1 /* 2 * Copyright (c) 2001, 2015, 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 bool ConcurrentMarkSweepThread::_should_terminate = false; 46 int ConcurrentMarkSweepThread::_CMS_flag = CMS_nil; 47 48 volatile jint ConcurrentMarkSweepThread::_pending_yields = 0; 49 50 SurrogateLockerThread* ConcurrentMarkSweepThread::_slt = NULL; 51 SurrogateLockerThread::SLT_msg_type 52 ConcurrentMarkSweepThread::_sltBuffer = SurrogateLockerThread::empty; 53 Monitor* ConcurrentMarkSweepThread::_sltMonitor = NULL; 54 55 ConcurrentMarkSweepThread::ConcurrentMarkSweepThread(CMSCollector* collector) 56 : ConcurrentGCThread() { 57 assert(UseConcMarkSweepGC, "UseConcMarkSweepGC should be set"); 58 assert(_cmst == NULL, "CMS thread already created"); 59 _cmst = this; 60 assert(_collector == NULL, "Collector already set"); 61 _collector = collector; 62 63 set_name("CMS Main Thread"); 64 65 if (os::create_thread(this, os::cgc_thread)) { 66 // An old comment here said: "Priority should be just less 67 // than that of VMThread". Since the VMThread runs at 68 // NearMaxPriority, the old comment was inaccurate, but 69 // changing the default priority to NearMaxPriority-1 70 // could change current behavior, so the default of 71 // NearMaxPriority stays in place. 72 // 73 // Note that there's a possibility of the VMThread 74 // starving if UseCriticalCMSThreadPriority is on. 75 // That won't happen on Solaris for various reasons, 76 // but may well happen on non-Solaris platforms. 77 int native_prio; 78 if (UseCriticalCMSThreadPriority) { 79 native_prio = os::java_to_os_priority[CriticalPriority]; 80 } else { 81 native_prio = os::java_to_os_priority[NearMaxPriority]; 82 } 83 os::set_native_priority(this, native_prio); 84 85 if (!DisableStartThread) { 86 os::start_thread(this); 87 } 88 } 89 _sltMonitor = SLT_lock; 90 } 91 92 void ConcurrentMarkSweepThread::run() { 93 assert(this == cmst(), "just checking"); 94 95 initialize_in_thread(); 96 // From this time Thread::current() should be working. 97 assert(this == Thread::current(), "just checking"); 98 if (BindCMSThreadToCPU && !os::bind_to_processor(CPUForCMSThread)) { 99 warning("Couldn't bind CMS thread to processor " UINTX_FORMAT, CPUForCMSThread); 100 } 101 // Wait until Universe::is_fully_initialized() 102 { 103 CMSLoopCountWarn loopX("CMS::run", "waiting for " 104 "Universe::is_fully_initialized()", 2); 105 MutexLockerEx x(CGC_lock, true); 106 set_CMS_flag(CMS_cms_wants_token); 107 // Wait until Universe is initialized and all initialization is completed. 108 while (!is_init_completed() && !Universe::is_fully_initialized() && 109 !_should_terminate) { 110 CGC_lock->wait(true, 200); 111 loopX.tick(); 112 } 113 // Wait until the surrogate locker thread that will do 114 // pending list locking on our behalf has been created. 115 // We cannot start the SLT thread ourselves since we need 116 // to be a JavaThread to do so. 117 CMSLoopCountWarn loopY("CMS::run", "waiting for SLT installation", 2); 118 while (_slt == NULL && !_should_terminate) { 119 CGC_lock->wait(true, 200); 120 loopY.tick(); 121 } 122 clear_CMS_flag(CMS_cms_wants_token); 123 } 124 125 while (!_should_terminate) { 126 sleepBeforeNextCycle(); 127 if (_should_terminate) break; 128 GCIdMark gc_id_mark; 129 GCCause::Cause cause = _collector->_full_gc_requested ? 130 _collector->_full_gc_cause : GCCause::_cms_concurrent_mark; 131 _collector->collect_in_background(cause); 132 } 133 assert(_should_terminate, "just checking"); 134 // Check that the state of any protocol for synchronization 135 // between background (CMS) and foreground collector is "clean" 136 // (i.e. will not potentially block the foreground collector, 137 // requiring action by us). 138 verify_ok_to_terminate(); 139 // Signal that it is terminated 140 { 141 MutexLockerEx mu(Terminator_lock, 142 Mutex::_no_safepoint_check_flag); 143 assert(_cmst == this, "Weird!"); 144 _cmst = NULL; 145 Terminator_lock->notify(); 146 } 147 } 148 149 #ifndef PRODUCT 150 void ConcurrentMarkSweepThread::verify_ok_to_terminate() const { 151 assert(!