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.inline.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; 152 153 154 // Statistic related statics 155 julong SafepointSynchronize::_coalesced_vmop_count = 0; 156 static jlong _safepoint_begin_time = 0; 157 static float _ts_of_current_safepoint = 0.0f; 158 static volatile int _nof_threads_hit_polling_page = 0; 159 160 // Roll all threads forward to a safepoint and suspend them all 161 void SafepointSynchronize::begin() { 162 EventSafepointBegin begin_event; 163 Thread* myThread = Thread::current(); 164 assert(myThread->is_VM_thread(), "Only VM thread may execute a safepoint"); 165 166 if (log_is_enabled(Debug, safepoint, stats)) { 167 _safepoint_begin_time = os::javaTimeNanos(); 168 _ts_of_current_safepoint = tty->time_stamp().seconds(); 169 _nof_threads_hit_polling_page = 0; 170 } 171 172 Universe::heap()->safepoint_synchronize_begin(); 173 174 // By getting the Threads_lock, we assure that no threads are about to start or 175 // exit. It is released again in SafepointSynchronize::end(). 176 Threads_lock->lock(); 177 178 assert( _state == _not_synchronized, "trying to safepoint synchronize with wrong state"); 179 180 int nof_threads = Threads::number_of_threads(); 181 182 log_debug(safepoint)("Safepoint synchronization initiated. (%d threads)", nof_threads); 183 184 RuntimeService::record_safepoint_begin(); 185 186 MutexLocker mu(Safepoint_lock); 187 188 // Reset the count of active JNI critical threads 189 _current_jni_active_count = 0; 190 191 // Set number of threads to wait for, before we initiate the callbacks 192 _waiting_to_block = nof_threads; 193 TryingToBlock = 0 ; 194 int still_running = nof_threads; 195 196 // Save the starting time, so that it can be compared to see if this has taken 197 // too long to complete. 198 jlong safepoint_limit_time = 0; 199 timeout_error_printed = false; 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 OrderAccess::storestore(); // storestore, global state -> local state 247 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) { 248 // Make sure the threads start polling, it is time to yield. 249 SafepointMechanism::arm_local_poll(cur); 250 } 251 } 252 OrderAccess::fence(); // storestore|storeload, global state -> local state 253 254 // Flush all thread states to memory 255 if (!UseMembar) { 256 os::serialize_thread_states(); 257 } 258 259 if (SafepointMechanism::uses_global_page_poll()) { 260 // Make interpreter safepoint aware 261 Interpreter::notice_safepoints(); 262 263 // Make polling safepoint aware 264 guarantee (PageArmed == 0, "invariant") ; 265 PageArmed = 1 ; 266 os::make_polling_page_unreadable(); 267 } 268 269 // Consider using active_processor_count() ... but that call is expensive. 270 int ncpus = os::processor_count() ; 271 unsigned int iterations = 0; 272 273 { 274 JavaThreadIteratorWithHandle jtiwh; 275 #ifdef ASSERT 276 for (; JavaThread *cur = jtiwh.next(); ) { 277 assert(cur->safepoint_state()->is_running(), "Illegal initial state"); 278 // Clear the visited flag to ensure that the critical counts are collected properly. 279 cur->set_visited_for_critical_count(false); 280 } 281 #endif // ASSERT 282 283 if (SafepointTimeout) 284 safepoint_limit_time = os::javaTimeNanos() + (jlong)SafepointTimeoutDelay * MICROUNITS; 285 286 // Iterate through all threads until it have been determined how to stop them all at a safepoint 287 int steps = 0 ; 288 while(still_running > 0) { 289 jtiwh.rewind(); 290 for (; JavaThread *cur = jtiwh.next(); ) { 291 assert(!cur->is_ConcurrentGC_thread(), "A concurrent GC thread is unexpectly being suspended"); 292 ThreadSafepointState *cur_state = cur->safepoint_state(); 293 if (cur_state->is_running()) { 294 cur_state->examine_state_of_thread(); 295 if (!cur_state->is_running()) { 296 still_running--; 297 // consider adjusting steps downward: 298 // steps = 0 299 // steps -= NNN 300 // steps >>= 1 301 // steps = MIN(steps, 2000-100) 302 // if (iterations != 0) steps -= NNN 303 } 304 LogTarget(Trace, safepoint) lt; 305 if (lt.is_enabled()) { 306 ResourceMark rm; 307 LogStream ls(lt); 308 cur_state->print_on(&ls); 309 } 310 } 311 } 312 313 if (iterations == 0) { 314 initial_running = still_running; 315 if (log_is_enabled(Debug, safepoint, stats)) { 316 begin_statistics(nof_threads, still_running); 317 } 318 } 319 320 if (still_running > 0) { 321 // Check for if it takes to long 322 if (SafepointTimeout && safepoint_limit_time < os::javaTimeNanos()) { 323 print_safepoint_timeout(_spinning_timeout); 324 } 325 326 // Spin to avoid context switching. 327 // There's a tension between allowing the mutators to run (and rendezvous) 328 // vs spinning. As the VM thread spins, wasting cycles, it consumes CPU that 329 // a mutator might otherwise use profitably to reach a safepoint. Excessive 330 // spinning by the VM thread on a saturated system can increase rendezvous latency. 331 // Blocking or yielding incur their own penalties in the form of context switching 332 // and the resultant loss of $ residency. 333 // 334 // Further complicating matters is that yield() does not work as naively expected 335 // on many platforms -- yield() does not guarantee that any other ready threads 336 // will run. As such we revert to naked_short_sleep() after some number of iterations. 337 // nakes_short_sleep() is implemented as a short unconditional sleep. 338 // Typical operating systems round a "short" sleep period up to 10 msecs, so sleeping 339 // can actually increase the time it takes the VM thread to detect that a system-wide 340 // stop-the-world safepoint has been reached. In a pathological scenario such as that 341 // described in CR6415670 the VMthread may sleep just before the mutator(s) become safe. 342 // In that case the mutators will be stalled waiting for the safepoint to complete and the 343 // the VMthread will be sleeping, waiting for the mutators to rendezvous. The VMthread 344 // will eventually wake up and detect that all mutators are safe, at which point 345 // we'll again make progress. 