1 /*
   2  * Copyright (c) 1997, 2017, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "classfile/stringTable.hpp"
  27 #include "classfile/symbolTable.hpp"
  28 #include "classfile/systemDictionary.hpp"
  29 #include "code/codeCache.hpp"
  30 #include "code/icBuffer.hpp"
  31 #include "code/nmethod.hpp"
  32 #include "code/pcDesc.hpp"
  33 #include "code/scopeDesc.hpp"
  34 #include "gc/shared/collectedHeap.hpp"
  35 #include "gc/shared/gcLocker.inline.hpp"
  36 #include "gc/shared/strongRootsScope.hpp"
  37 #include "gc/shared/workgroup.hpp"
  38 #include "interpreter/interpreter.hpp"
  39 #include "logging/log.hpp"
  40 #include "logging/logStream.hpp"
  41 #include "memory/resourceArea.hpp"
  42 #include "memory/universe.inline.hpp"
  43 #include "oops/oop.inline.hpp"
  44 #include "oops/symbol.hpp"
  45 #include "runtime/atomic.hpp"
  46 #include "runtime/compilationPolicy.hpp"
  47 #include "runtime/deoptimization.hpp"
  48 #include "runtime/frame.inline.hpp"
  49 #include "runtime/interfaceSupport.hpp"
  50 #include "runtime/mutexLocker.hpp"
  51 #include "runtime/orderAccess.inline.hpp"
  52 #include "runtime/osThread.hpp"
  53 #include "runtime/safepoint.hpp"
  54 #include "runtime/safepointMechanism.inline.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 
 185     if (SafepointMechanism::uses_thread_local_poll()) {
 186       // Arming the per thread poll while having _state != _not_synchronized means safepointing
 187       log_trace(safepoint)("Setting thread local yield flag for threads");
 188       for (JavaThread *cur = Threads::first(); cur != NULL; cur = cur->next()) {
 189         // Make sure the threads start polling, it is time to yield.
 190         SafepointMechanism::arm_local_poll(cur); // release store, global state -> local state
 191       }
 192     }
 193     OrderAccess::fence(); // storestore|storeload, global state -> local state
 194 
 195     // Flush all thread states to memory
 196     if (!UseMembar) {
 197       os::serialize_thread_states();
 198     }
 199 
 200     if (SafepointMechanism::uses_global_page_poll()) {
 201       // Make interpreter safepoint aware
 202       Interpreter::notice_safepoints();
 203 
 204       if (DeferPollingPageLoopCount < 0) {
 205         // Make polling safepoint aware
 206         guarantee (PageArmed == 0, "invariant") ;
 207         PageArmed = 1 ;
 208         os::make_polling_page_unreadable();
 209       }
 210     }
 211 
 212     // Consider using active_processor_count() ... but that call is expensive.
 213     int ncpus = os::processor_count() ;
 214 
 215 #ifdef ASSERT
 216     for (JavaThread *cur = Threads::first(); cur != NULL; cur = cur->next()) {
 217       assert(cur->safepoint_state()->is_running(), "Illegal initial state");
 218       // Clear the visited flag to ensure that the critical counts are collected properly.
 219       cur->set_visited_for_critical_count(false);
 220     }
 221 #endif // ASSERT
 222 
 223     if (SafepointTimeout)
 224       safepoint_limit_time = os::javaTimeNanos() + (jlong)SafepointTimeoutDelay * MICROUNITS;
 225 
 226     // Iterate through all threads until it have been determined how to stop them all at a safepoint
 227     unsigned int iterations = 0;
 228     int steps = 0 ;
 229     while(still_running > 0) {
 230       for (JavaThread *cur = Threads::first(); cur != NULL; cur = cur->next()) {
 231         assert(!cur->is_ConcurrentGC_thread(), "A concurrent GC thread is unexpectly being suspended");
 232         ThreadSafepointState *cur_state = cur->safepoint_state();
 233         if (cur_state->is_running()) {
 234           cur_state->examine_state_of_thread();
 235           if (!cur_state->is_running()) {
 236             still_running--;
 237             // consider adjusting steps downward:
 238             //   steps = 0
 239             //   steps -= NNN
 240             //   steps >>= 1
 241             //   steps = MIN(steps, 2000-100)
 242             //   if (iterations != 0) steps -= NNN
 243           }
 244           LogTarget(Trace, safepoint) lt;
 245           if (lt.is_enabled()) {
 246             ResourceMark rm;
 247             LogStream ls(lt);
 248             cur_state->print_on(&ls);
 249           }
 250         }
 251       }
 252 
 253       if (iterations == 0) {
 254         initial_running = still_running;
 255         if (PrintSafepointStatistics) {
 256           begin_statistics(nof_threads, still_running);
 257         }
 258       }
 259 
 260       if (still_running > 0) {
 261         // Check for if it takes to long
 262         if (SafepointTimeout && safepoint_limit_time < os::javaTimeNanos()) {
 263           print_safepoint_timeout(_spinning_timeout);
 264         }
 265 
 266         // Spin to avoid context switching.
 267         // There's a tension between allowing the mutators to run (and rendezvous)
 268         // vs spinning.  As the VM thread spins, wasting cycles, it consumes CPU that
 269         // a mutator might otherwise use profitably to reach a safepoint.  Excessive
 270         // spinning by the VM thread on a saturated system can increase rendezvous latency.
 271         // Blocking or yielding incur their own penalties in the form of context switching
 272         // and the resultant loss of $ residency.
 273         //
 274         // Further complicating matters is that yield() does not work as naively expected
 275         // on many platforms -- yield() does not guarantee that any other ready threads
 276         // will run.   As such we revert to naked_short_sleep() after some number of iterations.
 277         // nakes_short_sleep() is implemented as a short unconditional sleep.
 278         // Typical operating systems round a "short" sleep period up to 10 msecs, so sleeping
 279         // can actually increase the time it takes the VM thread to detect that a system-wide
 280         // stop-the-world safepoint has been reached.  In a pathological scenario such as that
 281         // described in CR6415670 the VMthread may sleep just before the mutator(s) become safe.
 282         // In that case the mutators will be stalled waiting for the safepoint to complete and the
 283         // the VMthread will be sleeping, waiting for the mutators to rendezvous.  The VMthread
 284         // will eventually wake up and detect that all mutators are safe, at which point
 285         // we'll again make progress.
 286         //
 287         // Beware too that that the VMThread typically runs at elevated priority.
 288         // Its default priority is higher than the default mutator priority.
 289         // Obviously, this complicates spinning.
 290         //
 291         // Note too that on Windows XP SwitchThreadTo() has quite different behavior than Sleep(0).
 292         // Sleep(0) will _not yield to lower priority threads, while SwitchThreadTo() will.
 293         //
 294         // See the comments in synchronizer.cpp for additional remarks on spinning.
 295         //
 296         // In the future we might:
 297         // 1. Modify the safepoint scheme to avoid potentially unbounded spinning.
