1 /*
   2  * Copyright (c) 1997, 2017, 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/stringTable.hpp"
  27 #include "classfile/symbolTable.hpp"
  28 #include "classfile/systemDictionary.hpp"
  29 #include "code/codeCache.hpp"
  30 #include "code/icBuffer.hpp"
  31 #include "code/nmethod.hpp"
  32 #include "code/pcDesc.hpp"
  33 #include "code/scopeDesc.hpp"
  34 #include "gc/shared/collectedHeap.hpp"
  35 #include "gc/shared/gcLocker.inline.hpp"
  36 #include "gc/shared/strongRootsScope.hpp"
  37 #include "gc/shared/workgroup.hpp"
  38 #include "interpreter/interpreter.hpp"
  39 #include "logging/log.hpp"
  40 #include "logging/logStream.hpp"
  41 #include "memory/resourceArea.hpp"
  42 #include "memory/universe.inline.hpp"
  43 #include "oops/oop.inline.hpp"
  44 #include "oops/symbol.hpp"
  45 #include "runtime/atomic.hpp"
  46 #include "runtime/compilationPolicy.hpp"
  47 #include "runtime/deoptimization.hpp"
  48 #include "runtime/frame.inline.hpp"
  49 #include "runtime/interfaceSupport.hpp"
  50 #include "runtime/mutexLocker.hpp"
  51 #include "runtime/orderAccess.inline.hpp"
  52 #include "runtime/osThread.hpp"
  53 #include "runtime/safepoint.hpp"
  54 #include "runtime/signature.hpp"
  55 #include "runtime/stubCodeGenerator.hpp"
  56 #include "runtime/stubRoutines.hpp"
  57 #include "runtime/sweeper.hpp"
  58 #include "runtime/synchronizer.hpp"
  59 #include "runtime/thread.inline.hpp"
  60 #include "runtime/threadSMR.hpp"
  61 #include "runtime/timerTrace.hpp"
  62 #include "services/runtimeService.hpp"
  63 #include "trace/tracing.hpp"
  64 #include "trace/traceMacros.hpp"
  65 #include "utilities/events.hpp"
  66 #include "utilities/macros.hpp"
  67 #if INCLUDE_ALL_GCS
  68 #include "gc/cms/concurrentMarkSweepThread.hpp"
  69 #include "gc/g1/suspendibleThreadSet.hpp"
  70 #endif // INCLUDE_ALL_GCS
  71 #ifdef COMPILER1
  72 #include "c1/c1_globals.hpp"
  73 #endif
  74 
  75 // --------------------------------------------------------------------------------------------------
  76 // Implementation of Safepoint begin/end
  77 
  78 SafepointSynchronize::SynchronizeState volatile SafepointSynchronize::_state = SafepointSynchronize::_not_synchronized;
  79 volatile int  SafepointSynchronize::_waiting_to_block = 0;
  80 volatile int SafepointSynchronize::_safepoint_counter = 0;
  81 int SafepointSynchronize::_current_jni_active_count = 0;
  82 long  SafepointSynchronize::_end_of_last_safepoint = 0;
  83 static volatile int PageArmed = 0 ;        // safepoint polling page is RO|RW vs PROT_NONE
  84 static volatile int TryingToBlock = 0 ;    // proximate value -- for advisory use only
  85 static bool timeout_error_printed = false;
  86 
  87 // Roll all threads forward to a safepoint and suspend them all
  88 void SafepointSynchronize::begin() {
  89   EventSafepointBegin begin_event;
  90   Thread* myThread = Thread::current();
  91   assert(myThread->is_VM_thread(), "Only VM thread may execute a safepoint");
  92 
  93   if (PrintSafepointStatistics || PrintSafepointStatisticsTimeout > 0) {
  94     _safepoint_begin_time = os::javaTimeNanos();
  95     _ts_of_current_safepoint = tty->time_stamp().seconds();
  96   }
  97 
  98 #if INCLUDE_ALL_GCS
  99   if (UseConcMarkSweepGC) {
 100     // In the future we should investigate whether CMS can use the
 101     // more-general mechanism below.  DLD (01/05).
 102     ConcurrentMarkSweepThread::synchronize(false);
 103   } else if (UseG1GC) {
 104     SuspendibleThreadSet::synchronize();
 105   }
 106 #endif // INCLUDE_ALL_GCS
 107 
 108   // By getting the Threads_lock, we assure that no threads are about to start or
 109   // exit. It is released again in SafepointSynchronize::end().
 110   Threads_lock->lock();
 111 
 112   assert( _state == _not_synchronized, "trying to safepoint synchronize with wrong state");
 113 
 114   int nof_threads = Threads::number_of_threads();
 115 
 116   log_debug(safepoint)("Safepoint synchronization initiated. (%d)", nof_threads);
 117 
 118   RuntimeService::record_safepoint_begin();
 119 
 120   MutexLocker mu(Safepoint_lock);
 121 
 122   // Reset the count of active JNI critical threads
 123   _current_jni_active_count = 0;
 124 
 125   // Set number of threads to wait for, before we initiate the callbacks
 126   _waiting_to_block = nof_threads;
 127   TryingToBlock     = 0 ;
 128   int still_running = nof_threads;
 129 
 130   // Save the starting time, so that it can be compared to see if this has taken
 131   // too long to complete.
 132   jlong safepoint_limit_time = 0;
 133   timeout_error_printed = false;
 134 
 135   // PrintSafepointStatisticsTimeout can be specified separately. When
 136   // specified, PrintSafepointStatistics will be set to true in
 137   // deferred_initialize_stat method. The initialization has to be done
 138   // early enough to avoid any races. See bug 6880029 for details.
 139   if (PrintSafepointStatistics || PrintSafepointStatisticsTimeout > 0) {
 140     deferred_initialize_stat();
 141   }
 142 
 143   // Begin the process of bringing the system to a safepoint.
 144   // Java threads can be in several different states and are
 145   // stopped by different mechanisms:
 146   //
 147   //  1. Running interpreted
 148   //     The interpreter dispatch table is changed to force it to
 149   //     check for a safepoint condition between bytecodes.
 150   //  2. Running in native code
 151   //     When returning from the native code, a Java thread must check
 152   //     the safepoint _state to see if we must block.  If the
 153   //     VM thread sees a Java thread in native, it does
 154   //     not wait for this thread to block.  The order of the memory
 155   //     writes and reads of both the safepoint state and the Java
 156   //     threads state is critical.  In order to guarantee that the
 157   //     memory writes are serialized with respect to each other,
 158   //     the VM thread issues a memory barrier instruction
 159   //     (on MP systems).  In order to avoid the overhead of issuing
 160   //     a memory barrier for each Java thread making native calls, each Java
 161   //     thread performs a write to a single memory page after changing
 162   //     the thread state.  The VM thread performs a sequence of
 163   //     mprotect OS calls which forces all previous writes from all
 164   //     Java threads to be serialized.  This is done in the
 165   //     os::serialize_thread_states() call.  This has proven to be
 166   //     much more efficient than executing a membar instruction
 167   //     on every call to native code.
 168   //  3. Running compiled Code
 169   //     Compiled code reads a global (Safepoint Polling) page that
 170   //     is set to fault if we are trying to get to a safepoint.
 171   //  4. Blocked
 172   //     A thread which is blocked will not be allowed to return from the
 173   //     block condition until the safepoint operation is complete.
 174   //  5. In VM or Transitioning between states
 175   //     If a Java thread is currently running in the VM or transitioning
 176   //     between states, the safepointing code will wait for the thread to
 177   //     block itself when it attempts transitions to a new state.
