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/classLoaderDataGraph.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 "oops/valueKlass.hpp" 48 #include "runtime/atomic.hpp" 49 #include "runtime/compilationPolicy.hpp" 50 #include "runtime/deoptimization.hpp" 51 #include "runtime/frame.inline.hpp" 52 #include "runtime/interfaceSupport.inline.hpp" 53 #include "runtime/mutexLocker.hpp" 54 #include "runtime/orderAccess.hpp" 55 #include "runtime/osThread.hpp" 56 #include "runtime/safepoint.hpp" 57 #include "runtime/safepointMechanism.inline.hpp" 58 #include "runtime/signature.hpp" 59 #include "runtime/stubCodeGenerator.hpp" 60 #include "runtime/stubRoutines.hpp" 61 #include "runtime/sweeper.hpp" 62 #include "runtime/synchronizer.hpp" 63 #include "runtime/thread.inline.hpp" 64 #include "runtime/threadSMR.hpp" 65 #include "runtime/timerTrace.hpp" 66 #include "services/runtimeService.hpp" 67 #include "utilities/events.hpp" 68 #include "utilities/macros.hpp" 69 #ifdef COMPILER1 70 #include "c1/c1_globals.hpp" 71 #endif 72 73 template <typename E> 74 static void set_current_safepoint_id(E* event, int adjustment = 0) { 75 assert(event != NULL, "invariant"); 76 event->set_safepointId(SafepointSynchronize::safepoint_counter() + adjustment); 77 } 78 79 static void post_safepoint_begin_event(EventSafepointBegin* event, 80 int thread_count, 81 int critical_thread_count) { 82 assert(event != NULL, "invariant"); 83 assert(event->should_commit(), "invariant"); 84 set_current_safepoint_id(event); 85 event->set_totalThreadCount(thread_count); 86 event->set_jniCriticalThreadCount(critical_thread_count); 87 event->commit(); 88 } 89 90 static void post_safepoint_cleanup_event(EventSafepointCleanup* event) { 91 assert(event != NULL, "invariant"); 92 assert(event->should_commit(), "invariant"); 93 set_current_safepoint_id(event); 94 event->commit(); 95 } 96 97 static void post_safepoint_synchronize_event(EventSafepointStateSynchronization* event, 98 int initial_number_of_threads, 99 int threads_waiting_to_block, 100 unsigned int iterations) { 101 assert(event != NULL, "invariant"); 102 if (event->should_commit()) { 103 // Group this event together with the ones committed after the counter is increased 104 set_current_safepoint_id(event, 1); 105 event->set_initialThreadCount(initial_number_of_threads); 106 event->set_runningThreadCount(threads_waiting_to_block); 107 event->set_iterations(iterations); 108 event->commit(); 109 } 110 } 111 112 static void post_safepoint_wait_blocked_event(EventSafepointWaitBlocked* event, 113 int initial_threads_waiting_to_block) { 114 assert(event != NULL, "invariant"); 115 assert(event->should_commit(), "invariant"); 116 set_current_safepoint_id(event); 117 event->set_runningThreadCount(initial_threads_waiting_to_block); 118 event->commit(); 119 } 120 121 static void post_safepoint_cleanup_task_event(EventSafepointCleanupTask* event, 122 const char* name) { 123 assert(event != NULL, "invariant"); 124 if (event->should_commit()) { 125 set_current_safepoint_id(event); 126 event->set_name(name); 127 event->commit(); 128 } 129 } 130 131 static void post_safepoint_end_event(EventSafepointEnd* event) { 132 assert(event != NULL, "invariant"); 133 if (event->should_commit()) { 134 // Group this event together with the ones committed before the counter increased 135 set_current_safepoint_id(event, -1); 136 event->commit(); 137 } 138 } 139 140 // -------------------------------------------------------------------------------------------------- 141 // Implementation of Safepoint begin/end 142 143 SafepointSynchronize::SynchronizeState volatile SafepointSynchronize::_state = SafepointSynchronize::_not_synchronized; 144 volatile int SafepointSynchronize::_waiting_to_block = 0; 145 volatile uint64_t SafepointSynchronize::_safepoint_counter = 0; 146 int SafepointSynchronize::_current_jni_active_count = 0; 147 long SafepointSynchronize::_end_of_last_safepoint = 0; 148 int SafepointSynchronize::_defer_thr_suspend_loop_count = 4000; 149 static const int safepoint_spin_before_yield = 2000; 150 static volatile int PageArmed = 0 ; // safepoint polling page is RO|RW vs PROT_NONE 151 static volatile int TryingToBlock = 0 ; // proximate value -- for advisory use only 152 static bool timeout_error_printed = false; 153 154 155 // Statistic related statics 156 julong SafepointSynchronize::_coalesced_vmop_count = 0; 157 static jlong _safepoint_begin_time = 0; 158 static float _ts_of_current_safepoint = 0.0f; 159 static volatile int _nof_threads_hit_polling_page = 0; 160 161 // Roll all threads forward to a safepoint and suspend them all 162 void SafepointSynchronize::begin() { 163 EventSafepointBegin begin_event; 164 Thread* myThread = Thread::current(); 165 assert(myThread->is_VM_thread(), "Only VM thread may execute a safepoint"); 166 167 if (log_is_enabled(Debug, safepoint, stats)) { 168 _safepoint_begin_time = os::javaTimeNanos(); 169 _ts_of_current_safepoint = tty->time_stamp().seconds(); 170 _nof_threads_hit_polling_page = 0; 171 } 172 173 Universe::heap()->safepoint_synchronize_begin(); 174 175 // By getting the Threads_lock, we assure that no threads are about to start or 176 // exit. It is released again in SafepointSynchronize::end(). 177 Threads_lock->lock(); 178 179 assert( _state == _not_synchronized, "trying to safepoint synchronize with wrong state"); 180 181 int nof_threads = Threads::number_of_threads(); 182 183 log_debug(safepoint)("Safepoint synchronization initiated. (%d threads)", nof_threads); 184 185 RuntimeService::record_safepoint_begin(); 186 187 MutexLocker mu(Safepoint_lock); 188 189 // Reset the count of active JNI critical threads 190 _current_jni_active_count = 0; 191 192 // Set number of threads to wait for, before we initiate the callbacks 193 _waiting_to_block = nof_threads; 194 TryingToBlock = 0 ; 195 int still_running = nof_threads; 196 197 // Save the starting time, so that it can be compared to see if this has taken 198 // too long to complete. 199 jlong safepoint_limit_time = 0; 200 timeout_error_printed = false; 201 202 // Begin the process of bringing the system to a safepoint. 203 // Java threads can be in several different states and are 204 // stopped by different mechanisms: 205 // 206 // 1. Running interpreted 207 // The interpreter dispatch table is changed to force it to 208 // check for a safepoint condition between bytecodes. 209 // 2. Running in native code 210 // When returning from the native code, a Java thread must check 211 // the safepoint _state to see if we must block. If the 212 // VM thread sees a Java thread in native, it does 213 // not wait for this thread to block. The order of the memory 214 // writes and reads of both the safepoint state and the Java 215 // threads state is critical. In order to guarantee that the 216 // memory writes are serialized with respect to each other, 217 // the VM thread issues a memory barrier instruction. 