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.hpp" 37 #include "gc/shared/strongRootsScope.hpp" 38 #include "gc/shared/workgroup.hpp" 39 #include "interpreter/interpreter.hpp" 40 #include "jfr/jfrEvents.hpp" 41 #include "logging/log.hpp" 42 #include "logging/logStream.hpp" 43 #include "memory/resourceArea.hpp" 44 #include "memory/universe.hpp" 45 #include "oops/oop.inline.hpp" 46 #include "oops/symbol.hpp" 47 #include "runtime/atomic.hpp" 48 #include "runtime/compilationPolicy.hpp" 49 #include "runtime/deoptimization.hpp" 50 #include "runtime/frame.inline.hpp" 51 #include "runtime/interfaceSupport.inline.hpp" 52 #include "runtime/mutexLocker.hpp" 53 #include "runtime/orderAccess.hpp" 54 #include "runtime/osThread.hpp" 55 #include "runtime/safepoint.hpp" 56 #include "runtime/safepointMechanism.inline.hpp" 57 #include "runtime/signature.hpp" 58 #include "runtime/stubCodeGenerator.hpp" 59 #include "runtime/stubRoutines.hpp" 60 #include "runtime/sweeper.hpp" 61 #include "runtime/synchronizer.hpp" 62 #include "runtime/thread.inline.hpp" 63 #include "runtime/threadSMR.hpp" 64 #include "runtime/timerTrace.hpp" 65 #include "services/runtimeService.hpp" 66 #include "utilities/events.hpp" 67 #include "utilities/macros.hpp" 68 #ifdef COMPILER1 69 #include "c1/c1_globals.hpp" 70 #endif 71 72 template <typename E> 73 static void set_current_safepoint_id(E* event, int adjustment = 0) { 74 assert(event != NULL, "invariant"); 75 event->set_safepointId(SafepointSynchronize::safepoint_counter() + adjustment); 76 } 77 78 static void post_safepoint_begin_event(EventSafepointBegin* event, 79 int thread_count, 80 int critical_thread_count) { 81 assert(event != NULL, "invariant"); 82 assert(event->should_commit(), "invariant"); 83 set_current_safepoint_id(event); 84 event->set_totalThreadCount(thread_count); 85 event->set_jniCriticalThreadCount(critical_thread_count); 86 event->commit(); 87 } 88 89 static void post_safepoint_cleanup_event(EventSafepointCleanup* event) { 90 assert(event != NULL, "invariant"); 91 assert(event->should_commit(), "invariant"); 92 set_current_safepoint_id(event); 93 event->commit(); 94 } 95 96 static void post_safepoint_synchronize_event(EventSafepointStateSynchronization* event, 97 int initial_number_of_threads, 98 int threads_waiting_to_block, 99 unsigned int iterations) { 100 assert(event != NULL, "invariant"); 101 if (event->should_commit()) { 102 // Group this event together with the ones committed after the counter is increased 103 set_current_safepoint_id(event, 1); 104 event->set_initialThreadCount(initial_number_of_threads); 105 event->set_runningThreadCount(threads_waiting_to_block); 106 event->set_iterations(iterations); 107 event->commit(); 108 } 109 } 110 111 static void post_safepoint_wait_blocked_event(EventSafepointWaitBlocked* event, 112 int initial_threads_waiting_to_block) { 113 assert(event != NULL, "invariant"); 114 assert(event->should_commit(), "invariant"); 115 set_current_safepoint_id(event); 116 event->set_runningThreadCount(initial_threads_waiting_to_block); 117 event->commit(); 118 } 119 120 static void post_safepoint_cleanup_task_event(EventSafepointCleanupTask* event, 121 const char* name) { 122 assert(event != NULL, "invariant"); 123 if (event->should_commit()) { 124 set_current_safepoint_id(event); 125 event->set_name(name); 126 event->commit(); 127 } 128 } 129 130 static void post_safepoint_end_event(EventSafepointEnd* event) { 131 assert(event != NULL, "invariant"); 132 if (event->should_commit()) { 133 // Group this event together with the ones committed before the counter increased 134 set_current_safepoint_id(event, -1); 135 event->commit(); 136 } 137 } 138 139 // -------------------------------------------------------------------------------------------------- 140 // Implementation of Safepoint begin/end 141 142 SafepointSynchronize::SynchronizeState volatile SafepointSynchronize::_state = SafepointSynchronize::_not_synchronized; 143 volatile int SafepointSynchronize::_waiting_to_block = 0; 144 volatile int SafepointSynchronize::_safepoint_counter = 0; 145 int SafepointSynchronize::_current_jni_active_count = 0; 146 long SafepointSynchronize::_end_of_last_safepoint = 0; 147 int SafepointSynchronize::_defer_thr_suspend_loop_count = 4000; 148 static const int safepoint_spin_before_yield = 2000; 149 static volatile int PageArmed = 0 ; // safepoint polling page is RO|RW vs PROT_NONE 150 static volatile int TryingToBlock = 0 ; // proximate value -- for advisory use only 151 static bool timeout_error_printed = false; 152 153 // Roll all threads forward to a safepoint and suspend them all 154 void SafepointSynchronize::begin() { 155 EventSafepointBegin begin_event; 156 Thread* myThread = Thread::current(); 157 assert(myThread->is_VM_thread(), "Only VM thread may execute a safepoint"); 158 159 if (PrintSafepointStatistics || PrintSafepointStatisticsTimeout > 0) { 160 _safepoint_begin_time = os::javaTimeNanos(); 161 _ts_of_current_safepoint = tty->time_stamp().seconds(); 162 } 163 164 Universe::heap()->safepoint_synchronize_begin(); 165 166 // By getting the Threads_lock, we assure that no threads are about to start or 167 // exit. It is released again in SafepointSynchronize::end(). 168 Threads_lock->lock(); 169 170 assert( _state == _not_synchronized, "trying to safepoint synchronize with wrong state"); 171 172 int nof_threads = Threads::number_of_threads(); 173 174 log_debug(safepoint)("Safepoint synchronization initiated. (%d threads)", nof_threads); 175 176 RuntimeService::record_safepoint_begin(); 177 178 MutexLocker mu(Safepoint_lock); 179 180 // Reset the count of active JNI critical threads 181 _current_jni_active_count = 0; 182 183 // Set number of threads to wait for, before we initiate the callbacks 184 _waiting_to_block = nof_threads; 185 TryingToBlock = 0 ; 186 int still_running = nof_threads; 187 188 // Save the starting time, so that it can be compared to see if this has taken 189 // too long to complete. 190 jlong safepoint_limit_time = 0; 191 timeout_error_printed = false; 192 193 // PrintSafepointStatisticsTimeout can be specified separately. When 194 // specified, PrintSafepointStatistics will be set to true in 195 // deferred_initialize_stat method. The initialization has to be done 196 // early enough to avoid any races. See bug 6880029 for details. 197 if (PrintSafepointStatistics || PrintSafepointStatisticsTimeout > 0) { 198 deferred_initialize_stat(); 199 } 200 201 // Begin the process of bringing the system to a safepoint. 202 // Java threads can be in several different states and are 203 // stopped by different mechanisms: 204 // 205 // 1. Running interpreted 206 // The interpreter dispatch table is changed to force it to 207 // check for a safepoint condition between bytecodes. 