 298         //    This is tricky as the path used by a thread exiting the JVM (say on
 299         //    on JNI call-out) simply stores into its state field.  The burden
 300         //    is placed on the VM thread, which must poll (spin).
 301         // 2. Find something useful to do while spinning.  If the safepoint is GC-related
 302         //    we might aggressively scan the stacks of threads that are already safe.
 303         // 3. Use Solaris schedctl to examine the state of the still-running mutators.
 304         //    If all the mutators are ONPROC there's no reason to sleep or yield.
 305         // 4. YieldTo() any still-running mutators that are ready but OFFPROC.
 306         // 5. Check system saturation.  If the system is not fully saturated then
 307         //    simply spin and avoid sleep/yield.
 308         // 6. As still-running mutators rendezvous they could unpark the sleeping
 309         //    VMthread.  This works well for still-running mutators that become
 310         //    safe.  The VMthread must still poll for mutators that call-out.
 311         // 7. Drive the policy on time-since-begin instead of iterations.
 312         // 8. Consider making the spin duration a function of the # of CPUs:
 313         //    Spin = (((ncpus-1) * M) + K) + F(still_running)
 314         //    Alternately, instead of counting iterations of the outer loop
 315         //    we could count the # of threads visited in the inner loop, above.
 316         // 9. On windows consider using the return value from SwitchThreadTo()
 317         //    to drive subsequent spin/SwitchThreadTo()/Sleep(N) decisions.
 318 
 319         if (SafepointMechanism::uses_global_page_poll() && int(iterations) == DeferPollingPageLoopCount) {
 320           guarantee (PageArmed == 0, "invariant") ;
 321           PageArmed = 1 ;
 322           os::make_polling_page_unreadable();
 323         }
 324 
 325         // Instead of (ncpus > 1) consider either (still_running < (ncpus + EPSILON)) or
 326         // ((still_running + _waiting_to_block - TryingToBlock)) < ncpus)
 327         ++steps ;
 328         if (ncpus > 1 && steps < SafepointSpinBeforeYield) {
 329           SpinPause() ;     // MP-Polite spin
 330         } else
 331           if (steps < DeferThrSuspendLoopCount) {
 332             os::naked_yield() ;
 333           } else {
 334             os::naked_short_sleep(1);
 335           }
 336 
 337         iterations ++ ;
 338       }
 339       assert(iterations < (uint)max_jint, "We have been iterating in the safepoint loop too long");
 340     }
 341     assert(still_running == 0, "sanity check");
 342 
 343     if (PrintSafepointStatistics) {
 344       update_statistics_on_spin_end();
 345     }
 346 
 347     if (sync_event.should_commit()) {
 348       sync_event.set_safepointId(safepoint_counter());
 349       sync_event.set_initialThreadCount(initial_running);
 350       sync_event.set_runningThreadCount(_waiting_to_block);
 351       sync_event.set_iterations(iterations);
 352       sync_event.commit();
 353     }
 354   } //EventSafepointStateSync
 355 
 356   // wait until all threads are stopped
 357   {
 358     EventSafepointWaitBlocked wait_blocked_event;
 359     int initial_waiting_to_block = _waiting_to_block;
 360 
 361     while (_waiting_to_block > 0) {
 362       log_debug(safepoint)("Waiting for %d thread(s) to block", _waiting_to_block);
 363       if (!SafepointTimeout || timeout_error_printed) {
 364         Safepoint_lock->wait(true);  // true, means with no safepoint checks
 365       } else {
 366         // Compute remaining time
 367         jlong remaining_time = safepoint_limit_time - os::javaTimeNanos();
 368 
 369         // If there is no remaining time, then there is an error
 370         if (remaining_time < 0 || Safepoint_lock->wait(true, remaining_time / MICROUNITS)) {
 371           print_safepoint_timeout(_blocking_timeout);
 372         }
 373       }
 374     }
 375     assert(_waiting_to_block == 0, "sanity check");
 376 
 377 #ifndef PRODUCT
 378     if (SafepointTimeout) {
 379       jlong current_time = os::javaTimeNanos();
 380       if (safepoint_limit_time < current_time) {
 381         tty->print_cr("# SafepointSynchronize: Finished after "
 382                       INT64_FORMAT_W(6) " ms",
 383                       (int64_t)((current_time - safepoint_limit_time) / MICROUNITS +
 384                                 (jlong)SafepointTimeoutDelay));
 385       }
 386     }
 387 #endif
 388 
 389     assert((_safepoint_counter & 0x1) == 0, "must be even");
 390     assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
 391     _safepoint_counter ++;
 392 
 393     // Record state
 394     _state = _synchronized;
 395 
 396     OrderAccess::fence();
 397 
 398     if (wait_blocked_event.should_commit()) {
 399       wait_blocked_event.set_safepointId(safepoint_counter());
 400       wait_blocked_event.set_runningThreadCount(initial_waiting_to_block);
 401       wait_blocked_event.commit();
 402     }
 403   } // EventSafepointWaitBlocked
 404 
 405 #ifdef ASSERT
 406   for (JavaThread *cur = Threads::first(); cur != NULL; cur = cur->next()) {
 407     // make sure all the threads were visited
 408     assert(cur->was_visited_for_critical_count(), "missed a thread");
 409   }
 410 #endif // ASSERT
 411 
 412   // Update the count of active JNI critical regions
 413   GCLocker::set_jni_lock_count(_current_jni_active_count);
 414 
 415   if (log_is_enabled(Debug, safepoint)) {
 416     log_debug(safepoint)("Entering safepoint region: %s", VMThread::vm_safepoint_description());
 417   }
 418 
 419   RuntimeService::record_safepoint_synchronized();
 420   if (PrintSafepointStatistics) {
 421     update_statistics_on_sync_end(os::javaTimeNanos());
 422   }
 423 
 424   // Call stuff that needs to be run when a safepoint is just about to be completed
 425   {
 426     EventSafepointCleanup cleanup_event;
 427     do_cleanup_tasks();
 428     if (cleanup_event.should_commit()) {
 429       cleanup_event.set_safepointId(safepoint_counter());
 430       cleanup_event.commit();
 431     }
 432   }
 433 
 434   if (PrintSafepointStatistics) {
 435     // Record how much time spend on the above cleanup tasks
 436     update_statistics_on_cleanup_end(os::javaTimeNanos());
 437   }
 438   if (begin_event.should_commit()) {
 439     begin_event.set_safepointId(safepoint_counter());
 440     begin_event.set_totalThreadCount(nof_threads);
 441     begin_event.set_jniCriticalThreadCount(_current_jni_active_count);
 442     begin_event.commit();
 443   }
 444 }
 445 
 446 // Wake up all threads, so they are ready to resume execution after the safepoint
 447 // operation has been carried out
 448 void SafepointSynchronize::end() {
 449   EventSafepointEnd event;
 450   int safepoint_id = safepoint_counter(); // Keep the odd counter as "id"
 451 
 452   assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
 453   assert((_safepoint_counter & 0x1) == 1, "must be odd");
 454   _safepoint_counter ++;
 455   // memory fence isn't required here since an odd _safepoint_counter
 456   // value can do no harm and a fence is issued below anyway.
