1 /*
   2  * Copyright (c) 1997, 2018, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "classfile/classLoaderData.hpp"
  27 #include "classfile/stringTable.hpp"
  28 #include "classfile/symbolTable.hpp"
  29 #include "classfile/systemDictionary.hpp"
  30 #include "code/codeCache.hpp"
  31 #include "code/icBuffer.hpp"
  32 #include "code/nmethod.hpp"
  33 #include "code/pcDesc.hpp"
  34 #include "code/scopeDesc.hpp"
  35 #include "gc/shared/collectedHeap.hpp"
  36 #include "gc/shared/gcLocker.inline.hpp"
  37 #include "gc/shared/strongRootsScope.hpp"
  38 #include "gc/shared/workgroup.hpp"
  39 #include "interpreter/interpreter.hpp"
  40 #include "logging/log.hpp"
  41 #include "logging/logStream.hpp"
  42 #include "memory/resourceArea.hpp"
  43 #include "memory/universe.hpp"
  44 #include "oops/oop.inline.hpp"
  45 #include "oops/symbol.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/safepointMechanism.inline.hpp"
  56 #include "runtime/signature.hpp"
  57 #include "runtime/stubCodeGenerator.hpp"
  58 #include "runtime/stubRoutines.hpp"
  59 #include "runtime/sweeper.hpp"
  60 #include "runtime/synchronizer.hpp"
  61 #include "runtime/thread.inline.hpp"
  62 #include "runtime/threadSMR.hpp"
  63 #include "runtime/timerTrace.hpp"
  64 #include "services/runtimeService.hpp"
  65 #include "trace/tracing.hpp"
  66 #include "trace/traceMacros.hpp"
  67 #include "utilities/events.hpp"
  68 #include "utilities/macros.hpp"
  69 #ifdef COMPILER1
  70 #include "c1/c1_globals.hpp"
  71 #endif
  72 
  73 // --------------------------------------------------------------------------------------------------
  74 // Implementation of Safepoint begin/end
  75 
  76 SafepointSynchronize::SynchronizeState volatile SafepointSynchronize::_state = SafepointSynchronize::_not_synchronized;
  77 volatile int  SafepointSynchronize::_waiting_to_block = 0;
  78 volatile int SafepointSynchronize::_safepoint_counter = 0;
  79 int SafepointSynchronize::_current_jni_active_count = 0;
  80 long  SafepointSynchronize::_end_of_last_safepoint = 0;
  81 int SafepointSynchronize::_defer_thr_suspend_loop_count = 4000;
  82 static const int safepoint_spin_before_yield = 2000;
  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   Universe::heap()->safepoint_synchronize_begin();
  99 
 100   // By getting the Threads_lock, we assure that no threads are about to start or
 101   // exit. It is released again in SafepointSynchronize::end().
 102   Threads_lock->lock();
 103 
 104   assert( _state == _not_synchronized, "trying to safepoint synchronize with wrong state");
 105 
 106   int nof_threads = Threads::number_of_threads();
 107 
 108   log_debug(safepoint)("Safepoint synchronization initiated. (%d threads)", nof_threads);
 109 
 110   RuntimeService::record_safepoint_begin();
 111 
 112   MutexLocker mu(Safepoint_lock);
 113 
 114   // Reset the count of active JNI critical threads
 115   _current_jni_active_count = 0;
 116 
 117   // Set number of threads to wait for, before we initiate the callbacks
 118   _waiting_to_block = nof_threads;
 119   TryingToBlock     = 0 ;
 120   int still_running = nof_threads;
 121 
 122   // Save the starting time, so that it can be compared to see if this has taken
 123   // too long to complete.
 124   jlong safepoint_limit_time = 0;
 125   timeout_error_printed = false;
 126 
 127   // PrintSafepointStatisticsTimeout can be specified separately. When
 128   // specified, PrintSafepointStatistics will be set to true in
 129   // deferred_initialize_stat method. The initialization has to be done
 130   // early enough to avoid any races. See bug 6880029 for details.
 131   if (PrintSafepointStatistics || PrintSafepointStatisticsTimeout > 0) {
 132     deferred_initialize_stat();
 133   }
 134 
 135   // Begin the process of bringing the system to a safepoint.
 136   // Java threads can be in several different states and are
 137   // stopped by different mechanisms:
 138   //
 139   //  1. Running interpreted
 140   //     The interpreter dispatch table is changed to force it to
 141   //     check for a safepoint condition between bytecodes.
 142   //  2. Running in native code
 143   //     When returning from the native code, a Java thread must check
 144   //     the safepoint _state to see if we must block.  If the
 145   //     VM thread sees a Java thread in native, it does
 146   //     not wait for this thread to block.  The order of the memory
 147   //     writes and reads of both the safepoint state and the Java
 148   //     threads state is critical.  In order to guarantee that the
 149   //     memory writes are serialized with respect to each other,
 150   //     the VM thread issues a memory barrier instruction
 151   //     (on MP systems).  In order to avoid the overhead of issuing
 152   //     a memory barrier for each Java thread making native calls, each Java
 153   //     thread performs a write to a single memory page after changing
 154   //     the thread state.  The VM thread performs a sequence of
 155   //     mprotect OS calls which forces all previous writes from all
 156   //     Java threads to be serialized.  This is done in the
 157   //     os::serialize_thread_states() call.  This has proven to be
 158   //     much more efficient than executing a membar instruction
 159   //     on every call to native code.
 160   //  3. Running compiled Code
 161   //     Compiled code reads a global (Safepoint Polling) page that
 162   //     is set to fault if we are trying to get to a safepoint.
 163   //  4. Blocked
 164   //     A thread which is blocked will not be allowed to return from the
 165   //     block condition until the safepoint operation is complete.
 166   //  5. In VM or Transitioning between states
 167   //     If a Java thread is currently running in the VM or transitioning
 168   //     between states, the safepointing code will wait for the thread to
 169   //     block itself when it attempts transitions to a new state.
 170   //
 171   {
 172     EventSafepointStateSynchronization sync_event;
 173     int initial_running = 0;
 174 
 175     _state            = _synchronizing;
 176 
 177     if (SafepointMechanism::uses_thread_local_poll()) {
 178       // Arming the per thread poll while having _state != _not_synchronized means safepointing
 179       log_trace(safepoint)("Setting thread local yield flag for threads");
 180       for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
 181         // Make sure the threads start polling, it is time to yield.
 182         SafepointMechanism::arm_local_poll(cur); // release store, global state -> local state
 183       }
 184     }
 185     OrderAccess::fence(); // storestore|storeload, global state -> local state
 186 
 187     // Flush all thread states to memory
 188     if (!UseMembar) {
 189       os::serialize_thread_states();
 190     }
 191 
 192     if (SafepointMechanism::uses_global_page_poll()) {
 193       // Make interpreter safepoint aware
 194       Interpreter::notice_safepoints();
 195 
 196       // Make polling safepoint aware
 197       guarantee (PageArmed == 0, "invariant") ;
 198       PageArmed = 1 ;
 199       os::make_polling_page_unreadable();
 200     }
 201 
 202     // Consider using active_processor_count() ... but that call is expensive.