346 // 347 // Beware too that that the VMThread typically runs at elevated priority. 348 // Its default priority is higher than the default mutator priority. 349 // Obviously, this complicates spinning. 350 // 351 // Note too that on Windows XP SwitchThreadTo() has quite different behavior than Sleep(0). 352 // Sleep(0) will _not yield to lower priority threads, while SwitchThreadTo() will. 353 // 354 // See the comments in synchronizer.cpp for additional remarks on spinning. 355 // 356 // In the future we might: 357 // -- Modify the safepoint scheme to avoid potentially unbounded spinning. 358 // This is tricky as the path used by a thread exiting the JVM (say on 359 // on JNI call-out) simply stores into its state field. The burden 360 // is placed on the VM thread, which must poll (spin). 361 // -- Find something useful to do while spinning. If the safepoint is GC-related 362 // we might aggressively scan the stacks of threads that are already safe. 363 // -- YieldTo() any still-running mutators that are ready but OFFPROC. 364 // -- Check system saturation. If the system is not fully saturated then 365 // simply spin and avoid sleep/yield. 366 // -- As still-running mutators rendezvous they could unpark the sleeping 367 // VMthread. This works well for still-running mutators that become 368 // safe. The VMthread must still poll for mutators that call-out. 369 // -- Drive the policy on time-since-begin instead of iterations. 370 // -- Consider making the spin duration a function of the # of CPUs: 371 // Spin = (((ncpus-1) * M) + K) + F(still_running) 372 // Alternately, instead of counting iterations of the outer loop 373 // we could count the # of threads visited in the inner loop, above. 374 // -- On windows consider using the return value from SwitchThreadTo() 375 // to drive subsequent spin/SwitchThreadTo()/Sleep(N) decisions. 376 377 if (int(iterations) == -1) { // overflow - something is wrong. 378 // We can only overflow here when we are using global 379 // polling pages. We keep this guarantee in its original 380 // form so that searches of the bug database for this 381 // failure mode find the right bugs. 382 guarantee (PageArmed == 0, "invariant"); 383 } 384 385 // Instead of (ncpus > 1) consider either (still_running < (ncpus + EPSILON)) or 386 // ((still_running + _waiting_to_block - TryingToBlock)) < ncpus) 387 ++steps ; 388 if (ncpus > 1 && steps < safepoint_spin_before_yield) { 389 SpinPause() ; // MP-Polite spin 390 } else 391 if (steps < _defer_thr_suspend_loop_count) { 392 os::naked_yield() ; 393 } else { 394 os::naked_short_sleep(1); 395 } 396 397 iterations ++ ; 398 } 399 assert(iterations < (uint)max_jint, "We have been iterating in the safepoint loop too long"); 400 } 401 } // ThreadsListHandle destroyed here. 402 assert(still_running == 0, "sanity check"); 403 404 if (log_is_enabled(Debug, safepoint, stats)) { 405 update_statistics_on_spin_end(); 406 } 407 if (sync_event.should_commit()) { 408 post_safepoint_synchronize_event(&sync_event, initial_running, _waiting_to_block, iterations); 409 } 410 } 411 412 // wait until all threads are stopped 413 { 414 EventSafepointWaitBlocked wait_blocked_event; 415 int initial_waiting_to_block = _waiting_to_block; 416 417 while (_waiting_to_block > 0) { 418 log_debug(safepoint)("Waiting for %d thread(s) to block", _waiting_to_block); 419 if (!SafepointTimeout || timeout_error_printed) { 420 Safepoint_lock->wait(true); // true, means with no safepoint checks 421 } else { 422 // Compute remaining time 423 jlong remaining_time = safepoint_limit_time - os::javaTimeNanos(); 424 425 // If there is no remaining time, then there is an error 426 if (remaining_time < 0 || Safepoint_lock->wait(true, remaining_time / MICROUNITS)) { 427 print_safepoint_timeout(_blocking_timeout); 428 } 429 } 430 } 431 assert(_waiting_to_block == 0, "sanity check"); 432 433 #ifndef PRODUCT 434 if (SafepointTimeout) { 435 jlong current_time = os::javaTimeNanos(); 436 if (safepoint_limit_time < current_time) { 437 log_warning(safepoint)("# SafepointSynchronize: Finished after " 438 INT64_FORMAT_W(6) " ms", 439 (int64_t)((current_time - safepoint_limit_time) / MICROUNITS + 440 (jlong)SafepointTimeoutDelay)); 441 } 442 } 443 #endif 444 445 assert((_safepoint_counter & 0x1) == 0, "must be even"); 446 assert(Threads_lock->owned_by_self(), "must hold Threads_lock"); 447 _safepoint_counter ++; 448 449 // Record state 450 _state = _synchronized; 451 452 OrderAccess::fence(); 453 if (wait_blocked_event.should_commit()) { 454 post_safepoint_wait_blocked_event(&wait_blocked_event, initial_waiting_to_block); 455 } 456 } 457 458 #ifdef ASSERT 459 // Make sure all the threads were visited. 460 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) { 461 assert(cur->was_visited_for_critical_count(), "missed a thread"); 462 } 463 #endif // ASSERT 464 465 // Update the count of active JNI critical regions 466 GCLocker::set_jni_lock_count(_current_jni_active_count); 467 468 log_info(safepoint)("Entering safepoint region: %s", VMThread::vm_safepoint_description()); 469 470 RuntimeService::record_safepoint_synchronized(); 471 if (log_is_enabled(Debug, safepoint, stats)) { 472 update_statistics_on_sync_end(os::javaTimeNanos()); 473 } 474 475 // Call stuff that needs to be run when a safepoint is just about to be completed 476 { 477 EventSafepointCleanup cleanup_event; 478 do_cleanup_tasks(); 479 if (cleanup_event.should_commit()) { 480 post_safepoint_cleanup_event(&cleanup_event); 481 } 482 } 483 484 if (log_is_enabled(Debug, safepoint, stats)) { 485 // Record how much time spend on the above cleanup tasks 486 update_statistics_on_cleanup_end(os::javaTimeNanos()); 487 } 488 489 if (begin_event.should_commit()) { 490 post_safepoint_begin_event(&begin_event, nof_threads, _current_jni_active_count); 491 } 492 } 493 494 // Wake up all threads, so they are ready to resume execution after the safepoint 495 // operation has been carried out 496 void SafepointSynchronize::end() { 497 assert(Threads_lock->owned_by_self(), "must hold Threads_lock"); 498 assert((_safepoint_counter & 0x1) == 1, "must be odd"); 499 EventSafepointEnd event; 500 _safepoint_counter ++; 501 // memory fence isn't required here since an odd _safepoint_counter 502 // value can do no harm and a fence is issued below anyway. 