1 /* 2 * Copyright (c) 2001, 2012, 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_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp" 28 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp" 29 #include "memory/genCollectedHeap.hpp" 30 #include "oops/instanceRefKlass.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 // The CMS thread is created when Concurrent Mark Sweep is used in the 43 // older of two generations in a generational memory system. 44 45 ConcurrentMarkSweepThread* 46 ConcurrentMarkSweepThread::_cmst = NULL; 47 CMSCollector* ConcurrentMarkSweepThread::_collector = NULL; 48 bool ConcurrentMarkSweepThread::_should_terminate = false; 49 int ConcurrentMarkSweepThread::_CMS_flag = CMS_nil; 50 51 volatile jint ConcurrentMarkSweepThread::_pending_yields = 0; 52 volatile jint ConcurrentMarkSweepThread::_pending_decrements = 0; 53 54 volatile jint ConcurrentMarkSweepThread::_icms_disabled = 0; 55 volatile bool ConcurrentMarkSweepThread::_should_run = false; 56 // When icms is enabled, the icms thread is stopped until explicitly 57 // started. 58 volatile bool ConcurrentMarkSweepThread::_should_stop = true; 59 60 SurrogateLockerThread* 61 ConcurrentMarkSweepThread::_slt = NULL; 62 SurrogateLockerThread::SLT_msg_type 63 ConcurrentMarkSweepThread::_sltBuffer = SurrogateLockerThread::empty; 64 Monitor* 65 ConcurrentMarkSweepThread::_sltMonitor = NULL; 66 67 ConcurrentMarkSweepThread::ConcurrentMarkSweepThread(CMSCollector* collector) 68 : ConcurrentGCThread() { 69 assert(UseConcMarkSweepGC, "UseConcMarkSweepGC should be set"); 70 assert(_cmst == NULL, "CMS thread already created"); 71 _cmst = this; 72 assert(_collector == NULL, "Collector already set"); 73 _collector = collector; 74 75 set_name("Concurrent Mark-Sweep GC Thread"); 76 77 if (os::create_thread(this, os::cgc_thread)) { 78 // An old comment here said: "Priority should be just less 79 // than that of VMThread". Since the VMThread runs at 80 // NearMaxPriority, the old comment was inaccurate, but 81 // changing the default priority to NearMaxPriority-1 82 // could change current behavior, so the default of 83 // NearMaxPriority stays in place. 84 // 85 // Note that there's a possibility of the VMThread 86 // starving if UseCriticalCMSThreadPriority is on. 87 // That won't happen on Solaris for various reasons, 88 // but may well happen on non-Solaris platforms. 89 int native_prio; 90 if (UseCriticalCMSThreadPriority) { 91 native_prio = os::java_to_os_priority[CriticalPriority]; 92 } else { 93 native_prio = os::java_to_os_priority[NearMaxPriority]; 94 } 95 os::set_native_priority(this, native_prio); 96 97 if (!DisableStartThread) { 98 os::start_thread(this); 99 } 100 } 101 _sltMonitor = SLT_lock; 102 assert(!CMSIncrementalMode || icms_is_enabled(), "Error"); 103 } 104 105 void ConcurrentMarkSweepThread::run() { 106 assert(this == cmst(), "just checking"); 107 108 this->record_stack_base_and_size(); 109 this->initialize_thread_local_storage(); 110 this->set_active_handles(JNIHandleBlock::allocate_block()); 111 // From this time Thread::current() should be working. 112 assert(this == Thread::current(), "just checking"); 113 if (BindCMSThreadToCPU && !os::bind_to_processor(CPUForCMSThread)) { 114 warning("Couldn't bind CMS thread to processor %u", CPUForCMSThread); 115 } 116 // Wait until Universe::is_fully_initialized() 117 { 118 CMSLoopCountWarn loopX("CMS::run", "waiting for " 119 "Universe::is_fully_initialized()", 2); 120 MutexLockerEx x(CGC_lock, true); 121 set_CMS_flag(CMS_cms_wants_token); 122 // Wait until Universe is initialized and all initialization is completed. 123 while (!is_init_completed() && !Universe::is_fully_initialized() && 124 !_should_terminate) { 125 CGC_lock->wait(true, 200); 126 loopX.tick(); 127 } 128 // Wait until the surrogate locker thread that will do 129 // pending list locking on our behalf has been created. 130 // We cannot start the SLT thread ourselves since we need 131 // to be a JavaThread to do so. 132 CMSLoopCountWarn loopY("CMS::run", "waiting for SLT installation", 2); 133 while (_slt == NULL && !_should_terminate) { 134 CGC_lock->wait(true, 200); 135 loopY.tick(); 136 } 137 clear_CMS_flag(CMS_cms_wants_token); 138 } 139 140 while (!