 203     int ncpus = os::processor_count() ;
 204     unsigned int iterations = 0;
 205 
 206     {
 207       JavaThreadIteratorWithHandle jtiwh;
 208 #ifdef ASSERT
 209       for (; JavaThread *cur = jtiwh.next(); ) {
 210         assert(cur->safepoint_state()->is_running(), "Illegal initial state");
 211         // Clear the visited flag to ensure that the critical counts are collected properly.
 212         cur->set_visited_for_critical_count(false);
 213       }
 214 #endif // ASSERT
 215 
 216       if (SafepointTimeout)
 217         safepoint_limit_time = os::javaTimeNanos() + (jlong)SafepointTimeoutDelay * MICROUNITS;
 218 
 219       // Iterate through all threads until it have been determined how to stop them all at a safepoint
 220       int steps = 0 ;
 221       while(still_running > 0) {
 222         jtiwh.rewind();
 223         for (; JavaThread *cur = jtiwh.next(); ) {
 224           assert(!cur->is_ConcurrentGC_thread(), "A concurrent GC thread is unexpectly being suspended");
 225           ThreadSafepointState *cur_state = cur->safepoint_state();
 226           if (cur_state->is_running()) {
 227             cur_state->examine_state_of_thread();
 228             if (!cur_state->is_running()) {
 229               still_running--;
 230               // consider adjusting steps downward:
 231               //   steps = 0
 232               //   steps -= NNN
 233               //   steps >>= 1
 234               //   steps = MIN(steps, 2000-100)
 235               //   if (iterations != 0) steps -= NNN
 236             }
 237             LogTarget(Trace, safepoint) lt;
 238             if (lt.is_enabled()) {
 239               ResourceMark rm;
 240               LogStream ls(lt);
 241               cur_state->print_on(&ls);
 242             }
 243           }
 244         }
 245 
 246         if (iterations == 0) {
 247           initial_running = still_running;
 248           if (PrintSafepointStatistics) {
 249             begin_statistics(nof_threads, still_running);
 250           }
 251         }
 252 
 253         if (still_running > 0) {
 254           // Check for if it takes to long
 255           if (SafepointTimeout && safepoint_limit_time < os::javaTimeNanos()) {
 256             print_safepoint_timeout(_spinning_timeout);
 257           }
 258 
 259           // Spin to avoid context switching.
 260           // There's a tension between allowing the mutators to run (and rendezvous)
 261           // vs spinning.  As the VM thread spins, wasting cycles, it consumes CPU that
 262           // a mutator might otherwise use profitably to reach a safepoint.  Excessive
 263           // spinning by the VM thread on a saturated system can increase rendezvous latency.
 264           // Blocking or yielding incur their own penalties in the form of context switching
 265           // and the resultant loss of $ residency.
 266           //
 267           // Further complicating matters is that yield() does not work as naively expected
 268           // on many platforms -- yield() does not guarantee that any other ready threads
 269           // will run.   As such we revert to naked_short_sleep() after some number of iterations.
 270           // nakes_short_sleep() is implemented as a short unconditional sleep.
 271           // Typical operating systems round a "short" sleep period up to 10 msecs, so sleeping
 272           // can actually increase the time it takes the VM thread to detect that a system-wide
 273           // stop-the-world safepoint has been reached.  In a pathological scenario such as that
 274           // described in CR6415670 the VMthread may sleep just before the mutator(s) become safe.
 275           // In that case the mutators will be stalled waiting for the safepoint to complete and the
 276           // the VMthread will be sleeping, waiting for the mutators to rendezvous.  The VMthread
 277           // will eventually wake up and detect that all mutators are safe, at which point
 278           // we'll again make progress.
 279           //
 280           // Beware too that that the VMThread typically runs at elevated priority.
 281           // Its default priority is higher than the default mutator priority.
 282           // Obviously, this complicates spinning.
 283           //
 284           // Note too that on Windows XP SwitchThreadTo() has quite different behavior than Sleep(0).
 285           // Sleep(0) will _not yield to lower priority threads, while SwitchThreadTo() will.
 286           //
 287           // See the comments in synchronizer.cpp for additional remarks on spinning.
 288           //
 289           // In the future we might:
 290           // 1. Modify the safepoint scheme to avoid potentially unbounded spinning.
 291           //    This is tricky as the path used by a thread exiting the JVM (say on
 292           //    on JNI call-out) simply stores into its state field.  The burden
 293           //    is placed on the VM thread, which must poll (spin).
 294           // 2. Find something useful to do while spinning.  If the safepoint is GC-related
 295           //    we might aggressively scan the stacks of threads that are already safe.
 296           // 3. Use Solaris schedctl to examine the state of the still-running mutators.
 297           //    If all the mutators are ONPROC there's no reason to sleep or yield.
 298           // 4. YieldTo() any still-running mutators that are ready but OFFPROC.
 299           // 5. Check system saturation.  If the system is not fully saturated then
 300           //    simply spin and avoid sleep/yield.
 301           // 6. As still-running mutators rendezvous they could unpark the sleeping
 302           //    VMthread.  This works well for still-running mutators that become
 303           //    safe.  The VMthread must still poll for mutators that call-out.
 304           // 7. Drive the policy on time-since-begin instead of iterations.
 305           // 8. Consider making the spin duration a function of the # of CPUs:
 306           //    Spin = (((ncpus-1) * M) + K) + F(still_running)
 307           //    Alternately, instead of counting iterations of the outer loop
 308           //    we could count the # of threads visited in the inner loop, above.
 309           // 9. On windows consider using the return value from SwitchThreadTo()
 310           //    to drive subsequent spin/SwitchThreadTo()/Sleep(N) decisions.
 311 
 312           if (int(iterations) == -1) { // overflow - something is wrong.
 313             // We can only overflow here when we are using global
 314             // polling pages. We keep this guarantee in its original
 315             // form so that searches of the bug database for this
 316             // failure mode find the right bugs.
 317             guarantee (PageArmed == 0, "invariant");
 318           }
 319 
 320           // Instead of (ncpus > 1) consider either (still_running < (ncpus + EPSILON)) or
 321           // ((still_running + _waiting_to_block - TryingToBlock)) < ncpus)
 322           ++steps ;
 323           if (ncpus > 1 && steps < safepoint_spin_before_yield) {
 324             SpinPause() ;     // MP-Polite spin
 325           } else
 326             if (steps < _defer_thr_suspend_loop_count) {
 327               os::naked_yield() ;
 328             } else {
 329               os::naked_short_sleep(1);
 330             }
 331 
 332           iterations ++ ;
 333         }
 334         assert(iterations < (uint)max_jint, "We have been iterating in the safepoint loop too long");
 335       }
 336     } // ThreadsListHandle destroyed here.
 337     assert(still_running == 0, "sanity check");
 338 
 339     if (PrintSafepointStatistics) {
 340       update_statistics_on_spin_end();
 341     }
 342 
 343     if (sync_event.should_commit()) {
 344       // Group this event together with the ones committed after the counter is increased
 345       sync_event.set_safepointId(safepoint_counter() + 1);
 346       sync_event.set_initialThreadCount(initial_running);
 347       sync_event.set_runningThreadCount(_waiting_to_block);
 348       sync_event.set_iterations(iterations);
 349       sync_event.commit();
 350     }
 351   } // EventSafepointStateSynchronization destroyed here.