503 504 DEBUG_ONLY(Thread* myThread = Thread::current();) 505 assert(myThread->is_VM_thread(), "Only VM thread can execute a safepoint"); 506 507 if (log_is_enabled(Debug, safepoint, stats)) { 508 end_statistics(os::javaTimeNanos()); 509 } 510 511 { 512 JavaThreadIteratorWithHandle jtiwh; 513 #ifdef ASSERT 514 // A pending_exception cannot be installed during a safepoint. The threads 515 // may install an async exception after they come back from a safepoint into 516 // pending_exception after they unblock. But that should happen later. 517 for (; JavaThread *cur = jtiwh.next(); ) { 518 assert (!(cur->has_pending_exception() && 519 cur->safepoint_state()->is_at_poll_safepoint()), 520 "safepoint installed a pending exception"); 521 } 522 #endif // ASSERT 523 524 if (PageArmed) { 525 assert(SafepointMechanism::uses_global_page_poll(), "sanity"); 526 // Make polling safepoint aware 527 os::make_polling_page_readable(); 528 PageArmed = 0 ; 529 } 530 531 if (SafepointMechanism::uses_global_page_poll()) { 532 // Remove safepoint check from interpreter 533 Interpreter::ignore_safepoints(); 534 } 535 536 { 537 MutexLocker mu(Safepoint_lock); 538 539 assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization"); 540 541 if (SafepointMechanism::uses_thread_local_poll()) { 542 _state = _not_synchronized; 543 OrderAccess::storestore(); // global state -> local state 544 jtiwh.rewind(); 545 for (; JavaThread *current = jtiwh.next(); ) { 546 ThreadSafepointState* cur_state = current->safepoint_state(); 547 cur_state->restart(); // TSS _running 548 SafepointMechanism::disarm_local_poll(current); 549 } 550 log_info(safepoint)("Leaving safepoint region"); 551 } else { 552 // Set to not synchronized, so the threads will not go into the signal_thread_blocked method 553 // when they get restarted. 554 _state = _not_synchronized; 555 OrderAccess::fence(); 556 557 log_info(safepoint)("Leaving safepoint region"); 558 559 // Start suspended threads 560 jtiwh.rewind(); 561 for (; JavaThread *current = jtiwh.next(); ) { 562 ThreadSafepointState* cur_state = current->safepoint_state(); 563 assert(cur_state->type() != ThreadSafepointState::_running, "Thread not suspended at safepoint"); 564 cur_state->restart(); 565 assert(cur_state->is_running(), "safepoint state has not been reset"); 566 } 567 } 568 569 RuntimeService::record_safepoint_end(); 570 571 // Release threads lock, so threads can be created/destroyed again. 572 // It will also release all threads blocked in signal_thread_blocked. 573 Threads_lock->unlock(); 574 } 575 } // ThreadsListHandle destroyed here. 576 577 Universe::heap()->safepoint_synchronize_end(); 578 // record this time so VMThread can keep track how much time has elapsed 579 // since last safepoint. 580 _end_of_last_safepoint = os::javaTimeMillis(); 581 if (event.should_commit()) { 582 post_safepoint_end_event(&event); 583 } 584 } 585 586 bool SafepointSynchronize::is_cleanup_needed() { 587 // Need a safepoint if there are many monitors to deflate. 588 if (ObjectSynchronizer::is_cleanup_needed()) return true; 589 // Need a safepoint if some inline cache buffers is non-empty 590 if (!InlineCacheBuffer::is_empty()) return true; 591 return false; 592 } 593 594 class ParallelSPCleanupThreadClosure : public ThreadClosure { 595 private: 596 CodeBlobClosure* _nmethod_cl; 597 DeflateMonitorCounters* _counters; 598 599 public: 600 ParallelSPCleanupThreadClosure(DeflateMonitorCounters* counters) : 601 _nmethod_cl(ThreadLocalHandshakes ? NULL : NMethodSweeper::prepare_mark_active_nmethods()), 602 _counters(counters) {} 603 604 void do_thread(Thread* thread) { 605 ObjectSynchronizer::deflate_thread_local_monitors(thread, _counters); 606 if (_nmethod_cl != NULL && thread->is_Java_thread() && 607 ! thread->is_Code_cache_sweeper_thread()) { 608 JavaThread* jt = (JavaThread*) thread; 609 jt->nmethods_do(_nmethod_cl); 610 } 611 } 612 }; 613 614 class ParallelSPCleanupTask : public AbstractGangTask { 615 private: 616 SubTasksDone _subtasks; 617 ParallelSPCleanupThreadClosure _cleanup_threads_cl; 618 uint _num_workers; 619 DeflateMonitorCounters* _counters; 620 public: 621 ParallelSPCleanupTask(uint num_workers, DeflateMonitorCounters* counters) : 622 AbstractGangTask("Parallel Safepoint Cleanup"), 623 _subtasks(SubTasksDone(SafepointSynchronize::SAFEPOINT_CLEANUP_NUM_TASKS)), 624 _cleanup_threads_cl(ParallelSPCleanupThreadClosure(counters)), 625 _num_workers(num_workers), 626 _counters(counters) {} 627 628 void work(uint worker_id) { 629 // All threads deflate monitors and mark nmethods (if necessary). 