 457 
 458   DEBUG_ONLY(Thread* myThread = Thread::current();)
 459   assert(myThread->is_VM_thread(), "Only VM thread can execute a safepoint");
 460 
 461   if (PrintSafepointStatistics) {
 462     end_statistics(os::javaTimeNanos());
 463   }
 464 
 465 #ifdef ASSERT
 466   // A pending_exception cannot be installed during a safepoint.  The threads
 467   // may install an async exception after they come back from a safepoint into
 468   // pending_exception after they unblock.  But that should happen later.
 469   for (JavaThread *cur = Threads::first(); cur; cur = cur->next()) {
 470     assert (!(cur->has_pending_exception() &&
 471               cur->safepoint_state()->is_at_poll_safepoint()),
 472             "safepoint installed a pending exception");
 473   }
 474 #endif // ASSERT
 475 
 476   if (PageArmed) {
 477     assert(SafepointMechanism::uses_global_page_poll(), "sanity");
 478     // Make polling safepoint aware
 479     os::make_polling_page_readable();
 480     PageArmed = 0 ;
 481   }
 482 
 483   if (SafepointMechanism::uses_global_page_poll()) {
 484     // Remove safepoint check from interpreter
 485     Interpreter::ignore_safepoints();
 486   }
 487 
 488   {
 489     MutexLocker mu(Safepoint_lock);
 490 
 491     assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization");
 492 
 493     if (SafepointMechanism::uses_thread_local_poll()) {
 494       _state = _not_synchronized;
 495       OrderAccess::storestore(); // global state -> local state
 496       for (JavaThread *current = Threads::first(); current; current = current->next()) {
 497         ThreadSafepointState* cur_state = current->safepoint_state();
 498         cur_state->restart(); // TSS _running
 499         SafepointMechanism::disarm_local_poll(current); // release store, local state -> polling page
 500       }
 501       log_debug(safepoint)("Leaving safepoint region");
 502     } else {
 503       // Set to not synchronized, so the threads will not go into the signal_thread_blocked method
 504       // when they get restarted.
 505       _state = _not_synchronized;
 506       OrderAccess::fence();
 507 
 508       log_debug(safepoint)("Leaving safepoint region");
 509 
 510       // Start suspended threads
 511       for (JavaThread *current = Threads::first(); current; current = current->next()) {
 512         // A problem occurring on Solaris is when attempting to restart threads
 513         // the first #cpus - 1 go well, but then the VMThread is preempted when we get
 514         // to the next one (since it has been running the longest).  We then have
 515         // to wait for a cpu to become available before we can continue restarting
 516         // threads.
 517         // FIXME: This causes the performance of the VM to degrade when active and with
 518         // large numbers of threads.  Apparently this is due to the synchronous nature
 519         // of suspending threads.
 520         //
 521         // TODO-FIXME: the comments above are vestigial and no longer apply.
 522         // Furthermore, using solaris' schedctl in this particular context confers no benefit
 523         if (VMThreadHintNoPreempt) {
 524           os::hint_no_preempt();
 525         }
 526         ThreadSafepointState* cur_state = current->safepoint_state();
 527         assert(cur_state->type() != ThreadSafepointState::_running, "Thread not suspended at safepoint");
 528         cur_state->restart();
 529         assert(cur_state->is_running(), "safepoint state has not been reset");
 530       }
 531     }
 532 
 533     RuntimeService::record_safepoint_end();
 534 
 535     // Release threads lock, so threads can be created/destroyed again. It will also starts all threads
 536     // blocked in signal_thread_blocked
 537     Threads_lock->unlock();
 538 
 539   }
 540 #if INCLUDE_ALL_GCS
 541   // If there are any concurrent GC threads resume them.
 542   if (UseConcMarkSweepGC) {
 543     ConcurrentMarkSweepThread::desynchronize(false);
 544   } else if (UseG1GC) {
 545     SuspendibleThreadSet::desynchronize();
 546   }
 547 #endif // INCLUDE_ALL_GCS
 548   // record this time so VMThread can keep track how much time has elapsed
 549   // since last safepoint.
 550   _end_of_last_safepoint = os::javaTimeMillis();
 551 
 552   if (event.should_commit()) {
 553     event.set_safepointId(safepoint_id);
 554     event.commit();
 555   }
 556 }
 557 
 558 bool SafepointSynchronize::is_cleanup_needed() {
 559   // Need a safepoint if there are many monitors to deflate.
 560   if (ObjectSynchronizer::is_cleanup_needed()) return true;
 561   // Need a safepoint if some inline cache buffers is non-empty
 562   if (!InlineCacheBuffer::is_empty()) return true;
 563   return false;
 564 }
 565 
 566 static void event_safepoint_cleanup_task_commit(EventSafepointCleanupTask& event, const char* name) {
 567   if (event.should_commit()) {
 568     event.set_safepointId(SafepointSynchronize::safepoint_counter());
 569     event.set_name(name);
 570     event.commit();
 571   }
 572 }
 573 
 574 class ParallelSPCleanupThreadClosure : public ThreadClosure {
 575 private:
 576   CodeBlobClosure* _nmethod_cl;
 577   DeflateMonitorCounters* _counters;
 578 
 579 public:
 580   ParallelSPCleanupThreadClosure(DeflateMonitorCounters* counters) :
 581     _counters(counters),
 582     _nmethod_cl(NMethodSweeper::prepare_mark_active_nmethods()) {}
 583 
 584   void do_thread(Thread* thread) {
 585     ObjectSynchronizer::deflate_thread_local_monitors(thread, _counters);
 586     if (_nmethod_cl != NULL && thread->is_Java_thread() &&
 587         ! thread->is_Code_cache_sweeper_thread()) {
 588       JavaThread* jt = (JavaThread*) thread;
 589       jt->nmethods_do(_nmethod_cl);
 590     }
 591   }
 592 };
 593 
 594 class ParallelSPCleanupTask : public AbstractGangTask {
 595 private:
 596   SubTasksDone _subtasks;
 597   ParallelSPCleanupThreadClosure _cleanup_threads_cl;
 598   uint _num_workers;
 599   DeflateMonitorCounters* _counters;
 600 public:
 601   ParallelSPCleanupTask(uint num_workers, DeflateMonitorCounters* counters) :
 602     AbstractGangTask("Parallel Safepoint Cleanup"),
 603     _cleanup_threads_cl(ParallelSPCleanupThreadClosure(counters)),
 604     _num_workers(num_workers),
 605     _subtasks(SubTasksDone(SafepointSynchronize::SAFEPOINT_CLEANUP_NUM_TASKS)),
 606     _counters(counters) {}
 607 
 608   void work(uint worker_id) {
 609     // All threads deflate monitors and mark nmethods (if necessary).