 352 
 353   // wait until all threads are stopped
 354   {
 355     EventSafepointWaitBlocked wait_blocked_event;
 356     int initial_waiting_to_block = _waiting_to_block;
 357 
 358     while (_waiting_to_block > 0) {
 359       log_debug(safepoint)("Waiting for %d thread(s) to block", _waiting_to_block);
 360       if (!SafepointTimeout || timeout_error_printed) {
 361         Safepoint_lock->wait(true);  // true, means with no safepoint checks
 362       } else {
 363         // Compute remaining time
 364         jlong remaining_time = safepoint_limit_time - os::javaTimeNanos();
 365 
 366         // If there is no remaining time, then there is an error
 367         if (remaining_time < 0 || Safepoint_lock->wait(true, remaining_time / MICROUNITS)) {
 368           print_safepoint_timeout(_blocking_timeout);
 369         }
 370       }
 371     }
 372     assert(_waiting_to_block == 0, "sanity check");
 373 
 374 #ifndef PRODUCT
 375     if (SafepointTimeout) {
 376       jlong current_time = os::javaTimeNanos();
 377       if (safepoint_limit_time < current_time) {
 378         tty->print_cr("# SafepointSynchronize: Finished after "
 379                       INT64_FORMAT_W(6) " ms",
 380                       (int64_t)((current_time - safepoint_limit_time) / MICROUNITS +
 381                                 (jlong)SafepointTimeoutDelay));
 382       }
 383     }
 384 #endif
 385 
 386     assert((_safepoint_counter & 0x1) == 0, "must be even");
 387     assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
 388     _safepoint_counter ++;
 389 
 390     // Record state
 391     _state = _synchronized;
 392 
 393     OrderAccess::fence();
 394 
 395     if (wait_blocked_event.should_commit()) {
 396       wait_blocked_event.set_safepointId(safepoint_counter());
 397       wait_blocked_event.set_runningThreadCount(initial_waiting_to_block);
 398       wait_blocked_event.commit();
 399     }
 400   } // EventSafepointWaitBlocked
 401 
 402 #ifdef ASSERT
 403   // Make sure all the threads were visited.
 404   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
 405     assert(cur->was_visited_for_critical_count(), "missed a thread");
 406   }
 407 #endif // ASSERT
 408 
 409   // Update the count of active JNI critical regions
 410   GCLocker::set_jni_lock_count(_current_jni_active_count);
 411 
 412   log_info(safepoint)("Entering safepoint region: %s", VMThread::vm_safepoint_description());
 413 
 414   RuntimeService::record_safepoint_synchronized();
 415   if (PrintSafepointStatistics) {
 416     update_statistics_on_sync_end(os::javaTimeNanos());
 417   }
 418 
 419   // Call stuff that needs to be run when a safepoint is just about to be completed
 420   {
 421     EventSafepointCleanup cleanup_event;
 422     do_cleanup_tasks();
 423     if (cleanup_event.should_commit()) {
 424       cleanup_event.set_safepointId(safepoint_counter());
 425       cleanup_event.commit();
 426     }
 427   }
 428 
 429   if (PrintSafepointStatistics) {
 430     // Record how much time spend on the above cleanup tasks
 431     update_statistics_on_cleanup_end(os::javaTimeNanos());
 432   }
 433   if (begin_event.should_commit()) {
 434     begin_event.set_safepointId(safepoint_counter());
 435     begin_event.set_totalThreadCount(nof_threads);
 436     begin_event.set_jniCriticalThreadCount(_current_jni_active_count);
 437     begin_event.commit();
 438   }
 439 }
 440 
 441 // Wake up all threads, so they are ready to resume execution after the safepoint
 442 // operation has been carried out
 443 void SafepointSynchronize::end() {
 444   EventSafepointEnd event;
 445   int safepoint_id = safepoint_counter(); // Keep the odd counter as "id"
 446 
 447   assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
 448   assert((_safepoint_counter & 0x1) == 1, "must be odd");
 449   _safepoint_counter ++;
 450   // memory fence isn't required here since an odd _safepoint_counter
 451   // value can do no harm and a fence is issued below anyway.
 452 
 453   DEBUG_ONLY(Thread* myThread = Thread::current();)
 454   assert(myThread->is_VM_thread(), "Only VM thread can execute a safepoint");
 455 
 456   if (PrintSafepointStatistics) {
 457     end_statistics(os::javaTimeNanos());
 458   }
 459 
 460   {
 461     JavaThreadIteratorWithHandle jtiwh;
 462 #ifdef ASSERT
 463     // A pending_exception cannot be installed during a safepoint.  The threads
 464     // may install an async exception after they come back from a safepoint into
 465     // pending_exception after they unblock.  But that should happen later.
 466     for (; JavaThread *cur = jtiwh.next(); ) {
 467       assert (!(cur->has_pending_exception() &&
 468                 cur->safepoint_state()->is_at_poll_safepoint()),
 469               "safepoint installed a pending exception");
 470     }
 471 #endif // ASSERT
 472 
 473     if (PageArmed) {
 474       assert(SafepointMechanism::uses_global_page_poll(), "sanity");
 475       // Make polling safepoint aware
 476       os::make_polling_page_readable();
 477       PageArmed = 0 ;
 478     }
 479 
 480     if (SafepointMechanism::uses_global_page_poll()) {
 481       // Remove safepoint check from interpreter
 482       Interpreter::ignore_safepoints();
 483     }
 484 
 485     {
 486       MutexLocker mu(Safepoint_lock);
 487 
 488       assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization");
 489 
 490       if (SafepointMechanism::uses_thread_local_poll()) {
 491         _state = _not_synchronized;
 492         OrderAccess::storestore(); // global state -> local state
 493         jtiwh.rewind();
 494         for (; JavaThread *current = jtiwh.next(); ) {
 495           ThreadSafepointState* cur_state = current->safepoint_state();
 496           cur_state->restart(); // TSS _running
 497           SafepointMechanism::disarm_local_poll(current); // release store, local state -> polling page
 498         }
 499         log_info(safepoint)("Leaving safepoint region");
 500       } else {
 501         // Set to not synchronized, so the threads will not go into the signal_thread_blocked method
 502         // when they get restarted.
 503         _state = _not_synchronized;
 504         OrderAccess::fence();
 505 
 506         log_info(safepoint)("Leaving safepoint region");
 507 
 508         // Start suspended threads
 509         jtiwh.rewind();
 510         for (; JavaThread *current = jtiwh.next(); ) {
 511           // A problem occurring on Solaris is when attempting to restart threads
 512           // the first #cpus - 1 go well, but then the VMThread is preempted when we get
 513           // to the next one (since it has been running the longest).  We then have
 514           // to wait for a cpu to become available before we can continue restarting
 515           // threads.
 516           // FIXME: This causes the performance of the VM to degrade when active and with
 517           // large numbers of threads.  Apparently this is due to the synchronous nature
 518           // of suspending threads.
 519           //
 520           // TODO-FIXME: the comments above are vestigial and no longer apply.
