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 "oops/valueKlass.hpp"
  46 #include "runtime/atomic.hpp"
  47 #include "runtime/compilationPolicy.hpp"
  48 #include "runtime/deoptimization.hpp"
  49 #include "runtime/frame.inline.hpp"
  50 #include "runtime/interfaceSupport.hpp"
  51 #include "runtime/mutexLocker.hpp"
  52 #include "runtime/orderAccess.inline.hpp"
  53 #include "runtime/osThread.hpp"
  54 #include "runtime/safepoint.hpp"
  55 #include "runtime/signature.hpp"
  56 #include "runtime/stubCodeGenerator.hpp"
  57 #include "runtime/stubRoutines.hpp"
  58 #include "runtime/sweeper.hpp"
  59 #include "runtime/synchronizer.hpp"
  60 #include "runtime/thread.inline.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 
 204 #ifdef ASSERT
 205     for (JavaThread *cur = Threads::first(); cur != NULL; cur = cur->next()) {
 206       assert(cur->safepoint_state()->is_running(), "Illegal initial state");
 207       // Clear the visited flag to ensure that the critical counts are collected properly.
 208       cur->set_visited_for_critical_count(false);
 209     }
 210 #endif // ASSERT
 211 
 212     if (SafepointTimeout)
 213       safepoint_limit_time = os::javaTimeNanos() + (jlong)SafepointTimeoutDelay * MICROUNITS;
 214 
 215     // Iterate through all threads until it have been determined how to stop them all at a safepoint
 216     unsigned int iterations = 0;
 217     int steps = 0 ;
 218     while(still_running > 0) {
 219       for (JavaThread *cur = Threads::first(); cur != NULL; cur = cur->next()) {
 220         assert(!cur->is_ConcurrentGC_thread(), "A concurrent GC thread is unexpectly being suspended");
 221         ThreadSafepointState *cur_state = cur->safepoint_state();
 222         if (cur_state->is_running()) {
 223           cur_state->examine_state_of_thread();
 224           if (!cur_state->is_running()) {
 225             still_running--;
 226             // consider adjusting steps downward:
 227             //   steps = 0
 228             //   steps -= NNN
 229             //   steps >>= 1
 230             //   steps = MIN(steps, 2000-100)
 231             //   if (iterations != 0) steps -= NNN
 232           }
 233           LogTarget(Trace, safepoint) lt;
 234           if (lt.is_enabled()) {
 235             ResourceMark rm;
 236             LogStream ls(lt);
 237             cur_state->print_on(&ls);
 238           }
 239         }
 240       }
 241 
 242       if (iterations == 0) {
 243         initial_running = still_running;
 244         if (PrintSafepointStatistics) {
 245           begin_statistics(nof_threads, still_running);
 246         }
 247       }
 248 
 249       if (still_running > 0) {
 250         // Check for if it takes to long
 251         if (SafepointTimeout && safepoint_limit_time < os::javaTimeNanos()) {
 252           print_safepoint_timeout(_spinning_timeout);
 253         }
 254 
 255         // Spin to avoid context switching.
 256         // There's a tension between allowing the mutators to run (and rendezvous)
 257         // vs spinning.  As the VM thread spins, wasting cycles, it consumes CPU that
 258         // a mutator might otherwise use profitably to reach a safepoint.  Excessive
 259         // spinning by the VM thread on a saturated system can increase rendezvous latency.
 260         // Blocking or yielding incur their own penalties in the form of context switching
 261         // and the resultant loss of $ residency.
 262         //
 263         // Further complicating matters is that yield() does not work as naively expected
 264         // on many platforms -- yield() does not guarantee that any other ready threads
 265         // will run.   As such we revert to naked_short_sleep() after some number of iterations.
 266         // nakes_short_sleep() is implemented as a short unconditional sleep.
 267         // Typical operating systems round a "short" sleep period up to 10 msecs, so sleeping
 268         // can actually increase the time it takes the VM thread to detect that a system-wide
 269         // stop-the-world safepoint has been reached.  In a pathological scenario such as that
 270         // described in CR6415670 the VMthread may sleep just before the mutator(s) become safe.
 271         // In that case the mutators will be stalled waiting for the safepoint to complete and the
 272         // the VMthread will be sleeping, waiting for the mutators to rendezvous.  The VMthread
 273         // will eventually wake up and detect that all mutators are safe, at which point
 274         // we'll again make progress.
 275         //
 276         // Beware too that that the VMThread typically runs at elevated priority.
 277         // Its default priority is higher than the default mutator priority.
 278         // Obviously, this complicates spinning.
 279         //
 280         // Note too that on Windows XP SwitchThreadTo() has quite different behavior than Sleep(0).
 281         // Sleep(0) will _not yield to lower priority threads, while SwitchThreadTo() will.
 282         //
 283         // See the comments in synchronizer.cpp for additional remarks on spinning.
 284         //
 285         // In the future we might:
 286         // 1. Modify the safepoint scheme to avoid potentially unbounded spinning.
 287         //    This is tricky as the path used by a thread exiting the JVM (say on
 288         //    on JNI call-out) simply stores into its state field.  The burden
 289         //    is placed on the VM thread, which must poll (spin).
 290         // 2. Find something useful to do while spinning.  If the safepoint is GC-related
 291         //    we might aggressively scan the stacks of threads that are already safe.
 292         // 3. Use Solaris schedctl to examine the state of the still-running mutators.
 293         //    If all the mutators are ONPROC there's no reason to sleep or yield.
 294         // 4. YieldTo() any still-running mutators that are ready but OFFPROC.
 295         // 5. Check system saturation.  If the system is not fully saturated then
 296         //    simply spin and avoid sleep/yield.
 297         // 6. As still-running mutators rendezvous they could unpark the sleeping
 298         //    VMthread.  This works well for still-running mutators that become
 299         //    safe.  The VMthread must still poll for mutators that call-out.
 300         // 7. Drive the policy on time-since-begin instead of iterations.
 301         // 8. Consider making the spin duration a function of the # of CPUs:
 302         //    Spin = (((ncpus-1) * M) + K) + F(still_running)
 303         //    Alternately, instead of counting iterations of the outer loop
 304         //    we could count the # of threads visited in the inner loop, above.
 305         // 9. On windows consider using the return value from SwitchThreadTo()
 306         //    to drive subsequent spin/SwitchThreadTo()/Sleep(N) decisions.
