1 /* 2 * Copyright (c) 1997, 2018, 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/classLoaderData.hpp" 27 #include "classfile/stringTable.hpp" 28 #include "classfile/symbolTable.hpp" 29 #include "classfile/systemDictionary.hpp" 30 #include "code/codeCache.hpp" 31 #include "code/icBuffer.hpp" 32 #include "code/nmethod.hpp" 33 #include "code/pcDesc.hpp" 34 #include "code/scopeDesc.hpp" 35 #include "gc/shared/collectedHeap.hpp" 36 #include "gc/shared/gcLocker.inline.hpp" 37 #include "gc/shared/strongRootsScope.hpp" 38 #include "gc/shared/workgroup.hpp" 39 #include "interpreter/interpreter.hpp" 40 #include "logging/log.hpp" 41 #include "logging/logStream.hpp" 42 #include "memory/resourceArea.hpp" 43 #include "memory/universe.hpp" 44 #include "oops/oop.inline.hpp" 45 #include "oops/symbol.hpp" 46 #include "runtime/atomic.hpp" 47 #include "runtime/compilationPolicy.hpp" 48 #include "runtime/deoptimization.hpp" 49 #include "runtime/frame.inline.hpp" 50 #include "runtime/interfaceSupport.inline.hpp" 51 #include "runtime/mutexLocker.hpp" 52 #include "runtime/orderAccess.inline.hpp" 53 #include "runtime/osThread.hpp" 54 #include "runtime/safepoint.hpp" 55 #include "runtime/safepointMechanism.inline.hpp" 56 #include "runtime/signature.hpp" 57 #include "runtime/stubCodeGenerator.hpp" 58 #include "runtime/stubRoutines.hpp" 59 #include "runtime/sweeper.hpp" 60 #include "runtime/synchronizer.hpp" 61 #include "runtime/thread.inline.hpp" 62 #include "runtime/threadSMR.hpp" 63 #include "runtime/timerTrace.hpp" 64 #include "services/runtimeService.hpp" 65 #include "trace/tracing.hpp" 66 #include "trace/traceMacros.hpp" 67 #include "utilities/events.hpp" 68 #include "utilities/macros.hpp" 69 #ifdef COMPILER1 70 #include "c1/c1_globals.hpp" 71 #endif 72 73 // -------------------------------------------------------------------------------------------------- 74 // Implementation of Safepoint begin/end 75 76 SafepointSynchronize::SynchronizeState volatile SafepointSynchronize::_state = SafepointSynchronize::_not_synchronized; 77 volatile int SafepointSynchronize::_waiting_to_block = 0; 78 volatile int SafepointSynchronize::_safepoint_counter = 0; 79 int SafepointSynchronize::_current_jni_active_count = 0; 80 long SafepointSynchronize::_end_of_last_safepoint = 0; 81 int SafepointSynchronize::_defer_thr_suspend_loop_count = 4000; 82 static const int safepoint_spin_before_yield = 2000; 83 static volatile int PageArmed = 0 ; // safepoint polling page is RO|RW vs PROT_NONE 84 static volatile int TryingToBlock = 0 ; // proximate value -- for advisory use only 85 static bool timeout_error_printed = false; 86 87 // Roll all threads forward to a safepoint and suspend them all 88 void SafepointSynchronize::begin() { 89 EventSafepointBegin begin_event; 90 Thread* myThread = Thread::current(); 91 assert(myThread->is_VM_thread(), "Only VM thread may execute a safepoint"); 92 93 if (PrintSafepointStatistics || PrintSafepointStatisticsTimeout > 0) { 94 _safepoint_begin_time = os::javaTimeNanos(); 95 _ts_of_current_safepoint = tty->time_stamp().seconds(); 96 } 97 98 Universe::heap()->safepoint_synchronize_begin(); 99 100 // By getting the Threads_lock, we assure that no threads are about to start or 101 // exit. It is released again in SafepointSynchronize::end(). 102 Threads_lock->lock(); 103 104 assert( _state == _not_synchronized, "trying to safepoint synchronize with wrong state"); 105 106 int nof_threads = Threads::number_of_threads(); 107 108 log_debug(safepoint)("Safepoint synchronization initiated. (%d threads)", nof_threads); 109 110 RuntimeService::record_safepoint_begin(); 111 112 MutexLocker mu(Safepoint_lock); 113 114 // Reset the count of active JNI critical threads 115 _current_jni_active_count = 0; 116 117 // Set number of threads to wait for, before we initiate the callbacks 118 _waiting_to_block = nof_threads; 119 TryingToBlock = 0 ; 120 int still_running = nof_threads; 121 122 // Save the starting time, so that it can be compared to see if this has taken 123 // too long to complete. 124 jlong safepoint_limit_time = 0; 125 timeout_error_printed = false; 126 127 // PrintSafepointStatisticsTimeout can be specified separately. When 128 // specified, PrintSafepointStatistics will be set to true in 129 // deferred_initialize_stat method. The initialization has to be done 130 // early enough to avoid any races. See bug 6880029 for details. 131 if (PrintSafepointStatistics || PrintSafepointStatisticsTimeout > 0) { 132 deferred_initialize_stat(); 133 } 134 135 // Begin the process of bringing the system to a safepoint. 136 // Java threads can be in several different states and are 137 // stopped by different mechanisms: 138 // 139 // 1. Running interpreted 140 // The interpreter dispatch table is changed to force it to 141 // check for a safepoint condition between bytecodes. 142 // 2. Running in native code 143 // When returning from the native code, a Java thread must check 144 // the safepoint _state to see if we must block. If the 145 // VM thread sees a Java thread in native, it does 146 // not wait for this thread to block. The order of the memory 147 // writes and reads of both the safepoint state and the Java 148 // threads state is critical. In order to guarantee that the 149 // memory writes are serialized with respect to each other, 150 // the VM thread issues a memory barrier instruction 151 // (on MP systems). In order to avoid the overhead of issuing 152 // a memory barrier for each Java thread making native calls, each Java 153 // thread performs a write to a single memory page after changing 154 // the thread state. The VM thread performs a sequence of 155 // mprotect OS calls which forces all previous writes from all 156 // Java threads to be serialized. This is done in the 157 // os::serialize_thread_states() call. This has proven to be 158 // much more efficient than executing a membar instruction 159 // on every call to native code. 160 // 3. Running compiled Code 161 // Compiled code reads a global (Safepoint Polling) page that 162 // is set to fault if we are trying to get to a safepoint. 163 // 4. Blocked 164 // A thread which is blocked will not be allowed to return from the 165 // block condition until the safepoint operation is complete. 166 // 5. In VM or Transitioning between states 167 // If a Java thread is currently running in the VM or transitioning 168 // between states, the safepointing code will wait for the thread to 169 // block itself when it attempts transitions to a new state. 170 // 171 { 172 EventSafepointStateSynchronization sync_event; 173 int initial_running = 0; 174 175 _state = _synchronizing; 176 177 if (SafepointMechanism::uses_thread_local_poll()) { 178 // Arming the per thread poll while having _state != _not_synchronized means safepointing 179 log_trace(safepoint)("Setting thread local yield flag for threads"); 180 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) { 181 // Make sure the threads start polling, it is time to yield. 