 610     Threads::parallel_java_threads_do(&_cleanup_threads_cl);
 611 
 612     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_DEFLATE_MONITORS)) {
 613       const char* name = "deflating idle monitors";
 614       EventSafepointCleanupTask event;
 615       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 616       ObjectSynchronizer::deflate_idle_monitors(_counters);
 617       event_safepoint_cleanup_task_commit(event, name);
 618     }
 619 
 620     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_UPDATE_INLINE_CACHES)) {
 621       const char* name = "updating inline caches";
 622       EventSafepointCleanupTask event;
 623       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 624       InlineCacheBuffer::update_inline_caches();
 625       event_safepoint_cleanup_task_commit(event, name);
 626     }
 627 
 628     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_COMPILATION_POLICY)) {
 629       const char* name = "compilation policy safepoint handler";
 630       EventSafepointCleanupTask event;
 631       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 632       CompilationPolicy::policy()->do_safepoint_work();
 633       event_safepoint_cleanup_task_commit(event, name);
 634     }
 635 
 636     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_SYMBOL_TABLE_REHASH)) {
 637       if (SymbolTable::needs_rehashing()) {
 638         const char* name = "rehashing symbol table";
 639         EventSafepointCleanupTask event;
 640         TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 641         SymbolTable::rehash_table();
 642         event_safepoint_cleanup_task_commit(event, name);
 643       }
 644     }
 645 
 646     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_STRING_TABLE_REHASH)) {
 647       if (StringTable::needs_rehashing()) {
 648         const char* name = "rehashing string table";
 649         EventSafepointCleanupTask event;
 650         TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 651         StringTable::rehash_table();
 652         event_safepoint_cleanup_task_commit(event, name);
 653       }
 654     }
 655 
 656     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_CLD_PURGE)) {
 657       // CMS delays purging the CLDG until the beginning of the next safepoint and to
 658       // make sure concurrent sweep is done
 659       const char* name = "purging class loader data graph";
 660       EventSafepointCleanupTask event;
 661       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 662       ClassLoaderDataGraph::purge_if_needed();
 663       event_safepoint_cleanup_task_commit(event, name);
 664     }
 665     _subtasks.all_tasks_completed(_num_workers);
 666   }
 667 };
 668 
 669 // Various cleaning tasks that should be done periodically at safepoints.
 670 void SafepointSynchronize::do_cleanup_tasks() {
 671 
 672   TraceTime timer("safepoint cleanup tasks", TRACETIME_LOG(Info, safepoint, cleanup));
 673 
 674   // Prepare for monitor deflation.
 675   DeflateMonitorCounters deflate_counters;
 676   ObjectSynchronizer::prepare_deflate_idle_monitors(&deflate_counters);
 677 
 678   CollectedHeap* heap = Universe::heap();
 679   assert(heap != NULL, "heap not initialized yet?");
 680   WorkGang* cleanup_workers = heap->get_safepoint_workers();
 681   if (cleanup_workers != NULL) {
 682     // Parallel cleanup using GC provided thread pool.
 683     uint num_cleanup_workers = cleanup_workers->active_workers();
 684     ParallelSPCleanupTask cleanup(num_cleanup_workers, &deflate_counters);
 685     StrongRootsScope srs(num_cleanup_workers);
 686     cleanup_workers->run_task(&cleanup);
 687   } else {
 688     // Serial cleanup using VMThread.
 689     ParallelSPCleanupTask cleanup(1, &deflate_counters);
 690     StrongRootsScope srs(1);
 691     cleanup.work(0);
 692   }
 693 
 694   // Finish monitor deflation.
 695   ObjectSynchronizer::finish_deflate_idle_monitors(&deflate_counters);
 696 }
 697 
 698 
 699 bool SafepointSynchronize::safepoint_safe(JavaThread *thread, JavaThreadState state) {
 700   switch(state) {
 701   case _thread_in_native:
 702     // native threads are safe if they have no java stack or have walkable stack
 703     return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable();
 704 
 705    // blocked threads should have already have walkable stack
 706   case _thread_blocked:
 707     assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable");
 708     return true;
 709 
 710   default:
 711     return false;
 712   }
 713 }
 714 
 715 
 716 // See if the thread is running inside a lazy critical native and
 717 // update the thread critical count if so.  Also set a suspend flag to
 718 // cause the native wrapper to return into the JVM to do the unlock
 719 // once the native finishes.
 720 void SafepointSynchronize::check_for_lazy_critical_native(JavaThread *thread, JavaThreadState state) {
 721   if (state == _thread_in_native &&
 722       thread->has_last_Java_frame() &&
 723       thread->frame_anchor()->walkable()) {
 724     // This thread might be in a critical native nmethod so look at
 725     // the top of the stack and increment the critical count if it
 726     // is.
 727     frame wrapper_frame = thread->last_frame();
 728     CodeBlob* stub_cb = wrapper_frame.cb();
 729     if (stub_cb != NULL &&
 730         stub_cb->is_nmethod() &&
 731         stub_cb->as_nmethod_or_null()->is_lazy_critical_native()) {
 732       // A thread could potentially be in a critical native across
 733       // more than one safepoint, so only update the critical state on
 734       // the first one.  When it returns it will perform the unlock.
 735       if (!thread->do_critical_native_unlock()) {
 736 #ifdef ASSERT
 737         if (!thread->in_critical()) {
 738           GCLocker::increment_debug_jni_lock_count();
 739         }
 740 #endif
 741         thread->enter_critical();
 742         // Make sure the native wrapper calls back on return to
 743         // perform the needed critical unlock.
 744         thread->set_critical_native_unlock();
 745       }
 746     }
 747   }
 748 }
 749 
 750 
 751 
 752 // -------------------------------------------------------------------------------------------------------
 753 // Implementation of Safepoint callback point
 754 
 755 void SafepointSynchronize::block(JavaThread *thread) {
 756   assert(thread != NULL, "thread must be set");
 757   assert(thread->is_Java_thread(), "not a Java thread");
 758 
 759   // Threads shouldn't block if they are in the middle of printing, but...
 760   ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id());
 761 
 762   // Only bail from the block() call if the thread is gone from the
 763   // thread list; starting to exit should still block.
 764   if (thread->is_terminated()) {
 765      // block current thread if we come here from native code when VM is gone
 766      thread->block_if_vm_exited();
 767 
 768      // otherwise do nothing
 769      return;
 770   }
 771 
 772   JavaThreadState state = thread->thread_state();
 773   thread->frame_anchor()->make_walkable(thread);
 774 
 775   // Check that we have a valid thread_state at this point
 776   switch(state) {
 777     case _thread_in_vm_trans:
 778     case _thread_in_Java:        // From compiled code
 779 
 780       // We are highly likely to block on the Safepoint_lock. In order to avoid blocking in this case,
 781       // we pretend we are still in the VM.