 178   //
 179   {
 180     EventSafepointStateSynchronization sync_event;
 181     int initial_running = 0;
 182 
 183     _state            = _synchronizing;
 184     OrderAccess::fence();
 185 
 186     // Flush all thread states to memory
 187     if (!UseMembar) {
 188       os::serialize_thread_states();
 189     }
 190 
 191     // Make interpreter safepoint aware
 192     Interpreter::notice_safepoints();
 193 
 194     if (DeferPollingPageLoopCount < 0) {
 195       // Make polling safepoint aware
 196       guarantee (PageArmed == 0, "invariant") ;
 197       PageArmed = 1 ;
 198       os::make_polling_page_unreadable();
 199     }
 200 
 201     // Consider using active_processor_count() ... but that call is expensive.
 202     int ncpus = os::processor_count() ;
 203     unsigned int iterations = 0;
 204 
 205     {
 206       ThreadsListHandle tlh;
 207       JavaThreadIterator jti(tlh.list());
 208 #ifdef ASSERT
 209       for (JavaThread *cur = jti.first(); cur != NULL; cur = jti.next()) {
 210         assert(cur->safepoint_state()->is_running(), "Illegal initial state");
 211         // Clear the visited flag to ensure that the critical counts are collected properly.
 212         cur->set_visited_for_critical_count(false);
 213       }
 214 #endif // ASSERT
 215 
 216       if (SafepointTimeout)
 217         safepoint_limit_time = os::javaTimeNanos() + (jlong)SafepointTimeoutDelay * MICROUNITS;
 218 
 219       // Iterate through all threads until it have been determined how to stop them all at a safepoint
 220       int steps = 0 ;
 221       while(still_running > 0) {
 222         for (JavaThread *cur = jti.first(); cur != NULL; cur = jti.next()) {
 223           assert(!cur->is_ConcurrentGC_thread(), "A concurrent GC thread is unexpectly being suspended");
 224           ThreadSafepointState *cur_state = cur->safepoint_state();
 225           if (cur_state->is_running()) {
 226             cur_state->examine_state_of_thread();
 227             if (!cur_state->is_running()) {
 228               still_running--;
 229               // consider adjusting steps downward:
 230               //   steps = 0
 231               //   steps -= NNN
 232               //   steps >>= 1
 233               //   steps = MIN(steps, 2000-100)
 234               //   if (iterations != 0) steps -= NNN
 235             }
 236             LogTarget(Trace, safepoint) lt;
 237             if (lt.is_enabled()) {
 238               ResourceMark rm;
 239               LogStream ls(lt);
 240               cur_state->print_on(&ls);
 241             }
 242           }
 243         }
 244 
 245         if (iterations == 0) {
 246           initial_running = still_running;
 247           if (PrintSafepointStatistics) {
 248             begin_statistics(nof_threads, still_running);
 249           }
 250         }
 251 
 252         if (still_running > 0) {
 253           // Check for if it takes to long
 254           if (SafepointTimeout && safepoint_limit_time < os::javaTimeNanos()) {
 255             print_safepoint_timeout(_spinning_timeout);
 256           }
 257 
 258           // Spin to avoid context switching.
 259           // There's a tension between allowing the mutators to run (and rendezvous)
 260           // vs spinning.  As the VM thread spins, wasting cycles, it consumes CPU that
 261           // a mutator might otherwise use profitably to reach a safepoint.  Excessive
 262           // spinning by the VM thread on a saturated system can increase rendezvous latency.
 263           // Blocking or yielding incur their own penalties in the form of context switching
 264           // and the resultant loss of $ residency.
 265           //
 266           // Further complicating matters is that yield() does not work as naively expected
 267           // on many platforms -- yield() does not guarantee that any other ready threads
 268           // will run.   As such we revert to naked_short_sleep() after some number of iterations.
 269           // nakes_short_sleep() is implemented as a short unconditional sleep.
 270           // Typical operating systems round a "short" sleep period up to 10 msecs, so sleeping
 271           // can actually increase the time it takes the VM thread to detect that a system-wide
 272           // stop-the-world safepoint has been reached.  In a pathological scenario such as that
 273           // described in CR6415670 the VMthread may sleep just before the mutator(s) become safe.
 274           // In that case the mutators will be stalled waiting for the safepoint to complete and the
 275           // the VMthread will be sleeping, waiting for the mutators to rendezvous.  The VMthread
 276           // will eventually wake up and detect that all mutators are safe, at which point
 277           // we'll again make progress.
 278           //
 279           // Beware too that that the VMThread typically runs at elevated priority.
 280           // Its default priority is higher than the default mutator priority.
 281           // Obviously, this complicates spinning.
 282           //
 283           // Note too that on Windows XP SwitchThreadTo() has quite different behavior than Sleep(0).
 284           // Sleep(0) will _not yield to lower priority threads, while SwitchThreadTo() will.
 285           //
 286           // See the comments in synchronizer.cpp for additional remarks on spinning.
 287           //
 288           // In the future we might:
 289           // 1. Modify the safepoint scheme to avoid potentially unbounded spinning.
 290           //    This is tricky as the path used by a thread exiting the JVM (say on
 291           //    on JNI call-out) simply stores into its state field.  The burden
 292           //    is placed on the VM thread, which must poll (spin).
 293           // 2. Find something useful to do while spinning.  If the safepoint is GC-related
 294           //    we might aggressively scan the stacks of threads that are already safe.
 295           // 3. Use Solaris schedctl to examine the state of the still-running mutators.
 296           //    If all the mutators are ONPROC there's no reason to sleep or yield.
 297           // 4. YieldTo() any still-running mutators that are ready but OFFPROC.
 298           // 5. Check system saturation.  If the system is not fully saturated then
 299           //    simply spin and avoid sleep/yield.
 300           // 6. As still-running mutators rendezvous they could unpark the sleeping
 301           //    VMthread.  This works well for still-running mutators that become
 302           //    safe.  The VMthread must still poll for mutators that call-out.
 303           // 7. Drive the policy on time-since-begin instead of iterations.
 304           // 8. Consider making the spin duration a function of the # of CPUs:
 305           //    Spin = (((ncpus-1) * M) + K) + F(still_running)
 306           //    Alternately, instead of counting iterations of the outer loop
 307           //    we could count the # of threads visited in the inner loop, above.
 308           // 9. On windows consider using the return value from SwitchThreadTo()
 309           //    to drive subsequent spin/SwitchThreadTo()/Sleep(N) decisions.
 310 
 311           if (int(iterations) == DeferPollingPageLoopCount) {
 312             guarantee (PageArmed == 0, "invariant") ;
 313             PageArmed = 1 ;
 314             os::make_polling_page_unreadable();
 315           }
 316 
 317           // Instead of (ncpus > 1) consider either (still_running < (ncpus + EPSILON)) or
 318           // ((still_running + _waiting_to_block - TryingToBlock)) < ncpus)
 319           ++steps ;
 320           if (ncpus > 1 && steps < SafepointSpinBeforeYield) {
 321             SpinPause() ;     // MP-Polite spin
 322           } else
 323             if (steps < DeferThrSuspendLoopCount) {
 324               os::naked_yield() ;
 325             } else {
 326               os::naked_short_sleep(1);
 327             }
 328 
 329           iterations ++ ;
 330         }
 331         assert(iterations < (uint)max_jint, "We have been iterating in the safepoint loop too long");
 332       }
 333     } // ThreadsListHandle destroyed here.