(CGC_lock->owned_by_self() || cms_thread_has_cms_token() || 152 cms_thread_wants_cms_token()), 153 "Must renounce all worldly possessions and desires for nirvana"); 154 _collector->verify_ok_to_terminate(); 155 } 156 #endif 157 158 // create and start a new ConcurrentMarkSweep Thread for given CMS generation 159 ConcurrentMarkSweepThread* ConcurrentMarkSweepThread::start(CMSCollector* collector) { 160 if (!_should_terminate) { 161 assert(cmst() == NULL, "start() called twice?"); 162 ConcurrentMarkSweepThread* th = new ConcurrentMarkSweepThread(collector); 163 assert(cmst() == th, "Where did the just-created CMS thread go?"); 164 return th; 165 } 166 return NULL; 167 } 168 169 void ConcurrentMarkSweepThread::stop() { 170 // it is ok to take late safepoints here, if needed 171 { 172 MutexLockerEx x(Terminator_lock); 173 _should_terminate = true; 174 } 175 { // Now post a notify on CGC_lock so as to nudge 176 // CMS thread(s) that might be slumbering in 177 // sleepBeforeNextCycle. 178 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); 179 CGC_lock->notify_all(); 180 } 181 { // Now wait until (all) CMS thread(s) have exited 182 MutexLockerEx x(Terminator_lock); 183 while(cmst() != NULL) { 184 Terminator_lock->wait(); 185 } 186 } 187 } 188 189 void ConcurrentMarkSweepThread::threads_do(ThreadClosure* tc) { 190 assert(tc != NULL, "Null ThreadClosure"); 191 if (_cmst != NULL) { 192 tc->do_thread(_cmst); 193 } 194 assert(Universe::is_fully_initialized(), 195 "Called too early, make sure heap is fully initialized"); 196 if (_collector != NULL) { 197 AbstractWorkGang* gang = _collector->conc_workers(); 198 if (gang != NULL) { 199 gang->threads_do(tc); 200 } 201 } 202 } 203 204 void ConcurrentMarkSweepThread::print_all_on(outputStream* st) { 205 if (_cmst != NULL) { 206 _cmst->print_on(st); 207 st->cr(); 208 } 209 if (_collector != NULL) { 210 AbstractWorkGang* gang = _collector->conc_workers(); 211 if (gang != NULL) { 212 gang->print_worker_threads_on(st); 213 } 214 } 215 } 216 217 void ConcurrentMarkSweepThread::synchronize(bool is_cms_thread) { 218 assert(UseConcMarkSweepGC, "just checking"); 219 220 MutexLockerEx x(CGC_lock, 221 Mutex::_no_safepoint_check_flag); 222 if (!is_cms_thread) { 223 assert(Thread::current()->is_VM_thread(), "Not a VM thread"); 224 CMSSynchronousYieldRequest yr; 225 while (CMS_flag_is_set(CMS_cms_has_token)) { 226 // indicate that we want to get the token 227 set_CMS_flag(CMS_vm_wants_token); 228 CGC_lock->wait(true); 229 } 230 // claim the token and proceed 231 clear_CMS_flag(CMS_vm_wants_token); 232 set_CMS_flag(CMS_vm_has_token); 233 } else { 234 assert(Thread::current()->is_ConcurrentGC_thread(), 235 "Not a CMS thread"); 236 // The following barrier assumes there's only one CMS thread. 237 // This will need to be modified is there are more CMS threads than one. 238 while (CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token)) { 239 set_CMS_flag(CMS_cms_wants_token); 240 CGC_lock->wait(true); 241 } 242 // claim the token 243 clear_CMS_flag(CMS_cms_wants_token); 244 set_CMS_flag(CMS_cms_has_token); 245 } 246 } 247 248 void ConcurrentMarkSweepThread::desynchronize(bool is_cms_thread) { 249 assert(UseConcMarkSweepGC, "just checking"); 250 251 MutexLockerEx x(CGC_lock, 252 Mutex::_no_safepoint_check_flag); 253 if (!is_cms_thread) { 254 assert(Thread::current()->is_VM_thread(), "Not a VM thread"); 255 assert(CMS_flag_is_set(CMS_vm_has_token), "just checking"); 256 clear_CMS_flag(CMS_vm_has_token); 257 if (CMS_flag_is_set(CMS_cms_wants_token)) { 258 // wake-up a waiting CMS thread 259 CGC_lock->notify(); 260 } 261 assert(!CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token), 262 "Should have been cleared"); 263 } else { 264 assert(Thread::current()->is_ConcurrentGC_thread(), 265 "Not a CMS thread"); 266 assert(CMS_flag_is_set(CMS_cms_has_token), "just checking"); 267 clear_CMS_flag(CMS_cms_has_token); 268 if (CMS_flag_is_set(CMS_vm_wants_token)) { 269 // wake-up a waiting VM thread 270 CGC_lock->notify(); 271 } 272 assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token), 273 "Should have been cleared"); 274 } 275 } 276 277 // Wait until any cms_lock event 278 void ConcurrentMarkSweepThread::wait_on_cms_lock(long t_millis) { 279 MutexLockerEx x(CGC_lock, 280 Mutex::_no_safepoint_check_flag); 281 if (_should_terminate || _collector->_full_gc_requested) { 282 return; 283 } 284 set_CMS_flag(CMS_cms_wants_token); // to provoke notifies 285 CGC_lock->wait(Mutex::_no_safepoint_check_flag, t_millis); 286 clear_CMS_flag(CMS_cms_wants_token); 287 assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token), 288 "Should not be set"); 289 } 290 291 // Wait until the next synchronous GC, a concurrent full gc request, 292 // or a timeout, whichever is earlier. 