208 // 2. Running in native code 209 // When returning from the native code, a Java thread must check 210 // the safepoint _state to see if we must block. If the 211 // VM thread sees a Java thread in native, it does 212 // not wait for this thread to block. The order of the memory 213 // writes and reads of both the safepoint state and the Java 214 // threads state is critical. In order to guarantee that the 215 // memory writes are serialized with respect to each other, 216 // the VM thread issues a memory barrier instruction 217 // (on MP systems). In order to avoid the overhead of issuing 218 // a memory barrier for each Java thread making native calls, each Java 219 // thread performs a write to a single memory page after changing 220 // the thread state. The VM thread performs a sequence of 221 // mprotect OS calls which forces all previous writes from all 222 // Java threads to be serialized. This is done in the 223 // os::serialize_thread_states() call. This has proven to be 224 // much more efficient than executing a membar instruction 225 // on every call to native code. 226 // 3. Running compiled Code 227 // Compiled code reads a global (Safepoint Polling) page that 228 // is set to fault if we are trying to get to a safepoint. 229 // 4. Blocked 230 // A thread which is blocked will not be allowed to return from the 231 // block condition until the safepoint operation is complete. 232 // 5. In VM or Transitioning between states 233 // If a Java thread is currently running in the VM or transitioning 234 // between states, the safepointing code will wait for the thread to 235 // block itself when it attempts transitions to a new state. 236 // 237 { 238 EventSafepointStateSynchronization sync_event; 239 int initial_running = 0; 240 241 _state = _synchronizing; 242 243 if (SafepointMechanism::uses_thread_local_poll()) { 244 // Arming the per thread poll while having _state != _not_synchronized means safepointing 245 log_trace(safepoint)("Setting thread local yield flag for threads"); 246 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) { 247 // Make sure the threads start polling, it is time to yield. 248 SafepointMechanism::arm_local_poll(cur); // release store, global state -> local state 249 } 250 } 251 OrderAccess::fence(); // storestore|storeload, global state -> local state 252 253 // Flush all thread states to memory 254 if (!UseMembar) { 255 os::serialize_thread_states(); 256 } 257 258 if (SafepointMechanism::uses_global_page_poll()) { 259 // Make interpreter safepoint aware 260 Interpreter::notice_safepoints(); 261 262 // Make polling safepoint aware 263 guarantee (PageArmed == 0, "invariant") ; 264 PageArmed = 1 ; 265 os::make_polling_page_unreadable(); 266 } 267 268 // Consider using active_processor_count() ... but that call is expensive. 269 int ncpus = os::processor_count() ; 270 unsigned int iterations = 0; 271 272 { 273 JavaThreadIteratorWithHandle jtiwh; 274 #ifdef ASSERT 275 for (; JavaThread *cur = jtiwh.next(); ) { 276 assert(cur->safepoint_state()->is_running(), "Illegal initial state"); 277 // Clear the visited flag to ensure that the critical counts are collected properly. 278 cur->set_visited_for_critical_count(false); 279 } 280 #endif // ASSERT 281 282 if (SafepointTimeout) 283 safepoint_limit_time = os::javaTimeNanos() + (jlong)SafepointTimeoutDelay * MICROUNITS; 284 285 // Iterate through all threads until it have been determined how to stop them all at a safepoint 286 int steps = 0 ; 287 while(still_running > 0) { 288 jtiwh.rewind(); 289 for (; JavaThread *cur = jtiwh.next(); ) { 290 assert(!cur->is_ConcurrentGC_thread(), "A concurrent GC thread is unexpectly being suspended"); 291 ThreadSafepointState *cur_state = cur->safepoint_state(); 292 if (cur_state->is_running()) { 293 cur_state->examine_state_of_thread(); 294 if (!cur_state->is_running()) { 295 still_running--; 296 // consider adjusting steps downward: 297 // steps = 0 298 // steps -= NNN 299 // steps >>= 1 300 // steps = MIN(steps, 2000-100) 301 // if (iterations != 0) steps -= NNN 302 } 303 LogTarget(Trace, safepoint) lt; 304 if (lt.is_enabled()) { 305 ResourceMark rm; 306 LogStream ls(lt); 307 cur_state->print_on(&ls); 308 } 309 } 310 } 311 312 if (iterations == 0) { 313 initial_running = still_running; 314 if (PrintSafepointStatistics) { 315 begin_statistics(nof_threads, still_running); 316 } 317 } 318 319 if (still_running > 0) { 320 // Check for if it takes to long 321 if (SafepointTimeout && safepoint_limit_time < os::javaTimeNanos()) { 322 print_safepoint_timeout(_spinning_timeout); 323 } 324 325 // Spin to avoid context switching. 326 // There's a tension between allowing the mutators to run (and rendezvous) 327 // vs spinning. As the VM thread spins, wasting cycles, it consumes CPU that 328 // a mutator might otherwise use profitably to reach a safepoint. Excessive 329 // spinning by the VM thread on a saturated system can increase rendezvous latency. 330 // Blocking or yielding incur their own penalties in the form of context switching 331 // and the resultant loss of $ residency. 332 // 333 // Further complicating matters is that yield() does not work as naively expected 334 // on many platforms -- yield() does not guarantee that any other ready threads 335 // will run. As such we revert to naked_short_sleep() after some number of iterations. 336 // nakes_short_sleep() is implemented as a short unconditional sleep. 337 // Typical operating systems round a "short" sleep period up to 10 msecs, so sleeping 338 // can actually increase the time it takes the VM thread to detect that a system-wide 339 // stop-the-world safepoint has been reached. In a pathological scenario such as that 340 // described in CR6415670 the VMthread may sleep just before the mutator(s) become safe. 341 // In that case the mutators will be stalled waiting for the safepoint to complete and the 342 // the VMthread will be sleeping, waiting for the mutators to rendezvous. The VMthread 343 // will eventually wake up and detect that all mutators are safe, at which point 344 // we'll again make progress. 345 // 346 // Beware too that that the VMThread typically runs at elevated priority. 347 // Its default priority is higher than the default mutator priority. 348 // Obviously, this complicates spinning. 349 // 350 // Note too that on Windows XP SwitchThreadTo() has quite different behavior than Sleep(0). 351 // Sleep(0) will _not yield to lower priority threads, while SwitchThreadTo() will. 352 // 353 // See the comments in synchronizer.cpp for additional remarks on spinning. 354 // 355 // In the future we might: 356 // 1. Modify the safepoint scheme to avoid potentially unbounded spinning. 357 // This is tricky as the path used by a thread exiting the JVM (say on 358 // on JNI call-out) simply stores into its state field. The burden 359 // is placed on the VM thread, which must poll (spin). 360 // 2. Find something useful to do while spinning. If the safepoint is GC-related 361 // we might aggressively scan the stacks of threads that are already safe. 362 // 3. Use Solaris schedctl to examine the state of the still-running mutators. 