218 // 3. Running compiled Code 219 // Compiled code reads a global (Safepoint Polling) page that 220 // is set to fault if we are trying to get to a safepoint. 221 // 4. Blocked 222 // A thread which is blocked will not be allowed to return from the 223 // block condition until the safepoint operation is complete. 224 // 5. In VM or Transitioning between states 225 // If a Java thread is currently running in the VM or transitioning 226 // between states, the safepointing code will wait for the thread to 227 // block itself when it attempts transitions to a new state. 228 // 229 { 230 EventSafepointStateSynchronization sync_event; 231 int initial_running = 0; 232 233 _state = _synchronizing; 234 235 if (SafepointMechanism::uses_thread_local_poll()) { 236 // Arming the per thread poll while having _state != _not_synchronized means safepointing 237 log_trace(safepoint)("Setting thread local yield flag for threads"); 238 OrderAccess::storestore(); // storestore, global state -> local state 239 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) { 240 // Make sure the threads start polling, it is time to yield. 241 SafepointMechanism::arm_local_poll(cur); 242 } 243 } 244 OrderAccess::fence(); // storestore|storeload, global state -> local state 245 246 if (SafepointMechanism::uses_global_page_poll()) { 247 // Make interpreter safepoint aware 248 Interpreter::notice_safepoints(); 249 250 // Make polling safepoint aware 251 guarantee (PageArmed == 0, "invariant") ; 252 PageArmed = 1 ; 253 os::make_polling_page_unreadable(); 254 } 255 256 // Consider using active_processor_count() ... but that call is expensive. 257 int ncpus = os::processor_count() ; 258 unsigned int iterations = 0; 259 260 { 261 JavaThreadIteratorWithHandle jtiwh; 262 #ifdef ASSERT 263 for (; JavaThread *cur = jtiwh.next(); ) { 264 assert(cur->safepoint_state()->is_running(), "Illegal initial state"); 265 // Clear the visited flag to ensure that the critical counts are collected properly. 266 cur->set_visited_for_critical_count(false); 267 } 268 #endif // ASSERT 269 270 if (SafepointTimeout) 271 safepoint_limit_time = os::javaTimeNanos() + (jlong)SafepointTimeoutDelay * MICROUNITS; 272 273 // Iterate through all threads until it have been determined how to stop them all at a safepoint 274 int steps = 0 ; 275 while(still_running > 0) { 276 jtiwh.rewind(); 277 for (; JavaThread *cur = jtiwh.next(); ) { 278 assert(!cur->is_ConcurrentGC_thread(), "A concurrent GC thread is unexpectly being suspended"); 279 ThreadSafepointState *cur_state = cur->safepoint_state(); 280 if (cur_state->is_running()) { 281 cur_state->examine_state_of_thread(); 282 if (!cur_state->is_running()) { 283 still_running--; 284 // consider adjusting steps downward: 285 // steps = 0 286 // steps -= NNN 287 // steps >>= 1 288 // steps = MIN(steps, 2000-100) 289 // if (iterations != 0) steps -= NNN 290 } 291 LogTarget(Trace, safepoint) lt; 292 if (lt.is_enabled()) { 293 ResourceMark rm; 294 LogStream ls(lt); 295 cur_state->print_on(&ls); 296 } 297 } 298 } 299 300 if (iterations == 0) { 301 initial_running = still_running; 302 if (log_is_enabled(Debug, safepoint, stats)) { 303 begin_statistics(nof_threads, still_running); 304 } 305 } 306 307 if (still_running > 0) { 308 // Check for if it takes to long 309 if (SafepointTimeout && safepoint_limit_time < os::javaTimeNanos()) { 310 print_safepoint_timeout(_spinning_timeout); 311 } 312 313 // Spin to avoid context switching. 314 // There's a tension between allowing the mutators to run (and rendezvous) 315 // vs spinning. As the VM thread spins, wasting cycles, it consumes CPU that 316 // a mutator might otherwise use profitably to reach a safepoint. Excessive 317 // spinning by the VM thread on a saturated system can increase rendezvous latency. 318 // Blocking or yielding incur their own penalties in the form of context switching 319 // and the resultant loss of $ residency. 320 // 321 // Further complicating matters is that yield() does not work as naively expected 322 // on many platforms -- yield() does not guarantee that any other ready threads 323 // will run. As such we revert to naked_short_sleep() after some number of iterations. 324 // nakes_short_sleep() is implemented as a short unconditional sleep. 325 // Typical operating systems round a "short" sleep period up to 10 msecs, so sleeping 326 // can actually increase the time it takes the VM thread to detect that a system-wide 327 // stop-the-world safepoint has been reached. In a pathological scenario such as that 328 // described in CR6415670 the VMthread may sleep just before the mutator(s) become safe. 329 // In that case the mutators will be stalled waiting for the safepoint to complete and the 330 // the VMthread will be sleeping, waiting for the mutators to rendezvous. The VMthread 331 // will eventually wake up and detect that all mutators are safe, at which point 332 // we'll again make progress. 333 // 334 // Beware too that that the VMThread typically runs at elevated priority. 335 // Its default priority is higher than the default mutator priority. 336 // Obviously, this complicates spinning. 337 // 338 // Note too that on Windows XP SwitchThreadTo() has quite different behavior than Sleep(0). 339 // Sleep(0) will _not yield to lower priority threads, while SwitchThreadTo() will. 340 // 341 // See the comments in synchronizer.cpp for additional remarks on spinning. 342 // 343 // In the future we might: 344 // -- Modify the safepoint scheme to avoid potentially unbounded spinning. 345 // This is tricky as the path used by a thread exiting the JVM (say on 346 // on JNI call-out) simply stores into its state field. The burden 347 // is placed on the VM thread, which must poll (spin). 348 // -- Find something useful to do while spinning. If the safepoint is GC-related 349 // we might aggressively scan the stacks of threads that are already safe. 350 // -- YieldTo() any still-running mutators that are ready but OFFPROC. 351 // -- Check system saturation. If the system is not fully saturated then 352 // simply spin and avoid sleep/yield. 353 // -- As still-running mutators rendezvous they could unpark the sleeping 354 // VMthread. This works well for still-running mutators that become 355 // safe. The VMthread must still poll for mutators that call-out. 356 // -- Drive the policy on time-since-begin instead of iterations. 357 // -- Consider making the spin duration a function of the # of CPUs: 358 // Spin = (((ncpus-1) * M) + K) + F(still_running) 359 // Alternately, instead of counting iterations of the outer loop 360 // we could count the # of threads visited in the inner loop, above. 