL) {
143 gang->print_worker_threads_on(st);
144 }
145 }
146 }
147
148 void ConcurrentMarkSweepThread::synchronize(bool is_cms_thread) {
149 assert(UseConcMarkSweepGC, "just checking");
150
151 MutexLockerEx x(CGC_lock,
152 Mutex::_no_safepoint_check_flag);
153 if (!is_cms_thread) {
154 assert(Thread::current()->is_VM_thread(), "Not a VM thread");
155 CMSSynchronousYieldRequest yr;
156 while (CMS_flag_is_set(CMS_cms_has_token)) {
157 // indicate that we want to get the token
158 set_CMS_flag(CMS_vm_wants_token);
159 CGC_lock->wait(true);
160 }
161 // claim the token and proceed
162 clear_CMS_flag(CMS_vm_wants_token);
163 set_CMS_flag(CMS_vm_has_token);
164 } else {
165 assert(Thread::current()->is_ConcurrentGC_thread(),
166 "Not a CMS thread");
167 // The following barrier assumes there's only one CMS thread.
168 // This will need to be modified is there are more CMS threads than one.
169 while (CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token)) {
170 set_CMS_flag(CMS_cms_wants_token);
171 CGC_lock->wait(true);
172 }
173 // claim the token
174 clear_CMS_flag(CMS_cms_wants_token);
175 set_CMS_flag(CMS_cms_has_token);
176 }
177 }
178
179 void ConcurrentMarkSweepThread::desynchronize(bool is_cms_thread) {
180 assert(UseConcMarkSweepGC, "just checking");
181
182 MutexLockerEx x(CGC_lock,
183 Mutex::_no_safepoint_check_flag);
184 if (!is_cms_thread) {
185 assert(Thread::current()->is_VM_thread(), "Not a VM thread");
186 assert(CMS_flag_is_set(CMS_vm_has_token), "just checking");
187 clear_CMS_flag(CMS_vm_has_token);
188 if (CMS_flag_is_set(CMS_cms_wants_token)) {
189 // wake-up a waiting CMS thread
190 CGC_lock->notify();
191 }
192 assert(!CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token),
193 "Should have been cleared");
194 } else {
195 assert(Thread::current()->is_ConcurrentGC_thread(),
196 "Not a CMS thread");
197 assert(CMS_flag_is_set(CMS_cms_has_token), "just checking");
198 clear_CMS_flag(CMS_cms_has_token);
199 if (CMS_flag_is_set(CMS_vm_wants_token)) {
200 // wake-up a waiting VM thread
201 CGC_lock->notify();
202 }
203 assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
204 "Should have been cleared");
205 }
206 }
207
208 // Wait until any cms_lock event
209 void ConcurrentMarkSweepThread::wait_on_cms_lock(long t_millis) {
210 MutexLockerEx x(CGC_lock,
211 Mutex::_no_safepoint_check_flag);
212 if (should_terminate() || _collector->_full_gc_requested) {
213 return;
214 }
215 set_CMS_flag(CMS_cms_wants_token); // to provoke notifies
216 CGC_lock->wait(Mutex::_no_safepoint_check_flag, t_millis);
217 clear_CMS_flag(CMS_cms_wants_token);
218 assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
219 "Should not be set");
220 }
221
222 // Wait until the next synchronous GC, a concurrent full gc request,
223 // or a timeout, whichever is earlier.
224 void ConcurrentMarkSweepThread::wait_on_cms_lock_for_scavenge(long t_millis) {
225 // Wait time in millis or 0 value representing infinite wait for a scavenge
226 assert(t_millis >= 0, "Wait time for scavenge should be 0 or positive");
227
228 CMSHeap* heap = CMSHeap::heap();
229 double start_time_secs = os::elapsedTime();
230 double end_time_secs = start_time_secs + (t_millis / ((double) MILLIUNITS));
231
232 // Total collections count before waiting loop
233 unsigned int before_count;
234 {
235 MutexLockerEx hl(Heap_lock, Mutex::_no_safepoint_check_flag);
236 before_count = heap->total_collections();
237 }
238
239 unsigned int loop_count = 0;
240
241 while(!should_terminate()) {
242 double now_time = os::elapsedTime();
243 long wait_time_millis;
244
245 if(t_millis != 0) {
246 // New wait limit
247 wait_time_millis = (long) ((end_time_secs - now_time) * MILLIUNITS);
248 if(wait_time_millis <= 0) {
249 // Wait time is over
250 break;
251 }
252 } else {
253 // No wait limit, wait if necessary forever
254 wait_time_millis = 0;
255 }
256
257 // Wait until the next event or the remaining timeout
258 {
259 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
260
261 if (should_terminate() || _collector->_full_gc_requested) {
262 return;
263 }
264 set_CMS_flag(CMS_cms_wants_token); // to provoke notifies
265 assert(t_millis == 0 || wait_time_millis > 0, "Sanity");
266 CGC_lock->wait(Mutex::_no_safepoint_check_flag, wait_time_millis);
267 clear_CMS_flag(CMS_cms_wants_token);
268 assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
269 "Should not be set");
270 }
271
272 // Extra wait time check before entering the heap lock to get the collection count
273 if(t_millis != 0 && os::elapsedTime() >= end_time_secs) {
274 // Wait time is over
275 break;
276 }
277
278 // Total collections count after the event
279 unsigned int after_count;
280 {
281 MutexLockerEx hl(Heap_lock, Mutex::_no_safepoint_check_flag);
282 after_count = heap->total_collections();
283 }
284
285 if(before_count != after_count) {
286 // There was a collection - success
287 break;
288 }
289
290 // Too many loops warning
291 if(++loop_count == 0) {
292 log_warning(gc)("wait_on_cms_lock_for_scavenge() has looped %u times", loop_count - 1);
293 }
294 }
295 }
296
297 void ConcurrentMarkSweepThread::sleepBeforeNextCycle() {
298 while (!should_terminate()) {
299 if(CMSWaitDuration >= 0) {
300 // Wait until the next synchronous GC, a concurrent full gc
301 // request or a timeout, whichever is earlier.
302 wait_on_cms_lock_for_scavenge(CMSWaitDuration);
303 } else {
304 // Wait until any cms_lock event or check interval not to call shouldConcurrentCollect permanently
305 wait_on_cms_lock(CMSCheckInterval);
306 }
307 // Check if we should start a CMS collection cycle
308 if (_collector->shouldConcurrentCollect()) {
309 return;
310 }
311 // .. collection criterion not yet met, let's go back
312 // and wait some more
313 }
314 }