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 log_warning(gc)("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 log_warning(gc)("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 }