 307 
 308         if (int(iterations) == DeferPollingPageLoopCount) {
 309           guarantee (PageArmed == 0, "invariant") ;
 310           PageArmed = 1 ;
 311           os::make_polling_page_unreadable();
 312         }
 313 
 314         // Instead of (ncpus > 1) consider either (still_running < (ncpus + EPSILON)) or
 315         // ((still_running + _waiting_to_block - TryingToBlock)) < ncpus)
 316         ++steps ;
 317         if (ncpus > 1 && steps < SafepointSpinBeforeYield) {
 318           SpinPause() ;     // MP-Polite spin
 319         } else
 320           if (steps < DeferThrSuspendLoopCount) {
 321             os::naked_yield() ;
 322           } else {
 323             os::naked_short_sleep(1);
 324           }
 325 
 326         iterations ++ ;
 327       }
 328       assert(iterations < (uint)max_jint, "We have been iterating in the safepoint loop too long");
 329     }
 330     assert(still_running == 0, "sanity check");
 331 
 332     if (PrintSafepointStatistics) {
 333       update_statistics_on_spin_end();
 334     }
 335 
 336     if (sync_event.should_commit()) {
 337       sync_event.set_safepointId(safepoint_counter());
 338       sync_event.set_initialThreadCount(initial_running);
 339       sync_event.set_runningThreadCount(_waiting_to_block);
 340       sync_event.set_iterations(iterations);
 341       sync_event.commit();
 342     }
 343   } //EventSafepointStateSync
 344 
 345   // wait until all threads are stopped
 346   {
 347     EventSafepointWaitBlocked wait_blocked_event;
 348     int initial_waiting_to_block = _waiting_to_block;
 349 
 350     while (_waiting_to_block > 0) {
 351       log_debug(safepoint)("Waiting for %d thread(s) to block", _waiting_to_block);
 352       if (!SafepointTimeout || timeout_error_printed) {
 353         Safepoint_lock->wait(true);  // true, means with no safepoint checks
 354       } else {
 355         // Compute remaining time
 356         jlong remaining_time = safepoint_limit_time - os::javaTimeNanos();
 357 
 358         // If there is no remaining time, then there is an error
 359         if (remaining_time < 0 || Safepoint_lock->wait(true, remaining_time / MICROUNITS)) {
 360           print_safepoint_timeout(_blocking_timeout);
 361         }
 362       }
 363     }
 364     assert(_waiting_to_block == 0, "sanity check");
 365 
 366 #ifndef PRODUCT
 367     if (SafepointTimeout) {
 368       jlong current_time = os::javaTimeNanos();
 369       if (safepoint_limit_time < current_time) {
 370         tty->print_cr("# SafepointSynchronize: Finished after "
 371                       INT64_FORMAT_W(6) " ms",
 372                       (int64_t)((current_time - safepoint_limit_time) / MICROUNITS +
 373                                 (jlong)SafepointTimeoutDelay));
 374       }
 375     }
 376 #endif
 377 
 378     assert((_safepoint_counter & 0x1) == 0, "must be even");
 379     assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
 380     _safepoint_counter ++;
 381 
 382     // Record state
 383     _state = _synchronized;
 384 
 385     OrderAccess::fence();
 386 
 387     if (wait_blocked_event.should_commit()) {
 388       wait_blocked_event.set_safepointId(safepoint_counter());
 389       wait_blocked_event.set_runningThreadCount(initial_waiting_to_block);
 390       wait_blocked_event.commit();
 391     }
 392   } // EventSafepointWaitBlocked
 393 
 394 #ifdef ASSERT
 395   for (JavaThread *cur = Threads::first(); cur != NULL; cur = cur->next()) {
 396     // make sure all the threads were visited
 397     assert(cur->was_visited_for_critical_count(), "missed a thread");
 398   }
 399 #endif // ASSERT
 400 
 401   // Update the count of active JNI critical regions
 402   GCLocker::set_jni_lock_count(_current_jni_active_count);
 403 
 404   if (log_is_enabled(Debug, safepoint)) {
 405     log_debug(safepoint)("Entering safepoint region: %s", VMThread::vm_safepoint_description());
 406   }
 407 
 408   RuntimeService::record_safepoint_synchronized();
 409   if (PrintSafepointStatistics) {
 410     update_statistics_on_sync_end(os::javaTimeNanos());
 411   }
 412 
 413   // Call stuff that needs to be run when a safepoint is just about to be completed
 414   {
 415     EventSafepointCleanup cleanup_event;
 416     do_cleanup_tasks();
 417     if (cleanup_event.should_commit()) {
 418       cleanup_event.set_safepointId(safepoint_counter());
 419       cleanup_event.commit();
 420     }
 421   }
 422 
 423   if (PrintSafepointStatistics) {
 424     // Record how much time spend on the above cleanup tasks
 425     update_statistics_on_cleanup_end(os::javaTimeNanos());
 426   }
 427   if (begin_event.should_commit()) {
 428     begin_event.set_safepointId(safepoint_counter());
 429     begin_event.set_totalThreadCount(nof_threads);
 430     begin_event.set_jniCriticalThreadCount(_current_jni_active_count);
 431     begin_event.commit();
 432   }
 433 }
 434 
 435 // Wake up all threads, so they are ready to resume execution after the safepoint
 436 // operation has been carried out
 437 void SafepointSynchronize::end() {
 438   EventSafepointEnd event;
 439   int safepoint_id = safepoint_counter(); // Keep the odd counter as "id"
 440 
 441   assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
 442   assert((_safepoint_counter & 0x1) == 1, "must be odd");
 443   _safepoint_counter ++;
 444   // memory fence isn't required here since an odd _safepoint_counter
 445   // value can do no harm and a fence is issued below anyway.
 446 
 447   DEBUG_ONLY(Thread* myThread = Thread::current();)
 448   assert(myThread->is_VM_thread(), "Only VM thread can execute a safepoint");
 449 
 450   if (PrintSafepointStatistics) {
 451     end_statistics(os::javaTimeNanos());
 452   }
 453 
 454 #ifdef ASSERT
 455   // A pending_exception cannot be installed during a safepoint.  The threads
 456   // may install an async exception after they come back from a safepoint into
 457   // pending_exception after they unblock.  But that should happen later.
 458   for(JavaThread *cur = Threads::first(); cur; cur = cur->next()) {
 459     assert (!(cur->has_pending_exception() &&
 460               cur->safepoint_state()->is_at_poll_safepoint()),
 461             "safepoint installed a pending exception");
 462   }
 463 #endif // ASSERT
 464 
 465   if (PageArmed) {
 466     // Make polling safepoint aware
 467     os::make_polling_page_readable();
 468     PageArmed = 0 ;
 469   }
 470 
 471   // Remove safepoint check from interpreter
 472   Interpreter::ignore_safepoints();
 473 
 474   {
 475     MutexLocker mu(Safepoint_lock);
 476 
 477     assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization");
 478 
 479     // Set to not synchronized, so the threads will not go into the signal_thread_blocked method
 480     // when they get restarted.