182 SafepointMechanism::arm_local_poll(cur); // release store, global state -> local state 183 } 184 } 185 OrderAccess::fence(); // storestore|storeload, global state -> local state 186 187 // Flush all thread states to memory 188 if (!UseMembar) { 189 os::serialize_thread_states(); 190 } 191 192 if (SafepointMechanism::uses_global_page_poll()) { 193 // Make interpreter safepoint aware 194 Interpreter::notice_safepoints(); 195 196 // Make polling safepoint aware 197 guarantee (PageArmed == 0, "invariant") ; 198 PageArmed = 1 ; 199 os::make_polling_page_unreadable(); 200 } 201 202 // Consider using active_processor_count() ... but that call is expensive. 203 int ncpus = os::processor_count() ; 204 unsigned int iterations = 0; 205 206 { 207 JavaThreadIteratorWithHandle jtiwh; 208 #ifdef ASSERT 209 for (; JavaThread *cur = jtiwh.next(); ) { 210 assert(cur->safepoint_state()->is_running(), "Illegal initial state"); 211 // Clear the visited flag to ensure that the critical counts are collected properly. 212 cur->set_visited_for_critical_count(false); 213 } 214 #endif // ASSERT 215 216 if (SafepointTimeout) 217 safepoint_limit_time = os::javaTimeNanos() + (jlong)SafepointTimeoutDelay * MICROUNITS; 218 219 // Iterate through all threads until it have been determined how to stop them all at a safepoint 220 int steps = 0 ; 221 while(still_running > 0) { 222 jtiwh.rewind(); 223 for (; JavaThread *cur = jtiwh.next(); ) { 224 assert(!cur->is_ConcurrentGC_thread(), "A concurrent GC thread is unexpectly being suspended"); 225 ThreadSafepointState *cur_state = cur->safepoint_state(); 226 if (cur_state->is_running()) { 227 cur_state->examine_state_of_thread(); 228 if (!cur_state->is_running()) { 229 still_running--; 230 // consider adjusting steps downward: 231 // steps = 0 232 // steps -= NNN 233 // steps >>= 1 234 // steps = MIN(steps, 2000-100) 235 // if (iterations != 0) steps -= NNN 236 } 237 LogTarget(Trace, safepoint) lt; 238 if (lt.is_enabled()) { 239 ResourceMark rm; 240 LogStream ls(lt); 241 cur_state->print_on(&ls); 242 } 243 } 244 } 245 246 if (iterations == 0) { 247 initial_running = still_running; 248 if (PrintSafepointStatistics) { 249 begin_statistics(nof_threads, still_running); 250 } 251 } 252 253 if (still_running > 0) { 254 // Check for if it takes to long 255 if (SafepointTimeout && safepoint_limit_time < os::javaTimeNanos()) { 256 print_safepoint_timeout(_spinning_timeout); 257 } 258 259 // Spin to avoid context switching. 260 // There's a tension between allowing the mutators to run (and rendezvous) 261 // vs spinning. As the VM thread spins, wasting cycles, it consumes CPU that 262 // a mutator might otherwise use profitably to reach a safepoint. Excessive 263 // spinning by the VM thread on a saturated system can increase rendezvous latency. 264 // Blocking or yielding incur their own penalties in the form of context switching 265 // and the resultant loss of $ residency. 266 // 267 // Further complicating matters is that yield() does not work as naively expected 268 // on many platforms -- yield() does not guarantee that any other ready threads 269 // will run. As such we revert to naked_short_sleep() after some number of iterations. 270 // nakes_short_sleep() is implemented as a short unconditional sleep. 271 // Typical operating systems round a "short" sleep period up to 10 msecs, so sleeping 272 // can actually increase the time it takes the VM thread to detect that a system-wide 273 // stop-the-world safepoint has been reached. In a pathological scenario such as that 274 // described in CR6415670 the VMthread may sleep just before the mutator(s) become safe. 275 // In that case the mutators will be stalled waiting for the safepoint to complete and the 276 // the VMthread will be sleeping, waiting for the mutators to rendezvous. The VMthread 277 // will eventually wake up and detect that all mutators are safe, at which point 278 // we'll again make progress. 279 // 280 // Beware too that that the VMThread typically runs at elevated priority. 281 // Its default priority is higher than the default mutator priority. 282 // Obviously, this complicates spinning. 283 // 284 // Note too that on Windows XP SwitchThreadTo() has quite different behavior than Sleep(0). 285 // Sleep(0) will _not yield to lower priority threads, while SwitchThreadTo() will. 286 // 287 // See the comments in synchronizer.cpp for additional remarks on spinning. 288 // 289 // In the future we might: 290 // 1. Modify the safepoint scheme to avoid potentially unbounded spinning. 291 // This is tricky as the path used by a thread exiting the JVM (say on 292 // on JNI call-out) simply stores into its state field. The burden 293 // is placed on the VM thread, which must poll (spin). 294 // 2. Find something useful to do while spinning. If the safepoint is GC-related 295 // we might aggressively scan the stacks of threads that are already safe. 296 // 3. Use Solaris schedctl to examine the state of the still-running mutators. 297 // If all the mutators are ONPROC there's no reason to sleep or yield. 298 // 4. YieldTo() any still-running mutators that are ready but OFFPROC. 299 // 5. Check system saturation. If the system is not fully saturated then 300 // simply spin and avoid sleep/yield. 301 // 6. As still-running mutators rendezvous they could unpark the sleeping 302 // VMthread. This works well for still-running mutators that become 303 // safe. The VMthread must still poll for mutators that call-out. 304 // 7. Drive the policy on time-since-begin instead of iterations. 305 // 8. Consider making the spin duration a function of the # of CPUs: 306 // Spin = (((ncpus-1) * M) + K) + F(still_running) 307 // Alternately, instead of counting iterations of the outer loop 308 // we could count the # of threads visited in the inner loop, above. 309 // 9. On windows consider using the return value from SwitchThreadTo() 310 // to drive subsequent spin/SwitchThreadTo()/Sleep(N) decisions. 311 312 if (int(iterations) == -1) { // overflow - something is wrong. 