 334     assert(still_running == 0, "sanity check");
 335 
 336     if (PrintSafepointStatistics) {
 337       update_statistics_on_spin_end();
 338     }
 339 
 340     if (sync_event.should_commit()) {
 341       sync_event.set_safepointId(safepoint_counter());
 342       sync_event.set_initialThreadCount(initial_running);
 343       sync_event.set_runningThreadCount(_waiting_to_block);
 344       sync_event.set_iterations(iterations);
 345       sync_event.commit();
 346     }
 347   } // EventSafepointStateSynchronization destroyed here.
 348 
 349   // wait until all threads are stopped
 350   {
 351     EventSafepointWaitBlocked wait_blocked_event;
 352     int initial_waiting_to_block = _waiting_to_block;
 353 
 354     while (_waiting_to_block > 0) {
 355       log_debug(safepoint)("Waiting for %d thread(s) to block", _waiting_to_block);
 356       if (!SafepointTimeout || timeout_error_printed) {
 357         Safepoint_lock->wait(true);  // true, means with no safepoint checks
 358       } else {
 359         // Compute remaining time
 360         jlong remaining_time = safepoint_limit_time - os::javaTimeNanos();
 361 
 362         // If there is no remaining time, then there is an error
 363         if (remaining_time < 0 || Safepoint_lock->wait(true, remaining_time / MICROUNITS)) {
 364           print_safepoint_timeout(_blocking_timeout);
 365         }
 366       }
 367     }
 368     assert(_waiting_to_block == 0, "sanity check");
 369 
 370 #ifndef PRODUCT
 371     if (SafepointTimeout) {
 372       jlong current_time = os::javaTimeNanos();
 373       if (safepoint_limit_time < current_time) {
 374         tty->print_cr("# SafepointSynchronize: Finished after "
 375                       INT64_FORMAT_W(6) " ms",
 376                       (int64_t)((current_time - safepoint_limit_time) / MICROUNITS +
 377                                 (jlong)SafepointTimeoutDelay));
 378       }
 379     }
 380 #endif
 381 
 382     assert((_safepoint_counter & 0x1) == 0, "must be even");
 383     assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
 384     _safepoint_counter ++;
 385 
 386     // Record state
 387     _state = _synchronized;
 388 
 389     OrderAccess::fence();
 390 
 391     if (wait_blocked_event.should_commit()) {
 392       wait_blocked_event.set_safepointId(safepoint_counter());
 393       wait_blocked_event.set_runningThreadCount(initial_waiting_to_block);
 394       wait_blocked_event.commit();
 395     }
 396   } // EventSafepointWaitBlocked
 397 
 398 #ifdef ASSERT
 399   {
 400     // Make sure all the threads were visited.
 401     ThreadsListHandle tlh;
 402     JavaThreadIterator jti(tlh.list());
 403     for (JavaThread *cur = jti.first(); cur != NULL; cur = jti.next()) {
 404       assert(cur->was_visited_for_critical_count(), "missed a thread");
 405     }
 406   }
 407 #endif // ASSERT
 408 
 409   // Update the count of active JNI critical regions
 410   GCLocker::set_jni_lock_count(_current_jni_active_count);
 411 
 412   if (log_is_enabled(Debug, safepoint)) {
 413     log_debug(safepoint)("Entering safepoint region: %s", VMThread::vm_safepoint_description());
 414   }
 415 
 416   RuntimeService::record_safepoint_synchronized();
 417   if (PrintSafepointStatistics) {
 418     update_statistics_on_sync_end(os::javaTimeNanos());
 419   }
 420 
 421   // Call stuff that needs to be run when a safepoint is just about to be completed
 422   {
 423     EventSafepointCleanup cleanup_event;
 424     do_cleanup_tasks();
 425     if (cleanup_event.should_commit()) {
 426       cleanup_event.set_safepointId(safepoint_counter());
 427       cleanup_event.commit();
 428     }
 429   }
 430 
 431   if (PrintSafepointStatistics) {
 432     // Record how much time spend on the above cleanup tasks
 433     update_statistics_on_cleanup_end(os::javaTimeNanos());
 434   }
 435   if (begin_event.should_commit()) {
 436     begin_event.set_safepointId(safepoint_counter());
 437     begin_event.set_totalThreadCount(nof_threads);
 438     begin_event.set_jniCriticalThreadCount(_current_jni_active_count);
 439     begin_event.commit();
 440   }
 441 }
 442 
 443 // Wake up all threads, so they are ready to resume execution after the safepoint
 444 // operation has been carried out
 445 void SafepointSynchronize::end() {
 446   EventSafepointEnd event;
 447   int safepoint_id = safepoint_counter(); // Keep the odd counter as "id"
 448 
 449   assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
 450   assert((_safepoint_counter & 0x1) == 1, "must be odd");
 451   _safepoint_counter ++;
 452   // memory fence isn't required here since an odd _safepoint_counter
 453   // value can do no harm and a fence is issued below anyway.
 454 
 455   DEBUG_ONLY(Thread* myThread = Thread::current();)
 456   assert(myThread->is_VM_thread(), "Only VM thread can execute a safepoint");
 457 
 458   if (PrintSafepointStatistics) {
 459     end_statistics(os::javaTimeNanos());
 460   }
 461 
 462   {
 463     ThreadsListHandle tlh;
 464     JavaThreadIterator jti(tlh.list());
 465 #ifdef ASSERT
 466     // A pending_exception cannot be installed during a safepoint.  The threads
 467     // may install an async exception after they come back from a safepoint into
 468     // pending_exception after they unblock.  But that should happen later.
 469     for (JavaThread *cur = jti.first(); cur != NULL; cur = jti.next()) {
 470       assert (!(cur->has_pending_exception() &&
 471                 cur->safepoint_state()->is_at_poll_safepoint()),
 472               "safepoint installed a pending exception");
 473     }
 474 #endif // ASSERT
 475 
 476     if (PageArmed) {
 477       // Make polling safepoint aware
 478       os::make_polling_page_readable();
 479       PageArmed = 0 ;
 480     }
 481 
 482     // Remove safepoint check from interpreter
 483     Interpreter::ignore_safepoints();
 484 
 485     {
 486       MutexLocker mu(Safepoint_lock);
 487 
 488       assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization");
 489 
 490       // Set to not synchronized, so the threads will not go into the signal_thread_blocked method
 491       // when they get restarted.
 492       _state = _not_synchronized;
 493       OrderAccess::fence();
 494 
 495       log_debug(safepoint)("Leaving safepoint region");
 496 
 497       // Start suspended threads
 498       for (JavaThread *current = jti.first(); current != NULL; current = jti.next()) {
 499         // A problem occurring on Solaris is when attempting to restart threads
 500         // the first #cpus - 1 go well, but then the VMThread is preempted when we get
 501         // to the next one (since it has been running the longest).  We then have
 502         // to wait for a cpu to become available before we can continue restarting
 503         // threads.
 504         // FIXME: This causes the performance of the VM to degrade when active and with
 505         // large numbers of threads.  Apparently this is due to the synchronous nature
 506         // of suspending threads.
 507         //
 508         // TODO-FIXME: the comments above are vestigial and no longer apply.
 509         // Furthermore, using solaris' schedctl in this particular context confers no benefit
 510         if (VMThreadHintNoPreempt) {
 511           os::hint_no_preempt();
 512         }
 513         ThreadSafepointState* cur_state = current->safepoint_state();
 514         assert(cur_state->type() != ThreadSafepointState::_running, "Thread not suspended at safepoint");
 515         cur_state->restart();
 516         assert(cur_state->is_running(), "safepoint state has not been reset");
 517       }
 518 
 519       RuntimeService::record_safepoint_end();
 520 
 521       // Release threads lock, so threads can be created/destroyed again.
 522       // It will also release all threads blocked in signal_thread_blocked.
