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