 521           // Furthermore, using solaris' schedctl in this particular context confers no benefit
 522           if (VMThreadHintNoPreempt) {
 523             os::hint_no_preempt();
 524           }
 525           ThreadSafepointState* cur_state = current->safepoint_state();
 526           assert(cur_state->type() != ThreadSafepointState::_running, "Thread not suspended at safepoint");
 527           cur_state->restart();
 528           assert(cur_state->is_running(), "safepoint state has not been reset");
 529         }
 530       }
 531 
 532       RuntimeService::record_safepoint_end();
 533 
 534       // Release threads lock, so threads can be created/destroyed again.
 535       // It will also release all threads blocked in signal_thread_blocked.
 536       Threads_lock->unlock();
 537     }
 538   } // ThreadsListHandle destroyed here.
 539 
 540   Universe::heap()->safepoint_synchronize_end();
 541   // record this time so VMThread can keep track how much time has elapsed
 542   // since last safepoint.
 543   _end_of_last_safepoint = os::javaTimeMillis();
 544 
 545   if (event.should_commit()) {
 546     event.set_safepointId(safepoint_id);
 547     event.commit();
 548   }
 549 }
 550 
 551 bool SafepointSynchronize::is_cleanup_needed() {
 552   // Need a safepoint if there are many monitors to deflate.
 553   if (ObjectSynchronizer::is_cleanup_needed()) return true;
 554   // Need a safepoint if some inline cache buffers is non-empty
 555   if (!InlineCacheBuffer::is_empty()) return true;
 556   return false;
 557 }
 558 
 559 static void event_safepoint_cleanup_task_commit(EventSafepointCleanupTask& event, const char* name) {
 560   if (event.should_commit()) {
 561     event.set_safepointId(SafepointSynchronize::safepoint_counter());
 562     event.set_name(name);
 563     event.commit();
 564   }
 565 }
 566 
 567 class ParallelSPCleanupThreadClosure : public ThreadClosure {
 568 private:
 569   CodeBlobClosure* _nmethod_cl;
 570   DeflateMonitorCounters* _counters;
 571 
 572 public:
 573   ParallelSPCleanupThreadClosure(DeflateMonitorCounters* counters) :
 574     _counters(counters),
 575     _nmethod_cl(NMethodSweeper::prepare_mark_active_nmethods()) {}
 576 
 577   void do_thread(Thread* thread) {
 578     ObjectSynchronizer::deflate_thread_local_monitors(thread, _counters);
 579     if (_nmethod_cl != NULL && thread->is_Java_thread() &&
 580         ! thread->is_Code_cache_sweeper_thread()) {
 581       JavaThread* jt = (JavaThread*) thread;
 582       jt->nmethods_do(_nmethod_cl);
 583     }
 584   }
 585 };
 586 
 587 class ParallelSPCleanupTask : public AbstractGangTask {
 588 private:
 589   SubTasksDone _subtasks;
 590   ParallelSPCleanupThreadClosure _cleanup_threads_cl;
 591   uint _num_workers;
 592   DeflateMonitorCounters* _counters;
 593 public:
 594   ParallelSPCleanupTask(uint num_workers, DeflateMonitorCounters* counters) :
 595     AbstractGangTask("Parallel Safepoint Cleanup"),
 596     _cleanup_threads_cl(ParallelSPCleanupThreadClosure(counters)),
 597     _num_workers(num_workers),
 598     _subtasks(SubTasksDone(SafepointSynchronize::SAFEPOINT_CLEANUP_NUM_TASKS)),
 599     _counters(counters) {}
 600 
 601   void work(uint worker_id) {
 602     // All threads deflate monitors and mark nmethods (if necessary).
 603     Threads::possibly_parallel_threads_do(true, &_cleanup_threads_cl);
 604 
 605     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_DEFLATE_MONITORS)) {
 606       const char* name = "deflating idle monitors";
 607       EventSafepointCleanupTask event;
 608       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 609       ObjectSynchronizer::deflate_idle_monitors(_counters);
 610       event_safepoint_cleanup_task_commit(event, name);
 611     }
 612 
 613     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_UPDATE_INLINE_CACHES)) {
 614       const char* name = "updating inline caches";
 615       EventSafepointCleanupTask event;
 616       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 617       InlineCacheBuffer::update_inline_caches();
 618       event_safepoint_cleanup_task_commit(event, name);
 619     }
 620 
 621     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_COMPILATION_POLICY)) {
 622       const char* name = "compilation policy safepoint handler";
 623       EventSafepointCleanupTask event;
 624       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 625       CompilationPolicy::policy()->do_safepoint_work();
 626       event_safepoint_cleanup_task_commit(event, name);
 627     }
 628 
 629     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_SYMBOL_TABLE_REHASH)) {
 630       if (SymbolTable::needs_rehashing()) {
 631         const char* name = "rehashing symbol table";
 632         EventSafepointCleanupTask event;
 633         TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 634         SymbolTable::rehash_table();
 635         event_safepoint_cleanup_task_commit(event, name);
 636       }
 637     }
 638 
 639     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_STRING_TABLE_REHASH)) {
 640       if (StringTable::needs_rehashing()) {
 641         const char* name = "rehashing string table";
 642         EventSafepointCleanupTask event;
 643         TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 644         StringTable::rehash_table();
 645         event_safepoint_cleanup_task_commit(event, name);
 646       }
 647     }
 648 
 649     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_CLD_PURGE)) {
 650       // CMS delays purging the CLDG until the beginning of the next safepoint and to
 651       // make sure concurrent sweep is done
 652       const char* name = "purging class loader data graph";
 653       EventSafepointCleanupTask event;
 654       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 655       ClassLoaderDataGraph::purge_if_needed();
 656       event_safepoint_cleanup_task_commit(event, name);
 657     }
 658 
 659     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_SYSTEM_DICTIONARY_RESIZE)) {
 660       const char* name = "resizing system dictionaries";
 661       EventSafepointCleanupTask event;
 662       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 663       ClassLoaderDataGraph::resize_if_needed();
 664       event_safepoint_cleanup_task_commit(event, name);
 665     }
 666     _subtasks.all_tasks_completed(_num_workers);
 667   }
 668 };
 669 
 670 // Various cleaning tasks that should be done periodically at safepoints.
 671 void SafepointSynchronize::do_cleanup_tasks() {
 672 
 673   TraceTime timer("safepoint cleanup tasks", TRACETIME_LOG(Info, safepoint, cleanup));
 674 
 675   // Prepare for monitor deflation.
 676   DeflateMonitorCounters deflate_counters;
 677   ObjectSynchronizer::prepare_deflate_idle_monitors(&deflate_counters);
 678 
 679   CollectedHeap* heap = Universe::heap();
 680   assert(heap != NULL, "heap not initialized yet?");
 681   WorkGang* cleanup_workers = heap->get_safepoint_workers();
 682   if (cleanup_workers != NULL) {
 683     // Parallel cleanup using GC provided thread pool.
 684     uint num_cleanup_workers = cleanup_workers->active_workers();
 685     ParallelSPCleanupTask cleanup(num_cleanup_workers, &deflate_counters);
 686     StrongRootsScope srs(num_cleanup_workers);
 687     cleanup_workers->run_task(&cleanup);
 688   } else {
 689     // Serial cleanup using VMThread.