630 Threads::possibly_parallel_threads_do(true, &_cleanup_threads_cl); 631 632 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_DEFLATE_MONITORS)) { 633 const char* name = "deflating idle monitors"; 634 EventSafepointCleanupTask event; 635 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 636 ObjectSynchronizer::deflate_idle_monitors(_counters); 637 if (event.should_commit()) { 638 post_safepoint_cleanup_task_event(&event, name); 639 } 640 } 641 642 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_UPDATE_INLINE_CACHES)) { 643 const char* name = "updating inline caches"; 644 EventSafepointCleanupTask event; 645 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 646 InlineCacheBuffer::update_inline_caches(); 647 if (event.should_commit()) { 648 post_safepoint_cleanup_task_event(&event, name); 649 } 650 } 651 652 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_COMPILATION_POLICY)) { 653 const char* name = "compilation policy safepoint handler"; 654 EventSafepointCleanupTask event; 655 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 656 CompilationPolicy::policy()->do_safepoint_work(); 657 if (event.should_commit()) { 658 post_safepoint_cleanup_task_event(&event, name); 659 } 660 } 661 662 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_SYMBOL_TABLE_REHASH)) { 663 if (SymbolTable::needs_rehashing()) { 664 const char* name = "rehashing symbol table"; 665 EventSafepointCleanupTask event; 666 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 667 SymbolTable::rehash_table(); 668 if (event.should_commit()) { 669 post_safepoint_cleanup_task_event(&event, name); 670 } 671 } 672 } 673 674 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_STRING_TABLE_REHASH)) { 675 if (StringTable::needs_rehashing()) { 676 const char* name = "rehashing string table"; 677 EventSafepointCleanupTask event; 678 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 679 StringTable::rehash_table(); 680 if (event.should_commit()) { 681 post_safepoint_cleanup_task_event(&event, name); 682 } 683 } 684 } 685 686 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_CLD_PURGE)) { 687 // CMS delays purging the CLDG until the beginning of the next safepoint and to 688 // make sure concurrent sweep is done 689 const char* name = "purging class loader data graph"; 690 EventSafepointCleanupTask event; 691 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 692 ClassLoaderDataGraph::purge_if_needed(); 693 if (event.should_commit()) { 694 post_safepoint_cleanup_task_event(&event, name); 695 } 696 } 697 698 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_SYSTEM_DICTIONARY_RESIZE)) { 699 const char* name = "resizing system dictionaries"; 700 EventSafepointCleanupTask event; 701 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 702 ClassLoaderDataGraph::resize_if_needed(); 703 if (event.should_commit()) { 704 post_safepoint_cleanup_task_event(&event, name); 705 } 706 } 707 708 _subtasks.all_tasks_completed(_num_workers); 709 } 710 }; 711 712 // Various cleaning tasks that should be done periodically at safepoints. 713 void SafepointSynchronize::do_cleanup_tasks() { 714 715 TraceTime timer("safepoint cleanup tasks", TRACETIME_LOG(Info, safepoint, cleanup)); 716 717 // Prepare for monitor deflation. 718 DeflateMonitorCounters deflate_counters; 719 ObjectSynchronizer::prepare_deflate_idle_monitors(&deflate_counters); 720 721 CollectedHeap* heap = Universe::heap(); 722 assert(heap != NULL, "heap not initialized yet?"); 723 WorkGang* cleanup_workers = heap->get_safepoint_workers(); 724 if (cleanup_workers != NULL) { 725 // Parallel cleanup using GC provided thread pool. 726 uint num_cleanup_workers = cleanup_workers->active_workers(); 727 ParallelSPCleanupTask cleanup(num_cleanup_workers, &deflate_counters); 728 StrongRootsScope srs(num_cleanup_workers); 729 cleanup_workers->run_task(&cleanup); 730 } else { 731 // Serial cleanup using VMThread. 732 ParallelSPCleanupTask cleanup(1, &deflate_counters); 733 StrongRootsScope srs(1); 734 cleanup.work(0); 735 } 736 737 // Needs to be done single threaded by the VMThread. This walks 738 // the thread stacks looking for references to metadata before 739 // deciding to remove it from the metaspaces. 740 if (ClassLoaderDataGraph::should_clean_metaspaces_and_reset()) { 741 const char* name = "cleanup live ClassLoaderData metaspaces"; 742 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 743 ClassLoaderDataGraph::walk_metadata_and_clean_metaspaces(); 744 } 745 746 // Finish monitor deflation. 747 ObjectSynchronizer::finish_deflate_idle_monitors(&deflate_counters); 748 749 } 750 751 752 bool SafepointSynchronize::safepoint_safe(JavaThread *thread, JavaThreadState state) { 753 switch(state) { 754 case _thread_in_native: 755 // native threads are safe if they have no java stack or have walkable stack 756 return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable(); 757 758 // blocked threads should have already have walkable stack 759 case _thread_blocked: 760 assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable"); 761 return true; 762 763 default: 764 return false; 765 } 766 } 767 768 769 // See if the thread is running inside a lazy critical native and 770 // update the thread critical count if so. Also set a suspend flag to 771 // cause the native wrapper to return into the JVM to do the unlock 772 // once the native finishes. 773 void SafepointSynchronize::check_for_lazy_critical_native(JavaThread *thread, JavaThreadState state) { 774 if (state == _thread_in_native && 775 thread->has_last_Java_frame() && 776 thread->frame_anchor()->walkable()) { 777 // This thread might be in a critical native nmethod so look at 778 // the top of the stack and increment the critical count if it 779 // is. 780 frame wrapper_frame = thread->last_frame(); 781 CodeBlob* stub_cb = wrapper_frame.cb(); 782 if (stub_cb != NULL && 783 stub_cb->is_nmethod() && 784 stub_cb->as_nmethod_or_null()->is_lazy_critical_native()) { 785 // A thread could potentially be in a critical native across 786 // more than one safepoint, so only update the critical state on 787 // the first one. When it returns it will perform the unlock. 788 if (!thread->do_critical_native_unlock()) { 789 #ifdef ASSERT 790 if (!thread->in_critical()) { 791 GCLocker::increment_debug_jni_lock_count(); 792 } 793 #endif 794 thread->enter_critical(); 795 // Make sure the native wrapper calls back on return to 796 // perform the needed critical unlock. 