363 // If all the mutators are ONPROC there's no reason to sleep or yield. 364 // 4. YieldTo() any still-running mutators that are ready but OFFPROC. 365 // 5. Check system saturation. If the system is not fully saturated then 366 // simply spin and avoid sleep/yield. 367 // 6. As still-running mutators rendezvous they could unpark the sleeping 368 // VMthread. This works well for still-running mutators that become 369 // safe. The VMthread must still poll for mutators that call-out. 370 // 7. Drive the policy on time-since-begin instead of iterations. 371 // 8. Consider making the spin duration a function of the # of CPUs: 372 // Spin = (((ncpus-1) * M) + K) + F(still_running) 373 // Alternately, instead of counting iterations of the outer loop 374 // we could count the # of threads visited in the inner loop, above. 375 // 9. On windows consider using the return value from SwitchThreadTo() 376 // to drive subsequent spin/SwitchThreadTo()/Sleep(N) decisions. 377 378 if (int(iterations) == -1) { // overflow - something is wrong. 379 // We can only overflow here when we are using global 380 // polling pages. We keep this guarantee in its original 381 // form so that searches of the bug database for this 382 // failure mode find the right bugs. 383 guarantee (PageArmed == 0, "invariant"); 384 } 385 386 // Instead of (ncpus > 1) consider either (still_running < (ncpus + EPSILON)) or 387 // ((still_running + _waiting_to_block - TryingToBlock)) < ncpus) 388 ++steps ; 389 if (ncpus > 1 && steps < safepoint_spin_before_yield) { 390 SpinPause() ; // MP-Polite spin 391 } else 392 if (steps < _defer_thr_suspend_loop_count) { 393 os::naked_yield() ; 394 } else { 395 os::naked_short_sleep(1); 396 } 397 398 iterations ++ ; 399 } 400 assert(iterations < (uint)max_jint, "We have been iterating in the safepoint loop too long"); 401 } 402 } // ThreadsListHandle destroyed here. 403 assert(still_running == 0, "sanity check"); 404 405 if (PrintSafepointStatistics) { 406 update_statistics_on_spin_end(); 407 } 408 if (sync_event.should_commit()) { 409 post_safepoint_synchronize_event(&sync_event, initial_running, _waiting_to_block, iterations); 410 } 411 } 412 413 // wait until all threads are stopped 414 { 415 EventSafepointWaitBlocked wait_blocked_event; 416 int initial_waiting_to_block = _waiting_to_block; 417 418 while (_waiting_to_block > 0) { 419 log_debug(safepoint)("Waiting for %d thread(s) to block", _waiting_to_block); 420 if (!SafepointTimeout || timeout_error_printed) { 421 Safepoint_lock->wait(true); // true, means with no safepoint checks 422 } else { 423 // Compute remaining time 424 jlong remaining_time = safepoint_limit_time - os::javaTimeNanos(); 425 426 // If there is no remaining time, then there is an error 427 if (remaining_time < 0 || Safepoint_lock->wait(true, remaining_time / MICROUNITS)) { 428 print_safepoint_timeout(_blocking_timeout); 429 } 430 } 431 } 432 assert(_waiting_to_block == 0, "sanity check"); 433 434 #ifndef PRODUCT 435 if (SafepointTimeout) { 436 jlong current_time = os::javaTimeNanos(); 437 if (safepoint_limit_time < current_time) { 438 tty->print_cr("# SafepointSynchronize: Finished after " 439 INT64_FORMAT_W(6) " ms", 440 (int64_t)((current_time - safepoint_limit_time) / MICROUNITS + 441 (jlong)SafepointTimeoutDelay)); 442 } 443 } 444 #endif 445 446 assert((_safepoint_counter & 0x1) == 0, "must be even"); 447 assert(Threads_lock->owned_by_self(), "must hold Threads_lock"); 448 _safepoint_counter ++; 449 450 // Record state 451 _state = _synchronized; 452 453 OrderAccess::fence(); 454 if (wait_blocked_event.should_commit()) { 455 post_safepoint_wait_blocked_event(&wait_blocked_event, initial_waiting_to_block); 456 } 457 } 458 459 #ifdef ASSERT 460 // Make sure all the threads were visited. 461 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) { 462 assert(cur->was_visited_for_critical_count(), "missed a thread"); 463 } 464 #endif // ASSERT 465 466 // Update the count of active JNI critical regions 467 GCLocker::set_jni_lock_count(_current_jni_active_count); 468 469 log_info(safepoint)("Entering safepoint region: %s", VMThread::vm_safepoint_description()); 470 471 RuntimeService::record_safepoint_synchronized(); 472 if (PrintSafepointStatistics) { 473 update_statistics_on_sync_end(os::javaTimeNanos()); 474 } 475 476 // Call stuff that needs to be run when a safepoint is just about to be completed 477 { 478 EventSafepointCleanup cleanup_event; 479 do_cleanup_tasks(); 480 if (cleanup_event.should_commit()) { 481 post_safepoint_cleanup_event(&cleanup_event); 482 } 483 } 484 485 if (PrintSafepointStatistics) { 486 // Record how much time spend on the above cleanup tasks 487 update_statistics_on_cleanup_end(os::javaTimeNanos()); 488 } 489 490 if (begin_event.should_commit()) { 491 post_safepoint_begin_event(&begin_event, nof_threads, _current_jni_active_count); 492 } 493 } 494 495 // Wake up all threads, so they are ready to resume execution after the safepoint 496 // operation has been carried out 497 void SafepointSynchronize::end() { 498 assert(Threads_lock->owned_by_self(), "must hold Threads_lock"); 499 assert((_safepoint_counter & 0x1) == 1, "must be odd"); 500 EventSafepointEnd event; 501 _safepoint_counter ++; 502 // memory fence isn't required here since an odd _safepoint_counter 503 // value can do no harm and a fence is issued below anyway. 504 505 DEBUG_ONLY(Thread* myThread = Thread::current();) 506 assert(myThread->is_VM_thread(), "Only VM thread can execute a safepoint"); 507 508 if (PrintSafepointStatistics) { 509 end_statistics(os::javaTimeNanos()); 510 } 511 512 { 513 JavaThreadIteratorWithHandle jtiwh; 514 #ifdef ASSERT 515 // A pending_exception cannot be installed during a safepoint. The threads 516 // may install an async exception after they come back from a safepoint into 517 // pending_exception after they unblock. But that should happen later. 518 for (; JavaThread *cur = jtiwh.next(); ) { 519 assert (!(cur->has_pending_exception() && 520 cur->safepoint_state()->is_at_poll_safepoint()), 521 "safepoint installed a pending exception"); 522 } 523 #endif // ASSERT 524 525 if (PageArmed) { 526 assert(SafepointMechanism::uses_global_page_poll(), "sanity"); 527 // Make polling safepoint aware 528 os::make_polling_page_readable(); 529 PageArmed = 0 ; 530 } 531 532 if (SafepointMechanism::uses_global_page_poll()) { 533 // Remove safepoint check from interpreter 534 Interpreter::ignore_safepoints(); 535 } 536 537 { 538 MutexLocker mu(Safepoint_lock); 539 540 assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization"); 541 542 if (SafepointMechanism::uses_thread_local_poll()) { 543 _state = _not_synchronized; 544 OrderAccess::storestore(); // global state -> local state 545 jtiwh.rewind(); 546 for (; JavaThread *current = jtiwh.next(); ) { 547 ThreadSafepointState* cur_state = current->safepoint_state(); 548 cur_state->restart(); // TSS _running 549 SafepointMechanism::disarm_local_poll(current); // release store, local state -> polling page 550 } 551 log_info(safepoint)("Leaving safepoint region"); 552 } else { 553 // Set to not synchronized, so the threads will not go into the signal_thread_blocked method 554 // when they get restarted. 