293 void ConcurrentMarkSweepThread::wait_on_cms_lock_for_scavenge(long t_millis) { 294 // Wait time in millis or 0 value representing infinite wait for a scavenge 295 assert(t_millis >= 0, "Wait time for scavenge should be 0 or positive"); 296 297 GenCollectedHeap* gch = GenCollectedHeap::heap(); 298 double start_time_secs = os::elapsedTime(); 299 double end_time_secs = start_time_secs + (t_millis / ((double) MILLIUNITS)); 300 301 // Total collections count before waiting loop 302 unsigned int before_count; 303 { 304 MutexLockerEx hl(Heap_lock, Mutex::_no_safepoint_check_flag); 305 before_count = gch->total_collections(); 306 } 307 308 unsigned int loop_count = 0; 309 310 while(!_should_terminate) { 311 double now_time = os::elapsedTime(); 312 long wait_time_millis; 313 314 if(t_millis != 0) { 315 // New wait limit 316 wait_time_millis = (long) ((end_time_secs - now_time) * MILLIUNITS); 317 if(wait_time_millis <= 0) { 318 // Wait time is over 319 break; 320 } 321 } else { 322 // No wait limit, wait if necessary forever 323 wait_time_millis = 0; 324 } 325 326 // Wait until the next event or the remaining timeout 327 { 328 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); 329 330 if (_should_terminate || _collector->_full_gc_requested) { 331 return; 332 } 333 set_CMS_flag(CMS_cms_wants_token); // to provoke notifies 334 assert(t_millis == 0 || wait_time_millis > 0, "Sanity"); 335 CGC_lock->wait(Mutex::_no_safepoint_check_flag, wait_time_millis); 336 clear_CMS_flag(CMS_cms_wants_token); 337 assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token), 338 "Should not be set"); 339 } 340 341 // Extra wait time check before entering the heap lock to get the collection count 342 if(t_millis != 0 && os::elapsedTime() >= end_time_secs) { 343 // Wait time is over 344 break; 345 } 346 347 // Total collections count after the event 348 unsigned int after_count; 349 { 350 MutexLockerEx hl(Heap_lock, Mutex::_no_safepoint_check_flag); 351 after_count = gch->total_collections(); 352 } 353 354 if(before_count != after_count) { 355 // There was a collection - success 356 break; 357 } 358 359 // Too many loops warning 360 if(++loop_count == 0) { 361 warning("wait_on_cms_lock_for_scavenge() has looped %u times", loop_count - 1); 362 } 363 } 364 } 365 366 void ConcurrentMarkSweepThread::sleepBeforeNextCycle() { 367 while (!_should_terminate) { 368 if(CMSWaitDuration >= 0) { 369 // Wait until the next synchronous GC, a concurrent full gc 370 // request or a timeout, whichever is earlier. 371 wait_on_cms_lock_for_scavenge(CMSWaitDuration); 372 } else { 373 // Wait until any cms_lock event or check interval not to call shouldConcurrentCollect permanently 374 wait_on_cms_lock(CMSCheckInterval); 375 } 376 // Check if we should start a CMS collection cycle 377 if (_collector->shouldConcurrentCollect()) { 378 return; 379 } 380 // .. collection criterion not yet met, let's go back 381 // and wait some more 382 } 383 } 384 385 // Note: this method, although exported by the ConcurrentMarkSweepThread, 386 // which is a non-JavaThread, can only be called by a JavaThread. 387 // Currently this is done at vm creation time (post-vm-init) by the 388 // main/Primordial (Java)Thread. 389 // XXX Consider changing this in the future to allow the CMS thread 390 // itself to create this thread? 391 void ConcurrentMarkSweepThread::makeSurrogateLockerThread(TRAPS) { 392 assert(UseConcMarkSweepGC, "SLT thread needed only for CMS GC"); 393 assert(_slt == NULL, "SLT already created"); 394 _slt = SurrogateLockerThread::make(THREAD); 395 }