313 // We can only overflow here when we are using global 314 // polling pages. We keep this guarantee in its original 315 // form so that searches of the bug database for this 316 // failure mode find the right bugs. 317 guarantee (PageArmed == 0, "invariant"); 318 } 319 320 // Instead of (ncpus > 1) consider either (still_running < (ncpus + EPSILON)) or 321 // ((still_running + _waiting_to_block - TryingToBlock)) < ncpus) 322 ++steps ; 323 if (ncpus > 1 && steps < safepoint_spin_before_yield) { 324 SpinPause() ; // MP-Polite spin 325 } else 326 if (steps < _defer_thr_suspend_loop_count) { 327 os::naked_yield() ; 328 } else { 329 os::naked_short_sleep(1); 330 } 331 332 iterations ++ ; 333 } 334 assert(iterations < (uint)max_jint, "We have been iterating in the safepoint loop too long"); 335 } 336 } // ThreadsListHandle destroyed here. 337 assert(still_running == 0, "sanity check"); 338 339 if (PrintSafepointStatistics) { 340 update_statistics_on_spin_end(); 341 } 342 343 if (sync_event.should_commit()) { 344 // Group this event together with the ones committed after the counter is increased 345 sync_event.set_safepointId(safepoint_counter() + 1); 346 sync_event.set_initialThreadCount(initial_running); 347 sync_event.set_runningThreadCount(_waiting_to_block); 348 sync_event.set_iterations(iterations); 349 sync_event.commit(); 350 } 351 } // EventSafepointStateSynchronization destroyed here. 352 353 // wait until all threads are stopped 354 { 355 EventSafepointWaitBlocked wait_blocked_event; 356 int initial_waiting_to_block = _waiting_to_block; 357 358 while (_waiting_to_block > 0) { 359 log_debug(safepoint)("Waiting for %d thread(s) to block", _waiting_to_block); 360 if (!SafepointTimeout || timeout_error_printed) { 361 Safepoint_lock->wait(true); // true, means with no safepoint checks 362 } else { 363 // Compute remaining time 364 jlong remaining_time = safepoint_limit_time - os::javaTimeNanos(); 365 366 // If there is no remaining time, then there is an error 367 if (remaining_time < 0 || Safepoint_lock->wait(true, remaining_time / MICROUNITS)) { 368 print_safepoint_timeout(_blocking_timeout); 369 } 370 } 371 } 372 assert(_waiting_to_block == 0, "sanity check"); 373 374 #ifndef PRODUCT 375 if (SafepointTimeout) { 376 jlong current_time = os::javaTimeNanos(); 377 if (safepoint_limit_time < current_time) { 378 tty->print_cr("# SafepointSynchronize: Finished after " 379 INT64_FORMAT_W(6) " ms", 380 (int64_t)((current_time - safepoint_limit_time) / MICROUNITS + 381 (jlong)SafepointTimeoutDelay)); 382 } 383 } 384 #endif 385 386 assert((_safepoint_counter & 0x1) == 0, "must be even"); 387 assert(Threads_lock->owned_by_self(), "must hold Threads_lock"); 388 _safepoint_counter ++; 389 390 // Record state 391 _state = _synchronized; 392 393 OrderAccess::fence(); 394 395 if (wait_blocked_event.should_commit()) { 396 wait_blocked_event.set_safepointId(safepoint_counter()); 397 wait_blocked_event.set_runningThreadCount(initial_waiting_to_block); 398 wait_blocked_event.commit(); 399 } 400 } // EventSafepointWaitBlocked 401 402 #ifdef ASSERT 403 // Make sure all the threads were visited. 404 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) { 405 assert(cur->was_visited_for_critical_count(), "missed a thread"); 406 } 407 #endif // ASSERT 408 409 // Update the count of active JNI critical regions 410 GCLocker::set_jni_lock_count(_current_jni_active_count); 411 412 log_info(safepoint)("Entering safepoint region: %s", VMThread::vm_safepoint_description()); 413 414 RuntimeService::record_safepoint_synchronized(); 415 if (PrintSafepointStatistics) { 416 update_statistics_on_sync_end(os::javaTimeNanos()); 417 } 418 419 // Call stuff that needs to be run when a safepoint is just about to be completed 420 { 421 EventSafepointCleanup cleanup_event; 422 do_cleanup_tasks(); 423 if (cleanup_event.should_commit()) { 424 cleanup_event.set_safepointId(safepoint_counter()); 425 cleanup_event.commit(); 426 } 427 } 428 429 if (PrintSafepointStatistics) { 430 // Record how much time spend on the above cleanup tasks 431 update_statistics_on_cleanup_end(os::javaTimeNanos()); 432 } 433 if (begin_event.should_commit()) { 434 begin_event.set_safepointId(safepoint_counter()); 435 begin_event.set_totalThreadCount(nof_threads); 436 begin_event.set_jniCriticalThreadCount(_current_jni_active_count); 437 begin_event.commit(); 438 } 439 } 440 441 // Wake up all threads, so they are ready to resume execution after the safepoint 442 // operation has been carried out 443 void SafepointSynchronize::end() { 444 EventSafepointEnd event; 445 int safepoint_id = safepoint_counter(); // Keep the odd counter as "id" 446 447 assert(Threads_lock->owned_by_self(), "must hold Threads_lock"); 448 assert((_safepoint_counter & 0x1) == 1, "must be odd"); 449 _safepoint_counter ++; 450 // memory fence isn't required here since an odd _safepoint_counter 451 // value can do no harm and a fence is issued below anyway. 452 453 DEBUG_ONLY(Thread* myThread = Thread::current();) 454 assert(myThread->is_VM_thread(), "Only VM thread can execute a safepoint"); 455 456 if (PrintSafepointStatistics) { 457 end_statistics(os::javaTimeNanos()); 458 } 459 460 { 461 JavaThreadIteratorWithHandle jtiwh; 462 #ifdef ASSERT 463 // A pending_exception cannot be installed during a safepoint. The threads 464 // may install an async exception after they come back from a safepoint into 465 // pending_exception after they unblock. But that should happen later. 466 for (; JavaThread *cur = jtiwh.next(); ) { 467 assert (!(cur->has_pending_exception() && 468 cur->safepoint_state()->is_at_poll_safepoint()), 469 "safepoint installed a pending exception"); 470 } 471 #endif // ASSERT 472 473 if (PageArmed) { 474 assert(SafepointMechanism::uses_global_page_poll(), "sanity"); 475 // Make polling safepoint aware 476 os::make_polling_page_readable(); 477 PageArmed = 0 ; 478 } 479 480 if (SafepointMechanism::uses_global_page_poll()) { 481 // Remove safepoint check from interpreter 482 Interpreter::ignore_safepoints(); 483 } 484 485 { 486 MutexLocker mu(Safepoint_lock); 487 488 assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization"); 489 490 if (SafepointMechanism::uses_thread_local_poll()) { 491 _state = _not_synchronized; 492 OrderAccess::storestore(); // global state -> local state 493 jtiwh.rewind(); 494 for (; JavaThread *current = jtiwh.next(); ) { 495 ThreadSafepointState* cur_state = current->safepoint_state(); 496 cur_state->restart(); // TSS _running 497 SafepointMechanism::disarm_local_poll(current); // release store, local state -> polling page 498 } 499 log_info(safepoint)("Leaving safepoint region"); 500 } else { 501 // Set to not synchronized, so the threads will not go into the signal_thread_blocked method 502 // when they get restarted. 503 _state = _not_synchronized; 504 OrderAccess::fence(); 505 506 log_info(safepoint)("Leaving safepoint region"); 507 508 // Start suspended threads 509 jtiwh.rewind(); 510 for (; JavaThread *current = jtiwh.next(); ) { 511 // A problem occurring on Solaris is when attempting to restart threads 512 // the first #cpus - 1 go well, but then the VMThread is preempted when we get 513 // to the next one (since it has been running the longest). We then have 514 // to wait for a cpu to become available before we can continue restarting 515 // threads. 