555 _state = _not_synchronized; 556 OrderAccess::fence(); 557 558 log_info(safepoint)("Leaving safepoint region"); 559 560 // Start suspended threads 561 jtiwh.rewind(); 562 for (; JavaThread *current = jtiwh.next(); ) { 563 // A problem occurring on Solaris is when attempting to restart threads 564 // the first #cpus - 1 go well, but then the VMThread is preempted when we get 565 // to the next one (since it has been running the longest). We then have 566 // to wait for a cpu to become available before we can continue restarting 567 // threads. 568 // FIXME: This causes the performance of the VM to degrade when active and with 569 // large numbers of threads. Apparently this is due to the synchronous nature 570 // of suspending threads. 571 // 572 // TODO-FIXME: the comments above are vestigial and no longer apply. 573 // Furthermore, using solaris' schedctl in this particular context confers no benefit 574 if (VMThreadHintNoPreempt) { 575 os::hint_no_preempt(); 576 } 577 ThreadSafepointState* cur_state = current->safepoint_state(); 578 assert(cur_state->type() != ThreadSafepointState::_running, "Thread not suspended at safepoint"); 579 cur_state->restart(); 580 assert(cur_state->is_running(), "safepoint state has not been reset"); 581 } 582 } 583 584 RuntimeService::record_safepoint_end(); 585 586 // Release threads lock, so threads can be created/destroyed again. 587 // It will also release all threads blocked in signal_thread_blocked. 588 Threads_lock->unlock(); 589 } 590 } // ThreadsListHandle destroyed here. 591 592 Universe::heap()->safepoint_synchronize_end(); 593 // record this time so VMThread can keep track how much time has elapsed 594 // since last safepoint. 595 _end_of_last_safepoint = os::javaTimeMillis(); 596 if (event.should_commit()) { 597 post_safepoint_end_event(&event); 598 } 599 } 600 601 bool SafepointSynchronize::is_cleanup_needed() { 602 // Need a safepoint if there are many monitors to deflate. 603 if (ObjectSynchronizer::is_cleanup_needed()) return true; 604 // Need a safepoint if some inline cache buffers is non-empty 605 if (!InlineCacheBuffer::is_empty()) return true; 606 return false; 607 } 608 609 class ParallelSPCleanupThreadClosure : public ThreadClosure { 610 private: 611 CodeBlobClosure* _nmethod_cl; 612 DeflateMonitorCounters* _counters; 613 614 public: 615 ParallelSPCleanupThreadClosure(DeflateMonitorCounters* counters) : 616 _counters(counters), 617 _nmethod_cl(NMethodSweeper::prepare_mark_active_nmethods()) {} 618 619 void do_thread(Thread* thread) { 620 ObjectSynchronizer::deflate_thread_local_monitors(thread, _counters); 621 if (_nmethod_cl != NULL && thread->is_Java_thread() && 622 ! thread->is_Code_cache_sweeper_thread()) { 623 JavaThread* jt = (JavaThread*) thread; 624 jt->nmethods_do(_nmethod_cl); 625 } 626 } 627 }; 628 629 class ParallelSPCleanupTask : public AbstractGangTask { 630 private: 631 SubTasksDone _subtasks; 632 ParallelSPCleanupThreadClosure _cleanup_threads_cl; 633 uint _num_workers; 634 DeflateMonitorCounters* _counters; 635 public: 636 ParallelSPCleanupTask(uint num_workers, DeflateMonitorCounters* counters) : 637 AbstractGangTask("Parallel Safepoint Cleanup"), 638 _cleanup_threads_cl(ParallelSPCleanupThreadClosure(counters)), 639 _num_workers(num_workers), 640 _subtasks(SubTasksDone(SafepointSynchronize::SAFEPOINT_CLEANUP_NUM_TASKS)), 641 _counters(counters) {} 642 643 void work(uint worker_id) { 644 // All threads deflate monitors and mark nmethods (if necessary). 645 Threads::possibly_parallel_threads_do(true, &_cleanup_threads_cl); 646 647 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_DEFLATE_MONITORS)) { 648 const char* name = "deflating idle monitors"; 649 EventSafepointCleanupTask event; 650 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 651 ObjectSynchronizer::deflate_idle_monitors(_counters); 652 if (event.should_commit()) { 653 post_safepoint_cleanup_task_event(&event, name); 654 } 655 } 656 657 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_UPDATE_INLINE_CACHES)) { 658 const char* name = "updating inline caches"; 659 EventSafepointCleanupTask event; 660 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 661 InlineCacheBuffer::update_inline_caches(); 662 if (event.should_commit()) { 663 post_safepoint_cleanup_task_event(&event, name); 664 } 665 } 666 667 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_COMPILATION_POLICY)) { 668 const char* name = "compilation policy safepoint handler"; 669 EventSafepointCleanupTask event; 670 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 671 CompilationPolicy::policy()->do_safepoint_work(); 672 if (event.should_commit()) { 673 post_safepoint_cleanup_task_event(&event, name); 674 } 675 } 676 677 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_SYMBOL_TABLE_REHASH)) { 678 if (SymbolTable::needs_rehashing()) { 679 const char* name = "rehashing symbol table"; 680 EventSafepointCleanupTask event; 681 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 682 SymbolTable::rehash_table(); 683 if (event.should_commit()) { 684 post_safepoint_cleanup_task_event(&event, name); 685 } 686 } 687 } 688 689 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_STRING_TABLE_REHASH)) { 690 if (StringTable::needs_rehashing()) { 691 const char* name = "rehashing string table"; 692 EventSafepointCleanupTask event; 693 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 694 StringTable::rehash_table(); 695 if (event.should_commit()) { 696 post_safepoint_cleanup_task_event(&event, name); 697 } 698 } 699 } 700 701 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_CLD_PURGE)) { 702 // CMS delays purging the CLDG until the beginning of the next safepoint and to 703 // make sure concurrent sweep is done 704 const char* name = "purging class loader data graph"; 705 EventSafepointCleanupTask event; 706 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 707 ClassLoaderDataGraph::purge_if_needed(); 708 if (event.should_commit()) { 709 post_safepoint_cleanup_task_event(&event, name); 710 } 711 } 712 713 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_SYSTEM_DICTIONARY_RESIZE)) { 714 const char* name = "resizing system dictionaries"; 715 EventSafepointCleanupTask event; 716 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 717 ClassLoaderDataGraph::resize_if_needed(); 718 if (event.should_commit()) { 719 post_safepoint_cleanup_task_event(&event, name); 720 } 721 } 722 _subtasks.all_tasks_completed(_num_workers); 723 } 724 }; 725 726 // Various cleaning tasks that should be done periodically at safepoints. 727 void SafepointSynchronize::do_cleanup_tasks() { 728 729 TraceTime timer("safepoint cleanup tasks", TRACETIME_LOG(Info, safepoint, cleanup)); 730 731 // Prepare for monitor deflation. 