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