 523       Threads_lock->unlock();
 524     }
 525   } // ThreadsListHandle destroyed here.
 526 
 527 #if INCLUDE_ALL_GCS
 528   // If there are any concurrent GC threads resume them.
 529   if (UseConcMarkSweepGC) {
 530     ConcurrentMarkSweepThread::desynchronize(false);
 531   } else if (UseG1GC) {
 532     SuspendibleThreadSet::desynchronize();
 533   }
 534 #endif // INCLUDE_ALL_GCS
 535   // record this time so VMThread can keep track how much time has elapsed
 536   // since last safepoint.
 537   _end_of_last_safepoint = os::javaTimeMillis();
 538 
 539   if (event.should_commit()) {
 540     event.set_safepointId(safepoint_id);
 541     event.commit();
 542   }
 543 }
 544 
 545 bool SafepointSynchronize::is_cleanup_needed() {
 546   // Need a safepoint if there are many monitors to deflate.
 547   if (ObjectSynchronizer::is_cleanup_needed()) return true;
 548   // Need a safepoint if some inline cache buffers is non-empty
 549   if (!InlineCacheBuffer::is_empty()) return true;
 550   return false;
 551 }
 552 
 553 static void event_safepoint_cleanup_task_commit(EventSafepointCleanupTask& event, const char* name) {
 554   if (event.should_commit()) {
 555     event.set_safepointId(SafepointSynchronize::safepoint_counter());
 556     event.set_name(name);
 557     event.commit();
 558   }
 559 }
 560 
 561 class ParallelSPCleanupThreadClosure : public ThreadClosure {
 562 private:
 563   CodeBlobClosure* _nmethod_cl;
 564   DeflateMonitorCounters* _counters;
 565 
 566 public:
 567   ParallelSPCleanupThreadClosure(DeflateMonitorCounters* counters) :
 568     _counters(counters),
 569     _nmethod_cl(NMethodSweeper::prepare_mark_active_nmethods()) {}
 570 
 571   void do_thread(Thread* thread) {
 572     ObjectSynchronizer::deflate_thread_local_monitors(thread, _counters);
 573     if (_nmethod_cl != NULL && thread->is_Java_thread() &&
 574         ! thread->is_Code_cache_sweeper_thread()) {
 575       JavaThread* jt = (JavaThread*) thread;
 576       jt->nmethods_do(_nmethod_cl);
 577     }
 578   }
 579 };
 580 
 581 class ParallelSPCleanupTask : public AbstractGangTask {
 582 private:
 583   SubTasksDone _subtasks;
 584   ParallelSPCleanupThreadClosure _cleanup_threads_cl;
 585   uint _num_workers;
 586   DeflateMonitorCounters* _counters;
 587 public:
 588   ParallelSPCleanupTask(uint num_workers, DeflateMonitorCounters* counters) :
 589     AbstractGangTask("Parallel Safepoint Cleanup"),
 590     _cleanup_threads_cl(ParallelSPCleanupThreadClosure(counters)),
 591     _num_workers(num_workers),
 592     _subtasks(SubTasksDone(SafepointSynchronize::SAFEPOINT_CLEANUP_NUM_TASKS)),
 593     _counters(counters) {}
 594 
 595   void work(uint worker_id) {
 596     // All threads deflate monitors and mark nmethods (if necessary).
 597     Threads::parallel_java_threads_do(&_cleanup_threads_cl);
 598 
 599     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_DEFLATE_MONITORS)) {
 600       const char* name = "deflating idle monitors";
 601       EventSafepointCleanupTask event;
 602       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 603       ObjectSynchronizer::deflate_idle_monitors(_counters);
 604       event_safepoint_cleanup_task_commit(event, name);
 605     }
 606 
 607     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_UPDATE_INLINE_CACHES)) {
 608       const char* name = "updating inline caches";
 609       EventSafepointCleanupTask event;
 610       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 611       InlineCacheBuffer::update_inline_caches();
 612       event_safepoint_cleanup_task_commit(event, name);
 613     }
 614 
 615     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_COMPILATION_POLICY)) {
 616       const char* name = "compilation policy safepoint handler";
 617       EventSafepointCleanupTask event;
 618       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 619       CompilationPolicy::policy()->do_safepoint_work();
 620       event_safepoint_cleanup_task_commit(event, name);
 621     }
 622 
 623     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_SYMBOL_TABLE_REHASH)) {
 624       if (SymbolTable::needs_rehashing()) {
 625         const char* name = "rehashing symbol table";
 626         EventSafepointCleanupTask event;
 627         TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 628         SymbolTable::rehash_table();
 629         event_safepoint_cleanup_task_commit(event, name);
 630       }
 631     }
 632 
 633     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_STRING_TABLE_REHASH)) {
 634       if (StringTable::needs_rehashing()) {
 635         const char* name = "rehashing string table";
 636         EventSafepointCleanupTask event;
 637         TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 638         StringTable::rehash_table();
 639         event_safepoint_cleanup_task_commit(event, name);
 640       }
 641     }
 642 
 643     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_CLD_PURGE)) {
 644       // CMS delays purging the CLDG until the beginning of the next safepoint and to
 645       // make sure concurrent sweep is done
 646       const char* name = "purging class loader data graph";
 647       EventSafepointCleanupTask event;
 648       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 649       ClassLoaderDataGraph::purge_if_needed();
 650       event_safepoint_cleanup_task_commit(event, name);
 651     }
 652     _subtasks.all_tasks_completed(_num_workers);
 653   }
 654 };
 655 
 656 // Various cleaning tasks that should be done periodically at safepoints.
 657 void SafepointSynchronize::do_cleanup_tasks() {
 658 
 659   TraceTime timer("safepoint cleanup tasks", TRACETIME_LOG(Info, safepoint, cleanup));
 660 
 661   // Prepare for monitor deflation.
 662   DeflateMonitorCounters deflate_counters;
 663   ObjectSynchronizer::prepare_deflate_idle_monitors(&deflate_counters);
 664 
 665   CollectedHeap* heap = Universe::heap();
 666   assert(heap != NULL, "heap not initialized yet?");
 667   WorkGang* cleanup_workers = heap->get_safepoint_workers();
 668   if (cleanup_workers != NULL) {
 669     // Parallel cleanup using GC provided thread pool.
 670     uint num_cleanup_workers = cleanup_workers->active_workers();
 671     ParallelSPCleanupTask cleanup(num_cleanup_workers, &deflate_counters);
 672     StrongRootsScope srs(num_cleanup_workers);
 673     cleanup_workers->run_task(&cleanup);
 674   } else {
 675     // Serial cleanup using VMThread.
 676     ParallelSPCleanupTask cleanup(1, &deflate_counters);
 677     StrongRootsScope srs(1);
 678     cleanup.work(0);
 679   }
 680 
 681   // Finish monitor deflation.
 682   ObjectSynchronizer::finish_deflate_idle_monitors(&deflate_counters);
 683 }
 684 
 685 
 686 bool SafepointSynchronize::safepoint_safe(JavaThread *thread, JavaThreadState state) {
 687   switch(state) {
 688   case _thread_in_native:
 689     // native threads are safe if they have no java stack or have walkable stack
 690     return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable();
 691 
 692    // blocked threads should have already have walkable stack
 693   case _thread_blocked:
 694     assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable");
 695     return true;
 696 
 697   default:
 698     return false;
 699   }
 700 }
 701 
 702 
 703 // See if the thread is running inside a lazy critical native and
 704 // update the thread critical count if so.  Also set a suspend flag to
 705 // cause the native wrapper to return into the JVM to do the unlock
 706 // once the native finishes.