516 // FIXME: This causes the performance of the VM to degrade when active and with 517 // large numbers of threads. Apparently this is due to the synchronous nature 518 // of suspending threads. 519 // 520 // TODO-FIXME: the comments above are vestigial and no longer apply. 521 // Furthermore, using solaris' schedctl in this particular context confers no benefit 522 if (VMThreadHintNoPreempt) { 523 os::hint_no_preempt(); 524 } 525 ThreadSafepointState* cur_state = current->safepoint_state(); 526 assert(cur_state->type() != ThreadSafepointState::_running, "Thread not suspended at safepoint"); 527 cur_state->restart(); 528 assert(cur_state->is_running(), "safepoint state has not been reset"); 529 } 530 } 531 532 RuntimeService::record_safepoint_end(); 533 534 // Release threads lock, so threads can be created/destroyed again. 535 // It will also release all threads blocked in signal_thread_blocked. 536 Threads_lock->unlock(); 537 } 538 } // ThreadsListHandle destroyed here. 539 540 Universe::heap()->safepoint_synchronize_end(); 541 // record this time so VMThread can keep track how much time has elapsed 542 // since last safepoint. 543 _end_of_last_safepoint = os::javaTimeMillis(); 544 545 if (event.should_commit()) { 546 event.set_safepointId(safepoint_id); 547 event.commit(); 548 } 549 } 550 551 bool SafepointSynchronize::is_cleanup_needed() { 552 // Need a safepoint if there are many monitors to deflate. 553 if (ObjectSynchronizer::is_cleanup_needed()) return true; 554 // Need a safepoint if some inline cache buffers is non-empty 555 if (!InlineCacheBuffer::is_empty()) return true; 556 return false; 557 } 558 559 static void event_safepoint_cleanup_task_commit(EventSafepointCleanupTask& event, const char* name) { 560 if (event.should_commit()) { 561 event.set_safepointId(SafepointSynchronize::safepoint_counter()); 562 event.set_name(name); 563 event.commit(); 564 } 565 } 566 567 class ParallelSPCleanupThreadClosure : public ThreadClosure { 568 private: 569 CodeBlobClosure* _nmethod_cl; 570 DeflateMonitorCounters* _counters; 571 572 public: 573 ParallelSPCleanupThreadClosure(DeflateMonitorCounters* counters) : 574 _counters(counters), 575 _nmethod_cl(NMethodSweeper::prepare_mark_active_nmethods()) {} 576 577 void do_thread(Thread* thread) { 578 ObjectSynchronizer::deflate_thread_local_monitors(thread, _counters); 579 if (_nmethod_cl != NULL && thread->is_Java_thread() && 580 ! thread->is_Code_cache_sweeper_thread()) { 581 JavaThread* jt = (JavaThread*) thread; 582 jt->nmethods_do(_nmethod_cl); 583 } 584 } 585 }; 586 587 class ParallelSPCleanupTask : public AbstractGangTask { 588 private: 589 SubTasksDone _subtasks; 590 ParallelSPCleanupThreadClosure _cleanup_threads_cl; 591 uint _num_workers; 592 DeflateMonitorCounters* _counters; 593 public: 594 ParallelSPCleanupTask(uint num_workers, DeflateMonitorCounters* counters) : 595 AbstractGangTask("Parallel Safepoint Cleanup"), 596 _cleanup_threads_cl(ParallelSPCleanupThreadClosure(counters)), 597 _num_workers(num_workers), 598 _subtasks(SubTasksDone(SafepointSynchronize::SAFEPOINT_CLEANUP_NUM_TASKS)), 599 _counters(counters) {} 600 601 void work(uint worker_id) { 602 // All threads deflate monitors and mark nmethods (if necessary). 603 Threads::possibly_parallel_threads_do(true, &_cleanup_threads_cl); 604 605 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_DEFLATE_MONITORS)) { 606 const char* name = "deflating idle monitors"; 607 EventSafepointCleanupTask event; 608 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 609 ObjectSynchronizer::deflate_idle_monitors(_counters); 610 event_safepoint_cleanup_task_commit(event, name); 611 } 612 613 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_UPDATE_INLINE_CACHES)) { 614 const char* name = "updating inline caches"; 615 EventSafepointCleanupTask event; 616 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 617 InlineCacheBuffer::update_inline_caches(); 618 event_safepoint_cleanup_task_commit(event, name); 619 } 620 621 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_COMPILATION_POLICY)) { 622 const char* name = "compilation policy safepoint handler"; 623 EventSafepointCleanupTask event; 624 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 625 CompilationPolicy::policy()->do_safepoint_work(); 626 event_safepoint_cleanup_task_commit(event, name); 627 } 628 629 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_SYMBOL_TABLE_REHASH)) { 630 if (SymbolTable::needs_rehashing()) { 631 const char* name = "rehashing symbol table"; 632 EventSafepointCleanupTask event; 633 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 634 SymbolTable::rehash_table(); 635 event_safepoint_cleanup_task_commit(event, name); 636 } 637 } 638 639 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_STRING_TABLE_REHASH)) { 640 if (StringTable::needs_rehashing()) { 641 const char* name = "rehashing string table"; 642 EventSafepointCleanupTask event; 643 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 644 StringTable::rehash_table(); 645 event_safepoint_cleanup_task_commit(event, name); 646 } 647 } 648 649 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_CLD_PURGE)) { 650 // CMS delays purging the CLDG until the beginning of the next safepoint and to 651 // make sure concurrent sweep is done 652 const char* name = "purging class loader data graph"; 653 EventSafepointCleanupTask event; 654 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 655 ClassLoaderDataGraph::purge_if_needed(); 656 event_safepoint_cleanup_task_commit(event, name); 657 } 658 659 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_SYSTEM_DICTIONARY_RESIZE)) { 660 const char* name = "resizing system dictionaries"; 661 EventSafepointCleanupTask event; 662 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 663 ClassLoaderDataGraph::resize_if_needed(); 664 event_safepoint_cleanup_task_commit(event, name); 665 } 666 _subtasks.all_tasks_completed(_num_workers); 667 } 668 }; 669 670 // Various cleaning tasks that should be done periodically at safepoints. 671 void SafepointSynchronize::do_cleanup_tasks() { 672 673 TraceTime timer("safepoint cleanup tasks", TRACETIME_LOG(Info, safepoint, cleanup)); 674 675 // Prepare for monitor deflation. 676 DeflateMonitorCounters deflate_counters; 677 ObjectSynchronizer::prepare_deflate_idle_monitors(&deflate_counters); 678 679 CollectedHeap* heap = Universe::heap(); 680 assert(heap != NULL, "heap not initialized yet?"); 681 WorkGang* cleanup_workers = heap->get_safepoint_workers(); 682 if (cleanup_workers != NULL) { 683 // Parallel cleanup using GC provided thread pool. 684 uint num_cleanup_workers = cleanup_workers->active_workers(); 685 ParallelSPCleanupTask cleanup(num_cleanup_workers, &deflate_counters); 686 StrongRootsScope srs(num_cleanup_workers); 687 cleanup_workers->run_task(&cleanup); 688 } else { 689 // Serial cleanup using VMThread. 