 690     ParallelSPCleanupTask cleanup(1, &deflate_counters);
 691     StrongRootsScope srs(1);
 692     cleanup.work(0);
 693   }
 694 
 695   // Finish monitor deflation.
 696   ObjectSynchronizer::finish_deflate_idle_monitors(&deflate_counters);
 697 }
 698 
 699 
 700 bool SafepointSynchronize::safepoint_safe(JavaThread *thread, JavaThreadState state) {
 701   switch(state) {
 702   case _thread_in_native:
 703     // native threads are safe if they have no java stack or have walkable stack
 704     return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable();
 705 
 706    // blocked threads should have already have walkable stack
 707   case _thread_blocked:
 708     assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable");
 709     return true;
 710 
 711   default:
 712     return false;
 713   }
 714 }
 715 
 716 
 717 // See if the thread is running inside a lazy critical native and
 718 // update the thread critical count if so.  Also set a suspend flag to
 719 // cause the native wrapper to return into the JVM to do the unlock
 720 // once the native finishes.
 721 void SafepointSynchronize::check_for_lazy_critical_native(JavaThread *thread, JavaThreadState state) {
 722   if (state == _thread_in_native &&
 723       thread->has_last_Java_frame() &&
 724       thread->frame_anchor()->walkable()) {
 725     // This thread might be in a critical native nmethod so look at
 726     // the top of the stack and increment the critical count if it
 727     // is.
 728     frame wrapper_frame = thread->last_frame();
 729     CodeBlob* stub_cb = wrapper_frame.cb();
 730     if (stub_cb != NULL &&
 731         stub_cb->is_nmethod() &&
 732         stub_cb->as_nmethod_or_null()->is_lazy_critical_native()) {
 733       // A thread could potentially be in a critical native across
 734       // more than one safepoint, so only update the critical state on
 735       // the first one.  When it returns it will perform the unlock.
 736       if (!thread->do_critical_native_unlock()) {
 737 #ifdef ASSERT
 738         if (!thread->in_critical()) {
 739           GCLocker::increment_debug_jni_lock_count();
 740         }
 741 #endif
 742         thread->enter_critical();
 743         // Make sure the native wrapper calls back on return to
 744         // perform the needed critical unlock.
 745         thread->set_critical_native_unlock();
 746       }
 747     }
 748   }
 749 }
 750 
 751 
 752 
 753 // -------------------------------------------------------------------------------------------------------
 754 // Implementation of Safepoint callback point
 755 
 756 void SafepointSynchronize::block(JavaThread *thread) {
 757   assert(thread != NULL, "thread must be set");
 758   assert(thread->is_Java_thread(), "not a Java thread");
 759 
 760   // Threads shouldn't block if they are in the middle of printing, but...
 761   ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id());
 762 
 763   // Only bail from the block() call if the thread is gone from the
 764   // thread list; starting to exit should still block.
 765   if (thread->is_terminated()) {
 766      // block current thread if we come here from native code when VM is gone
 767      thread->block_if_vm_exited();
 768 
 769      // otherwise do nothing
 770      return;
 771   }
 772 
 773   JavaThreadState state = thread->thread_state();
 774   thread->frame_anchor()->make_walkable(thread);
 775 
 776   // Check that we have a valid thread_state at this point
 777   switch(state) {
 778     case _thread_in_vm_trans:
 779     case _thread_in_Java:        // From compiled code
 780 
 781       // We are highly likely to block on the Safepoint_lock. In order to avoid blocking in this case,
 782       // we pretend we are still in the VM.
 783       thread->set_thread_state(_thread_in_vm);
 784 
 785       if (is_synchronizing()) {
 786          Atomic::inc (&TryingToBlock) ;
 787       }
 788 
 789       // We will always be holding the Safepoint_lock when we are examine the state
 790       // of a thread. Hence, the instructions between the Safepoint_lock->lock() and
 791       // Safepoint_lock->unlock() are happening atomic with regards to the safepoint code
 792       Safepoint_lock->lock_without_safepoint_check();
 793       if (is_synchronizing()) {
 794         // Decrement the number of threads to wait for and signal vm thread
 795         assert(_waiting_to_block > 0, "sanity check");
 796         _waiting_to_block--;
 797         thread->safepoint_state()->set_has_called_back(true);
 798 
 799         DEBUG_ONLY(thread->set_visited_for_critical_count(true));
 800         if (thread->in_critical()) {
 801           // Notice that this thread is in a critical section
 802           increment_jni_active_count();
 803         }
 804 
 805         // Consider (_waiting_to_block < 2) to pipeline the wakeup of the VM thread
 806         if (_waiting_to_block == 0) {
 807           Safepoint_lock->notify_all();
 808         }
 809       }
 810 
 811       // We transition the thread to state _thread_blocked here, but
 812       // we can't do our usual check for external suspension and then
 813       // self-suspend after the lock_without_safepoint_check() call
 814       // below because we are often called during transitions while
 815       // we hold different locks. That would leave us suspended while
 816       // holding a resource which results in deadlocks.
 817       thread->set_thread_state(_thread_blocked);
 818       Safepoint_lock->unlock();
 819 
 820       // We now try to acquire the threads lock. Since this lock is hold by the VM thread during
 821       // the entire safepoint, the threads will all line up here during the safepoint.
 822       Threads_lock->lock_without_safepoint_check();
 823       // restore original state. This is important if the thread comes from compiled code, so it
 824       // will continue to execute with the _thread_in_Java state.
 825       thread->set_thread_state(state);
 826       Threads_lock->unlock();
 827       break;
 828 
 829     case _thread_in_native_trans:
 830     case _thread_blocked_trans:
 831     case _thread_new_trans:
 832       if (thread->safepoint_state()->type() == ThreadSafepointState::_call_back) {
 833         thread->print_thread_state();
 834         fatal("Deadlock in safepoint code.  "
 835               "Should have called back to the VM before blocking.");
 836       }
 837 
 838       // We transition the thread to state _thread_blocked here, but
 839       // we can't do our usual check for external suspension and then
 840       // self-suspend after the lock_without_safepoint_check() call
 841       // below because we are often called during transitions while
 842       // we hold different locks. That would leave us suspended while
 843       // holding a resource which results in deadlocks.
 844       thread->set_thread_state(_thread_blocked);
 845 
 846       // It is not safe to suspend a thread if we discover it is in _thread_in_native_trans. Hence,
 847       // the safepoint code might still be waiting for it to block. We need to change the state here,
 848       // so it can see that it is at a safepoint.
 849 
 850       // Block until the safepoint operation is completed.
 851       Threads_lock->lock_without_safepoint_check();
 852 
 853       // Restore state
 854       thread->set_thread_state(state);
 855 
 856       Threads_lock->unlock();
 857       break;
 858 
 859     default:
 860      fatal("Illegal threadstate encountered: %d", state);
 861   }
 862 
 863   // Check for pending. async. exceptions or suspends - except if the
 864   // thread was blocked inside the VM. has_special_runtime_exit_condition()
 865   // is called last since it grabs a lock and we only want to do that when
 866   // we must.
 867   //
 868   // Note: we never deliver an async exception at a polling point as the
 869   // compiler may not have an exception handler for it. The polling
 870   // code will notice the async and deoptimize and the exception will
 871   // be delivered. (Polling at a return point is ok though). Sure is
 872   // a lot of bother for a deprecated feature...