361 // -- On windows consider using the return value from SwitchThreadTo() 362 // to drive subsequent spin/SwitchThreadTo()/Sleep(N) decisions. 363 364 if (int(iterations) == -1) { // overflow - something is wrong. 365 // We can only overflow here when we are using global 366 // polling pages. We keep this guarantee in its original 367 // form so that searches of the bug database for this 368 // failure mode find the right bugs. 369 guarantee (PageArmed == 0, "invariant"); 370 } 371 372 // Instead of (ncpus > 1) consider either (still_running < (ncpus + EPSILON)) or 373 // ((still_running + _waiting_to_block - TryingToBlock)) < ncpus) 374 ++steps ; 375 if (ncpus > 1 && steps < safepoint_spin_before_yield) { 376 SpinPause() ; // MP-Polite spin 377 } else 378 if (steps < _defer_thr_suspend_loop_count) { 379 os::naked_yield() ; 380 } else { 381 os::naked_short_sleep(1); 382 } 383 384 iterations ++ ; 385 } 386 assert(iterations < (uint)max_jint, "We have been iterating in the safepoint loop too long"); 387 } 388 } // ThreadsListHandle destroyed here. 389 assert(still_running == 0, "sanity check"); 390 391 if (log_is_enabled(Debug, safepoint, stats)) { 392 update_statistics_on_spin_end(); 393 } 394 if (sync_event.should_commit()) { 395 post_safepoint_synchronize_event(&sync_event, initial_running, _waiting_to_block, iterations); 396 } 397 } 398 399 // wait until all threads are stopped 400 { 401 EventSafepointWaitBlocked wait_blocked_event; 402 int initial_waiting_to_block = _waiting_to_block; 403 404 while (_waiting_to_block > 0) { 405 log_debug(safepoint)("Waiting for %d thread(s) to block", _waiting_to_block); 406 if (!SafepointTimeout || timeout_error_printed) { 407 Safepoint_lock->wait(true); // true, means with no safepoint checks 408 } else { 409 // Compute remaining time 410 jlong remaining_time = safepoint_limit_time - os::javaTimeNanos(); 411 412 // If there is no remaining time, then there is an error 413 if (remaining_time < 0 || Safepoint_lock->wait(true, remaining_time / MICROUNITS)) { 414 print_safepoint_timeout(_blocking_timeout); 415 } 416 } 417 } 418 assert(_waiting_to_block == 0, "sanity check"); 419 420 #ifndef PRODUCT 421 if (SafepointTimeout) { 422 jlong current_time = os::javaTimeNanos(); 423 if (safepoint_limit_time < current_time) { 424 log_warning(safepoint)("# SafepointSynchronize: Finished after " 425 INT64_FORMAT_W(6) " ms", 426 (int64_t)((current_time - safepoint_limit_time) / MICROUNITS + 427 (jlong)SafepointTimeoutDelay)); 428 } 429 } 430 #endif 431 432 assert((_safepoint_counter & 0x1) == 0, "must be even"); 433 assert(Threads_lock->owned_by_self(), "must hold Threads_lock"); 434 _safepoint_counter ++; 435 436 // Record state 437 _state = _synchronized; 438 439 OrderAccess::fence(); 440 if (wait_blocked_event.should_commit()) { 441 post_safepoint_wait_blocked_event(&wait_blocked_event, initial_waiting_to_block); 442 } 443 } 444 445 #ifdef ASSERT 446 // Make sure all the threads were visited. 447 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) { 448 assert(cur->was_visited_for_critical_count(), "missed a thread"); 449 } 450 #endif // ASSERT 451 452 // Update the count of active JNI critical regions 453 GCLocker::set_jni_lock_count(_current_jni_active_count); 454 455 log_info(safepoint)("Entering safepoint region: %s", VMThread::vm_safepoint_description()); 456 457 RuntimeService::record_safepoint_synchronized(); 458 if (log_is_enabled(Debug, safepoint, stats)) { 459 update_statistics_on_sync_end(os::javaTimeNanos()); 460 } 461 462 // Call stuff that needs to be run when a safepoint is just about to be completed 463 { 464 EventSafepointCleanup cleanup_event; 465 do_cleanup_tasks(); 466 if (cleanup_event.should_commit()) { 467 post_safepoint_cleanup_event(&cleanup_event); 468 } 469 } 470 471 if (log_is_enabled(Debug, safepoint, stats)) { 472 // Record how much time spend on the above cleanup tasks 473 update_statistics_on_cleanup_end(os::javaTimeNanos()); 474 } 475 476 if (begin_event.should_commit()) { 477 post_safepoint_begin_event(&begin_event, nof_threads, _current_jni_active_count); 478 } 479 } 480 481 // Wake up all threads, so they are ready to resume execution after the safepoint 482 // operation has been carried out 483 void SafepointSynchronize::end() { 484 assert(Threads_lock->owned_by_self(), "must hold Threads_lock"); 485 assert((_safepoint_counter & 0x1) == 1, "must be odd"); 486 EventSafepointEnd event; 487 _safepoint_counter ++; 488 // memory fence isn't required here since an odd _safepoint_counter 489 // value can do no harm and a fence is issued below anyway. 490 491 DEBUG_ONLY(Thread* myThread = Thread::current();) 492 assert(myThread->is_VM_thread(), "Only VM thread can execute a safepoint"); 493 494 if (log_is_enabled(Debug, safepoint, stats)) { 495 end_statistics(os::javaTimeNanos()); 496 } 497 498 { 499 JavaThreadIteratorWithHandle jtiwh; 500 #ifdef ASSERT 501 // A pending_exception cannot be installed during a safepoint. The threads 502 // may install an async exception after they come back from a safepoint into 503 // pending_exception after they unblock. But that should happen later. 504 for (; JavaThread *cur = jtiwh.next(); ) { 505 assert (!(cur->has_pending_exception() && 506 cur->safepoint_state()->is_at_poll_safepoint()), 507 "safepoint installed a pending exception"); 508 } 509 #endif // ASSERT 510 511 if (PageArmed) { 512 assert(SafepointMechanism::uses_global_page_poll(), "sanity"); 513 // Make polling safepoint aware 514 os::make_polling_page_readable(); 515 PageArmed = 0 ; 516 } 517 518 if (SafepointMechanism::uses_global_page_poll()) { 519 // Remove safepoint check from interpreter 520 Interpreter::ignore_safepoints(); 521 } 522 523 { 524 MutexLocker mu(Safepoint_lock); 525 526 assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization"); 527 528 if (SafepointMechanism::uses_thread_local_poll()) { 529 _state = _not_synchronized; 530 OrderAccess::storestore(); // global state -> local state 531 jtiwh.rewind(); 532 for (; JavaThread *current = jtiwh.next(); ) { 533 ThreadSafepointState* cur_state = current->safepoint_state(); 534 cur_state->restart(); // TSS _running 535 SafepointMechanism::disarm_local_poll(current); 536 } 537 log_info(safepoint)("Leaving safepoint region"); 538 } else { 539 // Set to not synchronized, so the threads will not go into the signal_thread_blocked method 540 // when they get restarted. 