690 ParallelSPCleanupTask cleanup(1, &deflate_counters); 691 StrongRootsScope srs(1); 692 cleanup.work(0); 693 } 694 695 // Finish monitor deflation. 696 ObjectSynchronizer::finish_deflate_idle_monitors(&deflate_counters); 697 } 698 699 700 bool SafepointSynchronize::safepoint_safe(JavaThread *thread, JavaThreadState state) { 701 switch(state) { 702 case _thread_in_native: 703 // native threads are safe if they have no java stack or have walkable stack 704 return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable(); 705 706 // blocked threads should have already have walkable stack 707 case _thread_blocked: 708 assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable"); 709 return true; 710 711 default: 712 return false; 713 } 714 } 715 716 717 // See if the thread is running inside a lazy critical native and 718 // update the thread critical count if so. Also set a suspend flag to 719 // cause the native wrapper to return into the JVM to do the unlock 720 // once the native finishes. 721 void SafepointSynchronize::check_for_lazy_critical_native(JavaThread *thread, JavaThreadState state) { 722 if (state == _thread_in_native && 723 thread->has_last_Java_frame() && 724 thread->frame_anchor()->walkable()) { 725 // This thread might be in a critical native nmethod so look at 726 // the top of the stack and increment the critical count if it 727 // is. 728 frame wrapper_frame = thread->last_frame(); 729 CodeBlob* stub_cb = wrapper_frame.cb(); 730 if (stub_cb != NULL && 731 stub_cb->is_nmethod() && 732 stub_cb->as_nmethod_or_null()->is_lazy_critical_native()) { 733 // A thread could potentially be in a critical native across 734 // more than one safepoint, so only update the critical state on 735 // the first one. When it returns it will perform the unlock. 736 if (!thread->do_critical_native_unlock()) { 737 #ifdef ASSERT 738 if (!thread->in_critical()) { 739 GCLocker::increment_debug_jni_lock_count(); 740 } 741 #endif 742 thread->enter_critical(); 743 // Make sure the native wrapper calls back on return to 744 // perform the needed critical unlock. 745 thread->set_critical_native_unlock(); 746 } 747 } 748 } 749 } 750 751 752 753 // ------------------------------------------------------------------------------------------------------- 754 // Implementation of Safepoint callback point 755 756 void SafepointSynchronize::block(JavaThread *thread) { 757 assert(thread != NULL, "thread must be set"); 758 assert(thread->is_Java_thread(), "not a Java thread"); 759 760 // Threads shouldn't block if they are in the middle of printing, but... 761 ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id()); 762 763 // Only bail from the block() call if the thread is gone from the 764 // thread list; starting to exit should still block. 765 if (thread->is_terminated()) { 766 // block current thread if we come here from native code when VM is gone 767 thread->block_if_vm_exited(); 768 769 // otherwise do nothing 770 return; 771 } 772 773 JavaThreadState state = thread->thread_state(); 774 thread->frame_anchor()->make_walkable(thread); 775 776 // Check that we have a valid thread_state at this point 777 switch(state) { 778 case _thread_in_vm_trans: 779 case _thread_in_Java: // From compiled code 780 781 // We are highly likely to block on the Safepoint_lock. In order to avoid blocking in this case, 782 // we pretend we are still in the VM. 783 thread->set_thread_state(_thread_in_vm); 784 785 if (is_synchronizing()) { 786 Atomic::inc (&TryingToBlock) ; 787 } 788 789 // We will always be holding the Safepoint_lock when we are examine the state 790 // of a thread. Hence, the instructions between the Safepoint_lock->lock() and 791 // Safepoint_lock->unlock() are happening atomic with regards to the safepoint code 792 Safepoint_lock->lock_without_safepoint_check(); 793 if (is_synchronizing()) { 794 // Decrement the number of threads to wait for and signal vm thread 795 assert(_waiting_to_block > 0, "sanity check"); 796 _waiting_to_block--; 797 thread->safepoint_state()->set_has_called_back(true); 798 799 DEBUG_ONLY(thread->set_visited_for_critical_count(true)); 800 if (thread->in_critical()) { 801 // Notice that this thread is in a critical section 802 increment_jni_active_count(); 803 } 804 805 // Consider (_waiting_to_block < 2) to pipeline the wakeup of the VM thread 806 if (_waiting_to_block == 0) { 807 Safepoint_lock->notify_all(); 808 } 809 } 810 811 // We transition the thread to state _thread_blocked here, but 812 // we can't do our usual check for external suspension and then 813 // self-suspend after the lock_without_safepoint_check() call 814 // below because we are often called during transitions while 815 // we hold different locks. That would leave us suspended while 816 // holding a resource which results in deadlocks. 817 thread->set_thread_state(_thread_blocked); 818 Safepoint_lock->unlock(); 819 820 // We now try to acquire the threads lock. Since this lock is hold by the VM thread during 821 // the entire safepoint, the threads will all line up here during the safepoint. 822 Threads_lock->lock_without_safepoint_check(); 823 // restore original state. This is important if the thread comes from compiled code, so it 824 // will continue to execute with the _thread_in_Java state. 825 thread->set_thread_state(state); 826 Threads_lock->unlock(); 827 break; 828 829 case _thread_in_native_trans: 830 case _thread_blocked_trans: 831 case _thread_new_trans: 832 if (thread->safepoint_state()->type() == ThreadSafepointState::_call_back) { 833 thread->print_thread_state(); 834 fatal("Deadlock in safepoint code. " 835 "Should have called back to the VM before blocking."); 836 } 837 838 // We transition the thread to state _thread_blocked here, but 839 // we can't do our usual check for external suspension and then 840 // self-suspend after the lock_without_safepoint_check() call 841 // below because we are often called during transitions while 842 // we hold different locks. That would leave us suspended while 843 // holding a resource which results in deadlocks. 844 thread->set_thread_state(_thread_blocked); 845 846 // It is not safe to suspend a thread if we discover it is in _thread_in_native_trans. Hence, 847 // the safepoint code might still be waiting for it to block. We need to change the state here, 848 // so it can see that it is at a safepoint. 849 850 // Block until the safepoint operation is completed. 