797 thread->set_critical_native_unlock(); 798 } 799 } 800 } 801 } 802 803 804 805 // ------------------------------------------------------------------------------------------------------- 806 // Implementation of Safepoint callback point 807 808 void SafepointSynchronize::block(JavaThread *thread) { 809 assert(thread != NULL, "thread must be set"); 810 assert(thread->is_Java_thread(), "not a Java thread"); 811 812 // Threads shouldn't block if they are in the middle of printing, but... 813 ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id()); 814 815 // Only bail from the block() call if the thread is gone from the 816 // thread list; starting to exit should still block. 817 if (thread->is_terminated()) { 818 // block current thread if we come here from native code when VM is gone 819 thread->block_if_vm_exited(); 820 821 // otherwise do nothing 822 return; 823 } 824 825 JavaThreadState state = thread->thread_state(); 826 thread->frame_anchor()->make_walkable(thread); 827 828 // Check that we have a valid thread_state at this point 829 switch(state) { 830 case _thread_in_vm_trans: 831 case _thread_in_Java: // From compiled code 832 833 // We are highly likely to block on the Safepoint_lock. In order to avoid blocking in this case, 834 // we pretend we are still in the VM. 835 thread->set_thread_state(_thread_in_vm); 836 837 if (is_synchronizing()) { 838 Atomic::inc (&TryingToBlock) ; 839 } 840 841 // We will always be holding the Safepoint_lock when we are examine the state 842 // of a thread. Hence, the instructions between the Safepoint_lock->lock() and 843 // Safepoint_lock->unlock() are happening atomic with regards to the safepoint code 844 Safepoint_lock->lock_without_safepoint_check(); 845 if (is_synchronizing()) { 846 // Decrement the number of threads to wait for and signal vm thread 847 assert(_waiting_to_block > 0, "sanity check"); 848 _waiting_to_block--; 849 thread->safepoint_state()->set_has_called_back(true); 850 851 DEBUG_ONLY(thread->set_visited_for_critical_count(true)); 852 if (thread->in_critical()) { 853 // Notice that this thread is in a critical section 854 increment_jni_active_count(); 855 } 856 857 // Consider (_waiting_to_block < 2) to pipeline the wakeup of the VM thread 858 if (_waiting_to_block == 0) { 859 Safepoint_lock->notify_all(); 860 } 861 } 862 863 // We transition the thread to state _thread_blocked here, but 864 // we can't do our usual check for external suspension and then 865 // self-suspend after the lock_without_safepoint_check() call 866 // below because we are often called during transitions while 867 // we hold different locks. That would leave us suspended while 868 // holding a resource which results in deadlocks. 869 thread->set_thread_state(_thread_blocked); 870 Safepoint_lock->unlock(); 871 872 // We now try to acquire the threads lock. Since this lock is hold by the VM thread during 873 // the entire safepoint, the threads will all line up here during the safepoint. 874 Threads_lock->lock_without_safepoint_check(); 875 // restore original state. This is important if the thread comes from compiled code, so it 876 // will continue to execute with the _thread_in_Java state. 877 thread->set_thread_state(state); 878 Threads_lock->unlock(); 879 break; 880 881 case _thread_in_native_trans: 882 case _thread_blocked_trans: 883 case _thread_new_trans: 884 if (thread->safepoint_state()->type() == ThreadSafepointState::_call_back) { 885 thread->print_thread_state(); 886 fatal("Deadlock in safepoint code. " 887 "Should have called back to the VM before blocking."); 888 } 889 890 // We transition the thread to state _thread_blocked here, but 891 // we can't do our usual check for external suspension and then 892 // self-suspend after the lock_without_safepoint_check() call 893 // below because we are often called during transitions while 894 // we hold different locks. That would leave us suspended while 895 // holding a resource which results in deadlocks. 896 thread->set_thread_state(_thread_blocked); 897 898 // It is not safe to suspend a thread if we discover it is in _thread_in_native_trans. Hence, 899 // the safepoint code might still be waiting for it to block. We need to change the state here, 900 // so it can see that it is at a safepoint. 901 902 // Block until the safepoint operation is completed. 903 Threads_lock->lock_without_safepoint_check(); 904 905 // Restore state 906 thread->set_thread_state(state); 907 908 Threads_lock->unlock(); 909 break; 910 911 default: 912 fatal("Illegal threadstate encountered: %d", state); 913 } 914 915 // Check for pending. async. exceptions or suspends - except if the 916 // thread was blocked inside the VM. has_special_runtime_exit_condition() 917 // is called last since it grabs a lock and we only want to do that when 918 // we must. 919 // 920 // Note: we never deliver an async exception at a polling point as the 921 // compiler may not have an exception handler for it. The polling 922 // code will notice the async and deoptimize and the exception will 923 // be delivered. (Polling at a return point is ok though). Sure is 924 // a lot of bother for a deprecated feature... 925 // 926 // We don't deliver an async exception if the thread state is 927 // _thread_in_native_trans so JNI functions won't be called with 928 // a surprising pending exception. If the thread state is going back to java, 929 // async exception is checked in check_special_condition_for_native_trans(). 