541 _state = _not_synchronized; 542 OrderAccess::fence(); 543 544 log_info(safepoint)("Leaving safepoint region"); 545 546 // Start suspended threads 547 jtiwh.rewind(); 548 for (; JavaThread *current = jtiwh.next(); ) { 549 ThreadSafepointState* cur_state = current->safepoint_state(); 550 assert(cur_state->type() != ThreadSafepointState::_running, "Thread not suspended at safepoint"); 551 cur_state->restart(); 552 assert(cur_state->is_running(), "safepoint state has not been reset"); 553 } 554 } 555 556 RuntimeService::record_safepoint_end(); 557 558 // Release threads lock, so threads can be created/destroyed again. 559 // It will also release all threads blocked in signal_thread_blocked. 560 Threads_lock->unlock(); 561 } 562 } // ThreadsListHandle destroyed here. 563 564 Universe::heap()->safepoint_synchronize_end(); 565 // record this time so VMThread can keep track how much time has elapsed 566 // since last safepoint. 567 _end_of_last_safepoint = os::javaTimeMillis(); 568 if (event.should_commit()) { 569 post_safepoint_end_event(&event); 570 } 571 } 572 573 bool SafepointSynchronize::is_cleanup_needed() { 574 // Need a safepoint if there are many monitors to deflate. 575 if (ObjectSynchronizer::is_cleanup_needed()) return true; 576 // Need a safepoint if some inline cache buffers is non-empty 577 if (!InlineCacheBuffer::is_empty()) return true; 578 return false; 579 } 580 581 class ParallelSPCleanupThreadClosure : public ThreadClosure { 582 private: 583 CodeBlobClosure* _nmethod_cl; 584 DeflateMonitorCounters* _counters; 585 586 public: 587 ParallelSPCleanupThreadClosure(DeflateMonitorCounters* counters) : 588 _nmethod_cl(UseCodeAging ? NMethodSweeper::prepare_reset_hotness_counters() : NULL), 589 _counters(counters) {} 590 591 void do_thread(Thread* thread) { 592 ObjectSynchronizer::deflate_thread_local_monitors(thread, _counters); 593 if (_nmethod_cl != NULL && thread->is_Java_thread() && 594 ! thread->is_Code_cache_sweeper_thread()) { 595 JavaThread* jt = (JavaThread*) thread; 596 jt->nmethods_do(_nmethod_cl); 597 } 598 } 599 }; 600 601 class ParallelSPCleanupTask : public AbstractGangTask { 602 private: 603 SubTasksDone _subtasks; 604 ParallelSPCleanupThreadClosure _cleanup_threads_cl; 605 uint _num_workers; 606 DeflateMonitorCounters* _counters; 607 public: 608 ParallelSPCleanupTask(uint num_workers, DeflateMonitorCounters* counters) : 609 AbstractGangTask("Parallel Safepoint Cleanup"), 610 _subtasks(SubTasksDone(SafepointSynchronize::SAFEPOINT_CLEANUP_NUM_TASKS)), 611 _cleanup_threads_cl(ParallelSPCleanupThreadClosure(counters)), 612 _num_workers(num_workers), 613 _counters(counters) {} 614 615 void work(uint worker_id) { 616 // All threads deflate monitors and mark nmethods (if necessary). 617 Threads::possibly_parallel_threads_do(true, &_cleanup_threads_cl); 618 619 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_DEFLATE_MONITORS)) { 620 const char* name = "deflating global idle monitors"; 621 EventSafepointCleanupTask event; 622 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 623 ObjectSynchronizer::deflate_idle_monitors(_counters); 624 if (event.should_commit()) { 625 post_safepoint_cleanup_task_event(&event, name); 626 } 627 } 628 629 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_UPDATE_INLINE_CACHES)) { 630 const char* name = "updating inline caches"; 631 EventSafepointCleanupTask event; 632 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 633 InlineCacheBuffer::update_inline_caches(); 634 if (event.should_commit()) { 635 post_safepoint_cleanup_task_event(&event, name); 636 } 637 } 638 639 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_COMPILATION_POLICY)) { 640 const char* name = "compilation policy safepoint handler"; 641 EventSafepointCleanupTask event; 642 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 643 CompilationPolicy::policy()->do_safepoint_work(); 644 if (event.should_commit()) { 645 post_safepoint_cleanup_task_event(&event, name); 646 } 647 } 648 649 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_SYMBOL_TABLE_REHASH)) { 650 if (SymbolTable::needs_rehashing()) { 651 const char* name = "rehashing symbol table"; 652 EventSafepointCleanupTask event; 653 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 654 SymbolTable::rehash_table(); 655 if (event.should_commit()) { 656 post_safepoint_cleanup_task_event(&event, name); 657 } 658 } 659 } 660 661 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_STRING_TABLE_REHASH)) { 662 if (StringTable::needs_rehashing()) { 663 const char* name = "rehashing string table"; 664 EventSafepointCleanupTask event; 665 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 666 StringTable::rehash_table(); 667 if (event.should_commit()) { 668 post_safepoint_cleanup_task_event(&event, name); 669 } 670 } 671 } 672 673 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_CLD_PURGE)) { 674 // CMS delays purging the CLDG until the beginning of the next safepoint and to 675 // make sure concurrent sweep is done 676 const char* name = "purging class loader data graph"; 677 EventSafepointCleanupTask event; 678 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 679 ClassLoaderDataGraph::purge_if_needed(); 680 if (event.should_commit()) { 681 post_safepoint_cleanup_task_event(&event, name); 682 } 683 } 684 685 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_SYSTEM_DICTIONARY_RESIZE)) { 686 const char* name = "resizing system dictionaries"; 687 EventSafepointCleanupTask event; 688 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 689 ClassLoaderDataGraph::resize_if_needed(); 690 if (event.should_commit()) { 691 post_safepoint_cleanup_task_event(&event, name); 692 } 693 } 694 695 _subtasks.all_tasks_completed(_num_workers); 696 } 697 }; 698 699 // Various cleaning tasks that should be done periodically at safepoints. 700 void SafepointSynchronize::do_cleanup_tasks() { 701 702 TraceTime timer("safepoint cleanup tasks", TRACETIME_LOG(Info, safepoint, cleanup)); 703 704 // Prepare for monitor deflation. 705 DeflateMonitorCounters deflate_counters; 706 ObjectSynchronizer::prepare_deflate_idle_monitors(&deflate_counters); 707 708 CollectedHeap* heap = Universe::heap(); 709 assert(heap != NULL, "heap not initialized yet?"); 710 WorkGang* cleanup_workers = heap->get_safepoint_workers(); 711 if (cleanup_workers != NULL) { 712 // Parallel cleanup using GC provided thread pool. 713 uint num_cleanup_workers = cleanup_workers->active_workers(); 714 ParallelSPCleanupTask cleanup(num_cleanup_workers, &deflate_counters); 715 StrongRootsScope srs(num_cleanup_workers); 716 cleanup_workers->run_task(&cleanup); 717 } else { 718 // Serial cleanup using VMThread. 719 ParallelSPCleanupTask cleanup(1, &deflate_counters); 720 StrongRootsScope srs(1); 721 cleanup.work(0); 722 } 723 724 // Needs to be done single threaded by the VMThread. This walks 725 // the thread stacks looking for references to metadata before 726 // deciding to remove it from the metaspaces. 