851 Threads_lock->lock_without_safepoint_check(); 852 853 // Restore state 854 thread->set_thread_state(state); 855 856 Threads_lock->unlock(); 857 break; 858 859 default: 860 fatal("Illegal threadstate encountered: %d", state); 861 } 862 863 // Check for pending. async. exceptions or suspends - except if the 864 // thread was blocked inside the VM. has_special_runtime_exit_condition() 865 // is called last since it grabs a lock and we only want to do that when 866 // we must. 867 // 868 // Note: we never deliver an async exception at a polling point as the 869 // compiler may not have an exception handler for it. The polling 870 // code will notice the async and deoptimize and the exception will 871 // be delivered. (Polling at a return point is ok though). Sure is 872 // a lot of bother for a deprecated feature... 873 // 874 // We don't deliver an async exception if the thread state is 875 // _thread_in_native_trans so JNI functions won't be called with 876 // a surprising pending exception. If the thread state is going back to java, 877 // async exception is checked in check_special_condition_for_native_trans(). 878 879 if (state != _thread_blocked_trans && 880 state != _thread_in_vm_trans && 881 thread->has_special_runtime_exit_condition()) { 882 thread->handle_special_runtime_exit_condition( 883 !thread->is_at_poll_safepoint() && (state != _thread_in_native_trans)); 884 } 885 } 886 887 // ------------------------------------------------------------------------------------------------------ 888 // Exception handlers 889 890 891 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) { 892 assert(thread->is_Java_thread(), "polling reference encountered by VM thread"); 893 assert(thread->thread_state() == _thread_in_Java, "should come from Java code"); 894 if (!ThreadLocalHandshakes) { 895 assert(SafepointSynchronize::is_synchronizing(), "polling encountered outside safepoint synchronization"); 896 } 897 898 if (PrintSafepointStatistics) { 899 inc_page_trap_count(); 900 } 901 902 ThreadSafepointState* state = thread->safepoint_state(); 903 904 state->handle_polling_page_exception(); 905 } 906 907 908 void SafepointSynchronize::print_safepoint_timeout(SafepointTimeoutReason reason) { 909 if (!timeout_error_printed) { 910 timeout_error_printed = true; 911 // Print out the thread info which didn't reach the safepoint for debugging 912 // purposes (useful when there are lots of threads in the debugger). 913 tty->cr(); 914 tty->print_cr("# SafepointSynchronize::begin: Timeout detected:"); 915 if (reason == _spinning_timeout) { 916 tty->print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint."); 917 } else if (reason == _blocking_timeout) { 918 tty->print_cr("# SafepointSynchronize::begin: Timed out while waiting for threads to stop."); 919 } 920 921 tty->print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:"); 922 ThreadSafepointState *cur_state; 923 ResourceMark rm; 924 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) { 925 cur_state = cur_thread->safepoint_state(); 926 927 if (cur_thread->thread_state() != _thread_blocked && 928 ((reason == _spinning_timeout && cur_state->is_running()) || 929 (reason == _blocking_timeout && !cur_state->has_called_back()))) { 930 tty->print("# "); 931 cur_thread->print(); 932 tty->cr(); 933 } 934 } 935 tty->print_cr("# SafepointSynchronize::begin: (End of list)"); 936 } 937 938 // To debug the long safepoint, specify both DieOnSafepointTimeout & 939 // ShowMessageBoxOnError. 940 if (DieOnSafepointTimeout) { 941 fatal("Safepoint sync time longer than " INTX_FORMAT "ms detected when executing %s.", 942 SafepointTimeoutDelay, VMThread::vm_safepoint_description()); 943 } 944 } 945 946 947 // ------------------------------------------------------------------------------------------------------- 948 // Implementation of ThreadSafepointState 949 950 ThreadSafepointState::ThreadSafepointState(JavaThread *thread) { 951 _thread = thread; 952 _type = _running; 953 _has_called_back = false; 954 _at_poll_safepoint = false; 955 } 956 957 void ThreadSafepointState::create(JavaThread *thread) { 958 ThreadSafepointState *state = new ThreadSafepointState(thread); 959 thread->set_safepoint_state(state); 960 } 961 962 void ThreadSafepointState::destroy(JavaThread *thread) { 963 if (thread->safepoint_state()) { 964 delete(thread->safepoint_state()); 965 thread->set_safepoint_state(NULL); 966 } 967 } 968 969 void ThreadSafepointState::examine_state_of_thread() { 970 assert(is_running(), "better be running or just have hit safepoint poll"); 971 972 JavaThreadState state = _thread->thread_state(); 973 974 // Save the state at the start of safepoint processing. 975 _orig_thread_state = state; 976 977 // Check for a thread that is suspended. Note that thread resume tries 978 // to grab the Threads_lock which we own here, so a thread cannot be 979 // resumed during safepoint synchronization. 980 981 // We check to see if this thread is suspended without locking to 982 // avoid deadlocking with a third thread that is waiting for this 983 // thread to be suspended. The third thread can notice the safepoint 984 // that we're trying to start at the beginning of its SR_lock->wait() 985 // call. If that happens, then the third thread will block on the 986 // safepoint while still holding the underlying SR_lock. We won't be 987 // able to get the SR_lock and we'll deadlock. 988 // 989 // We don't need to grab the SR_lock here for two reasons: 990 // 1) The suspend flags are both volatile and are set with an 991 // Atomic::cmpxchg() call so we should see the suspended 992 // state right away. 993 // 2) We're being called from the safepoint polling loop; if 994 // we don't see the suspended state on this iteration, then 995 // we'll come around again. 996 // 997 bool is_suspended = _thread->is_ext_suspended(); 998 if (is_suspended) { 999 roll_forward(_at_safepoint); 1000 return; 1001 } 1002 1003 // Some JavaThread states have an initial safepoint state of 1004 // running, but are actually at a safepoint. We will happily 1005 // agree and update the safepoint state here. 1006 if (SafepointSynchronize::safepoint_safe(_thread, state)) { 1007 SafepointSynchronize::check_for_lazy_critical_native(_thread, state); 1008 roll_forward(_at_safepoint); 1009 return; 1010 } 1011 1012 if (state == _thread_in_vm) { 1013 roll_forward(_call_back); 1014 return; 1015 } 1016 1017 // All other thread states will continue to run until they 1018 // transition and self-block in state _blocked 1019 // Safepoint polling in compiled code causes the Java threads to do the same. 1020 // Note: new threads may require a malloc so they must be allowed to finish 1021 1022 assert(is_running(), "examine_state_of_thread on non-running thread"); 1023 return; 1024 } 1025 1026 // Returns true is thread could not be rolled forward at present position. 