 481     _state = _not_synchronized;
 482     OrderAccess::fence();
 483 
 484     log_debug(safepoint)("Leaving safepoint region");
 485 
 486     // Start suspended threads
 487     for(JavaThread *current = Threads::first(); current; current = current->next()) {
 488       // A problem occurring on Solaris is when attempting to restart threads
 489       // the first #cpus - 1 go well, but then the VMThread is preempted when we get
 490       // to the next one (since it has been running the longest).  We then have
 491       // to wait for a cpu to become available before we can continue restarting
 492       // threads.
 493       // FIXME: This causes the performance of the VM to degrade when active and with
 494       // large numbers of threads.  Apparently this is due to the synchronous nature
 495       // of suspending threads.
 496       //
 497       // TODO-FIXME: the comments above are vestigial and no longer apply.
 498       // Furthermore, using solaris' schedctl in this particular context confers no benefit
 499       if (VMThreadHintNoPreempt) {
 500         os::hint_no_preempt();
 501       }
 502       ThreadSafepointState* cur_state = current->safepoint_state();
 503       assert(cur_state->type() != ThreadSafepointState::_running, "Thread not suspended at safepoint");
 504       cur_state->restart();
 505       assert(cur_state->is_running(), "safepoint state has not been reset");
 506     }
 507 
 508     RuntimeService::record_safepoint_end();
 509 
 510     // Release threads lock, so threads can be created/destroyed again. It will also starts all threads
 511     // blocked in signal_thread_blocked
 512     Threads_lock->unlock();
 513 
 514   }
 515 #if INCLUDE_ALL_GCS
 516   // If there are any concurrent GC threads resume them.
 517   if (UseConcMarkSweepGC) {
 518     ConcurrentMarkSweepThread::desynchronize(false);
 519   } else if (UseG1GC) {
 520     SuspendibleThreadSet::desynchronize();
 521   }
 522 #endif // INCLUDE_ALL_GCS
 523   // record this time so VMThread can keep track how much time has elapsed
 524   // since last safepoint.
 525   _end_of_last_safepoint = os::javaTimeMillis();
 526 
 527   if (event.should_commit()) {
 528     event.set_safepointId(safepoint_id);
 529     event.commit();
 530   }
 531 }
 532 
 533 bool SafepointSynchronize::is_cleanup_needed() {
 534   // Need a safepoint if there are many monitors to deflate.
 535   if (ObjectSynchronizer::is_cleanup_needed()) return true;
 536   // Need a safepoint if some inline cache buffers is non-empty
 537   if (!InlineCacheBuffer::is_empty()) return true;
 538   return false;
 539 }
 540 
 541 static void event_safepoint_cleanup_task_commit(EventSafepointCleanupTask& event, const char* name) {
 542   if (event.should_commit()) {
 543     event.set_safepointId(SafepointSynchronize::safepoint_counter());
 544     event.set_name(name);
 545     event.commit();
 546   }
 547 }
 548 
 549 class ParallelSPCleanupThreadClosure : public ThreadClosure {
 550 private:
 551   CodeBlobClosure* _nmethod_cl;
 552   DeflateMonitorCounters* _counters;
 553 
 554 public:
 555   ParallelSPCleanupThreadClosure(DeflateMonitorCounters* counters) :
 556     _counters(counters),
 557     _nmethod_cl(NMethodSweeper::prepare_mark_active_nmethods()) {}
 558 
 559   void do_thread(Thread* thread) {
 560     ObjectSynchronizer::deflate_thread_local_monitors(thread, _counters);
 561     if (_nmethod_cl != NULL && thread->is_Java_thread() &&
 562         ! thread->is_Code_cache_sweeper_thread()) {
 563       JavaThread* jt = (JavaThread*) thread;
 564       jt->nmethods_do(_nmethod_cl);
 565     }
 566   }
 567 };
 568 
 569 class ParallelSPCleanupTask : public AbstractGangTask {
 570 private:
 571   SubTasksDone _subtasks;
 572   ParallelSPCleanupThreadClosure _cleanup_threads_cl;
 573   uint _num_workers;
 574   DeflateMonitorCounters* _counters;
 575 public:
 576   ParallelSPCleanupTask(uint num_workers, DeflateMonitorCounters* counters) :
 577     AbstractGangTask("Parallel Safepoint Cleanup"),
 578     _cleanup_threads_cl(ParallelSPCleanupThreadClosure(counters)),
 579     _num_workers(num_workers),
 580     _subtasks(SubTasksDone(SafepointSynchronize::SAFEPOINT_CLEANUP_NUM_TASKS)),
 581     _counters(counters) {}
 582 
 583   void work(uint worker_id) {
 584     // All threads deflate monitors and mark nmethods (if necessary).
 585     Threads::parallel_java_threads_do(&_cleanup_threads_cl);
 586 
 587     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_DEFLATE_MONITORS)) {
 588       const char* name = "deflating idle monitors";
 589       EventSafepointCleanupTask event;
 590       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 591       ObjectSynchronizer::deflate_idle_monitors(_counters);
 592       event_safepoint_cleanup_task_commit(event, name);
 593     }
 594 
 595     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_UPDATE_INLINE_CACHES)) {
 596       const char* name = "updating inline caches";
 597       EventSafepointCleanupTask event;
 598       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 599       InlineCacheBuffer::update_inline_caches();
 600       event_safepoint_cleanup_task_commit(event, name);
 601     }
 602 
 603     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_COMPILATION_POLICY)) {
 604       const char* name = "compilation policy safepoint handler";
 605       EventSafepointCleanupTask event;
 606       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 607       CompilationPolicy::policy()->do_safepoint_work();
 608       event_safepoint_cleanup_task_commit(event, name);
 609     }
 610 
 611     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_SYMBOL_TABLE_REHASH)) {
 612       if (SymbolTable::needs_rehashing()) {
 613         const char* name = "rehashing symbol table";
 614         EventSafepointCleanupTask event;
 615         TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 616         SymbolTable::rehash_table();
 617         event_safepoint_cleanup_task_commit(event, name);
 618       }
 619     }
 620 
 621     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_STRING_TABLE_REHASH)) {
 622       if (StringTable::needs_rehashing()) {
 623         const char* name = "rehashing string table";
 624         EventSafepointCleanupTask event;
 625         TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 626         StringTable::rehash_table();
 627         event_safepoint_cleanup_task_commit(event, name);
 628       }
 629     }
 630 
 631     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_CLD_PURGE)) {
 632       // CMS delays purging the CLDG until the beginning of the next safepoint and to
 633       // make sure concurrent sweep is done
 634       const char* name = "purging class loader data graph";
 635       EventSafepointCleanupTask event;
 636       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 637       ClassLoaderDataGraph::purge_if_needed();
 638       event_safepoint_cleanup_task_commit(event, name);
 639     }
 640     _subtasks.all_tasks_completed(_num_workers);
 641   }
 642 };
 643 
 644 // Various cleaning tasks that should be done periodically at safepoints.