727 if (ClassLoaderDataGraph::should_clean_metaspaces_and_reset()) { 728 const char* name = "cleanup live ClassLoaderData metaspaces"; 729 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup)); 730 ClassLoaderDataGraph::walk_metadata_and_clean_metaspaces(); 731 } 732 733 // Finish monitor deflation. 734 ObjectSynchronizer::finish_deflate_idle_monitors(&deflate_counters); 735 736 } 737 738 739 bool SafepointSynchronize::safepoint_safe(JavaThread *thread, JavaThreadState state) { 740 switch(state) { 741 case _thread_in_native: 742 // native threads are safe if they have no java stack or have walkable stack 743 return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable(); 744 745 // blocked threads should have already have walkable stack 746 case _thread_blocked: 747 assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable"); 748 return true; 749 750 default: 751 return false; 752 } 753 } 754 755 756 // See if the thread is running inside a lazy critical native and 757 // update the thread critical count if so. Also set a suspend flag to 758 // cause the native wrapper to return into the JVM to do the unlock 759 // once the native finishes. 760 void SafepointSynchronize::check_for_lazy_critical_native(JavaThread *thread, JavaThreadState state) { 761 if (state == _thread_in_native && 762 thread->has_last_Java_frame() && 763 thread->frame_anchor()->walkable()) { 764 // This thread might be in a critical native nmethod so look at 765 // the top of the stack and increment the critical count if it 766 // is. 767 frame wrapper_frame = thread->last_frame(); 768 CodeBlob* stub_cb = wrapper_frame.cb(); 769 if (stub_cb != NULL && 770 stub_cb->is_nmethod() && 771 stub_cb->as_nmethod_or_null()->is_lazy_critical_native()) { 772 // A thread could potentially be in a critical native across 773 // more than one safepoint, so only update the critical state on 774 // the first one. When it returns it will perform the unlock. 775 if (!thread->do_critical_native_unlock()) { 776 #ifdef ASSERT 777 if (!thread->in_critical()) { 778 GCLocker::increment_debug_jni_lock_count(); 779 } 780 #endif 781 thread->enter_critical(); 782 // Make sure the native wrapper calls back on return to 783 // perform the needed critical unlock. 784 thread->set_critical_native_unlock(); 785 } 786 } 787 } 788 } 789 790 791 792 // ------------------------------------------------------------------------------------------------------- 793 // Implementation of Safepoint callback point 794 795 void SafepointSynchronize::block(JavaThread *thread) { 796 assert(thread != NULL, "thread must be set"); 797 assert(thread->is_Java_thread(), "not a Java thread"); 798 799 // Threads shouldn't block if they are in the middle of printing, but... 800 ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id()); 801 802 // Only bail from the block() call if the thread is gone from the 803 // thread list; starting to exit should still block. 804 if (thread->is_terminated()) { 805 // block current thread if we come here from native code when VM is gone 806 thread->block_if_vm_exited(); 807 808 // otherwise do nothing 809 return; 810 } 811 812 JavaThreadState state = thread->thread_state(); 813 thread->frame_anchor()->make_walkable(thread); 814 815 // Check that we have a valid thread_state at this point 816 switch(state) { 817 case _thread_in_vm_trans: 818 case _thread_in_Java: // From compiled code 819 820 // We are highly likely to block on the Safepoint_lock. In order to avoid blocking in this case, 821 // we pretend we are still in the VM. 822 thread->set_thread_state(_thread_in_vm); 823 824 if (is_synchronizing()) { 825 Atomic::inc (&TryingToBlock) ; 826 } 827 828 // We will always be holding the Safepoint_lock when we are examine the state 829 // of a thread. Hence, the instructions between the Safepoint_lock->lock() and 830 // Safepoint_lock->unlock() are happening atomic with regards to the safepoint code 831 Safepoint_lock->lock_without_safepoint_check(); 832 if (is_synchronizing()) { 833 // Decrement the number of threads to wait for and signal vm thread 834 assert(_waiting_to_block > 0, "sanity check"); 835 _waiting_to_block--; 836 thread->safepoint_state()->set_has_called_back(true); 837 838 DEBUG_ONLY(thread->set_visited_for_critical_count(true)); 839 if (thread->in_critical()) { 840 // Notice that this thread is in a critical section 841 increment_jni_active_count(); 842 } 843 844 // Consider (_waiting_to_block < 2) to pipeline the wakeup of the VM thread 845 if (_waiting_to_block == 0) { 846 Safepoint_lock->notify_all(); 847 } 848 } 849 850 // We transition the thread to state _thread_blocked here, but 851 // we can't do our usual check for external suspension and then 852 // self-suspend after the lock_without_safepoint_check() call 853 // below because we are often called during transitions while 854 // we hold different locks. That would leave us suspended while 855 // holding a resource which results in deadlocks. 856 thread->set_thread_state(_thread_blocked); 857 Safepoint_lock->unlock(); 858 859 // We now try to acquire the threads lock. Since this lock is hold by the VM thread during 860 // the entire safepoint, the threads will all line up here during the safepoint. 861 Threads_lock->lock_without_safepoint_check(); 862 // restore original state. This is important if the thread comes from compiled code, so it 863 // will continue to execute with the _thread_in_Java state. 864 thread->set_thread_state(state); 865 Threads_lock->unlock(); 866 break; 867 868 case _thread_in_native_trans: 869 case _thread_blocked_trans: 870 case _thread_new_trans: 871 if (thread->safepoint_state()->type() == ThreadSafepointState::_call_back) { 872 thread->print_thread_state(); 873 fatal("Deadlock in safepoint code. " 874 "Should have called back to the VM before blocking."); 875 } 876 877 // We transition the thread to state _thread_blocked here, but 878 // we can't do our usual check for external suspension and then 879 // self-suspend after the lock_without_safepoint_check() call 880 // below because we are often called during transitions while 881 // we hold different locks. That would leave us suspended while 882 // holding a resource which results in deadlocks. 883 thread->set_thread_state(_thread_blocked); 884 885 // It is not safe to suspend a thread if we discover it is in _thread_in_native_trans. Hence, 886 // the safepoint code might still be waiting for it to block. We need to change the state here, 887 // so it can see that it is at a safepoint. 888 889 // Block until the safepoint operation is completed. 