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 warning("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_all() { 138 assert(_cmst != NULL, "stop_all should be called after initialization"); 139 _cmst->stop(); 140 } 141 142 void ConcurrentMarkSweepThread::stop_service() { 143 // Now post a notify on CGC_lock so as to nudge 144 // CMS thread(s) that might be slumbering in 145 // sleepBeforeNextCycle. 146 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); 147 CGC_lock->notify_all(); 148 } 149 150 void ConcurrentMarkSweepThread::threads_do(ThreadClosure* tc) { 151 assert(tc != NULL, "Null ThreadClosure"); 152 if (cmst() != NULL && !cmst()->has_terminated()) { 153 tc->do_thread(cmst()); 154 } 155 assert(Universe::is_fully_initialized(), 156 "Called too early, make sure heap is fully initialized"); 157 if (_collector != NULL) { 158 AbstractWorkGang* gang = _collector->conc_workers(); 159 if (gang != NULL) { 160 gang->threads_do(tc); 161 } 162 } 163 } 164 165 void ConcurrentMarkSweepThread::print_all_on(outputStream* st) { 166 if (cmst() != NULL && !cmst()->has_terminated()) { 167 cmst()->print_on(st); 168 st->cr(); 169 } 170 if (_collector != NULL) { 171 AbstractWorkGang* gang = _collector->conc_workers(); 172 if (gang != NULL) { 173 gang->print_worker_threads_on(st); 174 } 175 } 176 } 177 178 void ConcurrentMarkSweepThread::synchronize(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 CMSSynchronousYieldRequest yr; 186 while (CMS_flag_is_set(CMS_cms_has_token)) { 187 // indicate that we want to get the token 188 set_CMS_flag(CMS_vm_wants_token); 189 CGC_lock->wait(true); 190 } 191 // claim the token and proceed 192 clear_CMS_flag(CMS_vm_wants_token); 193 set_CMS_flag(CMS_vm_has_token); 194 } else { 195 assert(Thread::current()->is_ConcurrentGC_thread(), 196 "Not a CMS thread"); 197 // The following barrier assumes there's only one CMS thread. 198 // This will need to be modified is there are more CMS threads than one. 199 while (CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token)) { 200 set_CMS_flag(CMS_cms_wants_token); 201 CGC_lock->wait(true); 202 } 203 // claim the token 204 clear_CMS_flag(CMS_cms_wants_token); 205 set_CMS_flag(CMS_cms_has_token); 206 } 207 } 208 209 void ConcurrentMarkSweepThread::desynchronize(bool is_cms_thread) { 210 assert(UseConcMarkSweepGC, "just checking"); 211 212 MutexLockerEx x(CGC_lock, 213 Mutex::_no_safepoint_check_flag); 214 if (!is_cms_thread) { 215 assert(Thread::current()->is_VM_thread(), "Not a VM thread"); 216 assert(CMS_flag_is_set(CMS_vm_has_token), "just checking"); 217 clear_CMS_flag(CMS_vm_has_token); 218 if (CMS_flag_is_set(CMS_cms_wants_token)) { 219 // wake-up a waiting CMS thread 220 CGC_lock->notify(); 221 } 222 assert(!CMS_flag_is_set(CMS_vm_has_token | CMS_vm_wants_token), 223 "Should have been cleared"); 224 } else { 225 assert(Thread::current()->is_ConcurrentGC_thread(), 226 "Not a CMS thread"); 227 assert(CMS_flag_is_set(CMS_cms_has_token), "just checking"); 228 clear_CMS_flag(CMS_cms_has_token); 229 if (CMS_flag_is_set(CMS_vm_wants_token)) { 230 // wake-up a waiting VM thread 231 CGC_lock->notify(); 232 } 233 assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token), 234 "Should have been cleared"); 235 } 236 } 237 238 // Wait until any cms_lock event 239 void ConcurrentMarkSweepThread::wait_on_cms_lock(long t_millis) { 240 MutexLockerEx x(CGC_lock, 241 Mutex::_no_safepoint_check_flag); 242 if (should_terminate() || _collector->_full_gc_requested) { 243 return; 244 } 245 set_CMS_flag(CMS_cms_wants_token); // to provoke notifies 246 CGC_lock->wait(Mutex::_no_safepoint_check_flag, t_millis); 247 clear_CMS_flag(CMS_cms_wants_token); 248 assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token), 249 "Should not be set"); 250 } 251 252 // Wait until the next synchronous GC, a concurrent full gc request, 253 // or a timeout, whichever is earlier. 