 645 void SafepointSynchronize::do_cleanup_tasks() {
 646 
 647   TraceTime timer("safepoint cleanup tasks", TRACETIME_LOG(Info, safepoint, cleanup));
 648 
 649   // Prepare for monitor deflation.
 650   DeflateMonitorCounters deflate_counters;
 651   ObjectSynchronizer::prepare_deflate_idle_monitors(&deflate_counters);
 652 
 653   CollectedHeap* heap = Universe::heap();
 654   assert(heap != NULL, "heap not initialized yet?");
 655   WorkGang* cleanup_workers = heap->get_safepoint_workers();
 656   if (cleanup_workers != NULL) {
 657     // Parallel cleanup using GC provided thread pool.
 658     uint num_cleanup_workers = cleanup_workers->active_workers();
 659     ParallelSPCleanupTask cleanup(num_cleanup_workers, &deflate_counters);
 660     StrongRootsScope srs(num_cleanup_workers);
 661     cleanup_workers->run_task(&cleanup);
 662   } else {
 663     // Serial cleanup using VMThread.
 664     ParallelSPCleanupTask cleanup(1, &deflate_counters);
 665     StrongRootsScope srs(1);
 666     cleanup.work(0);
 667   }
 668 
 669   // Finish monitor deflation.
 670   ObjectSynchronizer::finish_deflate_idle_monitors(&deflate_counters);
 671 }
 672 
 673 
 674 bool SafepointSynchronize::safepoint_safe(JavaThread *thread, JavaThreadState state) {
 675   switch(state) {
 676   case _thread_in_native:
 677     // native threads are safe if they have no java stack or have walkable stack
 678     return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable();
 679 
 680    // blocked threads should have already have walkable stack
 681   case _thread_blocked:
 682     assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable");
 683     return true;
 684 
 685   default:
 686     return false;
 687   }
 688 }
 689 
 690 
 691 // See if the thread is running inside a lazy critical native and
 692 // update the thread critical count if so.  Also set a suspend flag to
 693 // cause the native wrapper to return into the JVM to do the unlock
 694 // once the native finishes.
 695 void SafepointSynchronize::check_for_lazy_critical_native(JavaThread *thread, JavaThreadState state) {
 696   if (state == _thread_in_native &&
 697       thread->has_last_Java_frame() &&
 698       thread->frame_anchor()->walkable()) {
 699     // This thread might be in a critical native nmethod so look at
 700     // the top of the stack and increment the critical count if it
 701     // is.
 702     frame wrapper_frame = thread->last_frame();
 703     CodeBlob* stub_cb = wrapper_frame.cb();
 704     if (stub_cb != NULL &&
 705         stub_cb->is_nmethod() &&
 706         stub_cb->as_nmethod_or_null()->is_lazy_critical_native()) {
 707       // A thread could potentially be in a critical native across
 708       // more than one safepoint, so only update the critical state on
 709       // the first one.  When it returns it will perform the unlock.
 710       if (!thread->do_critical_native_unlock()) {
 711 #ifdef ASSERT
 712         if (!thread->in_critical()) {
 713           GCLocker::increment_debug_jni_lock_count();
 714         }
 715 #endif
 716         thread->enter_critical();
 717         // Make sure the native wrapper calls back on return to
 718         // perform the needed critical unlock.
 719         thread->set_critical_native_unlock();
 720       }
 721     }
 722   }
 723 }
 724 
 725 
 726 
 727 // -------------------------------------------------------------------------------------------------------
 728 // Implementation of Safepoint callback point
 729 
 730 void SafepointSynchronize::block(JavaThread *thread) {
 731   assert(thread != NULL, "thread must be set");
 732   assert(thread->is_Java_thread(), "not a Java thread");
 733 
 734   // Threads shouldn't block if they are in the middle of printing, but...
 735   ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id());
 736 
 737   // Only bail from the block() call if the thread is gone from the
 738   // thread list; starting to exit should still block.
 739   if (thread->is_terminated()) {
 740      // block current thread if we come here from native code when VM is gone
 741      thread->block_if_vm_exited();
 742 
 743      // otherwise do nothing
 744      return;
 745   }
 746 
 747   JavaThreadState state = thread->thread_state();
 748   thread->frame_anchor()->make_walkable(thread);
 749 
 750   // Check that we have a valid thread_state at this point
 751   switch(state) {
 752     case _thread_in_vm_trans:
 753     case _thread_in_Java:        // From compiled code
 754 
 755       // We are highly likely to block on the Safepoint_lock. In order to avoid blocking in this case,
 756       // we pretend we are still in the VM.
 757       thread->set_thread_state(_thread_in_vm);
 758 
 759       if (is_synchronizing()) {
 760          Atomic::inc (&TryingToBlock) ;
 761       }
 762 
 763       // We will always be holding the Safepoint_lock when we are examine the state
 764       // of a thread. Hence, the instructions between the Safepoint_lock->lock() and
 765       // Safepoint_lock->unlock() are happening atomic with regards to the safepoint code
 766       Safepoint_lock->lock_without_safepoint_check();
 767       if (is_synchronizing()) {
 768         // Decrement the number of threads to wait for and signal vm thread
 769         assert(_waiting_to_block > 0, "sanity check");
 770         _waiting_to_block--;
 771         thread->safepoint_state()->set_has_called_back(true);
 772 
 773         DEBUG_ONLY(thread->set_visited_for_critical_count(true));
 774         if (thread->in_critical()) {
 775           // Notice that this thread is in a critical section
 776           increment_jni_active_count();
 777         }
 778 
 779         // Consider (_waiting_to_block < 2) to pipeline the wakeup of the VM thread
 780         if (_waiting_to_block == 0) {
 781           Safepoint_lock->notify_all();
 782         }
 783       }
 784 
 785       // We transition the thread to state _thread_blocked here, but
 786       // we can't do our usual check for external suspension and then
 787       // self-suspend after the lock_without_safepoint_check() call
 788       // below because we are often called during transitions while
 789       // we hold different locks. That would leave us suspended while
 790       // holding a resource which results in deadlocks.
 791       thread->set_thread_state(_thread_blocked);
 792       Safepoint_lock->unlock();
 793 
 794       // We now try to acquire the threads lock. Since this lock is hold by the VM thread during
 795       // the entire safepoint, the threads will all line up here during the safepoint.
 796       Threads_lock->lock_without_safepoint_check();
 797       // restore original state. This is important if the thread comes from compiled code, so it
 798       // will continue to execute with the _thread_in_Java state.