930 931 if (state != _thread_blocked_trans && 932 state != _thread_in_vm_trans && 933 thread->has_special_runtime_exit_condition()) { 934 thread->handle_special_runtime_exit_condition( 935 !thread->is_at_poll_safepoint() && (state != _thread_in_native_trans)); 936 } 937 } 938 939 // ------------------------------------------------------------------------------------------------------ 940 // Exception handlers 941 942 943 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) { 944 assert(thread->is_Java_thread(), "polling reference encountered by VM thread"); 945 assert(thread->thread_state() == _thread_in_Java, "should come from Java code"); 946 if (!ThreadLocalHandshakes) { 947 assert(SafepointSynchronize::is_synchronizing(), "polling encountered outside safepoint synchronization"); 948 } 949 950 if (log_is_enabled(Debug, safepoint, stats)) { 951 Atomic::inc(&_nof_threads_hit_polling_page); 952 } 953 954 ThreadSafepointState* state = thread->safepoint_state(); 955 956 state->handle_polling_page_exception(); 957 } 958 959 960 void SafepointSynchronize::print_safepoint_timeout(SafepointTimeoutReason reason) { 961 if (!timeout_error_printed) { 962 timeout_error_printed = true; 963 // Print out the thread info which didn't reach the safepoint for debugging 964 // purposes (useful when there are lots of threads in the debugger). 965 LogTarget(Warning, safepoint) lt; 966 if (lt.is_enabled()) { 967 ResourceMark rm; 968 LogStream ls(lt); 969 970 ls.cr(); 971 ls.print_cr("# SafepointSynchronize::begin: Timeout detected:"); 972 if (reason == _spinning_timeout) { 973 ls.print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint."); 974 } else if (reason == _blocking_timeout) { 975 ls.print_cr("# SafepointSynchronize::begin: Timed out while waiting for threads to stop."); 976 } 977 978 ls.print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:"); 979 ThreadSafepointState *cur_state; 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 ls.print("# "); 987 cur_thread->print_on(&ls); 988 ls.cr(); 989 } 990 } 991 ls.print_cr("# SafepointSynchronize::begin: (End of list)"); 992 } 993 } 994 995 // To debug the long safepoint, specify both DieOnSafepointTimeout & 996 // ShowMessageBoxOnError. 997 if (DieOnSafepointTimeout) { 998 fatal("Safepoint sync time longer than " INTX_FORMAT "ms detected when executing %s.", 999 SafepointTimeoutDelay, VMThread::vm_safepoint_description()); 1000 } 1001 } 1002 1003 1004 // ------------------------------------------------------------------------------------------------------- 1005 // Implementation of ThreadSafepointState 1006 1007 ThreadSafepointState::ThreadSafepointState(JavaThread *thread) { 1008 _thread = thread; 1009 _type = _running; 1010 _has_called_back = false; 1011 _at_poll_safepoint = false; 1012 } 1013 1014 void ThreadSafepointState::create(JavaThread *thread) { 1015 ThreadSafepointState *state = new ThreadSafepointState(thread); 1016 thread->set_safepoint_state(state); 1017 } 1018 1019 void ThreadSafepointState::destroy(JavaThread *thread) { 1020 if (thread->safepoint_state()) { 1021 delete(thread->safepoint_state()); 1022 thread->set_safepoint_state(NULL); 1023 } 1024 } 1025 1026 void ThreadSafepointState::examine_state_of_thread() { 1027 assert(is_running(), "better be running or just have hit safepoint poll"); 1028 1029 JavaThreadState state = _thread->thread_state(); 1030 1031 // Save the state at the start of safepoint processing. 1032 _orig_thread_state = state; 1033 1034 // Check for a thread that is suspended. Note that thread resume tries 1035 // to grab the Threads_lock which we own here, so a thread cannot be 1036 // resumed during safepoint synchronization. 1037 1038 // We check to see if this thread is suspended without locking to 1039 // avoid deadlocking with a third thread that is waiting for this 1040 // thread to be suspended. The third thread can notice the safepoint 1041 // that we're trying to start at the beginning of its SR_lock->wait() 1042 // call. If that happens, then the third thread will block on the 1043 // safepoint while still holding the underlying SR_lock. We won't be 1044 // able to get the SR_lock and we'll deadlock. 1045 // 1046 // We don't need to grab the SR_lock here for two reasons: 1047 // 1) The suspend flags are both volatile and are set with an 1048 // Atomic::cmpxchg() call so we should see the suspended 1049 // state right away. 1050 // 2) We're being called from the safepoint polling loop; if 1051 // we don't see the suspended state on this iteration, then 1052 // we'll come around again. 1053 // 1054 bool is_suspended = _thread->is_ext_suspended(); 1055 if (is_suspended) { 1056 roll_forward(_at_safepoint); 1057 return; 1058 } 1059 1060 // Some JavaThread states have an initial safepoint state of 1061 // running, but are actually at a safepoint. We will happily 1062 // agree and update the safepoint state here. 1063 if (SafepointSynchronize::safepoint_safe(_thread, state)) { 1064 SafepointSynchronize::check_for_lazy_critical_native(_thread, state); 1065 roll_forward(_at_safepoint); 1066 return; 1067 } 1068 1069 if (state == _thread_in_vm) { 1070 roll_forward(_call_back); 1071 return; 1072 } 1073 1074 // All other thread states will continue to run until they 1075 // transition and self-block in state _blocked 1076 // Safepoint polling in compiled code causes the Java threads to do the same. 1077 // Note: new threads may require a malloc so they must be allowed to finish 1078 1079 assert(is_running(), "examine_state_of_thread on non-running thread"); 1080 return; 1081 } 1082 1083 // Returns true is thread could not be rolled forward at present position. 