_should_terminate) { 141 sleepBeforeNextCycle(); 142 if (_should_terminate) break; 143 _collector->collect_in_background(false); // !clear_all_soft_refs 144 } 145 assert(_should_terminate, "just checking"); 146 // Check that the state of any protocol for synchronization 147 // between background (CMS) and foreground collector is "clean" 148 // (i.e. will not potentially block the foreground collector, 149 // requiring action by us). 150 verify_ok_to_terminate(); 151 // Signal that it is terminated 152 { 153 MutexLockerEx mu(Terminator_lock, 154 Mutex::_no_safepoint_check_flag); 155 assert(_cmst == this, "Weird!"); 156 _cmst = NULL; 157 Terminator_lock->notify(); 158 } 159 160 // Thread destructor usually does this.. 161 ThreadLocalStorage::set_thread(NULL); 162 } 163 164 #ifndef PRODUCT 165 void ConcurrentMarkSweepThread::verify_ok_to_terminate() const { 166 assert(!(CGC_lock->owned_by_self() || cms_thread_has_cms_token() || 167 cms_thread_wants_cms_token()), 168 "Must renounce all worldly possessions and desires for nirvana"); 169 _collector->verify_ok_to_terminate(); 170 } 171 #endif 172 173 // create and start a new ConcurrentMarkSweep Thread for given CMS generation 174 ConcurrentMarkSweepThread* ConcurrentMarkSweepThread::start(CMSCollector* collector) { 175 if (!_should_terminate) { 176 assert(cmst() == NULL, "start() called twice?"); 177 ConcurrentMarkSweepThread* th = new ConcurrentMarkSweepThread(collector); 178 assert(cmst() == th, "Where did the just-created CMS thread go?"); 179 return th; 180 } 181 return NULL; 182 } 183 184 void ConcurrentMarkSweepThread::stop() { 185 if (CMSIncrementalMode) { 186 // Disable incremental mode and wake up the thread so it notices the change. 187 disable_icms(); 188 start_icms(); 189 } 190 // it is ok to take late safepoints here, if needed 191 { 192 MutexLockerEx x(Terminator_lock); 193 _should_terminate = true; 194 } 195 { // Now post a notify on CGC_lock so as to nudge 196 // CMS thread(s) that might be slumbering in 197 // sleepBeforeNextCycle. 198 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); 199 CGC_lock->notify_all(); 200 } 201 { // Now wait until (all) CMS thread(s) have exited 202 MutexLockerEx x(Terminator_lock); 203 while(cmst() != NULL) { 204 Terminator_lock->wait(); 205 } 206 } 207 } 208 209 void ConcurrentMarkSweepThread::threads_do(ThreadClosure* tc) { 210 assert(tc != NULL, "Null ThreadClosure"); 211 if (_cmst != NULL) { 212 tc->do_thread(_cmst); 213 } 214 assert(Universe::is_fully_initialized(), 215 "Called too early, make sure heap is fully initialized"); 216 if (_collector != NULL) { 217 AbstractWorkGang* gang = _collector->conc_workers(); 218 if (gang != NULL) { 219 gang->threads_do(tc); 220 } 221 } 222 } 223 224 void ConcurrentMarkSweepThread::print_on(outputStream* st) const { 225 st->print("\"%s\" ", name()); 226 Thread::print_on(st); 227 st->cr(); 228 } 229 230 void ConcurrentMarkSweepThread::print_all_on(outputStream* st) { 231 if (_cmst != NULL) { 232 _cmst->print_on(st); 233 } 234 if (_collector != NULL) { 235 AbstractWorkGang* gang = _collector->conc_workers(); 236 if (gang != NULL) { 237 gang->print_worker_threads_on(st); 238 } 239 } 240 } 241 242 void ConcurrentMarkSweepThread::synchronize(bool is_cms_thread) { 243 assert(UseConcMarkSweepGC, "just checking"); 244 245 MutexLockerEx x(CGC_lock, 246 Mutex::_no_safepoint_check_flag); 247 if (!is_cms_thread) { 248 assert(Thread::current()->is_VM_thread(), "Not a VM thread"); 249 CMSSynchronousYieldRequest yr; 250 while (CMS_flag_is_set(CMS_cms_has_token)) { 251 // indicate that we want to get the token 252 set_CMS_flag(CMS_vm_wants_token); 253 CGC_lock->wait(true); 254 } 255 // claim the token and proceed 256 clear_CMS_flag(CMS_vm_wants_token); 257 set_CMS_flag(CMS_vm_has_token); 258 } else { 259 assert(Thread::current()->is_ConcurrentGC_thread(), 260 "Not a CMS thread"); 261 // The following barrier assumes there's only one CMS thread. 