 799       thread->set_thread_state(state);
 800       Threads_lock->unlock();
 801       break;
 802 
 803     case _thread_in_native_trans:
 804     case _thread_blocked_trans:
 805     case _thread_new_trans:
 806       if (thread->safepoint_state()->type() == ThreadSafepointState::_call_back) {
 807         thread->print_thread_state();
 808         fatal("Deadlock in safepoint code.  "
 809               "Should have called back to the VM before blocking.");
 810       }
 811 
 812       // We transition the thread to state _thread_blocked here, but
 813       // we can't do our usual check for external suspension and then
 814       // self-suspend after the lock_without_safepoint_check() call
 815       // below because we are often called during transitions while
 816       // we hold different locks. That would leave us suspended while
 817       // holding a resource which results in deadlocks.
 818       thread->set_thread_state(_thread_blocked);
 819 
 820       // It is not safe to suspend a thread if we discover it is in _thread_in_native_trans. Hence,
 821       // the safepoint code might still be waiting for it to block. We need to change the state here,
 822       // so it can see that it is at a safepoint.
 823 
 824       // Block until the safepoint operation is completed.
 825       Threads_lock->lock_without_safepoint_check();
 826 
 827       // Restore state
 828       thread->set_thread_state(state);
 829 
 830       Threads_lock->unlock();
 831       break;
 832 
 833     default:
 834      fatal("Illegal threadstate encountered: %d", state);
 835   }
 836 
 837   // Check for pending. async. exceptions or suspends - except if the
 838   // thread was blocked inside the VM. has_special_runtime_exit_condition()
 839   // is called last since it grabs a lock and we only want to do that when
 840   // we must.
 841   //
 842   // Note: we never deliver an async exception at a polling point as the
 843   // compiler may not have an exception handler for it. The polling
 844   // code will notice the async and deoptimize and the exception will
 845   // be delivered. (Polling at a return point is ok though). Sure is
 846   // a lot of bother for a deprecated feature...
 847   //
 848   // We don't deliver an async exception if the thread state is
 849   // _thread_in_native_trans so JNI functions won't be called with
 850   // a surprising pending exception. If the thread state is going back to java,
 851   // async exception is checked in check_special_condition_for_native_trans().
 852 
 853   if (state != _thread_blocked_trans &&
 854       state != _thread_in_vm_trans &&
 855       thread->has_special_runtime_exit_condition()) {
 856     thread->handle_special_runtime_exit_condition(
 857       !thread->is_at_poll_safepoint() && (state != _thread_in_native_trans));
 858   }
 859 }
 860 
 861 // ------------------------------------------------------------------------------------------------------
 862 // Exception handlers
 863 
 864 
 865 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) {
 866   assert(thread->is_Java_thread(), "polling reference encountered by VM thread");
 867   assert(thread->thread_state() == _thread_in_Java, "should come from Java code");
 868   assert(SafepointSynchronize::is_synchronizing(), "polling encountered outside safepoint synchronization");
 869 
 870   if (ShowSafepointMsgs) {
 871     tty->print("handle_polling_page_exception: ");
 872   }
 873 
 874   if (PrintSafepointStatistics) {
 875     inc_page_trap_count();
 876   }
 877 
 878   ThreadSafepointState* state = thread->safepoint_state();
 879 
 880   state->handle_polling_page_exception();
 881 }
 882 
 883 
 884 void SafepointSynchronize::print_safepoint_timeout(SafepointTimeoutReason reason) {
 885   if (!timeout_error_printed) {
 886     timeout_error_printed = true;
 887     // Print out the thread info which didn't reach the safepoint for debugging
 888     // purposes (useful when there are lots of threads in the debugger).
 889     tty->cr();
 890     tty->print_cr("# SafepointSynchronize::begin: Timeout detected:");
 891     if (reason ==  _spinning_timeout) {
 892       tty->print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint.");
 893     } else if (reason == _blocking_timeout) {
 894       tty->print_cr("# SafepointSynchronize::begin: Timed out while waiting for threads to stop.");
 895     }
 896 
 897     tty->print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:");
 898     ThreadSafepointState *cur_state;
 899     ResourceMark rm;
 900     for(JavaThread *cur_thread = Threads::first(); cur_thread;
 901         cur_thread = cur_thread->next()) {
 902       cur_state = cur_thread->safepoint_state();
 903 
 904       if (cur_thread->thread_state() != _thread_blocked &&
 905           ((reason == _spinning_timeout && cur_state->is_running()) ||
 906            (reason == _blocking_timeout && !cur_state->has_called_back()))) {
 907         tty->print("# ");
 908         cur_thread->print();
 909         tty->cr();
 910       }
 911     }
 912     tty->print_cr("# SafepointSynchronize::begin: (End of list)");
 913   }
 914 
 915   // To debug the long safepoint, specify both DieOnSafepointTimeout &
 916   // ShowMessageBoxOnError.
 917   if (DieOnSafepointTimeout) {
 918     fatal("Safepoint sync time longer than " INTX_FORMAT "ms detected when executing %s.",
 919           SafepointTimeoutDelay, VMThread::vm_safepoint_description());
 920   }
 921 }
 922 
 923 
 924 // -------------------------------------------------------------------------------------------------------
 925 // Implementation of ThreadSafepointState
 926 
 927 ThreadSafepointState::ThreadSafepointState(JavaThread *thread) {
 928   _thread = thread;
 929   _type   = _running;
 930   _has_called_back = false;
 931   _at_poll_safepoint = false;
 932 }
 933 
 934 void ThreadSafepointState::create(JavaThread *thread) {
 935   ThreadSafepointState *state = new ThreadSafepointState(thread);
 936   thread->set_safepoint_state(state);
 937 }
 938 
 939 void ThreadSafepointState::destroy(JavaThread *thread) {
 940   if (thread->safepoint_state()) {
 941     delete(thread->safepoint_state());
 942     thread->set_safepoint_state(NULL);
 943   }
 944 }
 945 
 946 void ThreadSafepointState::examine_state_of_thread() {
 947   assert(is_running(), "better be running or just have hit safepoint poll");
 948 
 949   JavaThreadState state = _thread->thread_state();
 950 
 951   // Save the state at the start of safepoint processing.
 952   _orig_thread_state = state;
 953 
 954   // Check for a thread that is suspended. Note that thread resume tries
 955   // to grab the Threads_lock which we own here, so a thread cannot be
 956   // resumed during safepoint synchronization.
 957 
 958   // We check to see if this thread is suspended without locking to
 959   // avoid deadlocking with a third thread that is waiting for this
 960   // thread to be suspended. The third thread can notice the safepoint
 961   // that we're trying to start at the beginning of its SR_lock->wait()
 962   // call. If that happens, then the third thread will block on the
 963   // safepoint while still holding the underlying SR_lock. We won't be
 964   // able to get the SR_lock and we'll deadlock.