890 Threads_lock->lock_without_safepoint_check(); 891 892 // Restore state 893 thread->set_thread_state(state); 894 895 Threads_lock->unlock(); 896 break; 897 898 default: 899 fatal("Illegal threadstate encountered: %d", state); 900 } 901 902 // Check for pending. async. exceptions or suspends - except if the 903 // thread was blocked inside the VM. has_special_runtime_exit_condition() 904 // is called last since it grabs a lock and we only want to do that when 905 // we must. 906 // 907 // Note: we never deliver an async exception at a polling point as the 908 // compiler may not have an exception handler for it. The polling 909 // code will notice the async and deoptimize and the exception will 910 // be delivered. (Polling at a return point is ok though). Sure is 911 // a lot of bother for a deprecated feature... 912 // 913 // We don't deliver an async exception if the thread state is 914 // _thread_in_native_trans so JNI functions won't be called with 915 // a surprising pending exception. If the thread state is going back to java, 916 // async exception is checked in check_special_condition_for_native_trans(). 917 918 if (state != _thread_blocked_trans && 919 state != _thread_in_vm_trans && 920 thread->has_special_runtime_exit_condition()) { 921 thread->handle_special_runtime_exit_condition( 922 !thread->is_at_poll_safepoint() && (state != _thread_in_native_trans)); 923 } 924 } 925 926 // ------------------------------------------------------------------------------------------------------ 927 // Exception handlers 928 929 930 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) { 931 assert(thread->is_Java_thread(), "polling reference encountered by VM thread"); 932 assert(thread->thread_state() == _thread_in_Java, "should come from Java code"); 933 if (!ThreadLocalHandshakes) { 934 assert(SafepointSynchronize::is_synchronizing(), "polling encountered outside safepoint synchronization"); 935 } 936 937 if (log_is_enabled(Debug, safepoint, stats)) { 938 Atomic::inc(&_nof_threads_hit_polling_page); 939 } 940 941 ThreadSafepointState* state = thread->safepoint_state(); 942 943 state->handle_polling_page_exception(); 944 } 945 946 947 void SafepointSynchronize::print_safepoint_timeout(SafepointTimeoutReason reason) { 948 if (!timeout_error_printed) { 949 timeout_error_printed = true; 950 // Print out the thread info which didn't reach the safepoint for debugging 951 // purposes (useful when there are lots of threads in the debugger). 952 LogTarget(Warning, safepoint) lt; 953 if (lt.is_enabled()) { 954 ResourceMark rm; 955 LogStream ls(lt); 956 957 ls.cr(); 958 ls.print_cr("# SafepointSynchronize::begin: Timeout detected:"); 959 if (reason == _spinning_timeout) { 960 ls.print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint."); 961 } else if (reason == _blocking_timeout) { 962 ls.print_cr("# SafepointSynchronize::begin: Timed out while waiting for threads to stop."); 963 } 964 965 ls.print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:"); 966 ThreadSafepointState *cur_state; 967 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) { 968 cur_state = cur_thread->safepoint_state(); 969 970 if (cur_thread->thread_state() != _thread_blocked && 971 ((reason == _spinning_timeout && cur_state->is_running()) || 972 (reason == _blocking_timeout && !cur_state->has_called_back()))) { 973 ls.print("# "); 974 cur_thread->print_on(&ls); 975 ls.cr(); 976 } 977 } 978 ls.print_cr("# SafepointSynchronize::begin: (End of list)"); 979 } 980 } 981 982 // To debug the long safepoint, specify both AbortVMOnSafepointTimeout & 983 // ShowMessageBoxOnError. 984 if (AbortVMOnSafepointTimeout) { 985 fatal("Safepoint sync time longer than " INTX_FORMAT "ms detected when executing %s.", 986 SafepointTimeoutDelay, VMThread::vm_safepoint_description()); 987 } 988 } 989 990 991 // ------------------------------------------------------------------------------------------------------- 992 // Implementation of ThreadSafepointState 993 994 ThreadSafepointState::ThreadSafepointState(JavaThread *thread) { 995 _thread = thread; 996 _type = _running; 997 _has_called_back = false; 998 _at_poll_safepoint = false; 999 } 1000 1001 void ThreadSafepointState::create(JavaThread *thread) { 1002 ThreadSafepointState *state = new ThreadSafepointState(thread); 1003 thread->set_safepoint_state(state); 1004 } 1005 1006 void ThreadSafepointState::destroy(JavaThread *thread) { 1007 if (thread->safepoint_state()) { 1008 delete(thread->safepoint_state()); 1009 thread->set_safepoint_state(NULL); 1010 } 1011 } 1012 1013 void ThreadSafepointState::examine_state_of_thread() { 1014 assert(is_running(), "better be running or just have hit safepoint poll"); 1015 1016 JavaThreadState state = _thread->thread_state(); 1017 1018 // Save the state at the start of safepoint processing. 1019 _orig_thread_state = state; 1020 1021 // Check for a thread that is suspended. Note that thread resume tries 1022 // to grab the Threads_lock which we own here, so a thread cannot be 1023 // resumed during safepoint synchronization. 1024 1025 // We check to see if this thread is suspended without locking to 1026 // avoid deadlocking with a third thread that is waiting for this 1027 // thread to be suspended. The third thread can notice the safepoint 1028 // that we're trying to start at the beginning of its SR_lock->wait() 1029 // call. If that happens, then the third thread will block on the 1030 // safepoint while still holding the underlying SR_lock. We won't be 1031 // able to get the SR_lock and we'll deadlock. 1032 // 1033 // We don't need to grab the SR_lock here for two reasons: 1034 // 1) The suspend flags are both volatile and are set with an 1035 // Atomic::cmpxchg() call so we should see the suspended 1036 // state right away. 1037 // 2) We're being called from the safepoint polling loop; if 1038 // we don't see the suspended state on this iteration, then 1039 // we'll come around again. 1040 // 1041 bool is_suspended = _thread->is_ext_suspended(); 1042 if (is_suspended) { 1043 roll_forward(_at_safepoint); 1044 return; 1045 } 1046 1047 // Some JavaThread states have an initial safepoint state of 1048 // running, but are actually at a safepoint. We will happily 1049 // agree and update the safepoint state here. 1050 if (SafepointSynchronize::safepoint_safe(_thread, state)) { 1051 SafepointSynchronize::check_for_lazy_critical_native(_thread, state); 1052 roll_forward(_at_safepoint); 1053 return; 1054 } 1055 1056 if (state == _thread_in_vm) { 1057 roll_forward(_call_back); 1058 return; 1059 } 1060 1061 // All other thread states will continue to run until they 1062 // transition and self-block in state _blocked 1063 // Safepoint polling in compiled code causes the Java threads to do the same. 1064 // Note: new threads may require a malloc so they must be allowed to finish 1065 1066 assert(is_running(), "examine_state_of_thread on non-running thread"); 1067 return; 1068 } 1069 1070 // Returns true is thread could not be rolled forward at present position. 