 873   //
 874   // We don't deliver an async exception if the thread state is
 875   // _thread_in_native_trans so JNI functions won't be called with
 876   // a surprising pending exception. If the thread state is going back to java,
 877   // async exception is checked in check_special_condition_for_native_trans().
 878 
 879   if (state != _thread_blocked_trans &&
 880       state != _thread_in_vm_trans &&
 881       thread->has_special_runtime_exit_condition()) {
 882     thread->handle_special_runtime_exit_condition(
 883       !thread->is_at_poll_safepoint() && (state != _thread_in_native_trans));
 884   }
 885 }
 886 
 887 // ------------------------------------------------------------------------------------------------------
 888 // Exception handlers
 889 
 890 
 891 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) {
 892   assert(thread->is_Java_thread(), "polling reference encountered by VM thread");
 893   assert(thread->thread_state() == _thread_in_Java, "should come from Java code");
 894   if (!ThreadLocalHandshakes) {
 895     assert(SafepointSynchronize::is_synchronizing(), "polling encountered outside safepoint synchronization");
 896   }
 897 
 898   if (PrintSafepointStatistics) {
 899     inc_page_trap_count();
 900   }
 901 
 902   ThreadSafepointState* state = thread->safepoint_state();
 903 
 904   state->handle_polling_page_exception();
 905 }
 906 
 907 
 908 void SafepointSynchronize::print_safepoint_timeout(SafepointTimeoutReason reason) {
 909   if (!timeout_error_printed) {
 910     timeout_error_printed = true;
 911     // Print out the thread info which didn't reach the safepoint for debugging
 912     // purposes (useful when there are lots of threads in the debugger).
 913     tty->cr();
 914     tty->print_cr("# SafepointSynchronize::begin: Timeout detected:");
 915     if (reason ==  _spinning_timeout) {
 916       tty->print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint.");
 917     } else if (reason == _blocking_timeout) {
 918       tty->print_cr("# SafepointSynchronize::begin: Timed out while waiting for threads to stop.");
 919     }
 920 
 921     tty->print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:");
 922     ThreadSafepointState *cur_state;
 923     ResourceMark rm;
 924     for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
 925       cur_state = cur_thread->safepoint_state();
 926 
 927       if (cur_thread->thread_state() != _thread_blocked &&
 928         ((reason == _spinning_timeout && cur_state->is_running()) ||
 929            (reason == _blocking_timeout && !cur_state->has_called_back()))) {
 930         tty->print("# ");
 931         cur_thread->print();
 932         tty->cr();
 933       }
 934     }
 935     tty->print_cr("# SafepointSynchronize::begin: (End of list)");
 936   }
 937 
 938   // To debug the long safepoint, specify both DieOnSafepointTimeout &
 939   // ShowMessageBoxOnError.
 940   if (DieOnSafepointTimeout) {
 941     fatal("Safepoint sync time longer than " INTX_FORMAT "ms detected when executing %s.",
 942           SafepointTimeoutDelay, VMThread::vm_safepoint_description());
 943   }
 944 }
 945 
 946 
 947 // -------------------------------------------------------------------------------------------------------
 948 // Implementation of ThreadSafepointState
 949 
 950 ThreadSafepointState::ThreadSafepointState(JavaThread *thread) {
 951   _thread = thread;
 952   _type   = _running;
 953   _has_called_back = false;
 954   _at_poll_safepoint = false;
 955 }
 956 
 957 void ThreadSafepointState::create(JavaThread *thread) {
 958   ThreadSafepointState *state = new ThreadSafepointState(thread);
 959   thread->set_safepoint_state(state);
 960 }
 961 
 962 void ThreadSafepointState::destroy(JavaThread *thread) {
 963   if (thread->safepoint_state()) {
 964     delete(thread->safepoint_state());
 965     thread->set_safepoint_state(NULL);
 966   }
 967 }
 968 
 969 void ThreadSafepointState::examine_state_of_thread() {
 970   assert(is_running(), "better be running or just have hit safepoint poll");
 971 
 972   JavaThreadState state = _thread->thread_state();
 973 
 974   // Save the state at the start of safepoint processing.
 975   _orig_thread_state = state;
 976 
 977   // Check for a thread that is suspended. Note that thread resume tries
 978   // to grab the Threads_lock which we own here, so a thread cannot be
 979   // resumed during safepoint synchronization.
 980 
 981   // We check to see if this thread is suspended without locking to
 982   // avoid deadlocking with a third thread that is waiting for this
 983   // thread to be suspended. The third thread can notice the safepoint
 984   // that we're trying to start at the beginning of its SR_lock->wait()
 985   // call. If that happens, then the third thread will block on the
 986   // safepoint while still holding the underlying SR_lock. We won't be
 987   // able to get the SR_lock and we'll deadlock.
 988   //
 989   // We don't need to grab the SR_lock here for two reasons:
 990   // 1) The suspend flags are both volatile and are set with an
 991   //    Atomic::cmpxchg() call so we should see the suspended
 992   //    state right away.
 993   // 2) We're being called from the safepoint polling loop; if
 994   //    we don't see the suspended state on this iteration, then
 995   //    we'll come around again.
 996   //
 997   bool is_suspended = _thread->is_ext_suspended();
 998   if (is_suspended) {
 999     roll_forward(_at_safepoint);
1000     return;
1001   }
1002 
1003   // Some JavaThread states have an initial safepoint state of
1004   // running, but are actually at a safepoint. We will happily
1005   // agree and update the safepoint state here.
1006   if (SafepointSynchronize::safepoint_safe(_thread, state)) {
1007     SafepointSynchronize::check_for_lazy_critical_native(_thread, state);
1008     roll_forward(_at_safepoint);
1009     return;
1010   }
1011 
1012   if (state == _thread_in_vm) {
1013     roll_forward(_call_back);
1014     return;
1015   }
1016 
1017   // All other thread states will continue to run until they
1018   // transition and self-block in state _blocked
1019   // Safepoint polling in compiled code causes the Java threads to do the same.
1020   // Note: new threads may require a malloc so they must be allowed to finish
1021 
1022   assert(is_running(), "examine_state_of_thread on non-running thread");
1023   return;
1024 }
1025 
1026 // Returns true is thread could not be rolled forward at present position.
