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/java.hpp"
34 #include "runtime/javaCalls.hpp"
35 #include "runtime/mutexLocker.hpp"
36 #include "runtime/os.hpp"
37 #include "runtime/vmThread.hpp"
38
39 // ======= Concurrent Mark Sweep Thread ========
40
41 ConcurrentMarkSweepThread* ConcurrentMarkSweepThread::_cmst = NULL;
42 CMSCollector* ConcurrentMarkSweepThread::_collector = NULL;
43 int ConcurrentMarkSweepThread::_CMS_flag = CMS_nil;
44
45 volatile jint ConcurrentMarkSweepThread::_pending_yields = 0;
46
47 ConcurrentMarkSweepThread::ConcurrentMarkSweepThread(CMSCollector* collector)
48 : ConcurrentGCThread() {
49 assert(UseConcMarkSweepGC, "UseConcMarkSweepGC should be set");
50 assert(_cmst == NULL, "CMS thread already created");
51 _cmst = this;
52 assert(_collector == NULL, "Collector already set");
53 _collector = collector;
54
55 set_name("CMS Main Thread");
56
57 // An old comment here said: "Priority should be just less
58 // than that of VMThread". Since the VMThread runs at
59 // NearMaxPriority, the old comment was inaccurate, but
60 // changing the default priority to NearMaxPriority-1
61 // could change current behavior, so the default of
62 // NearMaxPriority stays in place.
63 //
64 // Note that there's a possibility of the VMThread
65 // starving if UseCriticalCMSThreadPriority is on.
66 // That won't happen on Solaris for various reasons,
67 // but may well happen on non-Solaris platforms.
68 create_and_start(UseCriticalCMSThreadPriority ? CriticalPriority : NearMaxPriority);
69 }
70
71 void ConcurrentMarkSweepThread::run_service() {
72 assert(this == cmst(), "just checking");
73
74 if (BindCMSThreadToCPU && !os::bind_to_processor(CPUForCMSThread)) {
75 log_warning(gc)("Couldn't bind CMS thread to processor " UINTX_FORMAT, CPUForCMSThread);
76 }
77
78 while (!should_terminate()) {
79 sleepBeforeNextCycle();
80 if (should_terminate()) break;
81 GCIdMark gc_id_mark;
82 GCCause::Cause cause = _collector->_full_gc_requested ?
83 _collector->_full_gc_cause : GCCause::_cms_concurrent_mark;
84 _collector->collect_in_background(cause);
85 }
86
87 // Check that the state of any protocol for synchronization
88 // between background (CMS) and foreground collector is "clean"
89 // (i.e. will not potentially block the foreground collector,
90 // requiring action by us).
91 verify_ok_to_terminate();
92 }
93
94 #ifndef PRODUCT
95 void ConcurrentMarkSweepThread::verify_ok_to_terminate() const {
96 assert(!(CGC_lock->owned_by_self() || cms_thread_has_cms_token() ||
97 cms_thread_wants_cms_token()),
98 "Must renounce all worldly possessions and desires for nirvana");
99 _collector->verify_ok_to_terminate();
100 }
101 #endif
102
103 // create and start a new ConcurrentMarkSweep Thread for given CMS generation
104 ConcurrentMarkSweepThread* ConcurrentMarkSweepThread::start(CMSCollector* collector) {
105 guarantee(_cmst == NULL, "start() called twice!");
106 ConcurrentMarkSweepThread* th = new ConcurrentMarkSweepThread(collector);
107 assert(_cmst == th, "Where did the just-created CMS thread go?");
108 return th;
109 }
110
111 void ConcurrentMarkSweepThread::stop_service() {
112 // Now post a notify on CGC_lock so as to nudge
113 // CMS thread(s) that might be slumbering in
114 // sleepBeforeNextCycle.
115 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
116 CGC_lock->notify_all();
117 }
118
119 void ConcurrentMarkSweepThread::threads_do(ThreadClosure* tc) {
120 assert(tc != NULL, "Null ThreadClosure");
121 if (cmst() != NULL && !cmst()->has_terminated()) {
122 tc->do_thread(cmst());
123 }
124 assert(Universe::is_fully_initialized(),
125 "Called too early, make sure heap is fully initialized");
126 if (_collector != NULL) {
127 AbstractWorkGang* gang = _collector->conc_workers();
128 if (gang != NULL) {
129 gang->threads_do(tc);
130 }
131 }
132 }
133
134 void ConcurrentMarkSweepThread::print_all_on(outputStream* st) {
135 if (cmst() != NULL && !cmst()->has_terminated()) {
136 cmst()->print_on(st);
137 st->cr();
138 }
139 if (_collector != NULL) {
140 AbstractWorkGang* gang = _collector->conc_workers();
141 if (gang != NULL) {
142 gang->print_worker_threads_on(st);
143 }
144 }
145 }
146
147 void ConcurrentMarkSweepThread::synchronize(bool is_cms_thread) {
148 assert(UseConcMarkSweepGC, "just checking");
149
150 MutexLockerEx x(CGC_lock,
151 Mutex::_no_safepoint_check_flag);
152 if (!is_cms_thread) {
153 assert(Thread::current()->is_VM_thread(), "Not a VM thread");
154 CMSSynchronousYieldRequest yr;
155 while (CMS_flag_is_set(CMS_cms_has_token)) {
156 // indicate that we want to get the token
157 set_CMS_flag(CMS_vm_wants_token);
158 CGC_lock->wait(true);
159 }
160 // claim the token and proceed
161 clear_CMS_flag(CMS_vm_wants_token);
162 set_CMS_flag(CMS_vm_has_token);
163 } else {
164 assert(Thread::current()->is_ConcurrentGC_thread(),
165 "Not a CMS thread");
166 // The following barrier assumes there's only one CMS thread.