1027 void ThreadSafepointState::roll_forward(suspend_type type) { 1028 _type = type; 1029 1030 switch(_type) { 1031 case _at_safepoint: 1032 SafepointSynchronize::signal_thread_at_safepoint(); 1033 DEBUG_ONLY(_thread->set_visited_for_critical_count(true)); 1034 if (_thread->in_critical()) { 1035 // Notice that this thread is in a critical section 1036 SafepointSynchronize::increment_jni_active_count(); 1037 } 1038 break; 1039 1040 case _call_back: 1041 set_has_called_back(false); 1042 break; 1043 1044 case _running: 1045 default: 1046 ShouldNotReachHere(); 1047 } 1048 } 1049 1050 void ThreadSafepointState::restart() { 1051 switch(type()) { 1052 case _at_safepoint: 1053 case _call_back: 1054 break; 1055 1056 case _running: 1057 default: 1058 tty->print_cr("restart thread " INTPTR_FORMAT " with state %d", 1059 p2i(_thread), _type); 1060 _thread->print(); 1061 ShouldNotReachHere(); 1062 } 1063 _type = _running; 1064 set_has_called_back(false); 1065 } 1066 1067 1068 void ThreadSafepointState::print_on(outputStream *st) const { 1069 const char *s = NULL; 1070 1071 switch(_type) { 1072 case _running : s = "_running"; break; 1073 case _at_safepoint : s = "_at_safepoint"; break; 1074 case _call_back : s = "_call_back"; break; 1075 default: 1076 ShouldNotReachHere(); 1077 } 1078 1079 st->print_cr("Thread: " INTPTR_FORMAT 1080 " [0x%2x] State: %s _has_called_back %d _at_poll_safepoint %d", 1081 p2i(_thread), _thread->osthread()->thread_id(), s, _has_called_back, 1082 _at_poll_safepoint); 1083 1084 _thread->print_thread_state_on(st); 1085 } 1086 1087 // --------------------------------------------------------------------------------------------------------------------- 1088 1089 // Block the thread at poll or poll return for safepoint/handshake. 1090 void ThreadSafepointState::handle_polling_page_exception() { 1091 1092 // Check state. block() will set thread state to thread_in_vm which will 1093 // cause the safepoint state _type to become _call_back. 1094 suspend_type t = type(); 1095 assert(!SafepointMechanism::uses_global_page_poll() || t == ThreadSafepointState::_running, 1096 "polling page exception on thread not running state: %u", uint(t)); 1097 1098 // Step 1: Find the nmethod from the return address 1099 address real_return_addr = thread()->saved_exception_pc(); 1100 1101 CodeBlob *cb = CodeCache::find_blob(real_return_addr); 1102 assert(cb != NULL && cb->is_compiled(), "return address should be in nmethod"); 1103 CompiledMethod* nm = (CompiledMethod*)cb; 1104 1105 // Find frame of caller 1106 frame stub_fr = thread()->last_frame(); 1107 CodeBlob* stub_cb = stub_fr.cb(); 1108 assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub"); 1109 RegisterMap map(thread(), true); 1110 frame caller_fr = stub_fr.sender(&map); 1111 1112 // Should only be poll_return or poll 1113 assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" ); 1114 1115 // This is a poll immediately before a return. The exception handling code 1116 // has already had the effect of causing the return to occur, so the execution 1117 // will continue immediately after the call. In addition, the oopmap at the 1118 // return point does not mark the return value as an oop (if it is), so 1119 // it needs a handle here to be updated. 1120 if( nm->is_at_poll_return(real_return_addr) ) { 1121 // See if return type is an oop. 1122 bool return_oop = nm->method()->is_returning_oop(); 1123 Handle return_value; 1124 if (return_oop) { 1125 // The oop result has been saved on the stack together with all 1126 // the other registers. In order to preserve it over GCs we need 1127 // to keep it in a handle. 1128 oop result = caller_fr.saved_oop_result(&map); 1129 assert(oopDesc::is_oop_or_null(result), "must be oop"); 1130 return_value = Handle(thread(), result); 1131 assert(Universe::heap()->is_in_or_null(result), "must be heap pointer"); 1132 } 1133 1134 // Block the thread 1135 SafepointMechanism::block_if_requested(thread()); 1136 1137 // restore oop result, if any 1138 if (return_oop) { 1139 caller_fr.set_saved_oop_result(&map, return_value()); 1140 } 1141 } 1142 1143 // This is a safepoint poll. Verify the return address and block. 1144 else { 1145 set_at_poll_safepoint(true); 1146 1147 // verify the blob built the "return address" correctly 1148 assert(real_return_addr == caller_fr.pc(), "must match"); 1149 1150 // Block the thread 1151 SafepointMechanism::block_if_requested(thread()); 1152 set_at_poll_safepoint(false); 1153 1154 // If we have a pending async exception deoptimize the frame 1155 // as otherwise we may never deliver it. 1156 if (thread()->has_async_condition()) { 1157 ThreadInVMfromJavaNoAsyncException __tiv(thread()); 1158 Deoptimization::deoptimize_frame(thread(), caller_fr.id()); 1159 } 1160 1161 // If an exception has been installed we must check for a pending deoptimization 1162 // Deoptimize frame if exception has been thrown. 1163 1164 if (thread()->has_pending_exception() ) { 1165 RegisterMap map(thread(), true); 1166 frame caller_fr = stub_fr.sender(&map); 1167 if (caller_fr.is_deoptimized_frame()) { 1168 // The exception patch will destroy registers that are still 1169 // live and will be needed during deoptimization. Defer the 1170 // Async exception should have deferred the exception until the 1171 // next safepoint which will be detected when we get into 1172 // the interpreter so if we have an exception now things 1173 // are messed up. 1174 1175 fatal("Exception installed and deoptimization is pending"); 1176 } 1177 } 1178 } 1179 } 1180 1181 1182 // 1183 // Statistics & Instrumentations 1184 // 1185 SafepointSynchronize::SafepointStats* SafepointSynchronize::_safepoint_stats = NULL; 1186 jlong SafepointSynchronize::_safepoint_begin_time = 0; 1187 int SafepointSynchronize::_cur_stat_index = 0; 1188 julong SafepointSynchronize::_safepoint_reasons[VM_Operation::VMOp_Terminating]; 1189 julong SafepointSynchronize::_coalesced_vmop_count = 0; 1190 jlong SafepointSynchronize::_max_sync_time = 0; 1191 jlong SafepointSynchronize::_max_vmop_time = 0; 1192 float SafepointSynchronize::_ts_of_current_safepoint = 0.0f; 1193 1194 static jlong cleanup_end_time = 0; 1195 static bool init_done = false; 1196 1197 // Helper method to print the header. 1198 static void print_header() { 1199 // The number of spaces is significant here, and should match the format 1200 // specifiers in print_statistics(). 1201 1202 tty->print(" vmop " 1203 "[ threads: total initially_running wait_to_block ]" 1204 "[ time: spin block sync cleanup vmop ] "); 1205 1206 tty->print_cr("page_trap_count"); 1207 } 1208 1209 void SafepointSynchronize::deferred_initialize_stat() { 1210 if (init_done) return; 1211 1212 // If PrintSafepointStatisticsTimeout is specified, the statistics data will 1213 // be printed right away, in which case, _safepoint_stats will regress to 1214 // a single element array. Otherwise, it is a circular ring buffer with default 1215 // size of PrintSafepointStatisticsCount. 