 965   //
 966   // We don't need to grab the SR_lock here for two reasons:
 967   // 1) The suspend flags are both volatile and are set with an
 968   //    Atomic::cmpxchg() call so we should see the suspended
 969   //    state right away.
 970   // 2) We're being called from the safepoint polling loop; if
 971   //    we don't see the suspended state on this iteration, then
 972   //    we'll come around again.
 973   //
 974   bool is_suspended = _thread->is_ext_suspended();
 975   if (is_suspended) {
 976     roll_forward(_at_safepoint);
 977     return;
 978   }
 979 
 980   // Some JavaThread states have an initial safepoint state of
 981   // running, but are actually at a safepoint. We will happily
 982   // agree and update the safepoint state here.
 983   if (SafepointSynchronize::safepoint_safe(_thread, state)) {
 984     SafepointSynchronize::check_for_lazy_critical_native(_thread, state);
 985     roll_forward(_at_safepoint);
 986     return;
 987   }
 988 
 989   if (state == _thread_in_vm) {
 990     roll_forward(_call_back);
 991     return;
 992   }
 993 
 994   // All other thread states will continue to run until they
 995   // transition and self-block in state _blocked
 996   // Safepoint polling in compiled code causes the Java threads to do the same.
 997   // Note: new threads may require a malloc so they must be allowed to finish
 998 
 999   assert(is_running(), "examine_state_of_thread on non-running thread");
1000   return;
1001 }
1002 
1003 // Returns true is thread could not be rolled forward at present position.
1004 void ThreadSafepointState::roll_forward(suspend_type type) {
1005   _type = type;
1006 
1007   switch(_type) {
1008     case _at_safepoint:
1009       SafepointSynchronize::signal_thread_at_safepoint();
1010       DEBUG_ONLY(_thread->set_visited_for_critical_count(true));
1011       if (_thread->in_critical()) {
1012         // Notice that this thread is in a critical section
1013         SafepointSynchronize::increment_jni_active_count();
1014       }
1015       break;
1016 
1017     case _call_back:
1018       set_has_called_back(false);
1019       break;
1020 
1021     case _running:
1022     default:
1023       ShouldNotReachHere();
1024   }
1025 }
1026 
1027 void ThreadSafepointState::restart() {
1028   switch(type()) {
1029     case _at_safepoint:
1030     case _call_back:
1031       break;
1032 
1033     case _running:
1034     default:
1035        tty->print_cr("restart thread " INTPTR_FORMAT " with state %d",
1036                      p2i(_thread), _type);
1037        _thread->print();
1038       ShouldNotReachHere();
1039   }
1040   _type = _running;
1041   set_has_called_back(false);
1042 }
1043 
1044 
1045 void ThreadSafepointState::print_on(outputStream *st) const {
1046   const char *s = NULL;
1047 
1048   switch(_type) {
1049     case _running                : s = "_running";              break;
1050     case _at_safepoint           : s = "_at_safepoint";         break;
1051     case _call_back              : s = "_call_back";            break;
1052     default:
1053       ShouldNotReachHere();
1054   }
1055 
1056   st->print_cr("Thread: " INTPTR_FORMAT
1057               "  [0x%2x] State: %s _has_called_back %d _at_poll_safepoint %d",
1058                p2i(_thread), _thread->osthread()->thread_id(), s, _has_called_back,
1059                _at_poll_safepoint);
1060 
1061   _thread->print_thread_state_on(st);
1062 }
1063 
1064 // ---------------------------------------------------------------------------------------------------------------------
1065 
1066 // Block the thread at the safepoint poll or poll return.
1067 void ThreadSafepointState::handle_polling_page_exception() {
1068 
1069   // Check state.  block() will set thread state to thread_in_vm which will
1070   // cause the safepoint state _type to become _call_back.
1071   assert(type() == ThreadSafepointState::_running,
1072          "polling page exception on thread not running state");
1073 
1074   // Step 1: Find the nmethod from the return address
1075   if (ShowSafepointMsgs && Verbose) {
1076     tty->print_cr("Polling page exception at " INTPTR_FORMAT, p2i(thread()->saved_exception_pc()));
1077   }
1078   address real_return_addr = thread()->saved_exception_pc();
1079 
1080   CodeBlob *cb = CodeCache::find_blob(real_return_addr);
1081   assert(cb != NULL && cb->is_compiled(), "return address should be in nmethod");
1082   CompiledMethod* nm = (CompiledMethod*)cb;
1083 
1084   // Find frame of caller
1085   frame stub_fr = thread()->last_frame();
1086   CodeBlob* stub_cb = stub_fr.cb();
1087   assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub");
1088   RegisterMap map(thread(), true);
1089   frame caller_fr = stub_fr.sender(&map);
1090 
1091   // Should only be poll_return or poll
1092   assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" );
1093 
1094   // This is a poll immediately before a return. The exception handling code
1095   // has already had the effect of causing the return to occur, so the execution
1096   // will continue immediately after the call. In addition, the oopmap at the
1097   // return point does not mark the return value as an oop (if it is), so
1098   // it needs a handle here to be updated.
1099   if( nm->is_at_poll_return(real_return_addr) ) {
1100     ResourceMark rm;
1101     // See if return type is an oop.
1102     Method* method = nm->method();
1103     bool return_oop = method->is_returning_oop();
1104 
1105     GrowableArray<Handle> return_values;
1106     ValueKlass* vk = NULL;
1107     if (method->is_returning_vt() && ValueTypeReturnedAsFields) {
1108       // Check if value type is returned as fields
1109       vk = ValueKlass::returned_value_klass(map);
1110       if (vk != NULL) {
1111         // We're at a safepoint at the return of a method that returns
1112         // multiple values. We must make sure we preserve the oop values
1113         // across the safepoint.
1114         assert(vk == method->returned_value_type(thread()), "bad value klass");
1115         vk->save_oop_fields(map, return_values);
1116         return_oop = false;
1117       }
1118     }
1119 
1120     if (return_oop) {
1121       // The oop result has been saved on the stack together with all
1122       // the other registers. In order to preserve it over GCs we need
1123       // to keep it in a handle.
1124       oop result = caller_fr.saved_oop_result(&map);
1125       assert(oopDesc::is_oop_or_null(result), "must be oop");
1126       return_values.push(Handle(thread(), result));
1127       assert(Universe::heap()->is_in_or_null(result), "must be heap pointer");
1128     }
1129 
1130     // Block the thread
1131     SafepointSynchronize::block(thread());
1132 
1133     // restore oop result, if any
1134     if (return_oop) {
1135       assert(return_values.length() == 1, "only one return value");
1136       caller_fr.set_saved_oop_result(&map, return_values.pop()());
1137     } else if (vk != NULL) {
1138       vk->restore_oop_results(map, return_values);
1139     }
1140   }
1141 
1142   // This is a safepoint poll. Verify the return address and block.