732 DeflateMonitorCounters deflate_counters; 733 ObjectSynchronizer::prepare_deflate_idle_monitors(&deflate_counters); 734 735 CollectedHeap* heap = Universe::heap(); 736 assert(heap != NULL, "heap not initialized yet?"); 737 WorkGang* cleanup_workers = heap->get_safepoint_workers(); 738 if (cleanup_workers != NULL) { 739 // Parallel cleanup using GC provided thread pool. 740 uint num_cleanup_workers = cleanup_workers->active_workers(); 741 ParallelSPCleanupTask cleanup(num_cleanup_workers, &deflate_counters); 742 StrongRootsScope srs(num_cleanup_workers); 743 cleanup_workers->run_task(&cleanup); 744 } else { 745 // Serial cleanup using VMThread. 746 ParallelSPCleanupTask cleanup(1, &deflate_counters); 747 StrongRootsScope srs(1); 748 cleanup.work(0); 749 } 750 751 // Finish monitor deflation. 752 ObjectSynchronizer::finish_deflate_idle_monitors(&deflate_counters); 753 } 754 755 756 bool SafepointSynchronize::safepoint_safe(JavaThread *thread, JavaThreadState state) { 757 switch(state) { 758 case _thread_in_native: 759 // native threads are safe if they have no java stack or have walkable stack 760 return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable(); 761 762 // blocked threads should have already have walkable stack 763 case _thread_blocked: 764 assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable"); 765 return true; 766 767 default: 768 return false; 769 } 770 } 771 772 773 // See if the thread is running inside a lazy critical native and 774 // update the thread critical count if so. Also set a suspend flag to 775 // cause the native wrapper to return into the JVM to do the unlock 776 // once the native finishes. 777 void SafepointSynchronize::check_for_lazy_critical_native(JavaThread *thread, JavaThreadState state) { 778 if (state == _thread_in_native && 779 thread->has_last_Java_frame() && 780 thread->frame_anchor()->walkable()) { 781 // This thread might be in a critical native nmethod so look at 782 // the top of the stack and increment the critical count if it 783 // is. 784 frame wrapper_frame = thread->last_frame(); 785 CodeBlob* stub_cb = wrapper_frame.cb(); 786 if (stub_cb != NULL && 787 stub_cb->is_nmethod() && 788 stub_cb->as_nmethod_or_null()->is_lazy_critical_native()) { 789 // A thread could potentially be in a critical native across 790 // more than one safepoint, so only update the critical state on 791 // the first one. When it returns it will perform the unlock. 792 if (!thread->do_critical_native_unlock()) { 793 #ifdef ASSERT 794 if (!thread->in_critical()) { 795 GCLocker::increment_debug_jni_lock_count(); 796 } 797 #endif 798 thread->enter_critical(); 799 // Make sure the native wrapper calls back on return to 800 // perform the needed critical unlock. 801 thread->set_critical_native_unlock(); 802 } 803 } 804 } 805 } 806 807 808 809 // ------------------------------------------------------------------------------------------------------- 810 // Implementation of Safepoint callback point 811 812 void SafepointSynchronize::block(JavaThread *thread) { 813 assert(thread != NULL, "thread must be set"); 814 assert(thread->is_Java_thread(), "not a Java thread"); 815 816 // Threads shouldn't block if they are in the middle of printing, but... 817 ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id()); 818 819 // Only bail from the block() call if the thread is gone from the 820 // thread list; starting to exit should still block. 821 if (thread->is_terminated()) { 822 // block current thread if we come here from native code when VM is gone 823 thread->block_if_vm_exited(); 824 825 // otherwise do nothing 826 return; 827 } 828 829 JavaThreadState state = thread->thread_state(); 830 thread->frame_anchor()->make_walkable(thread); 831 832 // Check that we have a valid thread_state at this point 833 switch(state) { 834 case _thread_in_vm_trans: 835 case _thread_in_Java: // From compiled code 836 837 // We are highly likely to block on the Safepoint_lock. In order to avoid blocking in this case, 838 // we pretend we are still in the VM. 839 thread->set_thread_state(_thread_in_vm); 840 841 if (is_synchronizing()) { 842 Atomic::inc (&TryingToBlock) ; 843 } 844 845 // We will always be holding the Safepoint_lock when we are examine the state 846 // of a thread. Hence, the instructions between the Safepoint_lock->lock() and 847 // Safepoint_lock->unlock() are happening atomic with regards to the safepoint code 848 Safepoint_lock->lock_without_safepoint_check(); 849 if (is_synchronizing()) { 850 // Decrement the number of threads to wait for and signal vm thread 851 assert(_waiting_to_block > 0, "sanity check"); 852 _waiting_to_block--; 853 thread->safepoint_state()->set_has_called_back(true); 854 855 DEBUG_ONLY(thread->set_visited_for_critical_count(true)); 856 if (thread->in_critical()) { 857 // Notice that this thread is in a critical section 858 increment_jni_active_count(); 859 } 860 861 // Consider (_waiting_to_block < 2) to pipeline the wakeup of the VM thread 862 if (_waiting_to_block == 0) { 863 Safepoint_lock->notify_all(); 864 } 865 } 866 867 // We transition the thread to state _thread_blocked here, but 868 // we can't do our usual check for external suspension and then 869 // self-suspend after the lock_without_safepoint_check() call 870 // below because we are often called during transitions while 871 // we hold different locks. That would leave us suspended while 872 // holding a resource which results in deadlocks. 873 thread->set_thread_state(_thread_blocked); 874 Safepoint_lock->unlock(); 875 876 // We now try to acquire the threads lock. Since this lock is hold by the VM thread during 877 // the entire safepoint, the threads will all line up here during the safepoint. 878 Threads_lock->lock_without_safepoint_check(); 879 // restore original state. This is important if the thread comes from compiled code, so it 880 // will continue to execute with the _thread_in_Java state. 881 thread->set_thread_state(state); 882 Threads_lock->unlock(); 883 break; 884 885 case _thread_in_native_trans: 886 case _thread_blocked_trans: 887 case _thread_new_trans: 888 if (thread->safepoint_state()->type() == ThreadSafepointState::_call_back) { 889 thread->print_thread_state(); 890 fatal("Deadlock in safepoint code. " 891 "Should have called back to the VM before blocking."); 892 } 893 894 // We transition the thread to state _thread_blocked here, but 895 // we can't do our usual check for external suspension and then 896 // self-suspend after the lock_without_safepoint_check() call 897 // below because we are often called during transitions while 898 // we hold different locks. That would leave us suspended while 899 // holding a resource which results in deadlocks. 900 thread->set_thread_state(_thread_blocked); 901 902 // It is not safe to suspend a thread if we discover it is in _thread_in_native_trans. Hence, 903 // the safepoint code might still be waiting for it to block. We need to change the state here, 904 // so it can see that it is at a safepoint. 