1071 void ThreadSafepointState::roll_forward(suspend_type type) { 1072 _type = type; 1073 1074 switch(_type) { 1075 case _at_safepoint: 1076 SafepointSynchronize::signal_thread_at_safepoint(); 1077 DEBUG_ONLY(_thread->set_visited_for_critical_count(true)); 1078 if (_thread->in_critical()) { 1079 // Notice that this thread is in a critical section 1080 SafepointSynchronize::increment_jni_active_count(); 1081 } 1082 break; 1083 1084 case _call_back: 1085 set_has_called_back(false); 1086 break; 1087 1088 case _running: 1089 default: 1090 ShouldNotReachHere(); 1091 } 1092 } 1093 1094 void ThreadSafepointState::restart() { 1095 switch(type()) { 1096 case _at_safepoint: 1097 case _call_back: 1098 break; 1099 1100 case _running: 1101 default: 1102 tty->print_cr("restart thread " INTPTR_FORMAT " with state %d", 1103 p2i(_thread), _type); 1104 _thread->print(); 1105 ShouldNotReachHere(); 1106 } 1107 _type = _running; 1108 set_has_called_back(false); 1109 } 1110 1111 1112 void ThreadSafepointState::print_on(outputStream *st) const { 1113 const char *s = NULL; 1114 1115 switch(_type) { 1116 case _running : s = "_running"; break; 1117 case _at_safepoint : s = "_at_safepoint"; break; 1118 case _call_back : s = "_call_back"; break; 1119 default: 1120 ShouldNotReachHere(); 1121 } 1122 1123 st->print_cr("Thread: " INTPTR_FORMAT 1124 " [0x%2x] State: %s _has_called_back %d _at_poll_safepoint %d", 1125 p2i(_thread), _thread->osthread()->thread_id(), s, _has_called_back, 1126 _at_poll_safepoint); 1127 1128 _thread->print_thread_state_on(st); 1129 } 1130 1131 // --------------------------------------------------------------------------------------------------------------------- 1132 1133 // Block the thread at poll or poll return for safepoint/handshake. 1134 void ThreadSafepointState::handle_polling_page_exception() { 1135 1136 // Check state. block() will set thread state to thread_in_vm which will 1137 // cause the safepoint state _type to become _call_back. 1138 suspend_type t = type(); 1139 assert(!SafepointMechanism::uses_global_page_poll() || t == ThreadSafepointState::_running, 1140 "polling page exception on thread not running state: %u", uint(t)); 1141 1142 // Step 1: Find the nmethod from the return address 1143 address real_return_addr = thread()->saved_exception_pc(); 1144 1145 CodeBlob *cb = CodeCache::find_blob(real_return_addr); 1146 assert(cb != NULL && cb->is_compiled(), "return address should be in nmethod"); 1147 CompiledMethod* nm = (CompiledMethod*)cb; 1148 1149 // Find frame of caller 1150 frame stub_fr = thread()->last_frame(); 1151 CodeBlob* stub_cb = stub_fr.cb(); 1152 assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub"); 1153 RegisterMap map(thread(), true); 1154 frame caller_fr = stub_fr.sender(&map); 1155 1156 // Should only be poll_return or poll 1157 assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" ); 1158 1159 // This is a poll immediately before a return. The exception handling code 1160 // has already had the effect of causing the return to occur, so the execution 1161 // will continue immediately after the call. In addition, the oopmap at the 1162 // return point does not mark the return value as an oop (if it is), so 1163 // it needs a handle here to be updated. 1164 if( nm->is_at_poll_return(real_return_addr) ) { 1165 ResourceMark rm; 1166 // See if return type is an oop. 1167 Method* method = nm->method(); 1168 bool return_oop = method->may_return_oop(); 1169 1170 GrowableArray<Handle> return_values; 1171 ValueKlass* vk = NULL; 1172 1173 if (return_oop && ValueTypeReturnedAsFields) { 1174 SignatureStream ss(method->signature()); 1175 while (!ss.at_return_type()) { 1176 ss.next(); 1177 } 1178 if (ss.type() == T_VALUETYPE) { 1179 // Check if value type is returned as fields 1180 vk = ValueKlass::returned_value_klass(map); 1181 if (vk != NULL) { 1182 // We're at a safepoint at the return of a method that returns 1183 // multiple values. We must make sure we preserve the oop values 1184 // across the safepoint. 1185 assert(vk == method->returned_value_type(thread()), "bad value klass"); 1186 vk->save_oop_fields(map, return_values); 1187 return_oop = false; 1188 } 1189 } 1190 } 1191 1192 if (return_oop) { 1193 // The oop result has been saved on the stack together with all 1194 // the other registers. In order to preserve it over GCs we need 1195 // to keep it in a handle. 1196 oop result = caller_fr.saved_oop_result(&map); 1197 assert(oopDesc::is_oop_or_null(result), "must be oop"); 1198 return_values.push(Handle(thread(), result)); 1199 assert(Universe::heap()->is_in_or_null(result), "must be heap pointer"); 1200 } 1201 1202 // Block the thread 1203 SafepointMechanism::block_if_requested(thread()); 1204 1205 // restore oop result, if any 1206 if (return_oop) { 1207 assert(return_values.length() == 1, "only one return value"); 1208 caller_fr.set_saved_oop_result(&map, return_values.pop()()); 1209 } else if (vk != NULL) { 1210 vk->restore_oop_results(map, return_values); 1211 } 1212 } 1213 1214 // This is a safepoint poll. Verify the return address and block. 1215 else { 1216 set_at_poll_safepoint(true); 1217 1218 // verify the blob built the "return address" correctly 1219 assert(real_return_addr == caller_fr.pc(), "must match"); 1220 1221 // Block the thread 1222 SafepointMechanism::block_if_requested(thread()); 1223 set_at_poll_safepoint(false); 1224 1225 // If we have a pending async exception deoptimize the frame 1226 // as otherwise we may never deliver it. 1227 if (thread()->has_async_condition()) { 1228 ThreadInVMfromJavaNoAsyncException __tiv(thread()); 1229 Deoptimization::deoptimize_frame(thread(), caller_fr.id()); 1230 } 1231 1232 // If an exception has been installed we must check for a pending deoptimization 1233 // Deoptimize frame if exception has been thrown. 