254 void ConcurrentMarkSweepThread::wait_on_cms_lock_for_scavenge(long t_millis) { 255 // Wait time in millis or 0 value representing infinite wait for a scavenge 256 assert(t_millis >= 0, "Wait time for scavenge should be 0 or positive"); 257 258 GenCollectedHeap* gch = GenCollectedHeap::heap(); 259 double start_time_secs = os::elapsedTime(); 260 double end_time_secs = start_time_secs + (t_millis / ((double) MILLIUNITS)); 261 262 // Total collections count before waiting loop 263 unsigned int before_count; 264 { 265 MutexLockerEx hl(Heap_lock, Mutex::_no_safepoint_check_flag); 266 before_count = gch->total_collections(); 267 } 268 269 unsigned int loop_count = 0; 270 271 while(!should_terminate()) { 272 double now_time = os::elapsedTime(); 273 long wait_time_millis; 274 275 if(t_millis != 0) { 276 // New wait limit 277 wait_time_millis = (long) ((end_time_secs - now_time) * MILLIUNITS); 278 if(wait_time_millis <= 0) { 279 // Wait time is over 280 break; 281 } 282 } else { 283 // No wait limit, wait if necessary forever 284 wait_time_millis = 0; 285 } 286 287 // Wait until the next event or the remaining timeout 288 { 289 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); 290 291 if (should_terminate() || _collector->_full_gc_requested) { 292 return; 293 } 294 set_CMS_flag(CMS_cms_wants_token); // to provoke notifies 295 assert(t_millis == 0 || wait_time_millis > 0, "Sanity"); 296 CGC_lock->wait(Mutex::_no_safepoint_check_flag, wait_time_millis); 297 clear_CMS_flag(CMS_cms_wants_token); 298 assert(!CMS_flag_is_set(CMS_cms_has_token | CMS_cms_wants_token), 299 "Should not be set"); 300 } 301 302 // Extra wait time check before entering the heap lock to get the collection count 303 if(t_millis != 0 && os::elapsedTime() >= end_time_secs) { 304 // Wait time is over 305 break; 306 } 307 308 // Total collections count after the event 309 unsigned int after_count; 310 { 311 MutexLockerEx hl(Heap_lock, Mutex::_no_safepoint_check_flag); 312 after_count = gch->total_collections(); 313 } 314 315 if(before_count != after_count) { 316 // There was a collection - success 317 break; 318 } 319 320 // Too many loops warning 321 if(++loop_count == 0) { 322 warning("wait_on_cms_lock_for_scavenge() has looped %u times", loop_count - 1); 323 } 324 } 325 } 326 327 void ConcurrentMarkSweepThread::sleepBeforeNextCycle() { 328 while (!should_terminate()) { 329 if(CMSWaitDuration >= 0) { 330 // Wait until the next synchronous GC, a concurrent full gc 331 // request or a timeout, whichever is earlier. 332 wait_on_cms_lock_for_scavenge(CMSWaitDuration); 333 } else { 334 // Wait until any cms_lock event or check interval not to call shouldConcurrentCollect permanently 335 wait_on_cms_lock(CMSCheckInterval); 336 } 337 // Check if we should start a CMS collection cycle 338 if (_collector->shouldConcurrentCollect()) { 339 return; 340 } 341 // .. collection criterion not yet met, let's go back 342 // and wait some more 343 } 344 } 345 346 // Note: this method, although exported by the ConcurrentMarkSweepThread, 347 // which is a non-JavaThread, can only be called by a JavaThread. 348 // Currently this is done at vm creation time (post-vm-init) by the 349 // main/Primordial (Java)Thread. 350 // XXX Consider changing this in the future to allow the CMS thread 351 // itself to create this thread? 352 void ConcurrentMarkSweepThread::makeSurrogateLockerThread(TRAPS) { 353 assert(UseConcMarkSweepGC, "SLT thread needed only for CMS GC"); 354 assert(_slt == NULL, "SLT already created"); 355 _slt = SurrogateLockerThread::make(THREAD); 356 }