 782       thread->set_thread_state(_thread_in_vm);
 783 
 784       if (is_synchronizing()) {
 785          Atomic::inc (&TryingToBlock) ;
 786       }
 787 
 788       // We will always be holding the Safepoint_lock when we are examine the state
 789       // of a thread. Hence, the instructions between the Safepoint_lock->lock() and
 790       // Safepoint_lock->unlock() are happening atomic with regards to the safepoint code
 791       Safepoint_lock->lock_without_safepoint_check();
 792       if (is_synchronizing()) {
 793         // Decrement the number of threads to wait for and signal vm thread
 794         assert(_waiting_to_block > 0, "sanity check");
 795         _waiting_to_block--;
 796         thread->safepoint_state()->set_has_called_back(true);
 797 
 798         DEBUG_ONLY(thread->set_visited_for_critical_count(true));
 799         if (thread->in_critical()) {
 800           // Notice that this thread is in a critical section
 801           increment_jni_active_count();
 802         }
 803 
 804         // Consider (_waiting_to_block < 2) to pipeline the wakeup of the VM thread
 805         if (_waiting_to_block == 0) {
 806           Safepoint_lock->notify_all();
 807         }
 808       }
 809 
 810       // We transition the thread to state _thread_blocked here, but
 811       // we can't do our usual check for external suspension and then
 812       // self-suspend after the lock_without_safepoint_check() call
 813       // below because we are often called during transitions while
 814       // we hold different locks. That would leave us suspended while
 815       // holding a resource which results in deadlocks.
 816       thread->set_thread_state(_thread_blocked);
 817       Safepoint_lock->unlock();
 818 
 819       // We now try to acquire the threads lock. Since this lock is hold by the VM thread during
 820       // the entire safepoint, the threads will all line up here during the safepoint.
 821       Threads_lock->lock_without_safepoint_check();
 822       // restore original state. This is important if the thread comes from compiled code, so it
 823       // will continue to execute with the _thread_in_Java state.
 824       thread->set_thread_state(state);
 825       Threads_lock->unlock();
 826       break;
 827 
 828     case _thread_in_native_trans:
 829     case _thread_blocked_trans:
 830     case _thread_new_trans:
 831       if (thread->safepoint_state()->type() == ThreadSafepointState::_call_back) {
 832         thread->print_thread_state();
 833         fatal("Deadlock in safepoint code.  "
 834               "Should have called back to the VM before blocking.");
 835       }
 836 
 837       // We transition the thread to state _thread_blocked here, but
 838       // we can't do our usual check for external suspension and then
 839       // self-suspend after the lock_without_safepoint_check() call
 840       // below because we are often called during transitions while
 841       // we hold different locks. That would leave us suspended while
 842       // holding a resource which results in deadlocks.
 843       thread->set_thread_state(_thread_blocked);
 844 
 845       // It is not safe to suspend a thread if we discover it is in _thread_in_native_trans. Hence,
 846       // the safepoint code might still be waiting for it to block. We need to change the state here,
 847       // so it can see that it is at a safepoint.
 848 
 849       // Block until the safepoint operation is completed.
 850       Threads_lock->lock_without_safepoint_check();
 851 
 852       // Restore state
 853       thread->set_thread_state(state);
 854 
 855       Threads_lock->unlock();
 856       break;
 857 
 858     default:
 859      fatal("Illegal threadstate encountered: %d", state);
 860   }
 861 
 862   // Check for pending. async. exceptions or suspends - except if the
 863   // thread was blocked inside the VM. has_special_runtime_exit_condition()
 864   // is called last since it grabs a lock and we only want to do that when
 865   // we must.
 866   //
 867   // Note: we never deliver an async exception at a polling point as the
 868   // compiler may not have an exception handler for it. The polling
 869   // code will notice the async and deoptimize and the exception will
 870   // be delivered. (Polling at a return point is ok though). Sure is
 871   // a lot of bother for a deprecated feature...
 872   //
 873   // We don't deliver an async exception if the thread state is
 874   // _thread_in_native_trans so JNI functions won't be called with
 875   // a surprising pending exception. If the thread state is going back to java,
 876   // async exception is checked in check_special_condition_for_native_trans().
 877 
 878   if (state != _thread_blocked_trans &&
 879       state != _thread_in_vm_trans &&
 880       thread->has_special_runtime_exit_condition()) {
 881     thread->handle_special_runtime_exit_condition(
 882       !thread->is_at_poll_safepoint() && (state != _thread_in_native_trans));
 883   }
 884 }
 885 
 886 // ------------------------------------------------------------------------------------------------------
 887 // Exception handlers
 888 
 889 
 890 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) {
 891   assert(thread->is_Java_thread(), "polling reference encountered by VM thread");
 892   assert(thread->thread_state() == _thread_in_Java, "should come from Java code");
 893   if (!ThreadLocalHandshakes) {
 894     assert(SafepointSynchronize::is_synchronizing(), "polling encountered outside safepoint synchronization");
 895   }
 896 
 897   if (ShowSafepointMsgs) {
 898     tty->print("handle_polling_page_exception: ");
 899   }
 900 
 901   if (PrintSafepointStatistics) {
 902     inc_page_trap_count();
 903   }
 904 
 905   ThreadSafepointState* state = thread->safepoint_state();
 906 
 907   state->handle_polling_page_exception();
 908 }
 909 
 910 
 911 void SafepointSynchronize::print_safepoint_timeout(SafepointTimeoutReason reason) {
 912   if (!timeout_error_printed) {
 913     timeout_error_printed = true;
 914     // Print out the thread info which didn't reach the safepoint for debugging
 915     // purposes (useful when there are lots of threads in the debugger).
 916     tty->cr();
 917     tty->print_cr("# SafepointSynchronize::begin: Timeout detected:");
 918     if (reason ==  _spinning_timeout) {
 919       tty->print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint.");
 920     } else if (reason == _blocking_timeout) {
 921       tty->print_cr("# SafepointSynchronize::begin: Timed out while waiting for threads to stop.");
 922     }
 923 
 924     tty->print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:");
 925     ThreadSafepointState *cur_state;
 926     ResourceMark rm;
 927     for (JavaThread *cur_thread = Threads::first(); cur_thread;
 928         cur_thread = cur_thread->next()) {
 929       cur_state = cur_thread->safepoint_state();
 930 
 931       if (cur_thread->thread_state() != _thread_blocked &&
 932           ((reason == _spinning_timeout && cur_state->is_running()) ||
 933            (reason == _blocking_timeout && !cur_state->has_called_back()))) {
 934         tty->print("# ");
 935         cur_thread->print();
 936         tty->cr();
 937       }
 938     }
 939     tty->print_cr("# SafepointSynchronize::begin: (End of list)");
 940   }
 941 
 942   // To debug the long safepoint, specify both DieOnSafepointTimeout &
 943   // ShowMessageBoxOnError.