1143   else {
1144     set_at_poll_safepoint(true);
1145 
1146     // verify the blob built the "return address" correctly
1147     assert(real_return_addr == caller_fr.pc(), "must match");
1148 
1149     // Block the thread
1150     SafepointSynchronize::block(thread());
1151     set_at_poll_safepoint(false);
1152 
1153     // If we have a pending async exception deoptimize the frame
1154     // as otherwise we may never deliver it.
1155     if (thread()->has_async_condition()) {
1156       ThreadInVMfromJavaNoAsyncException __tiv(thread());
1157       Deoptimization::deoptimize_frame(thread(), caller_fr.id());
1158     }
1159 
1160     // If an exception has been installed we must check for a pending deoptimization
1161     // Deoptimize frame if exception has been thrown.
1162 
1163     if (thread()->has_pending_exception() ) {
1164       RegisterMap map(thread(), true);
1165       frame caller_fr = stub_fr.sender(&map);
1166       if (caller_fr.is_deoptimized_frame()) {
1167         // The exception patch will destroy registers that are still
1168         // live and will be needed during deoptimization. Defer the
1169         // Async exception should have deferred the exception until the
1170         // next safepoint which will be detected when we get into
1171         // the interpreter so if we have an exception now things
1172         // are messed up.
1173 
1174         fatal("Exception installed and deoptimization is pending");
1175       }
1176     }
1177   }
1178 }
1179 
1180 
1181 //
1182 //                     Statistics & Instrumentations
1183 //
1184 SafepointSynchronize::SafepointStats*  SafepointSynchronize::_safepoint_stats = NULL;
1185 jlong  SafepointSynchronize::_safepoint_begin_time = 0;
1186 int    SafepointSynchronize::_cur_stat_index = 0;
1187 julong SafepointSynchronize::_safepoint_reasons[VM_Operation::VMOp_Terminating];
1188 julong SafepointSynchronize::_coalesced_vmop_count = 0;
1189 jlong  SafepointSynchronize::_max_sync_time = 0;
1190 jlong  SafepointSynchronize::_max_vmop_time = 0;
1191 float  SafepointSynchronize::_ts_of_current_safepoint = 0.0f;
1192 
1193 static jlong  cleanup_end_time = 0;
1194 static bool   need_to_track_page_armed_status = false;
1195 static bool   init_done = false;
1196 
1197 // Helper method to print the header.
1198 static void print_header() {
1199   // The number of spaces is significant here, and should match the format
1200   // specifiers in print_statistics().
1201 
1202   tty->print("          vmop                            "
1203              "[ threads:    total initially_running wait_to_block ]"
1204              "[ time:    spin   block    sync cleanup    vmop ] ");
1205 
1206   // no page armed status printed out if it is always armed.
1207   if (need_to_track_page_armed_status) {
1208     tty->print("page_armed ");
1209   }
1210 
1211   tty->print_cr("page_trap_count");
1212 }
1213 
1214 void SafepointSynchronize::deferred_initialize_stat() {
1215   if (init_done) return;
1216 
1217   // If PrintSafepointStatisticsTimeout is specified, the statistics data will
1218   // be printed right away, in which case, _safepoint_stats will regress to
1219   // a single element array. Otherwise, it is a circular ring buffer with default
1220   // size of PrintSafepointStatisticsCount.
1221   int stats_array_size;
1222   if (PrintSafepointStatisticsTimeout > 0) {
1223     stats_array_size = 1;
1224     PrintSafepointStatistics = true;
1225   } else {
1226     stats_array_size = PrintSafepointStatisticsCount;
1227   }
1228   _safepoint_stats = (SafepointStats*)os::malloc(stats_array_size
1229                                                  * sizeof(SafepointStats), mtInternal);
1230   guarantee(_safepoint_stats != NULL,
1231             "not enough memory for safepoint instrumentation data");
1232 
1233   if (DeferPollingPageLoopCount >= 0) {
1234     need_to_track_page_armed_status = true;
1235   }
1236   init_done = true;
1237 }
1238 
1239 void SafepointSynchronize::begin_statistics(int nof_threads, int nof_running) {
1240   assert(init_done, "safepoint statistics array hasn't been initialized");
1241   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1242 
1243   spstat->_time_stamp = _ts_of_current_safepoint;
1244 
1245   VM_Operation *op = VMThread::vm_operation();
1246   spstat->_vmop_type = (op != NULL ? op->type() : -1);
1247   if (op != NULL) {
1248     _safepoint_reasons[spstat->_vmop_type]++;
1249   }
1250 
1251   spstat->_nof_total_threads = nof_threads;
1252   spstat->_nof_initial_running_threads = nof_running;
1253   spstat->_nof_threads_hit_page_trap = 0;
1254 
1255   // Records the start time of spinning. The real time spent on spinning
1256   // will be adjusted when spin is done. Same trick is applied for time
1257   // spent on waiting for threads to block.
1258   if (nof_running != 0) {
1259     spstat->_time_to_spin = os::javaTimeNanos();
1260   }  else {
1261     spstat->_time_to_spin = 0;
1262   }
1263 }
1264 
1265 void SafepointSynchronize::update_statistics_on_spin_end() {
1266   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1267 
1268   jlong cur_time = os::javaTimeNanos();
1269 
1270   spstat->_nof_threads_wait_to_block = _waiting_to_block;
1271   if (spstat->_nof_initial_running_threads != 0) {
1272     spstat->_time_to_spin = cur_time - spstat->_time_to_spin;
1273   }
1274 
1275   if (need_to_track_page_armed_status) {
1276     spstat->_page_armed = (PageArmed == 1);
1277   }
1278 
1279   // Records the start time of waiting for to block. Updated when block is done.
1280   if (_waiting_to_block != 0) {
1281     spstat->_time_to_wait_to_block = cur_time;
1282   } else {
1283     spstat->_time_to_wait_to_block = 0;
1284   }
1285 }
1286 
1287 void SafepointSynchronize::update_statistics_on_sync_end(jlong end_time) {
1288   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1289 
1290   if (spstat->_nof_threads_wait_to_block != 0) {
1291     spstat->_time_to_wait_to_block = end_time -
1292       spstat->_time_to_wait_to_block;
1293   }
1294 
1295   // Records the end time of sync which will be used to calculate the total
1296   // vm operation time. Again, the real time spending in syncing will be deducted
1297   // from the start of the sync time later when end_statistics is called.