905 906 // Block until the safepoint operation is completed. 907 Threads_lock->lock_without_safepoint_check(); 908 909 // Restore state 910 thread->set_thread_state(state); 911 912 Threads_lock->unlock(); 913 break; 914 915 default: 916 fatal("Illegal threadstate encountered: %d", state); 917 } 918 919 // Check for pending. async. exceptions or suspends - except if the 920 // thread was blocked inside the VM. has_special_runtime_exit_condition() 921 // is called last since it grabs a lock and we only want to do that when 922 // we must. 923 // 924 // Note: we never deliver an async exception at a polling point as the 925 // compiler may not have an exception handler for it. The polling 926 // code will notice the async and deoptimize and the exception will 927 // be delivered. (Polling at a return point is ok though). Sure is 928 // a lot of bother for a deprecated feature... 929 // 930 // We don't deliver an async exception if the thread state is 931 // _thread_in_native_trans so JNI functions won't be called with 932 // a surprising pending exception. If the thread state is going back to java, 933 // async exception is checked in check_special_condition_for_native_trans(). 934 935 if (state != _thread_blocked_trans && 936 state != _thread_in_vm_trans && 937 thread->has_special_runtime_exit_condition()) { 938 thread->handle_special_runtime_exit_condition( 939 !thread->is_at_poll_safepoint() && (state != _thread_in_native_trans)); 940 } 941 } 942 943 // ------------------------------------------------------------------------------------------------------ 944 // Exception handlers 945 946 947 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) { 948 assert(thread->is_Java_thread(), "polling reference encountered by VM thread"); 949 assert(thread->thread_state() == _thread_in_Java, "should come from Java code"); 950 if (!ThreadLocalHandshakes) { 951 assert(SafepointSynchronize::is_synchronizing(), "polling encountered outside safepoint synchronization"); 952 } 953 954 if (PrintSafepointStatistics) { 955 inc_page_trap_count(); 956 } 957 958 ThreadSafepointState* state = thread->safepoint_state(); 959 960 state->handle_polling_page_exception(); 961 } 962 963 964 void SafepointSynchronize::print_safepoint_timeout(SafepointTimeoutReason reason) { 965 if (!timeout_error_printed) { 966 timeout_error_printed = true; 967 // Print out the thread info which didn't reach the safepoint for debugging 968 // purposes (useful when there are lots of threads in the debugger). 969 tty->cr(); 970 tty->print_cr("# SafepointSynchronize::begin: Timeout detected:"); 971 if (reason == _spinning_timeout) { 972 tty->print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint."); 973 } else if (reason == _blocking_timeout) { 974 tty->print_cr("# SafepointSynchronize::begin: Timed out while waiting for threads to stop."); 975 } 976 977 tty->print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:"); 978 ThreadSafepointState *cur_state; 979 ResourceMark rm; 980 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) { 981 cur_state = cur_thread->safepoint_state(); 982 983 if (cur_thread->thread_state() != _thread_blocked && 984 ((reason == _spinning_timeout && cur_state->is_running()) || 985 (reason == _blocking_timeout && !cur_state->has_called_back()))) { 986 tty->print("# "); 987 cur_thread->print(); 988 tty->cr(); 989 } 990 } 991 tty->print_cr("# SafepointSynchronize::begin: (End of list)"); 992 } 993 994 // To debug the long safepoint, specify both DieOnSafepointTimeout & 995 // ShowMessageBoxOnError. 996 if (DieOnSafepointTimeout) { 997 fatal("Safepoint sync time longer than " INTX_FORMAT "ms detected when executing %s.", 998 SafepointTimeoutDelay, VMThread::vm_safepoint_description()); 999 } 1000 } 1001 1002 1003 // ------------------------------------------------------------------------------------------------------- 1004 // Implementation of ThreadSafepointState 1005 1006 ThreadSafepointState::ThreadSafepointState(JavaThread *thread) { 1007 _thread = thread; 1008 _type = _running; 1009 _has_called_back = false; 1010 _at_poll_safepoint = false; 1011 } 1012 1013 void ThreadSafepointState::create(JavaThread *thread) { 1014 ThreadSafepointState *state = new ThreadSafepointState(thread); 1015 thread->set_safepoint_state(state); 1016 } 1017 1018 void ThreadSafepointState::destroy(JavaThread *thread) { 1019 if (thread->safepoint_state()) { 1020 delete(thread->safepoint_state()); 1021 thread->set_safepoint_state(NULL); 1022 } 1023 } 1024 1025 void ThreadSafepointState::examine_state_of_thread() { 1026 assert(is_running(), "better be running or just have hit safepoint poll"); 1027 1028 JavaThreadState state = _thread->thread_state(); 1029 1030 // Save the state at the start of safepoint processing. 1031 _orig_thread_state = state; 1032 1033 // Check for a thread that is suspended. Note that thread resume tries 1034 // to grab the Threads_lock which we own here, so a thread cannot be 1035 // resumed during safepoint synchronization. 1036 1037 // We check to see if this thread is suspended without locking to 1038 // avoid deadlocking with a third thread that is waiting for this 1039 // thread to be suspended. The third thread can notice the safepoint 1040 // that we're trying to start at the beginning of its SR_lock->wait() 1041 // call. If that happens, then the third thread will block on the 1042 // safepoint while still holding the underlying SR_lock. We won't be 1043 // able to get the SR_lock and we'll deadlock. 1044 // 1045 // We don't need to grab the SR_lock here for two reasons: 1046 // 1) The suspend flags are both volatile and are set with an 1047 // Atomic::cmpxchg() call so we should see the suspended 1048 // state right away. 1049 // 2) We're being called from the safepoint polling loop; if 1050 // we don't see the suspended state on this iteration, then 1051 // we'll come around again. 1052 // 1053 bool is_suspended = _thread->is_ext_suspended(); 1054 if (is_suspended) { 1055 roll_forward(_at_safepoint); 1056 return; 1057 } 1058 1059 // Some JavaThread states have an initial safepoint state of 1060 // running, but are actually at a safepoint. We will happily 1061 // agree and update the safepoint state here. 1062 if (SafepointSynchronize::safepoint_safe(_thread, state)) { 1063 SafepointSynchronize::check_for_lazy_critical_native(_thread, state); 1064 roll_forward(_at_safepoint); 1065 return; 1066 } 1067 1068 if (state == _thread_in_vm) { 1069 roll_forward(_call_back); 1070 return; 1071 } 1072 1073 // All other thread states will continue to run until they 1074 // transition and self-block in state _blocked 1075 // Safepoint polling in compiled code causes the Java threads to do the same. 1076 // Note: new threads may require a malloc so they must be allowed to finish 1077 1078 assert(is_running(), "examine_state_of_thread on non-running thread"); 1079 return; 1080 } 1081 1082 // Returns true is thread could not be rolled forward at present position. 