 707 void SafepointSynchronize::check_for_lazy_critical_native(JavaThread *thread, JavaThreadState state) {
 708   if (state == _thread_in_native &&
 709       thread->has_last_Java_frame() &&
 710       thread->frame_anchor()->walkable()) {
 711     // This thread might be in a critical native nmethod so look at
 712     // the top of the stack and increment the critical count if it
 713     // is.
 714     frame wrapper_frame = thread->last_frame();
 715     CodeBlob* stub_cb = wrapper_frame.cb();
 716     if (stub_cb != NULL &&
 717         stub_cb->is_nmethod() &&
 718         stub_cb->as_nmethod_or_null()->is_lazy_critical_native()) {
 719       // A thread could potentially be in a critical native across
 720       // more than one safepoint, so only update the critical state on
 721       // the first one.  When it returns it will perform the unlock.
 722       if (!thread->do_critical_native_unlock()) {
 723 #ifdef ASSERT
 724         if (!thread->in_critical()) {
 725           GCLocker::increment_debug_jni_lock_count();
 726         }
 727 #endif
 728         thread->enter_critical();
 729         // Make sure the native wrapper calls back on return to
 730         // perform the needed critical unlock.
 731         thread->set_critical_native_unlock();
 732       }
 733     }
 734   }
 735 }
 736 
 737 
 738 
 739 // -------------------------------------------------------------------------------------------------------
 740 // Implementation of Safepoint callback point
 741 
 742 void SafepointSynchronize::block(JavaThread *thread) {
 743   assert(thread != NULL, "thread must be set");
 744   assert(thread->is_Java_thread(), "not a Java thread");
 745 
 746   // Threads shouldn't block if they are in the middle of printing, but...
 747   ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id());
 748 
 749   // Only bail from the block() call if the thread is gone from the
 750   // thread list; starting to exit should still block.
 751   if (thread->is_terminated()) {
 752      // block current thread if we come here from native code when VM is gone
 753      thread->block_if_vm_exited();
 754 
 755      // otherwise do nothing
 756      return;
 757   }
 758 
 759   JavaThreadState state = thread->thread_state();
 760   thread->frame_anchor()->make_walkable(thread);
 761 
 762   // Check that we have a valid thread_state at this point
 763   switch(state) {
 764     case _thread_in_vm_trans:
 765     case _thread_in_Java:        // From compiled code
 766 
 767       // We are highly likely to block on the Safepoint_lock. In order to avoid blocking in this case,
 768       // we pretend we are still in the VM.
 769       thread->set_thread_state(_thread_in_vm);
 770 
 771       if (is_synchronizing()) {
 772          Atomic::inc (&TryingToBlock) ;
 773       }
 774 
 775       // We will always be holding the Safepoint_lock when we are examine the state
 776       // of a thread. Hence, the instructions between the Safepoint_lock->lock() and
 777       // Safepoint_lock->unlock() are happening atomic with regards to the safepoint code
 778       Safepoint_lock->lock_without_safepoint_check();
 779       if (is_synchronizing()) {
 780         // Decrement the number of threads to wait for and signal vm thread
 781         assert(_waiting_to_block > 0, "sanity check");
 782         _waiting_to_block--;
 783         thread->safepoint_state()->set_has_called_back(true);
 784 
 785         DEBUG_ONLY(thread->set_visited_for_critical_count(true));
 786         if (thread->in_critical()) {
 787           // Notice that this thread is in a critical section
 788           increment_jni_active_count();
 789         }
 790 
 791         // Consider (_waiting_to_block < 2) to pipeline the wakeup of the VM thread
 792         if (_waiting_to_block == 0) {
 793           Safepoint_lock->notify_all();
 794         }
 795       }
 796 
 797       // We transition the thread to state _thread_blocked here, but
 798       // we can't do our usual check for external suspension and then
 799       // self-suspend after the lock_without_safepoint_check() call
 800       // below because we are often called during transitions while
 801       // we hold different locks. That would leave us suspended while
 802       // holding a resource which results in deadlocks.
 803       thread->set_thread_state(_thread_blocked);
 804       Safepoint_lock->unlock();
 805 
 806       // We now try to acquire the threads lock. Since this lock is hold by the VM thread during
 807       // the entire safepoint, the threads will all line up here during the safepoint.
 808       Threads_lock->lock_without_safepoint_check();
 809       // restore original state. This is important if the thread comes from compiled code, so it
 810       // will continue to execute with the _thread_in_Java state.
 811       thread->set_thread_state(state);
 812       Threads_lock->unlock();
 813       break;
 814 
 815     case _thread_in_native_trans:
 816     case _thread_blocked_trans:
 817     case _thread_new_trans:
 818       if (thread->safepoint_state()->type() == ThreadSafepointState::_call_back) {
 819         thread->print_thread_state();
 820         fatal("Deadlock in safepoint code.  "
 821               "Should have called back to the VM before blocking.");
 822       }
 823 
 824       // We transition the thread to state _thread_blocked here, but
 825       // we can't do our usual check for external suspension and then
 826       // self-suspend after the lock_without_safepoint_check() call
 827       // below because we are often called during transitions while
 828       // we hold different locks. That would leave us suspended while
 829       // holding a resource which results in deadlocks.
 830       thread->set_thread_state(_thread_blocked);
 831 
 832       // It is not safe to suspend a thread if we discover it is in _thread_in_native_trans. Hence,
 833       // the safepoint code might still be waiting for it to block. We need to change the state here,
 834       // so it can see that it is at a safepoint.
 835 
 836       // Block until the safepoint operation is completed.
 837       Threads_lock->lock_without_safepoint_check();
 838 
 839       // Restore state
 840       thread->set_thread_state(state);
 841 
 842       Threads_lock->unlock();
 843       break;
 844 
 845     default:
 846      fatal("Illegal threadstate encountered: %d", state);
 847   }
 848 
 849   // Check for pending. async. exceptions or suspends - except if the
 850   // thread was blocked inside the VM. has_special_runtime_exit_condition()
 851   // is called last since it grabs a lock and we only want to do that when
 852   // we must.
 853   //
 854   // Note: we never deliver an async exception at a polling point as the
 855   // compiler may not have an exception handler for it. The polling
 856   // code will notice the async and deoptimize and the exception will
 857   // be delivered. (Polling at a return point is ok though). Sure is
 858   // a lot of bother for a deprecated feature...
 859   //
 860   // We don't deliver an async exception if the thread state is
 861   // _thread_in_native_trans so JNI functions won't be called with
 862   // a surprising pending exception. If the thread state is going back to java,
 863   // async exception is checked in check_special_condition_for_native_trans().
 864 
 865   if (state != _thread_blocked_trans &&
 866       state != _thread_in_vm_trans &&
 867       thread->has_special_runtime_exit_condition()) {
 868     thread->handle_special_runtime_exit_condition(
 869       !thread->is_at_poll_safepoint() && (state != _thread_in_native_trans));
 870   }
 871 }
 872 
 873 // ------------------------------------------------------------------------------------------------------
 874 // Exception handlers
 875 
 876 
 877 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) {
 878   assert(thread->is_Java_thread(), "polling reference encountered by VM thread");
 879   assert(thread->thread_state() == _thread_in_Java, "should come from Java code");
 880   assert(SafepointSynchronize::is_synchronizing(), "polling encountered outside safepoint synchronization");
 881 
 882   if (ShowSafepointMsgs) {
 883     tty->print("handle_polling_page_exception: ");
 884   }
 885 
 886   if (PrintSafepointStatistics) {
 887     inc_page_trap_count();
 888   }
 889 
 890   ThreadSafepointState* state = thread->safepoint_state();
 891 
 892   state->handle_polling_page_exception();
 893 }
 894 
 895 
 896 void SafepointSynchronize::print_safepoint_timeout(SafepointTimeoutReason reason) {
 897   if (!timeout_error_printed) {
 898     timeout_error_printed = true;
 899     // Print out the thread info which didn't reach the safepoint for debugging
 900     // purposes (useful when there are lots of threads in the debugger).