1216 int stats_array_size; 1217 if (PrintSafepointStatisticsTimeout > 0) { 1218 stats_array_size = 1; 1219 PrintSafepointStatistics = true; 1220 } else { 1221 stats_array_size = PrintSafepointStatisticsCount; 1222 } 1223 _safepoint_stats = (SafepointStats*)os::malloc(stats_array_size 1224 * sizeof(SafepointStats), mtInternal); 1225 guarantee(_safepoint_stats != NULL, 1226 "not enough memory for safepoint instrumentation data"); 1227 1228 init_done = true; 1229 } 1230 1231 void SafepointSynchronize::begin_statistics(int nof_threads, int nof_running) { 1232 assert(init_done, "safepoint statistics array hasn't been initialized"); 1233 SafepointStats *spstat = &_safepoint_stats[_cur_stat_index]; 1234 1235 spstat->_time_stamp = _ts_of_current_safepoint; 1236 1237 VM_Operation *op = VMThread::vm_operation(); 1238 spstat->_vmop_type = (op != NULL ? op->type() : -1); 1239 if (op != NULL) { 1240 _safepoint_reasons[spstat->_vmop_type]++; 1241 } 1242 1243 spstat->_nof_total_threads = nof_threads; 1244 spstat->_nof_initial_running_threads = nof_running; 1245 spstat->_nof_threads_hit_page_trap = 0; 1246 1247 // Records the start time of spinning. The real time spent on spinning 1248 // will be adjusted when spin is done. Same trick is applied for time 1249 // spent on waiting for threads to block. 1250 if (nof_running != 0) { 1251 spstat->_time_to_spin = os::javaTimeNanos(); 1252 } else { 1253 spstat->_time_to_spin = 0; 1254 } 1255 } 1256 1257 void SafepointSynchronize::update_statistics_on_spin_end() { 1258 SafepointStats *spstat = &_safepoint_stats[_cur_stat_index]; 1259 1260 jlong cur_time = os::javaTimeNanos(); 1261 1262 spstat->_nof_threads_wait_to_block = _waiting_to_block; 1263 if (spstat->_nof_initial_running_threads != 0) { 1264 spstat->_time_to_spin = cur_time - spstat->_time_to_spin; 1265 } 1266 1267 // Records the start time of waiting for to block. Updated when block is done. 1268 if (_waiting_to_block != 0) { 1269 spstat->_time_to_wait_to_block = cur_time; 1270 } else { 1271 spstat->_time_to_wait_to_block = 0; 1272 } 1273 } 1274 1275 void SafepointSynchronize::update_statistics_on_sync_end(jlong end_time) { 1276 SafepointStats *spstat = &_safepoint_stats[_cur_stat_index]; 1277 1278 if (spstat->_nof_threads_wait_to_block != 0) { 1279 spstat->_time_to_wait_to_block = end_time - 1280 spstat->_time_to_wait_to_block; 1281 } 1282 1283 // Records the end time of sync which will be used to calculate the total 1284 // vm operation time. Again, the real time spending in syncing will be deducted 1285 // from the start of the sync time later when end_statistics is called. 1286 spstat->_time_to_sync = end_time - _safepoint_begin_time; 1287 if (spstat->_time_to_sync > _max_sync_time) { 1288 _max_sync_time = spstat->_time_to_sync; 1289 } 1290 1291 spstat->_time_to_do_cleanups = end_time; 1292 } 1293 1294 void SafepointSynchronize::update_statistics_on_cleanup_end(jlong end_time) { 1295 SafepointStats *spstat = &_safepoint_stats[_cur_stat_index]; 1296 1297 // Record how long spent in cleanup tasks. 1298 spstat->_time_to_do_cleanups = end_time - spstat->_time_to_do_cleanups; 1299 1300 cleanup_end_time = end_time; 1301 } 1302 1303 void SafepointSynchronize::end_statistics(jlong vmop_end_time) { 1304 SafepointStats *spstat = &_safepoint_stats[_cur_stat_index]; 1305 1306 // Update the vm operation time. 1307 spstat->_time_to_exec_vmop = vmop_end_time - cleanup_end_time; 1308 if (spstat->_time_to_exec_vmop > _max_vmop_time) { 1309 _max_vmop_time = spstat->_time_to_exec_vmop; 1310 } 1311 // Only the sync time longer than the specified 1312 // PrintSafepointStatisticsTimeout will be printed out right away. 1313 // By default, it is -1 meaning all samples will be put into the list. 1314 if ( PrintSafepointStatisticsTimeout > 0) { 1315 if (spstat->_time_to_sync > (jlong)PrintSafepointStatisticsTimeout * MICROUNITS) { 1316 print_statistics(); 1317 } 1318 } else { 1319 // The safepoint statistics will be printed out when the _safepoin_stats 1320 // array fills up. 1321 if (_cur_stat_index == PrintSafepointStatisticsCount - 1) { 1322 print_statistics(); 1323 _cur_stat_index = 0; 1324 } else { 1325 _cur_stat_index++; 1326 } 1327 } 1328 } 1329 1330 void SafepointSynchronize::print_statistics() { 1331 for (int index = 0; index <= _cur_stat_index; index++) { 1332 if (index % 30 == 0) { 1333 print_header(); 1334 } 1335 SafepointStats* sstats = &_safepoint_stats[index]; 1336 tty->print("%8.3f: ", sstats->_time_stamp); 1337 tty->print("%-30s [ " 1338 INT32_FORMAT_W(8) " " INT32_FORMAT_W(17) " " INT32_FORMAT_W(13) " " 1339 "]", 1340 (sstats->_vmop_type == -1 ? "no vm operation" : VM_Operation::name(sstats->_vmop_type)), 1341 sstats->_nof_total_threads, 1342 sstats->_nof_initial_running_threads, 1343 sstats->_nof_threads_wait_to_block); 1344 // "/ MICROUNITS " is to convert the unit from nanos to millis. 1345 tty->print("[ " 1346 INT64_FORMAT_W(7) " " INT64_FORMAT_W(7) " " 1347 INT64_FORMAT_W(7) " " INT64_FORMAT_W(7) " " 1348 INT64_FORMAT_W(7) " ] ", 1349 (int64_t)(sstats->_time_to_spin / MICROUNITS), 1350 (int64_t)(sstats->_time_to_wait_to_block / MICROUNITS), 1351 (int64_t)(sstats->_time_to_sync / MICROUNITS), 1352 (int64_t)(sstats->_time_to_do_cleanups / MICROUNITS), 1353 (int64_t)(sstats->_time_to_exec_vmop / MICROUNITS)); 1354 1355 tty->print_cr(INT32_FORMAT_W(15) " ", sstats->_nof_threads_hit_page_trap); 1356 } 1357 } 1358 1359 // This method will be called when VM exits. It will first call 1360 // print_statistics to print out the rest of the sampling. Then 1361 // it tries to summarize the sampling. 1362 void SafepointSynchronize::print_stat_on_exit() { 1363 if (_safepoint_stats == NULL) return; 1364 1365 SafepointStats *spstat = &_safepoint_stats[_cur_stat_index]; 1366 1367 // During VM exit, end_statistics may not get called and in that 1368 // case, if the sync time is less than PrintSafepointStatisticsTimeout, 1369 // don't print it out. 1370 // Approximate the vm op time. 1371 _safepoint_stats[_cur_stat_index]._time_to_exec_vmop = 1372 os::javaTimeNanos() - cleanup_end_time; 1373 1374 if ( PrintSafepointStatisticsTimeout < 0 || 1375 spstat->_time_to_sync > (jlong)PrintSafepointStatisticsTimeout * MICROUNITS) { 1376 print_statistics(); 1377 } 1378 tty->cr(); 1379 1380 // Print out polling page sampling status. 1381 tty->print_cr("Polling page always armed"); 1382 1383 for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) { 1384 if (_safepoint_reasons[index] != 0) { 1385 tty->print_cr("%-26s" UINT64_FORMAT_W(10), VM_Operation::name(index), 1386 _safepoint_reasons[index]); 1387 } 1388 } 1389 1390 tty->print_cr(UINT64_FORMAT_W(5) " VM operations coalesced during safepoint", 1391 _coalesced_vmop_count); 1392 tty->print_cr("Maximum sync time " INT64_FORMAT_W(5) " ms", 1393 (int64_t)(_max_sync_time / MICROUNITS)); 1394 tty->print_cr("Maximum vm operation time (except for Exit VM operation) " 1395 INT64_FORMAT_W(5) " ms", 1396 (int64_t)(_max_vmop_time / MICROUNITS)); 1397 }