1083 void ThreadSafepointState::roll_forward(suspend_type type) { 1084 _type = type; 1085 1086 switch(_type) { 1087 case _at_safepoint: 1088 SafepointSynchronize::signal_thread_at_safepoint(); 1089 DEBUG_ONLY(_thread->set_visited_for_critical_count(true)); 1090 if (_thread->in_critical()) { 1091 // Notice that this thread is in a critical section 1092 SafepointSynchronize::increment_jni_active_count(); 1093 } 1094 break; 1095 1096 case _call_back: 1097 set_has_called_back(false); 1098 break; 1099 1100 case _running: 1101 default: 1102 ShouldNotReachHere(); 1103 } 1104 } 1105 1106 void ThreadSafepointState::restart() { 1107 switch(type()) { 1108 case _at_safepoint: 1109 case _call_back: 1110 break; 1111 1112 case _running: 1113 default: 1114 tty->print_cr("restart thread " INTPTR_FORMAT " with state %d", 1115 p2i(_thread), _type); 1116 _thread->print(); 1117 ShouldNotReachHere(); 1118 } 1119 _type = _running; 1120 set_has_called_back(false); 1121 } 1122 1123 1124 void ThreadSafepointState::print_on(outputStream *st) const { 1125 const char *s = NULL; 1126 1127 switch(_type) { 1128 case _running : s = "_running"; break; 1129 case _at_safepoint : s = "_at_safepoint"; break; 1130 case _call_back : s = "_call_back"; break; 1131 default: 1132 ShouldNotReachHere(); 1133 } 1134 1135 st->print_cr("Thread: " INTPTR_FORMAT 1136 " [0x%2x] State: %s _has_called_back %d _at_poll_safepoint %d", 1137 p2i(_thread), _thread->osthread()->thread_id(), s, _has_called_back, 1138 _at_poll_safepoint); 1139 1140 _thread->print_thread_state_on(st); 1141 } 1142 1143 // --------------------------------------------------------------------------------------------------------------------- 1144 1145 // Block the thread at poll or poll return for safepoint/handshake. 1146 void ThreadSafepointState::handle_polling_page_exception() { 1147 1148 // Check state. block() will set thread state to thread_in_vm which will 1149 // cause the safepoint state _type to become _call_back. 1150 suspend_type t = type(); 1151 assert(!SafepointMechanism::uses_global_page_poll() || t == ThreadSafepointState::_running, 1152 "polling page exception on thread not running state: %u", uint(t)); 1153 1154 // Step 1: Find the nmethod from the return address 1155 address real_return_addr = thread()->saved_exception_pc(); 1156 1157 CodeBlob *cb = CodeCache::find_blob(real_return_addr); 1158 assert(cb != NULL && cb->is_compiled(), "return address should be in nmethod"); 1159 CompiledMethod* nm = (CompiledMethod*)cb; 1160 1161 // Find frame of caller 1162 frame stub_fr = thread()->last_frame(); 1163 CodeBlob* stub_cb = stub_fr.cb(); 1164 assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub"); 1165 RegisterMap map(thread(), true); 1166 frame caller_fr = stub_fr.sender(&map); 1167 1168 // Should only be poll_return or poll 1169 assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" ); 1170 1171 // This is a poll immediately before a return. The exception handling code 1172 // has already had the effect of causing the return to occur, so the execution 1173 // will continue immediately after the call. In addition, the oopmap at the 1174 // return point does not mark the return value as an oop (if it is), so 1175 // it needs a handle here to be updated. 1176 if( nm->is_at_poll_return(real_return_addr) ) { 1177 // See if return type is an oop. 1178 bool return_oop = nm->method()->is_returning_oop(); 1179 Handle return_value; 1180 if (return_oop) { 1181 // The oop result has been saved on the stack together with all 1182 // the other registers. In order to preserve it over GCs we need 1183 // to keep it in a handle. 1184 oop result = caller_fr.saved_oop_result(&map); 1185 assert(oopDesc::is_oop_or_null(result), "must be oop"); 1186 return_value = Handle(thread(), result); 1187 assert(Universe::heap()->is_in_or_null(result), "must be heap pointer"); 1188 } 1189 1190 // Block the thread 1191 SafepointMechanism::block_if_requested(thread()); 1192 1193 // restore oop result, if any 1194 if (return_oop) { 1195 caller_fr.set_saved_oop_result(&map, return_value()); 1196 } 1197 } 1198 1199 // This is a safepoint poll. Verify the return address and block. 1200 else { 1201 set_at_poll_safepoint(true); 1202 1203 // verify the blob built the "return address" correctly 1204 assert(real_return_addr == caller_fr.pc(), "must match"); 1205 1206 // Block the thread 1207 SafepointMechanism::block_if_requested(thread()); 1208 set_at_poll_safepoint(false); 1209 1210 // If we have a pending async exception deoptimize the frame 1211 // as otherwise we may never deliver it. 1212 if (thread()->has_async_condition()) { 1213 ThreadInVMfromJavaNoAsyncException __tiv(thread()); 1214 Deoptimization::deoptimize_frame(thread(), caller_fr.id()); 1215 } 1216 1217 // If an exception has been installed we must check for a pending deoptimization 1218 // Deoptimize frame if exception has been thrown. 1219 1220 if (thread()->has_pending_exception() ) { 1221 RegisterMap map(thread(), true); 1222 frame caller_fr = stub_fr.sender(&map); 1223 if (caller_fr.is_deoptimized_frame()) { 1224 // The exception patch will destroy registers that are still 1225 // live and will be needed during deoptimization. Defer the 1226 // Async exception should have deferred the exception until the 1227 // next safepoint which will be detected when we get into 1228 // the interpreter so if we have an exception now things 1229 // are messed up. 1230 1231 fatal("Exception installed and deoptimization is pending"); 1232 } 1233 } 1234 } 1235 } 1236 1237 1238 // 1239 // Statistics & Instrumentations 1240 // 1241 SafepointSynchronize::SafepointStats* SafepointSynchronize::_safepoint_stats = NULL; 1242 jlong SafepointSynchronize::_safepoint_begin_time = 0; 1243 int SafepointSynchronize::_cur_stat_index = 0; 1244 julong SafepointSynchronize::_safepoint_reasons[VM_Operation::VMOp_Terminating]; 1245 julong SafepointSynchronize::_coalesced_vmop_count = 0; 1246 jlong SafepointSynchronize::_max_sync_time = 0; 1247 jlong SafepointSynchronize::_max_vmop_time = 0; 1248 float SafepointSynchronize::_ts_of_current_safepoint = 0.0f; 1249 1250 static jlong cleanup_end_time = 0; 1251 static bool init_done = false; 1252 1253 // Helper method to print the header. 1254 static void print_header() { 1255 // The number of spaces is significant here, and should match the format 1256 // specifiers in print_statistics(). 1257 1258 tty->print(" vmop " 1259 "[ threads: total initially_running wait_to_block ]" 1260 "[ time: spin block sync cleanup vmop ] "); 1261 1262 tty->print_cr("page_trap_count"); 1263 } 1264 1265 void SafepointSynchronize::deferred_initialize_stat() { 1266 if (init_done) return; 1267 1268 // If PrintSafepointStatisticsTimeout is specified, the statistics data will 1269 // be printed right away, in which case, _safepoint_stats will regress to 1270 // a single element array. Otherwise, it is a circular ring buffer with default 1271 // size of PrintSafepointStatisticsCount. 