 901     tty->cr();
 902     tty->print_cr("# SafepointSynchronize::begin: Timeout detected:");
 903     if (reason ==  _spinning_timeout) {
 904       tty->print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint.");
 905     } else if (reason == _blocking_timeout) {
 906       tty->print_cr("# SafepointSynchronize::begin: Timed out while waiting for threads to stop.");
 907     }
 908 
 909     tty->print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:");
 910     ThreadSafepointState *cur_state;
 911     ResourceMark rm;
 912     {
 913       ThreadsListHandle tlh;
 914       JavaThreadIterator jti(tlh.list());
 915       for (JavaThread *cur_thread = jti.first(); cur_thread != NULL; cur_thread = jti.next()) {
 916         cur_state = cur_thread->safepoint_state();
 917 
 918         if (cur_thread->thread_state() != _thread_blocked &&
 919             ((reason == _spinning_timeout && cur_state->is_running()) ||
 920              (reason == _blocking_timeout && !cur_state->has_called_back()))) {
 921           tty->print("# ");
 922           cur_thread->print();
 923           tty->cr();
 924         }
 925       }
 926     }
 927     tty->print_cr("# SafepointSynchronize::begin: (End of list)");
 928   }
 929 
 930   // To debug the long safepoint, specify both DieOnSafepointTimeout &
 931   // ShowMessageBoxOnError.
 932   if (DieOnSafepointTimeout) {
 933     fatal("Safepoint sync time longer than " INTX_FORMAT "ms detected when executing %s.",
 934           SafepointTimeoutDelay, VMThread::vm_safepoint_description());
 935   }
 936 }
 937 
 938 
 939 // -------------------------------------------------------------------------------------------------------
 940 // Implementation of ThreadSafepointState
 941 
 942 ThreadSafepointState::ThreadSafepointState(JavaThread *thread) {
 943   _thread = thread;
 944   _type   = _running;
 945   _has_called_back = false;
 946   _at_poll_safepoint = false;
 947 }
 948 
 949 void ThreadSafepointState::create(JavaThread *thread) {
 950   ThreadSafepointState *state = new ThreadSafepointState(thread);
 951   thread->set_safepoint_state(state);
 952 }
 953 
 954 void ThreadSafepointState::destroy(JavaThread *thread) {
 955   if (thread->safepoint_state()) {
 956     delete(thread->safepoint_state());
 957     thread->set_safepoint_state(NULL);
 958   }
 959 }
 960 
 961 void ThreadSafepointState::examine_state_of_thread() {
 962   assert(is_running(), "better be running or just have hit safepoint poll");
 963 
 964   JavaThreadState state = _thread->thread_state();
 965 
 966   // Save the state at the start of safepoint processing.
 967   _orig_thread_state = state;
 968 
 969   // Check for a thread that is suspended. Note that thread resume tries
 970   // to grab the Threads_lock which we own here, so a thread cannot be
 971   // resumed during safepoint synchronization.
 972 
 973   // We check to see if this thread is suspended without locking to
 974   // avoid deadlocking with a third thread that is waiting for this
 975   // thread to be suspended. The third thread can notice the safepoint
 976   // that we're trying to start at the beginning of its SR_lock->wait()
 977   // call. If that happens, then the third thread will block on the
 978   // safepoint while still holding the underlying SR_lock. We won't be
 979   // able to get the SR_lock and we'll deadlock.
 980   //
 981   // We don't need to grab the SR_lock here for two reasons:
 982   // 1) The suspend flags are both volatile and are set with an
 983   //    Atomic::cmpxchg() call so we should see the suspended
 984   //    state right away.
 985   // 2) We're being called from the safepoint polling loop; if
 986   //    we don't see the suspended state on this iteration, then
 987   //    we'll come around again.
 988   //
 989   bool is_suspended = _thread->is_ext_suspended();
 990   if (is_suspended) {
 991     roll_forward(_at_safepoint);
 992     return;
 993   }
 994 
 995   // Some JavaThread states have an initial safepoint state of
 996   // running, but are actually at a safepoint. We will happily
 997   // agree and update the safepoint state here.
 998   if (SafepointSynchronize::safepoint_safe(_thread, state)) {
 999     SafepointSynchronize::check_for_lazy_critical_native(_thread, state);
1000     roll_forward(_at_safepoint);
1001     return;
1002   }
1003 
1004   if (state == _thread_in_vm) {
1005     roll_forward(_call_back);
1006     return;
1007   }
1008 
1009   // All other thread states will continue to run until they
1010   // transition and self-block in state _blocked
1011   // Safepoint polling in compiled code causes the Java threads to do the same.
1012   // Note: new threads may require a malloc so they must be allowed to finish
1013 
1014   assert(is_running(), "examine_state_of_thread on non-running thread");
1015   return;
1016 }
1017 
1018 // Returns true is thread could not be rolled forward at present position.
1019 void ThreadSafepointState::roll_forward(suspend_type type) {
1020   _type = type;
1021 
1022   switch(_type) {
1023     case _at_safepoint:
1024       SafepointSynchronize::signal_thread_at_safepoint();
1025       DEBUG_ONLY(_thread->set_visited_for_critical_count(true));
1026       if (_thread->in_critical()) {
1027         // Notice that this thread is in a critical section
1028         SafepointSynchronize::increment_jni_active_count();
1029       }
1030       break;
1031 
1032     case _call_back:
1033       set_has_called_back(false);
1034       break;
1035 
1036     case _running:
1037     default:
1038       ShouldNotReachHere();
1039   }
1040 }
1041 
1042 void ThreadSafepointState::restart() {
1043   switch(type()) {
1044     case _at_safepoint:
1045     case _call_back:
1046       break;
1047 
1048     case _running:
1049     default:
1050        tty->print_cr("restart thread " INTPTR_FORMAT " with state %d",
1051                      p2i(_thread), _type);
1052        _thread->print();
1053       ShouldNotReachHere();
1054   }
1055   _type = _running;
1056   set_has_called_back(false);
1057 }
1058 
1059 
1060 void ThreadSafepointState::print_on(outputStream *st) const {
1061   const char *s = NULL;
1062 
1063   switch(_type) {
1064     case _running                : s = "_running";              break;
1065     case _at_safepoint           : s = "_at_safepoint";         break;
1066     case _call_back              : s = "_call_back";            break;
1067     default:
1068       ShouldNotReachHere();
1069   }
1070 
1071   st->print_cr("Thread: " INTPTR_FORMAT
1072               "  [0x%2x] State: %s _has_called_back %d _at_poll_safepoint %d",
1073                p2i(_thread), _thread->osthread()->thread_id(), s, _has_called_back,
1074                _at_poll_safepoint);
1075 
1076   _thread->print_thread_state_on(st);
1077 }
1078 
1079 // ---------------------------------------------------------------------------------------------------------------------
1080 
1081 // Block the thread at the safepoint poll or poll return.
1082 void ThreadSafepointState::handle_polling_page_exception() {
1083 
1084   // Check state.  block() will set thread state to thread_in_vm which will
1085   // cause the safepoint state _type to become _call_back.