1027 void ThreadSafepointState::roll_forward(suspend_type type) {
1028   _type = type;
1029 
1030   switch(_type) {
1031     case _at_safepoint:
1032       SafepointSynchronize::signal_thread_at_safepoint();
1033       DEBUG_ONLY(_thread->set_visited_for_critical_count(true));
1034       if (_thread->in_critical()) {
1035         // Notice that this thread is in a critical section
1036         SafepointSynchronize::increment_jni_active_count();
1037       }
1038       break;
1039 
1040     case _call_back:
1041       set_has_called_back(false);
1042       break;
1043 
1044     case _running:
1045     default:
1046       ShouldNotReachHere();
1047   }
1048 }
1049 
1050 void ThreadSafepointState::restart() {
1051   switch(type()) {
1052     case _at_safepoint:
1053     case _call_back:
1054       break;
1055 
1056     case _running:
1057     default:
1058        tty->print_cr("restart thread " INTPTR_FORMAT " with state %d",
1059                      p2i(_thread), _type);
1060        _thread->print();
1061       ShouldNotReachHere();
1062   }
1063   _type = _running;
1064   set_has_called_back(false);
1065 }
1066 
1067 
1068 void ThreadSafepointState::print_on(outputStream *st) const {
1069   const char *s = NULL;
1070 
1071   switch(_type) {
1072     case _running                : s = "_running";              break;
1073     case _at_safepoint           : s = "_at_safepoint";         break;
1074     case _call_back              : s = "_call_back";            break;
1075     default:
1076       ShouldNotReachHere();
1077   }
1078 
1079   st->print_cr("Thread: " INTPTR_FORMAT
1080               "  [0x%2x] State: %s _has_called_back %d _at_poll_safepoint %d",
1081                p2i(_thread), _thread->osthread()->thread_id(), s, _has_called_back,
1082                _at_poll_safepoint);
1083 
1084   _thread->print_thread_state_on(st);
1085 }
1086 
1087 // ---------------------------------------------------------------------------------------------------------------------
1088 
1089 // Block the thread at poll or poll return for safepoint/handshake.
1090 void ThreadSafepointState::handle_polling_page_exception() {
1091 
1092   // Check state.  block() will set thread state to thread_in_vm which will
1093   // cause the safepoint state _type to become _call_back.
1094   suspend_type t = type();
1095   assert(!SafepointMechanism::uses_global_page_poll() || t == ThreadSafepointState::_running,
1096          "polling page exception on thread not running state: %u", uint(t));
1097 
1098   // Step 1: Find the nmethod from the return address
1099   address real_return_addr = thread()->saved_exception_pc();
1100 
1101   CodeBlob *cb = CodeCache::find_blob(real_return_addr);
1102   assert(cb != NULL && cb->is_compiled(), "return address should be in nmethod");
1103   CompiledMethod* nm = (CompiledMethod*)cb;
1104 
1105   // Find frame of caller
1106   frame stub_fr = thread()->last_frame();
1107   CodeBlob* stub_cb = stub_fr.cb();
1108   assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub");
1109   RegisterMap map(thread(), true);
1110   frame caller_fr = stub_fr.sender(&map);
1111 
1112   // Should only be poll_return or poll
1113   assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" );
1114 
1115   // This is a poll immediately before a return. The exception handling code
1116   // has already had the effect of causing the return to occur, so the execution
1117   // will continue immediately after the call. In addition, the oopmap at the
1118   // return point does not mark the return value as an oop (if it is), so
1119   // it needs a handle here to be updated.
1120   if( nm->is_at_poll_return(real_return_addr) ) {
1121     // See if return type is an oop.
1122     bool return_oop = nm->method()->is_returning_oop();
1123     Handle return_value;
1124     if (return_oop) {
1125       // The oop result has been saved on the stack together with all
1126       // the other registers. In order to preserve it over GCs we need
1127       // to keep it in a handle.
1128       oop result = caller_fr.saved_oop_result(&map);
1129       assert(oopDesc::is_oop_or_null(result), "must be oop");
1130       return_value = Handle(thread(), result);
1131       assert(Universe::heap()->is_in_or_null(result), "must be heap pointer");
1132     }
1133 
1134     // Block the thread
1135     SafepointMechanism::block_if_requested(thread());
1136 
1137     // restore oop result, if any
1138     if (return_oop) {
1139       caller_fr.set_saved_oop_result(&map, return_value());
1140     }
1141   }
1142 
1143   // This is a safepoint poll. Verify the return address and block.
1144   else {
1145     set_at_poll_safepoint(true);
1146 
1147     // verify the blob built the "return address" correctly
1148     assert(real_return_addr == caller_fr.pc(), "must match");
1149 
1150     // Block the thread
1151     SafepointMechanism::block_if_requested(thread());
1152     set_at_poll_safepoint(false);
1153 
1154     // If we have a pending async exception deoptimize the frame
1155     // as otherwise we may never deliver it.
1156     if (thread()->has_async_condition()) {
1157       ThreadInVMfromJavaNoAsyncException __tiv(thread());
1158       Deoptimization::deoptimize_frame(thread(), caller_fr.id());
1159     }
1160 
1161     // If an exception has been installed we must check for a pending deoptimization
1162     // Deoptimize frame if exception has been thrown.
1163 
1164     if (thread()->has_pending_exception() ) {
1165       RegisterMap map(thread(), true);
1166       frame caller_fr = stub_fr.sender(&map);
1167       if (caller_fr.is_deoptimized_frame()) {
1168         // The exception patch will destroy registers that are still
1169         // live and will be needed during deoptimization. Defer the
1170         // Async exception should have deferred the exception until the
1171         // next safepoint which will be detected when we get into
1172         // the interpreter so if we have an exception now things
1173         // are messed up.
1174 
1175         fatal("Exception installed and deoptimization is pending");
1176       }
1177     }
1178   }
1179 }
1180 
1181 
1182 //
1183 //                     Statistics & Instrumentations
1184 //
1185 SafepointSynchronize::SafepointStats*  SafepointSynchronize::_safepoint_stats = NULL;
1186 jlong  SafepointSynchronize::_safepoint_begin_time = 0;
1187 int    SafepointSynchronize::_cur_stat_index = 0;
1188 julong SafepointSynchronize::_safepoint_reasons[VM_Operation::VMOp_Terminating];
1189 julong SafepointSynchronize::_coalesced_vmop_count = 0;
1190 jlong  SafepointSynchronize::_max_sync_time = 0;
1191 jlong  SafepointSynchronize::_max_vmop_time = 0;
1192 float  SafepointSynchronize::_ts_of_current_safepoint = 0.0f;
1193 
1194 static jlong  cleanup_end_time = 0;
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   tty->print_cr("page_trap_count");
1207 }
1208 
1209 void SafepointSynchronize::deferred_initialize_stat() {
1210   if (init_done) return;
1211 
1212   // If PrintSafepointStatisticsTimeout is specified, the statistics data will
1213   // be printed right away, in which case, _safepoint_stats will regress to
1214   // a single element array. Otherwise, it is a circular ring buffer with default
1215   // size of PrintSafepointStatisticsCount.
1216   int stats_array_size;
1217   if (PrintSafepointStatisticsTimeout > 0) {
1218     stats_array_size = 1;
1219     PrintSafepointStatistics = true;
1220   } else {
1221     stats_array_size = PrintSafepointStatisticsCount;
1222   }
1223   _safepoint_stats = (SafepointStats*)os::malloc(stats_array_size
1224                                                  * sizeof(SafepointStats), mtInternal);
1225   guarantee(_safepoint_stats != NULL,
1226             "not enough memory for safepoint instrumentation data");
1227 
1228   init_done = true;
1229 }
1230 
1231 void SafepointSynchronize::begin_statistics(int nof_threads, int nof_running) {
1232   assert(init_done, "safepoint statistics array hasn't been initialized");
1233   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1234 
1235   spstat->_time_stamp = _ts_of_current_safepoint;
1236 
1237   VM_Operation *op = VMThread::vm_operation();
1238   spstat->_vmop_type = (op != NULL ? op->type() : -1);
1239   if (op != NULL) {
1240     _safepoint_reasons[spstat->_vmop_type]++;
1241   }
1242 
1243   spstat->_nof_total_threads = nof_threads;
1244   spstat->_nof_initial_running_threads = nof_running;
1245   spstat->_nof_threads_hit_page_trap = 0;
1246 
1247   // Records the start time of spinning. The real time spent on spinning
1248   // will be adjusted when spin is done. Same trick is applied for time
1249   // spent on waiting for threads to block.