167 // This will need to be modified is there are more CMS threads than one.
168 while (CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token)) {
169 set_CMS_flag(CMS_cms_wants_token);
170 CGC_lock->wait(true);
171 }
172 // claim the token
173 clear_CMS_flag(CMS_cms_wants_token);
174 set_CMS_flag(CMS_cms_has_token);
175 }
176 }
177
178 void ConcurrentMarkSweepThread::desynchronize(bool is_cms_thread) {
179 assert(UseConcMarkSweepGC, "just checking");
180
181 MutexLockerEx x(CGC_lock,
182 Mutex::_no_safepoint_check_flag);
183 if (!is_cms_thread) {
184 assert(Thread::current()->is_VM_thread(), "Not a VM thread");
185 assert(CMS_flag_is_set(CMS_vm_has_token), "just checking");
186 clear_CMS_flag(CMS_vm_has_token);
187 if (CMS_flag_is_set(CMS_cms_wants_token)) {
188 // wake-up a waiting CMS thread
189 CGC_lock->notify();
190 }
191 assert(!CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token),
192 "Should have been cleared");
193 } else {
194 assert(Thread::current()->is_ConcurrentGC_thread(),
195 "Not a CMS thread");
196 assert(CMS_flag_is_set(CMS_cms_has_token), "just checking");
197 clear_CMS_flag(CMS_cms_has_token);
198 if (CMS_flag_is_set(CMS_vm_wants_token)) {
199 // wake-up a waiting VM thread
200 CGC_lock->notify();
201 }
202 assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
203 "Should have been cleared");
204 }
205 }
206
207 // Wait until any cms_lock event
208 void ConcurrentMarkSweepThread::wait_on_cms_lock(long t_millis) {
209 MutexLockerEx x(CGC_lock,
210 Mutex::_no_safepoint_check_flag);
211 if (should_terminate() || _collector->_full_gc_requested) {
212 return;
213 }
214 set_CMS_flag(CMS_cms_wants_token); // to provoke notifies
215 CGC_lock->wait(Mutex::_no_safepoint_check_flag, t_millis);
216 clear_CMS_flag(CMS_cms_wants_token);
217 assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
218 "Should not be set");
219 }
220
221 // Wait until the next synchronous GC, a concurrent full gc request,
222 // or a timeout, whichever is earlier.
223 void ConcurrentMarkSweepThread::wait_on_cms_lock_for_scavenge(long t_millis) {
224 // Wait time in millis or 0 value representing infinite wait for a scavenge
225 assert(t_millis >= 0, "Wait time for scavenge should be 0 or positive");
226
227 CMSHeap* heap = CMSHeap::heap();
228 double start_time_secs = os::elapsedTime();
229 double end_time_secs = start_time_secs + (t_millis / ((double) MILLIUNITS));
230
231 // Total collections count before waiting loop
232 unsigned int before_count;
233 {
234 MutexLockerEx hl(Heap_lock, Mutex::_no_safepoint_check_flag);
235 before_count = heap->total_collections();
236 }
237
238 unsigned int loop_count = 0;
239
240 while(!should_terminate()) {
241 double now_time = os::elapsedTime();
242 long wait_time_millis;
243
244 if(t_millis != 0) {
245 // New wait limit
246 wait_time_millis = (long) ((end_time_secs - now_time) * MILLIUNITS);
247 if(wait_time_millis <= 0) {
248 // Wait time is over
249 break;
250 }
251 } else {
252 // No wait limit, wait if necessary forever
253 wait_time_millis = 0;
254 }
255
256 // Wait until the next event or the remaining timeout
257 {
258 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
259
260 if (should_terminate() || _collector->_full_gc_requested) {
261 return;
262 }
263 set_CMS_flag(CMS_cms_wants_token); // to provoke notifies
264 assert(t_millis == 0 || wait_time_millis > 0, "Sanity");
265 CGC_lock->wait(Mutex::_no_safepoint_check_flag, wait_time_millis);
266 clear_CMS_flag(CMS_cms_wants_token);
267 assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token),
268 "Should not be set");
269 }
270
271 // Extra wait time check before entering the heap lock to get the collection count
272 if(t_millis != 0 && os::elapsedTime() >= end_time_secs) {
273 // Wait time is over
274 break;
275 }
276
277 // Total collections count after the event
278 unsigned int after_count;
279 {
280 MutexLockerEx hl(Heap_lock, Mutex::_no_safepoint_check_flag);
281 after_count = heap->total_collections();
282 }
283
284 if(before_count != after_count) {
285 // There was a collection - success
286 break;
287 }
288
289 // Too many loops warning
290 if(++loop_count == 0) {
291 log_warning(gc)("wait_on_cms_lock_for_scavenge() has looped %u times", loop_count - 1);
292 }
293 }
294 }
295
296 void ConcurrentMarkSweepThread::sleepBeforeNextCycle() {
297 while (!should_terminate()) {
298 if(CMSWaitDuration >= 0) {
299 // Wait until the next synchronous GC, a concurrent full gc
300 // request or a timeout, whichever is earlier.
301 wait_on_cms_lock_for_scavenge(CMSWaitDuration);
302 } else {
303 // Wait until any cms_lock event or check interval not to call shouldConcurrentCollect permanently
304 wait_on_cms_lock(CMSCheckInterval);
305 }
306 // Check if we should start a CMS collection cycle
307 if (_collector->shouldConcurrentCollect()) {
308 return;
309 }
310 // .. collection criterion not yet met, let's go back
311 // and wait some more
312 }
313 }