 944   if (DieOnSafepointTimeout) {
 945     fatal("Safepoint sync time longer than " INTX_FORMAT "ms detected when executing %s.",
 946           SafepointTimeoutDelay, VMThread::vm_safepoint_description());
 947   }
 948 }
 949 
 950 
 951 // -------------------------------------------------------------------------------------------------------
 952 // Implementation of ThreadSafepointState
 953 
 954 ThreadSafepointState::ThreadSafepointState(JavaThread *thread) {
 955   _thread = thread;
 956   _type   = _running;
 957   _has_called_back = false;
 958   _at_poll_safepoint = false;
 959 }
 960 
 961 void ThreadSafepointState::create(JavaThread *thread) {
 962   ThreadSafepointState *state = new ThreadSafepointState(thread);
 963   thread->set_safepoint_state(state);
 964 }
 965 
 966 void ThreadSafepointState::destroy(JavaThread *thread) {
 967   if (thread->safepoint_state()) {
 968     delete(thread->safepoint_state());
 969     thread->set_safepoint_state(NULL);
 970   }
 971 }
 972 
 973 void ThreadSafepointState::examine_state_of_thread() {
 974   assert(is_running(), "better be running or just have hit safepoint poll");
 975 
 976   JavaThreadState state = _thread->thread_state();
 977 
 978   // Save the state at the start of safepoint processing.
 979   _orig_thread_state = state;
 980 
 981   // Check for a thread that is suspended. Note that thread resume tries
 982   // to grab the Threads_lock which we own here, so a thread cannot be
 983   // resumed during safepoint synchronization.
 984 
 985   // We check to see if this thread is suspended without locking to
 986   // avoid deadlocking with a third thread that is waiting for this
 987   // thread to be suspended. The third thread can notice the safepoint
 988   // that we're trying to start at the beginning of its SR_lock->wait()
 989   // call. If that happens, then the third thread will block on the
 990   // safepoint while still holding the underlying SR_lock. We won't be
 991   // able to get the SR_lock and we'll deadlock.
 992   //
 993   // We don't need to grab the SR_lock here for two reasons:
 994   // 1) The suspend flags are both volatile and are set with an
 995   //    Atomic::cmpxchg() call so we should see the suspended
 996   //    state right away.
 997   // 2) We're being called from the safepoint polling loop; if
 998   //    we don't see the suspended state on this iteration, then
 999   //    we'll come around again.
1000   //
1001   bool is_suspended = _thread->is_ext_suspended();
1002   if (is_suspended) {
1003     roll_forward(_at_safepoint);
1004     return;
1005   }
1006 
1007   // Some JavaThread states have an initial safepoint state of
1008   // running, but are actually at a safepoint. We will happily
1009   // agree and update the safepoint state here.
1010   if (SafepointSynchronize::safepoint_safe(_thread, state)) {
1011     SafepointSynchronize::check_for_lazy_critical_native(_thread, state);
1012     roll_forward(_at_safepoint);
1013     return;
1014   }
1015 
1016   if (state == _thread_in_vm) {
1017     roll_forward(_call_back);
1018     return;
1019   }
1020 
1021   // All other thread states will continue to run until they
1022   // transition and self-block in state _blocked
1023   // Safepoint polling in compiled code causes the Java threads to do the same.
1024   // Note: new threads may require a malloc so they must be allowed to finish
1025 
1026   assert(is_running(), "examine_state_of_thread on non-running thread");
1027   return;
1028 }
1029 
1030 // Returns true is thread could not be rolled forward at present position.
1031 void ThreadSafepointState::roll_forward(suspend_type type) {
1032   _type = type;
1033 
1034   switch(_type) {
1035     case _at_safepoint:
1036       SafepointSynchronize::signal_thread_at_safepoint();
1037       DEBUG_ONLY(_thread->set_visited_for_critical_count(true));
1038       if (_thread->in_critical()) {
1039         // Notice that this thread is in a critical section
1040         SafepointSynchronize::increment_jni_active_count();
1041       }
1042       break;
1043 
1044     case _call_back:
1045       set_has_called_back(false);
1046       break;
1047 
1048     case _running:
1049     default:
1050       ShouldNotReachHere();
1051   }
1052 }
1053 
1054 void ThreadSafepointState::restart() {
1055   switch(type()) {
1056     case _at_safepoint:
1057     case _call_back:
1058       break;
1059 
1060     case _running:
1061     default:
1062        tty->print_cr("restart thread " INTPTR_FORMAT " with state %d",
1063                      p2i(_thread), _type);
1064        _thread->print();
1065       ShouldNotReachHere();
1066   }
1067   _type = _running;
1068   set_has_called_back(false);
1069 }
1070 
1071 
1072 void ThreadSafepointState::print_on(outputStream *st) const {
1073   const char *s = NULL;
1074 
1075   switch(_type) {
1076     case _running                : s = "_running";              break;
1077     case _at_safepoint           : s = "_at_safepoint";         break;
1078     case _call_back              : s = "_call_back";            break;
1079     default:
1080       ShouldNotReachHere();
1081   }
1082 
1083   st->print_cr("Thread: " INTPTR_FORMAT
1084               "  [0x%2x] State: %s _has_called_back %d _at_poll_safepoint %d",
1085                p2i(_thread), _thread->osthread()->thread_id(), s, _has_called_back,
1086                _at_poll_safepoint);
1087 
1088   _thread->print_thread_state_on(st);
1089 }
1090 
1091 // ---------------------------------------------------------------------------------------------------------------------
1092 
1093 // Block the thread at poll or poll return for safepoint/handshake.
1094 void ThreadSafepointState::handle_polling_page_exception() {
1095 
1096   // Check state.  block() will set thread state to thread_in_vm which will
1097   // cause the safepoint state _type to become _call_back.
1098   suspend_type t = type();
1099   assert(!SafepointMechanism::uses_global_page_poll() || t == ThreadSafepointState::_running,
1100          "polling page exception on thread not running state: %u", uint(t));
1101 
1102   // Step 1: Find the nmethod from the return address
1103   if (ShowSafepointMsgs && Verbose) {
1104     tty->print_cr("Polling page exception at " INTPTR_FORMAT, p2i(thread()->saved_exception_pc()));
1105   }
1106   address real_return_addr = thread()->saved_exception_pc();
1107 
1108   CodeBlob *cb = CodeCache::find_blob(real_return_addr);
1109   assert(cb != NULL && cb->is_compiled(), "return address should be in nmethod");
1110   CompiledMethod* nm = (CompiledMethod*)cb;
1111 
1112   // Find frame of caller
1113   frame stub_fr = thread()->last_frame();
1114   CodeBlob* stub_cb = stub_fr.cb();
1115   assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub");
1116   RegisterMap map(thread(), true);
1117   frame caller_fr = stub_fr.sender(&map);
1118 
1119   // Should only be poll_return or poll
1120   assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" );
1121 
1122   // This is a poll immediately before a return. The exception handling code
1123   // has already had the effect of causing the return to occur, so the execution
1124   // will continue immediately after the call. In addition, the oopmap at the
1125   // return point does not mark the return value as an oop (if it is), so
1126   // it needs a handle here to be updated.
1127   if( nm->is_at_poll_return(real_return_addr) ) {
1128     // See if return type is an oop.