1250   if (nof_running != 0) {
1251     spstat->_time_to_spin = os::javaTimeNanos();
1252   }  else {
1253     spstat->_time_to_spin = 0;
1254   }
1255 }
1256 
1257 void SafepointSynchronize::update_statistics_on_spin_end() {
1258   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1259 
1260   jlong cur_time = os::javaTimeNanos();
1261 
1262   spstat->_nof_threads_wait_to_block = _waiting_to_block;
1263   if (spstat->_nof_initial_running_threads != 0) {
1264     spstat->_time_to_spin = cur_time - spstat->_time_to_spin;
1265   }
1266 
1267   // Records the start time of waiting for to block. Updated when block is done.
1268   if (_waiting_to_block != 0) {
1269     spstat->_time_to_wait_to_block = cur_time;
1270   } else {
1271     spstat->_time_to_wait_to_block = 0;
1272   }
1273 }
1274 
1275 void SafepointSynchronize::update_statistics_on_sync_end(jlong end_time) {
1276   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1277 
1278   if (spstat->_nof_threads_wait_to_block != 0) {
1279     spstat->_time_to_wait_to_block = end_time -
1280       spstat->_time_to_wait_to_block;
1281   }
1282 
1283   // Records the end time of sync which will be used to calculate the total
1284   // vm operation time. Again, the real time spending in syncing will be deducted
1285   // from the start of the sync time later when end_statistics is called.
1286   spstat->_time_to_sync = end_time - _safepoint_begin_time;
1287   if (spstat->_time_to_sync > _max_sync_time) {
1288     _max_sync_time = spstat->_time_to_sync;
1289   }
1290 
1291   spstat->_time_to_do_cleanups = end_time;
1292 }
1293 
1294 void SafepointSynchronize::update_statistics_on_cleanup_end(jlong end_time) {
1295   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1296 
1297   // Record how long spent in cleanup tasks.
1298   spstat->_time_to_do_cleanups = end_time - spstat->_time_to_do_cleanups;
1299 
1300   cleanup_end_time = end_time;
1301 }
1302 
1303 void SafepointSynchronize::end_statistics(jlong vmop_end_time) {
1304   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1305 
1306   // Update the vm operation time.
1307   spstat->_time_to_exec_vmop = vmop_end_time -  cleanup_end_time;
1308   if (spstat->_time_to_exec_vmop > _max_vmop_time) {
1309     _max_vmop_time = spstat->_time_to_exec_vmop;
1310   }
1311   // Only the sync time longer than the specified
1312   // PrintSafepointStatisticsTimeout will be printed out right away.
1313   // By default, it is -1 meaning all samples will be put into the list.
1314   if ( PrintSafepointStatisticsTimeout > 0) {
1315     if (spstat->_time_to_sync > (jlong)PrintSafepointStatisticsTimeout * MICROUNITS) {
1316       print_statistics();
1317     }
1318   } else {
1319     // The safepoint statistics will be printed out when the _safepoin_stats
1320     // array fills up.
1321     if (_cur_stat_index == PrintSafepointStatisticsCount - 1) {
1322       print_statistics();
1323       _cur_stat_index = 0;
1324     } else {
1325       _cur_stat_index++;
1326     }
1327   }
1328 }
1329 
1330 void SafepointSynchronize::print_statistics() {
1331   for (int index = 0; index <= _cur_stat_index; index++) {
1332     if (index % 30 == 0) {
1333       print_header();
1334     }
1335     SafepointStats* sstats = &_safepoint_stats[index];
1336     tty->print("%8.3f: ", sstats->_time_stamp);
1337     tty->print("%-30s  [          "
1338                INT32_FORMAT_W(8) " " INT32_FORMAT_W(17) " " INT32_FORMAT_W(13) " "
1339                "]",
1340                (sstats->_vmop_type == -1 ? "no vm operation" : VM_Operation::name(sstats->_vmop_type)),
1341                sstats->_nof_total_threads,
1342                sstats->_nof_initial_running_threads,
1343                sstats->_nof_threads_wait_to_block);
1344     // "/ MICROUNITS " is to convert the unit from nanos to millis.
1345     tty->print("[       "
1346                INT64_FORMAT_W(7) " " INT64_FORMAT_W(7) " "
1347                INT64_FORMAT_W(7) " " INT64_FORMAT_W(7) " "
1348                INT64_FORMAT_W(7) " ] ",
1349                (int64_t)(sstats->_time_to_spin / MICROUNITS),
1350                (int64_t)(sstats->_time_to_wait_to_block / MICROUNITS),
1351                (int64_t)(sstats->_time_to_sync / MICROUNITS),
1352                (int64_t)(sstats->_time_to_do_cleanups / MICROUNITS),
1353                (int64_t)(sstats->_time_to_exec_vmop / MICROUNITS));
1354 
1355     tty->print_cr(INT32_FORMAT_W(15) " ", sstats->_nof_threads_hit_page_trap);
1356   }
1357 }
1358 
1359 // This method will be called when VM exits. It will first call
1360 // print_statistics to print out the rest of the sampling.  Then
1361 // it tries to summarize the sampling.
1362 void SafepointSynchronize::print_stat_on_exit() {
1363   if (_safepoint_stats == NULL) return;
1364 
1365   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1366 
1367   // During VM exit, end_statistics may not get called and in that
1368   // case, if the sync time is less than PrintSafepointStatisticsTimeout,
1369   // don't print it out.
1370   // Approximate the vm op time.
1371   _safepoint_stats[_cur_stat_index]._time_to_exec_vmop =
1372     os::javaTimeNanos() - cleanup_end_time;
1373 
1374   if ( PrintSafepointStatisticsTimeout < 0 ||
1375        spstat->_time_to_sync > (jlong)PrintSafepointStatisticsTimeout * MICROUNITS) {
1376     print_statistics();
1377   }
1378   tty->cr();
1379 
1380   // Print out polling page sampling status.
1381   tty->print_cr("Polling page always armed");
1382 
1383   for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) {
1384     if (_safepoint_reasons[index] != 0) {
1385       tty->print_cr("%-26s" UINT64_FORMAT_W(10), VM_Operation::name(index),
1386                     _safepoint_reasons[index]);
1387     }
1388   }
1389 
1390   tty->print_cr(UINT64_FORMAT_W(5) " VM operations coalesced during safepoint",
1391                 _coalesced_vmop_count);
1392   tty->print_cr("Maximum sync time  " INT64_FORMAT_W(5) " ms",
1393                 (int64_t)(_max_sync_time / MICROUNITS));
1394   tty->print_cr("Maximum vm operation time (except for Exit VM operation)  "
1395                 INT64_FORMAT_W(5) " ms",
1396                 (int64_t)(_max_vmop_time / MICROUNITS));
1397 }