262 // This will need to be modified is there are more CMS threads than one. 263 while (CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token)) { 264 set_CMS_flag(CMS_cms_wants_token); 265 CGC_lock->wait(true); 266 } 267 // claim the token 268 clear_CMS_flag(CMS_cms_wants_token); 269 set_CMS_flag(CMS_cms_has_token); 270 } 271 } 272 273 void ConcurrentMarkSweepThread::desynchronize(bool is_cms_thread) { 274 assert(UseConcMarkSweepGC, "just checking"); 275 276 MutexLockerEx x(CGC_lock, 277 Mutex::_no_safepoint_check_flag); 278 if (!is_cms_thread) { 279 assert(Thread::current()->is_VM_thread(), "Not a VM thread"); 280 assert(CMS_flag_is_set(CMS_vm_has_token), "just checking"); 281 clear_CMS_flag(CMS_vm_has_token); 282 if (CMS_flag_is_set(CMS_cms_wants_token)) { 283 // wake-up a waiting CMS thread 284 CGC_lock->notify(); 285 } 286 assert(!CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token), 287 "Should have been cleared"); 288 } else { 289 assert(Thread::current()->is_ConcurrentGC_thread(), 290 "Not a CMS thread"); 291 assert(CMS_flag_is_set(CMS_cms_has_token), "just checking"); 292 clear_CMS_flag(CMS_cms_has_token); 293 if (CMS_flag_is_set(CMS_vm_wants_token)) { 294 // wake-up a waiting VM thread 295 CGC_lock->notify(); 296 } 297 assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token), 298 "Should have been cleared"); 299 } 300 } 301 302 // Wait until the next synchronous GC, a concurrent full gc request, 303 // or a timeout, whichever is earlier. 304 void ConcurrentMarkSweepThread::wait_on_cms_lock(long t_millis) { 305 MutexLockerEx x(CGC_lock, 306 Mutex::_no_safepoint_check_flag); 307 if (_should_terminate || _collector->_full_gc_requested) { 308 return; 309 } 310 set_CMS_flag(CMS_cms_wants_token); // to provoke notifies 311 CGC_lock->wait(Mutex::_no_safepoint_check_flag, t_millis); 312 clear_CMS_flag(CMS_cms_wants_token); 313 assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token), 314 "Should not be set"); 315 } 316 317 void ConcurrentMarkSweepThread::sleepBeforeNextCycle() { 318 while (!_should_terminate) { 319 if (CMSIncrementalMode) { 320 icms_wait(); 321 return; 322 } else { 323 // Wait until the next synchronous GC, a concurrent full gc 324 // request or a timeout, whichever is earlier. 325 wait_on_cms_lock(CMSWaitDuration); 326 } 327 // Check if we should start a CMS collection cycle 328 if (_collector->shouldConcurrentCollect()) { 329 return; 330 } 331 // .. collection criterion not yet met, let's go back 332 // and wait some more 333 } 334 } 335 336 // Incremental CMS 337 void ConcurrentMarkSweepThread::start_icms() { 338 assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking"); 339 MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag); 340 trace_state("start_icms"); 341 _should_run = true; 342 iCMS_lock->notify_all(); 343 } 344 345 void ConcurrentMarkSweepThread::stop_icms() { 346 assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking"); 347 MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag); 348 if (!_should_stop) { 349 trace_state("stop_icms"); 350 _should_stop = true; 351 _should_run = false; 352 asynchronous_yield_request(); 353 iCMS_lock->notify_all(); 354 } 355 } 356 357 void ConcurrentMarkSweepThread::icms_wait() { 358 assert(UseConcMarkSweepGC && CMSIncrementalMode, "just checking"); 359 if (_should_stop && icms_is_enabled()) { 360 MutexLockerEx x(iCMS_lock, Mutex::_no_safepoint_check_flag); 361 trace_state("pause_icms"); 362 _collector->stats().stop_cms_timer(); 363 while(!_should_run && icms_is_enabled()) { 364 iCMS_lock->wait(Mutex::_no_safepoint_check_flag); 365 } 366 _collector->stats().start_cms_timer(); 367 _should_stop = false; 368 trace_state("pause_icms end"); 369 } 370 } 371 372 // Note: this method, although exported by the ConcurrentMarkSweepThread, 373 // which is a non-JavaThread, can only be called by a JavaThread. 374 // Currently this is done at vm creation time (post-vm-init) by the 375 // main/Primordial (Java)Thread. 376 // XXX Consider changing this in the future to allow the CMS thread 377 // itself to create this thread? 378 void ConcurrentMarkSweepThread::makeSurrogateLockerThread(TRAPS) { 379 assert(UseConcMarkSweepGC, "SLT thread needed only for CMS GC"); 380 assert(_slt == NULL, "SLT already created"); 381 _slt = SurrogateLockerThread::make(THREAD); 382 }