1129     bool return_oop = nm->method()->is_returning_oop();
1130     Handle return_value;
1131     if (return_oop) {
1132       // The oop result has been saved on the stack together with all
1133       // the other registers. In order to preserve it over GCs we need
1134       // to keep it in a handle.
1135       oop result = caller_fr.saved_oop_result(&map);
1136       assert(oopDesc::is_oop_or_null(result), "must be oop");
1137       return_value = Handle(thread(), result);
1138       assert(Universe::heap()->is_in_or_null(result), "must be heap pointer");
1139     }
1140 
1141     // Block the thread
1142     SafepointMechanism::block_if_requested(thread());
1143 
1144     // restore oop result, if any
1145     if (return_oop) {
1146       caller_fr.set_saved_oop_result(&map, return_value());
1147     }
1148   }
1149 
1150   // This is a safepoint poll. Verify the return address and block.
1151   else {
1152     set_at_poll_safepoint(true);
1153 
1154     // verify the blob built the "return address" correctly
1155     assert(real_return_addr == caller_fr.pc(), "must match");
1156 
1157     // Block the thread
1158     SafepointMechanism::block_if_requested(thread());
1159     set_at_poll_safepoint(false);
1160 
1161     // If we have a pending async exception deoptimize the frame
1162     // as otherwise we may never deliver it.
1163     if (thread()->has_async_condition()) {
1164       ThreadInVMfromJavaNoAsyncException __tiv(thread());
1165       Deoptimization::deoptimize_frame(thread(), caller_fr.id());
1166     }
1167 
1168     // If an exception has been installed we must check for a pending deoptimization
1169     // Deoptimize frame if exception has been thrown.
1170 
1171     if (thread()->has_pending_exception() ) {
1172       RegisterMap map(thread(), true);
1173       frame caller_fr = stub_fr.sender(&map);
1174       if (caller_fr.is_deoptimized_frame()) {
1175         // The exception patch will destroy registers that are still
1176         // live and will be needed during deoptimization. Defer the
1177         // Async exception should have deferred the exception until the
1178         // next safepoint which will be detected when we get into
1179         // the interpreter so if we have an exception now things
1180         // are messed up.
1181 
1182         fatal("Exception installed and deoptimization is pending");
1183       }
1184     }
1185   }
1186 }
1187 
1188 
1189 //
1190 //                     Statistics & Instrumentations
1191 //
1192 SafepointSynchronize::SafepointStats*  SafepointSynchronize::_safepoint_stats = NULL;
1193 jlong  SafepointSynchronize::_safepoint_begin_time = 0;
1194 int    SafepointSynchronize::_cur_stat_index = 0;
1195 julong SafepointSynchronize::_safepoint_reasons[VM_Operation::VMOp_Terminating];
1196 julong SafepointSynchronize::_coalesced_vmop_count = 0;
1197 jlong  SafepointSynchronize::_max_sync_time = 0;
1198 jlong  SafepointSynchronize::_max_vmop_time = 0;
1199 float  SafepointSynchronize::_ts_of_current_safepoint = 0.0f;
1200 
1201 static jlong  cleanup_end_time = 0;
1202 static bool   need_to_track_page_armed_status = false;
1203 static bool   init_done = false;
1204 
1205 // Helper method to print the header.
1206 static void print_header() {
1207   // The number of spaces is significant here, and should match the format
1208   // specifiers in print_statistics().
1209 
1210   tty->print("          vmop                            "
1211              "[ threads:    total initially_running wait_to_block ]"
1212              "[ time:    spin   block    sync cleanup    vmop ] ");
1213 
1214   // no page armed status printed out if it is always armed.
1215   if (need_to_track_page_armed_status) {
1216     tty->print("page_armed ");
1217   }
1218 
1219   tty->print_cr("page_trap_count");
1220 }
1221 
1222 void SafepointSynchronize::deferred_initialize_stat() {
1223   if (init_done) return;
1224 
1225   // If PrintSafepointStatisticsTimeout is specified, the statistics data will
1226   // be printed right away, in which case, _safepoint_stats will regress to
1227   // a single element array. Otherwise, it is a circular ring buffer with default
1228   // size of PrintSafepointStatisticsCount.
1229   int stats_array_size;
1230   if (PrintSafepointStatisticsTimeout > 0) {
1231     stats_array_size = 1;
1232     PrintSafepointStatistics = true;
1233   } else {
1234     stats_array_size = PrintSafepointStatisticsCount;
1235   }
1236   _safepoint_stats = (SafepointStats*)os::malloc(stats_array_size
1237                                                  * sizeof(SafepointStats), mtInternal);
1238   guarantee(_safepoint_stats != NULL,
1239             "not enough memory for safepoint instrumentation data");
1240 
1241   if (DeferPollingPageLoopCount >= 0) {
1242     need_to_track_page_armed_status = true;
1243   }
1244   init_done = true;
1245 }
1246 
1247 void SafepointSynchronize::begin_statistics(int nof_threads, int nof_running) {
1248   assert(init_done, "safepoint statistics array hasn't been initialized");
1249   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1250 
1251   spstat->_time_stamp = _ts_of_current_safepoint;
1252 
1253   VM_Operation *op = VMThread::vm_operation();
1254   spstat->_vmop_type = (op != NULL ? op->type() : -1);
1255   if (op != NULL) {
1256     _safepoint_reasons[spstat->_vmop_type]++;
1257   }
1258 
1259   spstat->_nof_total_threads = nof_threads;
1260   spstat->_nof_initial_running_threads = nof_running;
1261   spstat->_nof_threads_hit_page_trap = 0;
1262 
1263   // Records the start time of spinning. The real time spent on spinning
1264   // will be adjusted when spin is done. Same trick is applied for time
1265   // spent on waiting for threads to block.
1266   if (nof_running != 0) {
1267     spstat->_time_to_spin = os::javaTimeNanos();
1268   }  else {
1269     spstat->_time_to_spin = 0;
1270   }
1271 }
1272 
1273 void SafepointSynchronize::update_statistics_on_spin_end() {
1274   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1275 
1276   jlong cur_time = os::javaTimeNanos();
1277 
1278   spstat->_nof_threads_wait_to_block = _waiting_to_block;
1279   if (spstat->_nof_initial_running_threads != 0) {
1280     spstat->_time_to_spin = cur_time - spstat->_time_to_spin;
1281   }
1282 
1283   if (need_to_track_page_armed_status) {
1284     spstat->_page_armed = (PageArmed == 1);
1285   }
1286 
1287   // Records the start time of waiting for to block. Updated when block is done.
1288   if (_waiting_to_block != 0) {
1289     spstat->_time_to_wait_to_block = cur_time;
1290   } else {
1291     spstat->_time_to_wait_to_block = 0;
1292   }
1293 }
1294 
1295 void SafepointSynchronize::update_statistics_on_sync_end(jlong end_time) {
1296   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1297 
1298   if (spstat->_nof_threads_wait_to_block != 0) {
1299     spstat->_time_to_wait_to_block = end_time -
1300       spstat->_time_to_wait_to_block;
1301   }
1302 
1303   // Records the end time of sync which will be used to calculate the total
1304   // vm operation time. Again, the real time spending in syncing will be deducted
1305   // from the start of the sync time later when end_statistics is called.