1084 void ThreadSafepointState::roll_forward(suspend_type type) { 1085 _type = type; 1086 1087 switch(_type) { 1088 case _at_safepoint: 1089 SafepointSynchronize::signal_thread_at_safepoint(); 1090 DEBUG_ONLY(_thread->set_visited_for_critical_count(true)); 1091 if (_thread->in_critical()) { 1092 // Notice that this thread is in a critical section 1093 SafepointSynchronize::increment_jni_active_count(); 1094 } 1095 break; 1096 1097 case _call_back: 1098 set_has_called_back(false); 1099 break; 1100 1101 case _running: 1102 default: 1103 ShouldNotReachHere(); 1104 } 1105 } 1106 1107 void ThreadSafepointState::restart() { 1108 switch(type()) { 1109 case _at_safepoint: 1110 case _call_back: 1111 break; 1112 1113 case _running: 1114 default: 1115 tty->print_cr("restart thread " INTPTR_FORMAT " with state %d", 1116 p2i(_thread), _type); 1117 _thread->print(); 1118 ShouldNotReachHere(); 1119 } 1120 _type = _running; 1121 set_has_called_back(false); 1122 } 1123 1124 1125 void ThreadSafepointState::print_on(outputStream *st) const { 1126 const char *s = NULL; 1127 1128 switch(_type) { 1129 case _running : s = "_running"; break; 1130 case _at_safepoint : s = "_at_safepoint"; break; 1131 case _call_back : s = "_call_back"; break; 1132 default: 1133 ShouldNotReachHere(); 1134 } 1135 1136 st->print_cr("Thread: " INTPTR_FORMAT 1137 " [0x%2x] State: %s _has_called_back %d _at_poll_safepoint %d", 1138 p2i(_thread), _thread->osthread()->thread_id(), s, _has_called_back, 1139 _at_poll_safepoint); 1140 1141 _thread->print_thread_state_on(st); 1142 } 1143 1144 // --------------------------------------------------------------------------------------------------------------------- 1145 1146 // Block the thread at poll or poll return for safepoint/handshake. 1147 void ThreadSafepointState::handle_polling_page_exception() { 1148 1149 // Check state. block() will set thread state to thread_in_vm which will 1150 // cause the safepoint state _type to become _call_back. 1151 suspend_type t = type(); 1152 assert(!SafepointMechanism::uses_global_page_poll() || t == ThreadSafepointState::_running, 1153 "polling page exception on thread not running state: %u", uint(t)); 1154 1155 // Step 1: Find the nmethod from the return address 1156 address real_return_addr = thread()->saved_exception_pc(); 1157 1158 CodeBlob *cb = CodeCache::find_blob(real_return_addr); 1159 assert(cb != NULL && cb->is_compiled(), "return address should be in nmethod"); 1160 CompiledMethod* nm = (CompiledMethod*)cb; 1161 1162 // Find frame of caller 1163 frame stub_fr = thread()->last_frame(); 1164 CodeBlob* stub_cb = stub_fr.cb(); 1165 assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub"); 1166 RegisterMap map(thread(), true); 1167 frame caller_fr = stub_fr.sender(&map); 1168 1169 // Should only be poll_return or poll 1170 assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" ); 1171 1172 // This is a poll immediately before a return. The exception handling code 1173 // has already had the effect of causing the return to occur, so the execution 1174 // will continue immediately after the call. In addition, the oopmap at the 1175 // return point does not mark the return value as an oop (if it is), so 1176 // it needs a handle here to be updated. 1177 if( nm->is_at_poll_return(real_return_addr) ) { 1178 // See if return type is an oop. 1179 bool return_oop = nm->method()->is_returning_oop(); 1180 Handle return_value; 1181 if (return_oop) { 1182 // The oop result has been saved on the stack together with all 1183 // the other registers. In order to preserve it over GCs we need 1184 // to keep it in a handle. 1185 oop result = caller_fr.saved_oop_result(&map); 1186 assert(oopDesc::is_oop_or_null(result), "must be oop"); 1187 return_value = Handle(thread(), result); 1188 assert(Universe::heap()->is_in_or_null(result), "must be heap pointer"); 1189 } 1190 1191 // Block the thread 1192 SafepointMechanism::block_if_requested(thread()); 1193 1194 // restore oop result, if any 1195 if (return_oop) { 1196 caller_fr.set_saved_oop_result(&map, return_value()); 1197 } 1198 } 1199 1200 // This is a safepoint poll. Verify the return address and block. 1201 else { 1202 set_at_poll_safepoint(true); 1203 1204 // verify the blob built the "return address" correctly 1205 assert(real_return_addr == caller_fr.pc(), "must match"); 1206 1207 // Block the thread 1208 SafepointMechanism::block_if_requested(thread()); 1209 set_at_poll_safepoint(false); 1210 1211 // If we have a pending async exception deoptimize the frame 1212 // as otherwise we may never deliver it. 1213 if (thread()->has_async_condition()) { 1214 ThreadInVMfromJavaNoAsyncException __tiv(thread()); 1215 Deoptimization::deoptimize_frame(thread(), caller_fr.id()); 1216 } 1217 1218 // If an exception has been installed we must check for a pending deoptimization 1219 // Deoptimize frame if exception has been thrown. 1220 1221 if (thread()->has_pending_exception() ) { 1222 RegisterMap map(thread(), true); 1223 frame caller_fr = stub_fr.sender(&map); 1224 if (caller_fr.is_deoptimized_frame()) { 1225 // The exception patch will destroy registers that are still 1226 // live and will be needed during deoptimization. Defer the 1227 // Async exception should have deferred the exception until the 1228 // next safepoint which will be detected when we get into 1229 // the interpreter so if we have an exception now things 1230 // are messed up. 1231 1232 fatal("Exception installed and deoptimization is pending"); 1233 } 1234 } 1235 } 1236 } 1237 1238 1239 // 1240 // Statistics & Instrumentations 1241 // 1242 struct SafepointStats { 1243 float _time_stamp; // record when the current safepoint occurs in seconds 1244 int _vmop_type; // tyep of VM operation triggers the safepoint 1245 int _nof_total_threads; // total number of Java threads 1246 int _nof_initial_running_threads; // total number of initially seen running threads 1247 int _nof_threads_wait_to_block; // total number of threads waiting for to block 1248 bool _page_armed; // true if polling page is armed, false otherwise 1249 int _nof_threads_hit_page_trap; // total number of threads hitting the page trap 1250 jlong _time_to_spin; // total time in millis spent in spinning 1251 jlong _time_to_wait_to_block; // total time in millis spent in waiting for to block 1252 jlong _time_to_do_cleanups; // total time in millis spent in performing cleanups 1253 jlong _time_to_sync; // total time in millis spent in getting to _synchronized 1254 jlong _time_to_exec_vmop; // total time in millis spent in vm operation itself 1255 }; 1256 1257 static const int _statistics_header_count = 30; 1258 static int _cur_stat_index = 0; 1259 static SafepointStats safepoint_stats = {0}; // zero initialize 1260 static SafepointStats* spstat = &safepoint_stats; 1261 1262 static julong _safepoint_reasons[VM_Operation::VMOp_Terminating]; 1263 static jlong _max_sync_time = 0; 1264 static jlong _max_vmop_time = 0; 1265 1266 static jlong cleanup_end_time = 0; 1267 1268 void SafepointSynchronize::begin_statistics(int nof_threads, int nof_running) { 1269 1270 spstat->_time_stamp = _ts_of_current_safepoint; 1271 1272 VM_Operation *op = VMThread::vm_operation(); 1273 spstat->_vmop_type = op != NULL ? op->type() : VM_Operation::VMOp_None; 1274 _safepoint_reasons[spstat->_vmop_type]++; 1275 1276 spstat->_nof_total_threads = nof_threads; 1277 spstat->_nof_initial_running_threads = nof_running; 1278 1279 // Records the start time of spinning. The real time spent on spinning 1280 // will be adjusted when spin is done. Same trick is applied for time 1281 // spent on waiting for threads to block. 1282 if (nof_running != 0) { 1283 spstat->_time_to_spin = os::javaTimeNanos(); 1284 } else { 1285 spstat->_time_to_spin = 0; 1286 } 1287 } 1288 1289 void SafepointSynchronize::update_statistics_on_spin_end() { 1290 jlong cur_time = os::javaTimeNanos(); 1291 1292 spstat->_nof_threads_wait_to_block = _waiting_to_block; 1293 if (spstat->_nof_initial_running_threads != 0) { 1294 spstat->_time_to_spin = cur_time - spstat->_time_to_spin; 1295 } 1296 1297 // Records the start time of waiting for to block. Updated when block is done. 1298 if (_waiting_to_block != 0) { 1299 spstat->_time_to_wait_to_block = cur_time; 1300 } else { 1301 spstat->_time_to_wait_to_block = 0; 1302 } 1303 } 1304 1305 void SafepointSynchronize::update_statistics_on_sync_end(jlong end_time) { 1306 1307 if (spstat->_nof_threads_wait_to_block != 0) { 1308 spstat->_time_to_wait_to_block = end_time - 1309 spstat->_time_to_wait_to_block; 1310 } 1311 1312 // Records the end time of sync which will be used to calculate the total 1313 // vm operation time. Again, the real time spending in syncing will be deducted 1314 // from the start of the sync time later when end_statistics is called. 1315 spstat->_time_to_sync = end_time - _safepoint_begin_time; 1316 if (spstat->_time_to_sync > _max_sync_time) { 1317 _max_sync_time = spstat->_time_to_sync; 1318 } 1319 1320 spstat->_time_to_do_cleanups = end_time; 1321 } 1322 1323 void SafepointSynchronize::update_statistics_on_cleanup_end(jlong end_time) { 1324 1325 // Record how long spent in cleanup tasks. 1326 spstat->_time_to_do_cleanups = end_time - spstat->_time_to_do_cleanups; 1327 cleanup_end_time = end_time; 1328 } 1329 1330 void SafepointSynchronize::end_statistics(jlong vmop_end_time) { 1331 1332 // Update the vm operation time. 1333 spstat->_time_to_exec_vmop = vmop_end_time - cleanup_end_time; 1334 if (spstat->_time_to_exec_vmop > _max_vmop_time) { 1335 _max_vmop_time = spstat->_time_to_exec_vmop; 1336 } 1337 1338 spstat->_nof_threads_hit_page_trap = _nof_threads_hit_polling_page; 1339 1340 print_statistics(); 1341 } 1342 1343 // Helper method to print the header. 1344 static void print_header(outputStream* st) { 1345 // The number of spaces is significant here, and should match the format 1346 // specifiers in print_statistics(). 1347 1348 st->print(" vmop " 1349 "[ threads: total initially_running wait_to_block ]" 1350 "[ time: spin block sync cleanup vmop ] "); 1351 1352 st->print_cr("page_trap_count"); 1353 } 1354 1355 // This prints a nice table. To get the statistics to not shift due to the logging uptime 1356 // decorator, use the option as: -Xlog:safepoint+stats=debug:[outputfile]:none 1357 void SafepointSynchronize::print_statistics() { 1358 LogTarget(Debug, safepoint, stats) lt; 1359 assert (lt.is_enabled(), "should only be called when printing statistics is enabled"); 1360 LogStream ls(lt); 1361 1362 // Print header every 30 entries 1363 if ((_cur_stat_index % _statistics_header_count) == 0) { 1364 print_header(&ls); 1365 _cur_stat_index = 1; // wrap 1366 } else { 1367 _cur_stat_index++; 1368 } 1369 1370 ls.print("%8.3f: ", spstat->_time_stamp); 1371 ls.print("%-28s [ " 1372 INT32_FORMAT_W(8) " " INT32_FORMAT_W(17) " " INT32_FORMAT_W(13) " " 1373 "]", 1374 VM_Operation::name(spstat->_vmop_type), 1375 spstat->_nof_total_threads, 1376 spstat->_nof_initial_running_threads, 1377 spstat->_nof_threads_wait_to_block); 1378 // "/ MICROUNITS " is to convert the unit from nanos to millis. 1379 ls.print("[ " 1380 INT64_FORMAT_W(7) " " INT64_FORMAT_W(7) " " 1381 INT64_FORMAT_W(7) " " INT64_FORMAT_W(7) " " 1382 INT64_FORMAT_W(7) " ] ", 1383 (int64_t)(spstat->_time_to_spin / MICROUNITS), 1384 (int64_t)(spstat->_time_to_wait_to_block / MICROUNITS), 1385 (int64_t)(spstat->_time_to_sync / MICROUNITS), 1386 (int64_t)(spstat->_time_to_do_cleanups / MICROUNITS), 1387 (int64_t)(spstat->_time_to_exec_vmop / MICROUNITS)); 1388 1389 ls.print_cr(INT32_FORMAT_W(15) " ", spstat->_nof_threads_hit_page_trap); 1390 } 1391 1392 // This method will be called when VM exits. This tries to summarize the sampling. 1393 // Current thread may already be deleted, so don't use ResourceMark. 1394 void SafepointSynchronize::print_stat_on_exit() { 1395 1396 for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) { 1397 if (_safepoint_reasons[index] != 0) { 1398 log_debug(safepoint, stats)("%-28s" UINT64_FORMAT_W(10), VM_Operation::name(index), 1399 _safepoint_reasons[index]); 1400 } 1401 } 1402 1403 log_debug(safepoint, stats)("VM operations coalesced during safepoint " INT64_FORMAT, 1404 _coalesced_vmop_count); 1405 log_debug(safepoint, stats)("Maximum sync time " INT64_FORMAT" ms", 1406 (int64_t)(_max_sync_time / MICROUNITS)); 1407 log_debug(safepoint, stats)("Maximum vm operation time (except for Exit VM operation) " 1408 INT64_FORMAT " ms", 1409 (int64_t)(_max_vmop_time / MICROUNITS)); 1410 }