1086   assert(type() == ThreadSafepointState::_running,
1087          "polling page exception on thread not running state");
1088 
1089   // Step 1: Find the nmethod from the return address
1090   if (ShowSafepointMsgs && Verbose) {
1091     tty->print_cr("Polling page exception at " INTPTR_FORMAT, p2i(thread()->saved_exception_pc()));
1092   }
1093   address real_return_addr = thread()->saved_exception_pc();
1094 
1095   CodeBlob *cb = CodeCache::find_blob(real_return_addr);
1096   assert(cb != NULL && cb->is_compiled(), "return address should be in nmethod");
1097   CompiledMethod* nm = (CompiledMethod*)cb;
1098 
1099   // Find frame of caller
1100   frame stub_fr = thread()->last_frame();
1101   CodeBlob* stub_cb = stub_fr.cb();
1102   assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub");
1103   RegisterMap map(thread(), true);
1104   frame caller_fr = stub_fr.sender(&map);
1105 
1106   // Should only be poll_return or poll
1107   assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" );
1108 
1109   // This is a poll immediately before a return. The exception handling code
1110   // has already had the effect of causing the return to occur, so the execution
1111   // will continue immediately after the call. In addition, the oopmap at the
1112   // return point does not mark the return value as an oop (if it is), so
1113   // it needs a handle here to be updated.
1114   if( nm->is_at_poll_return(real_return_addr) ) {
1115     // See if return type is an oop.
1116     bool return_oop = nm->method()->is_returning_oop();
1117     Handle return_value;
1118     if (return_oop) {
1119       // The oop result has been saved on the stack together with all
1120       // the other registers. In order to preserve it over GCs we need
1121       // to keep it in a handle.
1122       oop result = caller_fr.saved_oop_result(&map);
1123       assert(oopDesc::is_oop_or_null(result), "must be oop");
1124       return_value = Handle(thread(), result);
1125       assert(Universe::heap()->is_in_or_null(result), "must be heap pointer");
1126     }
1127 
1128     // Block the thread
1129     SafepointSynchronize::block(thread());
1130 
1131     // restore oop result, if any
1132     if (return_oop) {
1133       caller_fr.set_saved_oop_result(&map, return_value());
1134     }
1135   }
1136 
1137   // This is a safepoint poll. Verify the return address and block.
1138   else {
1139     set_at_poll_safepoint(true);
1140 
1141     // verify the blob built the "return address" correctly
1142     assert(real_return_addr == caller_fr.pc(), "must match");
1143 
1144     // Block the thread
1145     SafepointSynchronize::block(thread());
1146     set_at_poll_safepoint(false);
1147 
1148     // If we have a pending async exception deoptimize the frame
1149     // as otherwise we may never deliver it.
1150     if (thread()->has_async_condition()) {
1151       ThreadInVMfromJavaNoAsyncException __tiv(thread());
1152       Deoptimization::deoptimize_frame(thread(), caller_fr.id());
1153     }
1154 
1155     // If an exception has been installed we must check for a pending deoptimization
1156     // Deoptimize frame if exception has been thrown.
1157 
1158     if (thread()->has_pending_exception() ) {
1159       RegisterMap map(thread(), true);
1160       frame caller_fr = stub_fr.sender(&map);
1161       if (caller_fr.is_deoptimized_frame()) {
1162         // The exception patch will destroy registers that are still
1163         // live and will be needed during deoptimization. Defer the
1164         // Async exception should have deferred the exception until the
1165         // next safepoint which will be detected when we get into
1166         // the interpreter so if we have an exception now things
1167         // are messed up.
1168 
1169         fatal("Exception installed and deoptimization is pending");
1170       }
1171     }
1172   }
1173 }
1174 
1175 
1176 //
1177 //                     Statistics & Instrumentations
1178 //
1179 SafepointSynchronize::SafepointStats*  SafepointSynchronize::_safepoint_stats = NULL;
1180 jlong  SafepointSynchronize::_safepoint_begin_time = 0;
1181 int    SafepointSynchronize::_cur_stat_index = 0;
1182 julong SafepointSynchronize::_safepoint_reasons[VM_Operation::VMOp_Terminating];
1183 julong SafepointSynchronize::_coalesced_vmop_count = 0;
1184 jlong  SafepointSynchronize::_max_sync_time = 0;
1185 jlong  SafepointSynchronize::_max_vmop_time = 0;
1186 float  SafepointSynchronize::_ts_of_current_safepoint = 0.0f;
1187 
1188 static jlong  cleanup_end_time = 0;
1189 static bool   need_to_track_page_armed_status = false;
1190 static bool   init_done = false;
1191 
1192 // Helper method to print the header.
1193 static void print_header() {
1194   // The number of spaces is significant here, and should match the format
1195   // specifiers in print_statistics().
1196 
1197   tty->print("          vmop                            "
1198              "[ threads:    total initially_running wait_to_block ]"
1199              "[ time:    spin   block    sync cleanup    vmop ] ");
1200 
1201   // no page armed status printed out if it is always armed.
1202   if (need_to_track_page_armed_status) {
1203     tty->print("page_armed ");
1204   }
1205 
1206   tty->print_cr("page_trap_count");
1207 }
1208 
1209 void SafepointSynchronize::deferred_initialize_stat() {
1210   if (init_done) return;
1211 
1212   // If PrintSafepointStatisticsTimeout is specified, the statistics data will
1213   // be printed right away, in which case, _safepoint_stats will regress to
1214   // a single element array. Otherwise, it is a circular ring buffer with default
1215   // size of PrintSafepointStatisticsCount.
1216   int stats_array_size;
1217   if (PrintSafepointStatisticsTimeout > 0) {
1218     stats_array_size = 1;
1219     PrintSafepointStatistics = true;
1220   } else {
1221     stats_array_size = PrintSafepointStatisticsCount;
1222   }
1223   _safepoint_stats = (SafepointStats*)os::malloc(stats_array_size
1224                                                  * sizeof(SafepointStats), mtInternal);
1225   guarantee(_safepoint_stats != NULL,
1226             "not enough memory for safepoint instrumentation data");
1227 
1228   if (DeferPollingPageLoopCount >= 0) {
1229     need_to_track_page_armed_status = true;
1230   }
1231   init_done = true;
1232 }
1233 
1234 void SafepointSynchronize::begin_statistics(int nof_threads, int nof_running) {
1235   assert(init_done, "safepoint statistics array hasn't been initialized");
1236   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1237 
1238   spstat->_time_stamp = _ts_of_current_safepoint;
1239 
1240   VM_Operation *op = VMThread::vm_operation();
1241   spstat->_vmop_type = (op != NULL ? op->type() : -1);
1242   if (op != NULL) {
1243     _safepoint_reasons[spstat->_vmop_type]++;
1244   }
1245 
1246   spstat->_nof_total_threads = nof_threads;
1247   spstat->_nof_initial_running_threads = nof_running;
1248   spstat->_nof_threads_hit_page_trap = 0;
1249 
1250   // Records the start time of spinning. The real time spent on spinning
1251   // will be adjusted when spin is done. Same trick is applied for time
1252   // spent on waiting for threads to block.
1253   if (nof_running != 0) {
1254     spstat->_time_to_spin = os::javaTimeNanos();
1255   }  else {
1256     spstat->_time_to_spin = 0;
1257   }
1258 }
1259 
1260 void SafepointSynchronize::update_statistics_on_spin_end() {
1261   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1262 
1263   jlong cur_time = os::javaTimeNanos();
1264 
1265   spstat->_nof_threads_wait_to_block = _waiting_to_block;
1266   if (spstat->_nof_initial_running_threads != 0) {
1267     spstat->_time_to_spin = cur_time - spstat->_time_to_spin;
1268   }
1269 
1270   if (need_to_track_page_armed_status) {
1271     spstat->_page_armed = (PageArmed == 1);
1272   }
1273 
1274   // Records the start time of waiting for to block. Updated when block is done.