1234 1235 if (thread()->has_pending_exception() ) { 1236 RegisterMap map(thread(), true); 1237 frame caller_fr = stub_fr.sender(&map); 1238 if (caller_fr.is_deoptimized_frame()) { 1239 // The exception patch will destroy registers that are still 1240 // live and will be needed during deoptimization. Defer the 1241 // Async exception should have deferred the exception until the 1242 // next safepoint which will be detected when we get into 1243 // the interpreter so if we have an exception now things 1244 // are messed up. 1245 1246 fatal("Exception installed and deoptimization is pending"); 1247 } 1248 } 1249 } 1250 } 1251 1252 1253 // 1254 // Statistics & Instrumentations 1255 // 1256 struct SafepointStats { 1257 float _time_stamp; // record when the current safepoint occurs in seconds 1258 int _vmop_type; // tyep of VM operation triggers the safepoint 1259 int _nof_total_threads; // total number of Java threads 1260 int _nof_initial_running_threads; // total number of initially seen running threads 1261 int _nof_threads_wait_to_block; // total number of threads waiting for to block 1262 bool _page_armed; // true if polling page is armed, false otherwise 1263 int _nof_threads_hit_page_trap; // total number of threads hitting the page trap 1264 jlong _time_to_spin; // total time in millis spent in spinning 1265 jlong _time_to_wait_to_block; // total time in millis spent in waiting for to block 1266 jlong _time_to_do_cleanups; // total time in millis spent in performing cleanups 1267 jlong _time_to_sync; // total time in millis spent in getting to _synchronized 1268 jlong _time_to_exec_vmop; // total time in millis spent in vm operation itself 1269 }; 1270 1271 static const int _statistics_header_count = 30; 1272 static int _cur_stat_index = 0; 1273 static SafepointStats safepoint_stats = {0}; // zero initialize 1274 static SafepointStats* spstat = &safepoint_stats; 1275 1276 static julong _safepoint_reasons[VM_Operation::VMOp_Terminating]; 1277 static jlong _max_sync_time = 0; 1278 static jlong _max_vmop_time = 0; 1279 1280 static jlong cleanup_end_time = 0; 1281 1282 void SafepointSynchronize::begin_statistics(int nof_threads, int nof_running) { 1283 1284 spstat->_time_stamp = _ts_of_current_safepoint; 1285 1286 VM_Operation *op = VMThread::vm_operation(); 1287 spstat->_vmop_type = op != NULL ? op->type() : VM_Operation::VMOp_None; 1288 _safepoint_reasons[spstat->_vmop_type]++; 1289 1290 spstat->_nof_total_threads = nof_threads; 1291 spstat->_nof_initial_running_threads = nof_running; 1292 1293 // Records the start time of spinning. The real time spent on spinning 1294 // will be adjusted when spin is done. Same trick is applied for time 1295 // spent on waiting for threads to block. 1296 if (nof_running != 0) { 1297 spstat->_time_to_spin = os::javaTimeNanos(); 1298 } else { 1299 spstat->_time_to_spin = 0; 1300 } 1301 } 1302 1303 void SafepointSynchronize::update_statistics_on_spin_end() { 1304 jlong cur_time = os::javaTimeNanos(); 1305 1306 spstat->_nof_threads_wait_to_block = _waiting_to_block; 1307 if (spstat->_nof_initial_running_threads != 0) { 1308 spstat->_time_to_spin = cur_time - spstat->_time_to_spin; 1309 } 1310 1311 // Records the start time of waiting for to block. Updated when block is done. 1312 if (_waiting_to_block != 0) { 1313 spstat->_time_to_wait_to_block = cur_time; 1314 } else { 1315 spstat->_time_to_wait_to_block = 0; 1316 } 1317 } 1318 1319 void SafepointSynchronize::update_statistics_on_sync_end(jlong end_time) { 1320 1321 if (spstat->_nof_threads_wait_to_block != 0) { 1322 spstat->_time_to_wait_to_block = end_time - 1323 spstat->_time_to_wait_to_block; 1324 } 1325 1326 // Records the end time of sync which will be used to calculate the total 1327 // vm operation time. Again, the real time spending in syncing will be deducted 1328 // from the start of the sync time later when end_statistics is called. 1329 spstat->_time_to_sync = end_time - _safepoint_begin_time; 1330 if (spstat->_time_to_sync > _max_sync_time) { 1331 _max_sync_time = spstat->_time_to_sync; 1332 } 1333 1334 spstat->_time_to_do_cleanups = end_time; 1335 } 1336 1337 void SafepointSynchronize::update_statistics_on_cleanup_end(jlong end_time) { 1338 1339 // Record how long spent in cleanup tasks. 1340 spstat->_time_to_do_cleanups = end_time - spstat->_time_to_do_cleanups; 1341 cleanup_end_time = end_time; 1342 } 1343 1344 void SafepointSynchronize::end_statistics(jlong vmop_end_time) { 1345 1346 // Update the vm operation time. 1347 spstat->_time_to_exec_vmop = vmop_end_time - cleanup_end_time; 1348 if (spstat->_time_to_exec_vmop > _max_vmop_time) { 1349 _max_vmop_time = spstat->_time_to_exec_vmop; 1350 } 1351 1352 spstat->_nof_threads_hit_page_trap = _nof_threads_hit_polling_page; 1353 1354 print_statistics(); 1355 } 1356 1357 // Helper method to print the header. 1358 static void print_header(outputStream* st) { 1359 // The number of spaces is significant here, and should match the format 1360 // specifiers in print_statistics(). 1361 1362 st->print(" vmop " 1363 "[ threads: total initially_running wait_to_block ]" 1364 "[ time: spin block sync cleanup vmop ] "); 1365 1366 st->print_cr("page_trap_count"); 1367 } 1368 1369 // This prints a nice table. To get the statistics to not shift due to the logging uptime 1370 // decorator, use the option as: -Xlog:safepoint+stats=debug:[outputfile]:none 1371 void SafepointSynchronize::print_statistics() { 1372 LogTarget(Debug, safepoint, stats) lt; 1373 assert (lt.is_enabled(), "should only be called when printing statistics is enabled"); 1374 LogStream ls(lt); 1375 1376 // Print header every 30 entries 1377 if ((_cur_stat_index % _statistics_header_count) == 0) { 1378 print_header(&ls); 1379 _cur_stat_index = 1; // wrap 1380 } else { 1381 _cur_stat_index++; 1382 } 1383 1384 ls.print("%8.3f: ", spstat->_time_stamp); 1385 ls.print("%-28s [ " 1386 INT32_FORMAT_W(8) " " INT32_FORMAT_W(17) " " INT32_FORMAT_W(13) " " 1387 "]", 1388 VM_Operation::name(spstat->_vmop_type), 1389 spstat->_nof_total_threads, 1390 spstat->_nof_initial_running_threads, 1391 spstat->_nof_threads_wait_to_block); 1392 // "/ MICROUNITS " is to convert the unit from nanos to millis. 1393 ls.print("[ " 1394 INT64_FORMAT_W(7) " " INT64_FORMAT_W(7) " " 1395 INT64_FORMAT_W(7) " " INT64_FORMAT_W(7) " " 1396 INT64_FORMAT_W(7) " ] ", 1397 (int64_t)(spstat->_time_to_spin / MICROUNITS), 1398 (int64_t)(spstat->_time_to_wait_to_block / MICROUNITS), 1399 (int64_t)(spstat->_time_to_sync / MICROUNITS), 1400 (int64_t)(spstat->_time_to_do_cleanups / MICROUNITS), 1401 (int64_t)(spstat->_time_to_exec_vmop / MICROUNITS)); 1402 1403 ls.print_cr(INT32_FORMAT_W(15) " ", spstat->_nof_threads_hit_page_trap); 1404 } 1405 1406 // This method will be called when VM exits. This tries to summarize the sampling. 1407 // Current thread may already be deleted, so don't use ResourceMark. 1408 void SafepointSynchronize::print_stat_on_exit() { 1409 1410 for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) { 1411 if (_safepoint_reasons[index] != 0) { 1412 log_debug(safepoint, stats)("%-28s" UINT64_FORMAT_W(10), VM_Operation::name(index), 1413 _safepoint_reasons[index]); 1414 } 1415 } 1416 1417 log_debug(safepoint, stats)("VM operations coalesced during safepoint " INT64_FORMAT, 1418 _coalesced_vmop_count); 1419 log_debug(safepoint, stats)("Maximum sync time " INT64_FORMAT" ms", 1420 (int64_t)(_max_sync_time / MICROUNITS)); 1421 log_debug(safepoint, stats)("Maximum vm operation time (except for Exit VM operation) " 1422 INT64_FORMAT " ms", 1423 (int64_t)(_max_vmop_time / MICROUNITS)); 1424 }