1272 int stats_array_size; 1273 if (PrintSafepointStatisticsTimeout > 0) { 1274 stats_array_size = 1; 1275 PrintSafepointStatistics = true; 1276 } else { 1277 stats_array_size = PrintSafepointStatisticsCount; 1278 } 1279 _safepoint_stats = (SafepointStats*)os::malloc(stats_array_size 1280 * sizeof(SafepointStats), mtInternal); 1281 guarantee(_safepoint_stats != NULL, 1282 "not enough memory for safepoint instrumentation data"); 1283 1284 init_done = true; 1285 } 1286 1287 void SafepointSynchronize::begin_statistics(int nof_threads, int nof_running) { 1288 assert(init_done, "safepoint statistics array hasn't been initialized"); 1289 SafepointStats *spstat = &_safepoint_stats[_cur_stat_index]; 1290 1291 spstat->_time_stamp = _ts_of_current_safepoint; 1292 1293 VM_Operation *op = VMThread::vm_operation(); 1294 spstat->_vmop_type = (op != NULL ? op->type() : -1); 1295 if (op != NULL) { 1296 _safepoint_reasons[spstat->_vmop_type]++; 1297 } 1298 1299 spstat->_nof_total_threads = nof_threads; 1300 spstat->_nof_initial_running_threads = nof_running; 1301 spstat->_nof_threads_hit_page_trap = 0; 1302 1303 // Records the start time of spinning. The real time spent on spinning 1304 // will be adjusted when spin is done. Same trick is applied for time 1305 // spent on waiting for threads to block. 1306 if (nof_running != 0) { 1307 spstat->_time_to_spin = os::javaTimeNanos(); 1308 } else { 1309 spstat->_time_to_spin = 0; 1310 } 1311 } 1312 1313 void SafepointSynchronize::update_statistics_on_spin_end() { 1314 SafepointStats *spstat = &_safepoint_stats[_cur_stat_index]; 1315 1316 jlong cur_time = os::javaTimeNanos(); 1317 1318 spstat->_nof_threads_wait_to_block = _waiting_to_block; 1319 if (spstat->_nof_initial_running_threads != 0) { 1320 spstat->_time_to_spin = cur_time - spstat->_time_to_spin; 1321 } 1322 1323 // Records the start time of waiting for to block. Updated when block is done. 1324 if (_waiting_to_block != 0) { 1325 spstat->_time_to_wait_to_block = cur_time; 1326 } else { 1327 spstat->_time_to_wait_to_block = 0; 1328 } 1329 } 1330 1331 void SafepointSynchronize::update_statistics_on_sync_end(jlong end_time) { 1332 SafepointStats *spstat = &_safepoint_stats[_cur_stat_index]; 1333 1334 if (spstat->_nof_threads_wait_to_block != 0) { 1335 spstat->_time_to_wait_to_block = end_time - 1336 spstat->_time_to_wait_to_block; 1337 } 1338 1339 // Records the end time of sync which will be used to calculate the total 1340 // vm operation time. Again, the real time spending in syncing will be deducted 1341 // from the start of the sync time later when end_statistics is called. 1342 spstat->_time_to_sync = end_time - _safepoint_begin_time; 1343 if (spstat->_time_to_sync > _max_sync_time) { 1344 _max_sync_time = spstat->_time_to_sync; 1345 } 1346 1347 spstat->_time_to_do_cleanups = end_time; 1348 } 1349 1350 void SafepointSynchronize::update_statistics_on_cleanup_end(jlong end_time) { 1351 SafepointStats *spstat = &_safepoint_stats[_cur_stat_index]; 1352 1353 // Record how long spent in cleanup tasks. 1354 spstat->_time_to_do_cleanups = end_time - spstat->_time_to_do_cleanups; 1355 1356 cleanup_end_time = end_time; 1357 } 1358 1359 void SafepointSynchronize::end_statistics(jlong vmop_end_time) { 1360 SafepointStats *spstat = &_safepoint_stats[_cur_stat_index]; 1361 1362 // Update the vm operation time. 1363 spstat->_time_to_exec_vmop = vmop_end_time - cleanup_end_time; 1364 if (spstat->_time_to_exec_vmop > _max_vmop_time) { 1365 _max_vmop_time = spstat->_time_to_exec_vmop; 1366 } 1367 // Only the sync time longer than the specified 1368 // PrintSafepointStatisticsTimeout will be printed out right away. 1369 // By default, it is -1 meaning all samples will be put into the list. 1370 if ( PrintSafepointStatisticsTimeout > 0) { 1371 if (spstat->_time_to_sync > (jlong)PrintSafepointStatisticsTimeout * MICROUNITS) { 1372 print_statistics(); 1373 } 1374 } else { 1375 // The safepoint statistics will be printed out when the _safepoin_stats 1376 // array fills up. 1377 if (_cur_stat_index == PrintSafepointStatisticsCount - 1) { 1378 print_statistics(); 1379 _cur_stat_index = 0; 1380 } else { 1381 _cur_stat_index++; 1382 } 1383 } 1384 } 1385 1386 void SafepointSynchronize::print_statistics() { 1387 for (int index = 0; index <= _cur_stat_index; index++) { 1388 if (index % 30 == 0) { 1389 print_header(); 1390 } 1391 SafepointStats* sstats = &_safepoint_stats[index]; 1392 tty->print("%8.3f: ", sstats->_time_stamp); 1393 tty->print("%-30s [ " 1394 INT32_FORMAT_W(8) " " INT32_FORMAT_W(17) " " INT32_FORMAT_W(13) " " 1395 "]", 1396 (sstats->_vmop_type == -1 ? "no vm operation" : VM_Operation::name(sstats->_vmop_type)), 1397 sstats->_nof_total_threads, 1398 sstats->_nof_initial_running_threads, 1399 sstats->_nof_threads_wait_to_block); 1400 // "/ MICROUNITS " is to convert the unit from nanos to millis. 1401 tty->print("[ " 1402 INT64_FORMAT_W(7) " " INT64_FORMAT_W(7) " " 1403 INT64_FORMAT_W(7) " " INT64_FORMAT_W(7) " " 1404 INT64_FORMAT_W(7) " ] ", 1405 (int64_t)(sstats->_time_to_spin / MICROUNITS), 1406 (int64_t)(sstats->_time_to_wait_to_block / MICROUNITS), 1407 (int64_t)(sstats->_time_to_sync / MICROUNITS), 1408 (int64_t)(sstats->_time_to_do_cleanups / MICROUNITS), 1409 (int64_t)(sstats->_time_to_exec_vmop / MICROUNITS)); 1410 1411 tty->print_cr(INT32_FORMAT_W(15) " ", sstats->_nof_threads_hit_page_trap); 1412 } 1413 } 1414 1415 // This method will be called when VM exits. It will first call 1416 // print_statistics to print out the rest of the sampling. Then 1417 // it tries to summarize the sampling. 1418 void SafepointSynchronize::print_stat_on_exit() { 1419 if (_safepoint_stats == NULL) return; 1420 1421 SafepointStats *spstat = &_safepoint_stats[_cur_stat_index]; 1422 1423 // During VM exit, end_statistics may not get called and in that 1424 // case, if the sync time is less than PrintSafepointStatisticsTimeout, 1425 // don't print it out. 1426 // Approximate the vm op time. 1427 _safepoint_stats[_cur_stat_index]._time_to_exec_vmop = 1428 os::javaTimeNanos() - cleanup_end_time; 1429 1430 if ( PrintSafepointStatisticsTimeout < 0 || 1431 spstat->_time_to_sync > (jlong)PrintSafepointStatisticsTimeout * MICROUNITS) { 1432 print_statistics(); 1433 } 1434 tty->cr(); 1435 1436 // Print out polling page sampling status. 1437 tty->print_cr("Polling page always armed"); 1438 1439 for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) { 1440 if (_safepoint_reasons[index] != 0) { 1441 tty->print_cr("%-26s" UINT64_FORMAT_W(10), VM_Operation::name(index), 1442 _safepoint_reasons[index]); 1443 } 1444 } 1445 1446 tty->print_cr(UINT64_FORMAT_W(5) " VM operations coalesced during safepoint", 1447 _coalesced_vmop_count); 1448 tty->print_cr("Maximum sync time " INT64_FORMAT_W(5) " ms", 1449 (int64_t)(_max_sync_time / MICROUNITS)); 1450 tty->print_cr("Maximum vm operation time (except for Exit VM operation) " 1451 INT64_FORMAT_W(5) " ms", 1452 (int64_t)(_max_vmop_time / MICROUNITS)); 1453 }