1306   spstat->_time_to_sync = end_time - _safepoint_begin_time;
1307   if (spstat->_time_to_sync > _max_sync_time) {
1308     _max_sync_time = spstat->_time_to_sync;
1309   }
1310 
1311   spstat->_time_to_do_cleanups = end_time;
1312 }
1313 
1314 void SafepointSynchronize::update_statistics_on_cleanup_end(jlong end_time) {
1315   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1316 
1317   // Record how long spent in cleanup tasks.
1318   spstat->_time_to_do_cleanups = end_time - spstat->_time_to_do_cleanups;
1319 
1320   cleanup_end_time = end_time;
1321 }
1322 
1323 void SafepointSynchronize::end_statistics(jlong vmop_end_time) {
1324   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1325 
1326   // Update the vm operation time.
1327   spstat->_time_to_exec_vmop = vmop_end_time -  cleanup_end_time;
1328   if (spstat->_time_to_exec_vmop > _max_vmop_time) {
1329     _max_vmop_time = spstat->_time_to_exec_vmop;
1330   }
1331   // Only the sync time longer than the specified
1332   // PrintSafepointStatisticsTimeout will be printed out right away.
1333   // By default, it is -1 meaning all samples will be put into the list.
1334   if ( PrintSafepointStatisticsTimeout > 0) {
1335     if (spstat->_time_to_sync > (jlong)PrintSafepointStatisticsTimeout * MICROUNITS) {
1336       print_statistics();
1337     }
1338   } else {
1339     // The safepoint statistics will be printed out when the _safepoin_stats
1340     // array fills up.
1341     if (_cur_stat_index == PrintSafepointStatisticsCount - 1) {
1342       print_statistics();
1343       _cur_stat_index = 0;
1344     } else {
1345       _cur_stat_index++;
1346     }
1347   }
1348 }
1349 
1350 void SafepointSynchronize::print_statistics() {
1351   for (int index = 0; index <= _cur_stat_index; index++) {
1352     if (index % 30 == 0) {
1353       print_header();
1354     }
1355     SafepointStats* sstats = &_safepoint_stats[index];
1356     tty->print("%8.3f: ", sstats->_time_stamp);
1357     tty->print("%-30s  [          "
1358                INT32_FORMAT_W(8) " " INT32_FORMAT_W(17) " " INT32_FORMAT_W(13) " "
1359                "]",
1360                (sstats->_vmop_type == -1 ? "no vm operation" : VM_Operation::name(sstats->_vmop_type)),
1361                sstats->_nof_total_threads,
1362                sstats->_nof_initial_running_threads,
1363                sstats->_nof_threads_wait_to_block);
1364     // "/ MICROUNITS " is to convert the unit from nanos to millis.
1365     tty->print("[       "
1366                INT64_FORMAT_W(7) " " INT64_FORMAT_W(7) " "
1367                INT64_FORMAT_W(7) " " INT64_FORMAT_W(7) " "
1368                INT64_FORMAT_W(7) " ] ",
1369                (int64_t)(sstats->_time_to_spin / MICROUNITS),
1370                (int64_t)(sstats->_time_to_wait_to_block / MICROUNITS),
1371                (int64_t)(sstats->_time_to_sync / MICROUNITS),
1372                (int64_t)(sstats->_time_to_do_cleanups / MICROUNITS),
1373                (int64_t)(sstats->_time_to_exec_vmop / MICROUNITS));
1374 
1375     if (need_to_track_page_armed_status) {
1376       tty->print(INT32_FORMAT_W(10) " ", sstats->_page_armed);
1377     }
1378     tty->print_cr(INT32_FORMAT_W(15) " ", sstats->_nof_threads_hit_page_trap);
1379   }
1380 }
1381 
1382 // This method will be called when VM exits. It will first call
1383 // print_statistics to print out the rest of the sampling.  Then
1384 // it tries to summarize the sampling.
1385 void SafepointSynchronize::print_stat_on_exit() {
1386   if (_safepoint_stats == NULL) return;
1387 
1388   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1389 
1390   // During VM exit, end_statistics may not get called and in that
1391   // case, if the sync time is less than PrintSafepointStatisticsTimeout,
1392   // don't print it out.
1393   // Approximate the vm op time.
1394   _safepoint_stats[_cur_stat_index]._time_to_exec_vmop =
1395     os::javaTimeNanos() - cleanup_end_time;
1396 
1397   if ( PrintSafepointStatisticsTimeout < 0 ||
1398        spstat->_time_to_sync > (jlong)PrintSafepointStatisticsTimeout * MICROUNITS) {
1399     print_statistics();
1400   }
1401   tty->cr();
1402 
1403   // Print out polling page sampling status.
1404   if (!need_to_track_page_armed_status) {
1405     tty->print_cr("Polling page always armed");
1406   } else {
1407     tty->print_cr("Defer polling page loop count = " INTX_FORMAT "\n",
1408                   DeferPollingPageLoopCount);
1409   }
1410 
1411   for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) {
1412     if (_safepoint_reasons[index] != 0) {
1413       tty->print_cr("%-26s" UINT64_FORMAT_W(10), VM_Operation::name(index),
1414                     _safepoint_reasons[index]);
1415     }
1416   }
1417 
1418   tty->print_cr(UINT64_FORMAT_W(5) " VM operations coalesced during safepoint",
1419                 _coalesced_vmop_count);
1420   tty->print_cr("Maximum sync time  " INT64_FORMAT_W(5) " ms",
1421                 (int64_t)(_max_sync_time / MICROUNITS));
1422   tty->print_cr("Maximum vm operation time (except for Exit VM operation)  "
1423                 INT64_FORMAT_W(5) " ms",
1424                 (int64_t)(_max_vmop_time / MICROUNITS));
1425 }
1426 
1427 // ------------------------------------------------------------------------------------------------
1428 // Non-product code
1429 
1430 #ifndef PRODUCT
1431 
1432 void SafepointSynchronize::print_state() {
1433   if (_state == _not_synchronized) {
1434     tty->print_cr("not synchronized");
1435   } else if (_state == _synchronizing || _state == _synchronized) {
1436     tty->print_cr("State: %s", (_state == _synchronizing) ? "synchronizing" :
1437                   "synchronized");
1438 
1439     for (JavaThread *cur = Threads::first(); cur; cur = cur->next()) {
1440        cur->safepoint_state()->print();
1441     }
1442   }
1443 }
1444 
1445 void SafepointSynchronize::safepoint_msg(const char* format, ...) {
1446   if (ShowSafepointMsgs) {
1447     va_list ap;
1448     va_start(ap, format);
1449     tty->vprint_cr(format, ap);
1450     va_end(ap);
1451   }
1452 }
1453 
1454 #endif // !PRODUCT