1298   spstat->_time_to_sync = end_time - _safepoint_begin_time;
1299   if (spstat->_time_to_sync > _max_sync_time) {
1300     _max_sync_time = spstat->_time_to_sync;
1301   }
1302 
1303   spstat->_time_to_do_cleanups = end_time;
1304 }
1305 
1306 void SafepointSynchronize::update_statistics_on_cleanup_end(jlong end_time) {
1307   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1308 
1309   // Record how long spent in cleanup tasks.
1310   spstat->_time_to_do_cleanups = end_time - spstat->_time_to_do_cleanups;
1311 
1312   cleanup_end_time = end_time;
1313 }
1314 
1315 void SafepointSynchronize::end_statistics(jlong vmop_end_time) {
1316   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1317 
1318   // Update the vm operation time.
1319   spstat->_time_to_exec_vmop = vmop_end_time -  cleanup_end_time;
1320   if (spstat->_time_to_exec_vmop > _max_vmop_time) {
1321     _max_vmop_time = spstat->_time_to_exec_vmop;
1322   }
1323   // Only the sync time longer than the specified
1324   // PrintSafepointStatisticsTimeout will be printed out right away.
1325   // By default, it is -1 meaning all samples will be put into the list.
1326   if ( PrintSafepointStatisticsTimeout > 0) {
1327     if (spstat->_time_to_sync > (jlong)PrintSafepointStatisticsTimeout * MICROUNITS) {
1328       print_statistics();
1329     }
1330   } else {
1331     // The safepoint statistics will be printed out when the _safepoin_stats
1332     // array fills up.
1333     if (_cur_stat_index == PrintSafepointStatisticsCount - 1) {
1334       print_statistics();
1335       _cur_stat_index = 0;
1336     } else {
1337       _cur_stat_index++;
1338     }
1339   }
1340 }
1341 
1342 void SafepointSynchronize::print_statistics() {
1343   for (int index = 0; index <= _cur_stat_index; index++) {
1344     if (index % 30 == 0) {
1345       print_header();
1346     }
1347     SafepointStats* sstats = &_safepoint_stats[index];
1348     tty->print("%8.3f: ", sstats->_time_stamp);
1349     tty->print("%-30s  [          "
1350                INT32_FORMAT_W(8) " " INT32_FORMAT_W(17) " " INT32_FORMAT_W(13) " "
1351                "]",
1352                (sstats->_vmop_type == -1 ? "no vm operation" : VM_Operation::name(sstats->_vmop_type)),
1353                sstats->_nof_total_threads,
1354                sstats->_nof_initial_running_threads,
1355                sstats->_nof_threads_wait_to_block);
1356     // "/ MICROUNITS " is to convert the unit from nanos to millis.
1357     tty->print("[       "
1358                INT64_FORMAT_W(7) " " INT64_FORMAT_W(7) " "
1359                INT64_FORMAT_W(7) " " INT64_FORMAT_W(7) " "
1360                INT64_FORMAT_W(7) " ] ",
1361                (int64_t)(sstats->_time_to_spin / MICROUNITS),
1362                (int64_t)(sstats->_time_to_wait_to_block / MICROUNITS),
1363                (int64_t)(sstats->_time_to_sync / MICROUNITS),
1364                (int64_t)(sstats->_time_to_do_cleanups / MICROUNITS),
1365                (int64_t)(sstats->_time_to_exec_vmop / MICROUNITS));
1366 
1367     if (need_to_track_page_armed_status) {
1368       tty->print(INT32_FORMAT_W(10) " ", sstats->_page_armed);
1369     }
1370     tty->print_cr(INT32_FORMAT_W(15) " ", sstats->_nof_threads_hit_page_trap);
1371   }
1372 }
1373 
1374 // This method will be called when VM exits. It will first call
1375 // print_statistics to print out the rest of the sampling.  Then
1376 // it tries to summarize the sampling.
1377 void SafepointSynchronize::print_stat_on_exit() {
1378   if (_safepoint_stats == NULL) return;
1379 
1380   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1381 
1382   // During VM exit, end_statistics may not get called and in that
1383   // case, if the sync time is less than PrintSafepointStatisticsTimeout,
1384   // don't print it out.
1385   // Approximate the vm op time.
1386   _safepoint_stats[_cur_stat_index]._time_to_exec_vmop =
1387     os::javaTimeNanos() - cleanup_end_time;
1388 
1389   if ( PrintSafepointStatisticsTimeout < 0 ||
1390        spstat->_time_to_sync > (jlong)PrintSafepointStatisticsTimeout * MICROUNITS) {
1391     print_statistics();
1392   }
1393   tty->cr();
1394 
1395   // Print out polling page sampling status.
1396   if (!need_to_track_page_armed_status) {
1397     tty->print_cr("Polling page always armed");
1398   } else {
1399     tty->print_cr("Defer polling page loop count = " INTX_FORMAT "\n",
1400                   DeferPollingPageLoopCount);
1401   }
1402 
1403   for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) {
1404     if (_safepoint_reasons[index] != 0) {
1405       tty->print_cr("%-26s" UINT64_FORMAT_W(10), VM_Operation::name(index),
1406                     _safepoint_reasons[index]);
1407     }
1408   }
1409 
1410   tty->print_cr(UINT64_FORMAT_W(5) " VM operations coalesced during safepoint",
1411                 _coalesced_vmop_count);
1412   tty->print_cr("Maximum sync time  " INT64_FORMAT_W(5) " ms",
1413                 (int64_t)(_max_sync_time / MICROUNITS));
1414   tty->print_cr("Maximum vm operation time (except for Exit VM operation)  "
1415                 INT64_FORMAT_W(5) " ms",
1416                 (int64_t)(_max_vmop_time / MICROUNITS));
1417 }
1418 
1419 // ------------------------------------------------------------------------------------------------
1420 // Non-product code
1421 
1422 #ifndef PRODUCT
1423 
1424 void SafepointSynchronize::print_state() {
1425   if (_state == _not_synchronized) {
1426     tty->print_cr("not synchronized");
1427   } else if (_state == _synchronizing || _state == _synchronized) {
1428     tty->print_cr("State: %s", (_state == _synchronizing) ? "synchronizing" :
1429                   "synchronized");
1430 
1431     for(JavaThread *cur = Threads::first(); cur; cur = cur->next()) {
1432        cur->safepoint_state()->print();
1433     }
1434   }
1435 }
1436 
1437 void SafepointSynchronize::safepoint_msg(const char* format, ...) {
1438   if (ShowSafepointMsgs) {
1439     va_list ap;
1440     va_start(ap, format);
1441     tty->vprint_cr(format, ap);
1442     va_end(ap);
1443   }
1444 }
1445 
1446 #endif // !PRODUCT