1275   if (_waiting_to_block != 0) {
1276     spstat->_time_to_wait_to_block = cur_time;
1277   } else {
1278     spstat->_time_to_wait_to_block = 0;
1279   }
1280 }
1281 
1282 void SafepointSynchronize::update_statistics_on_sync_end(jlong end_time) {
1283   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1284 
1285   if (spstat->_nof_threads_wait_to_block != 0) {
1286     spstat->_time_to_wait_to_block = end_time -
1287       spstat->_time_to_wait_to_block;
1288   }
1289 
1290   // Records the end time of sync which will be used to calculate the total
1291   // vm operation time. Again, the real time spending in syncing will be deducted
1292   // from the start of the sync time later when end_statistics is called.
1293   spstat->_time_to_sync = end_time - _safepoint_begin_time;
1294   if (spstat->_time_to_sync > _max_sync_time) {
1295     _max_sync_time = spstat->_time_to_sync;
1296   }
1297 
1298   spstat->_time_to_do_cleanups = end_time;
1299 }
1300 
1301 void SafepointSynchronize::update_statistics_on_cleanup_end(jlong end_time) {
1302   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1303 
1304   // Record how long spent in cleanup tasks.
1305   spstat->_time_to_do_cleanups = end_time - spstat->_time_to_do_cleanups;
1306 
1307   cleanup_end_time = end_time;
1308 }
1309 
1310 void SafepointSynchronize::end_statistics(jlong vmop_end_time) {
1311   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1312 
1313   // Update the vm operation time.
1314   spstat->_time_to_exec_vmop = vmop_end_time -  cleanup_end_time;
1315   if (spstat->_time_to_exec_vmop > _max_vmop_time) {
1316     _max_vmop_time = spstat->_time_to_exec_vmop;
1317   }
1318   // Only the sync time longer than the specified
1319   // PrintSafepointStatisticsTimeout will be printed out right away.
1320   // By default, it is -1 meaning all samples will be put into the list.
1321   if ( PrintSafepointStatisticsTimeout > 0) {
1322     if (spstat->_time_to_sync > (jlong)PrintSafepointStatisticsTimeout * MICROUNITS) {
1323       print_statistics();
1324     }
1325   } else {
1326     // The safepoint statistics will be printed out when the _safepoin_stats
1327     // array fills up.
1328     if (_cur_stat_index == PrintSafepointStatisticsCount - 1) {
1329       print_statistics();
1330       _cur_stat_index = 0;
1331     } else {
1332       _cur_stat_index++;
1333     }
1334   }
1335 }
1336 
1337 void SafepointSynchronize::print_statistics() {
1338   for (int index = 0; index <= _cur_stat_index; index++) {
1339     if (index % 30 == 0) {
1340       print_header();
1341     }
1342     SafepointStats* sstats = &_safepoint_stats[index];
1343     tty->print("%8.3f: ", sstats->_time_stamp);
1344     tty->print("%-30s  [          "
1345                INT32_FORMAT_W(8) " " INT32_FORMAT_W(17) " " INT32_FORMAT_W(13) " "
1346                "]",
1347                (sstats->_vmop_type == -1 ? "no vm operation" : VM_Operation::name(sstats->_vmop_type)),
1348                sstats->_nof_total_threads,
1349                sstats->_nof_initial_running_threads,
1350                sstats->_nof_threads_wait_to_block);
1351     // "/ MICROUNITS " is to convert the unit from nanos to millis.
1352     tty->print("[       "
1353                INT64_FORMAT_W(7) " " INT64_FORMAT_W(7) " "
1354                INT64_FORMAT_W(7) " " INT64_FORMAT_W(7) " "
1355                INT64_FORMAT_W(7) " ] ",
1356                (int64_t)(sstats->_time_to_spin / MICROUNITS),
1357                (int64_t)(sstats->_time_to_wait_to_block / MICROUNITS),
1358                (int64_t)(sstats->_time_to_sync / MICROUNITS),
1359                (int64_t)(sstats->_time_to_do_cleanups / MICROUNITS),
1360                (int64_t)(sstats->_time_to_exec_vmop / MICROUNITS));
1361 
1362     if (need_to_track_page_armed_status) {
1363       tty->print(INT32_FORMAT_W(10) " ", sstats->_page_armed);
1364     }
1365     tty->print_cr(INT32_FORMAT_W(15) " ", sstats->_nof_threads_hit_page_trap);
1366   }
1367 }
1368 
1369 // This method will be called when VM exits. It will first call
1370 // print_statistics to print out the rest of the sampling.  Then
1371 // it tries to summarize the sampling.
1372 void SafepointSynchronize::print_stat_on_exit() {
1373   if (_safepoint_stats == NULL) return;
1374 
1375   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1376 
1377   // During VM exit, end_statistics may not get called and in that
1378   // case, if the sync time is less than PrintSafepointStatisticsTimeout,
1379   // don't print it out.
1380   // Approximate the vm op time.
1381   _safepoint_stats[_cur_stat_index]._time_to_exec_vmop =
1382     os::javaTimeNanos() - cleanup_end_time;
1383 
1384   if ( PrintSafepointStatisticsTimeout < 0 ||
1385        spstat->_time_to_sync > (jlong)PrintSafepointStatisticsTimeout * MICROUNITS) {
1386     print_statistics();
1387   }
1388   tty->cr();
1389 
1390   // Print out polling page sampling status.
1391   if (!need_to_track_page_armed_status) {
1392     tty->print_cr("Polling page always armed");
1393   } else {
1394     tty->print_cr("Defer polling page loop count = " INTX_FORMAT "\n",
1395                   DeferPollingPageLoopCount);
1396   }
1397 
1398   for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) {
1399     if (_safepoint_reasons[index] != 0) {
1400       tty->print_cr("%-26s" UINT64_FORMAT_W(10), VM_Operation::name(index),
1401                     _safepoint_reasons[index]);
1402     }
1403   }
1404 
1405   tty->print_cr(UINT64_FORMAT_W(5) " VM operations coalesced during safepoint",
1406                 _coalesced_vmop_count);
1407   tty->print_cr("Maximum sync time  " INT64_FORMAT_W(5) " ms",
1408                 (int64_t)(_max_sync_time / MICROUNITS));
1409   tty->print_cr("Maximum vm operation time (except for Exit VM operation)  "
1410                 INT64_FORMAT_W(5) " ms",
1411                 (int64_t)(_max_vmop_time / MICROUNITS));
1412 }
1413 
1414 // ------------------------------------------------------------------------------------------------
1415 // Non-product code
1416 
1417 #ifndef PRODUCT
1418 
1419 void SafepointSynchronize::print_state() {
1420   if (_state == _not_synchronized) {
1421     tty->print_cr("not synchronized");
1422   } else if (_state == _synchronizing || _state == _synchronized) {
1423     tty->print_cr("State: %s", (_state == _synchronizing) ? "synchronizing" :
1424                   "synchronized");
1425 
1426     ThreadsListHandle tlh;
1427     JavaThreadIterator jti(tlh.list());
1428     for (JavaThread *cur = jti.first(); cur != NULL; cur = jti.next()) {
1429        cur->safepoint_state()->print();
1430     }
1431   }
1432 }
1433 
1434 void SafepointSynchronize::safepoint_msg(const char* format, ...) {
1435   if (ShowSafepointMsgs) {
1436     va_list ap;
1437     va_start(ap, format);
1438     tty->vprint_cr(format, ap);
1439     va_end(ap);
1440   }
1441 }
1442 
1443 #endif // !PRODUCT