1 /*
   2  * Copyright (c) 1997, 2018, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "classfile/classLoaderData.hpp"
  27 #include "classfile/stringTable.hpp"
  28 #include "classfile/symbolTable.hpp"
  29 #include "classfile/systemDictionary.hpp"
  30 #include "code/codeCache.hpp"
  31 #include "code/icBuffer.hpp"
  32 #include "code/nmethod.hpp"
  33 #include "code/pcDesc.hpp"
  34 #include "code/scopeDesc.hpp"
  35 #include "gc/shared/collectedHeap.hpp"
  36 #include "gc/shared/gcLocker.hpp"
  37 #include "gc/shared/strongRootsScope.hpp"
  38 #include "gc/shared/workgroup.hpp"
  39 #include "interpreter/interpreter.hpp"
  40 #include "jfr/jfrEvents.hpp"
  41 #include "logging/log.hpp"
  42 #include "logging/logStream.hpp"
  43 #include "memory/resourceArea.hpp"
  44 #include "memory/universe.hpp"
  45 #include "oops/oop.inline.hpp"
  46 #include "oops/symbol.hpp"
  47 #include "runtime/atomic.hpp"
  48 #include "runtime/compilationPolicy.hpp"
  49 #include "runtime/deoptimization.hpp"
  50 #include "runtime/frame.inline.hpp"
  51 #include "runtime/interfaceSupport.inline.hpp"
  52 #include "runtime/mutexLocker.hpp"
  53 #include "runtime/orderAccess.hpp"
  54 #include "runtime/osThread.hpp"
  55 #include "runtime/safepoint.hpp"
  56 #include "runtime/safepointMechanism.inline.hpp"
  57 #include "runtime/signature.hpp"
  58 #include "runtime/stubCodeGenerator.hpp"
  59 #include "runtime/stubRoutines.hpp"
  60 #include "runtime/sweeper.hpp"
  61 #include "runtime/synchronizer.hpp"
  62 #include "runtime/thread.inline.hpp"
  63 #include "runtime/threadSMR.hpp"
  64 #include "runtime/timerTrace.hpp"
  65 #include "services/runtimeService.hpp"
  66 #include "utilities/events.hpp"
  67 #include "utilities/macros.hpp"
  68 #ifdef COMPILER1
  69 #include "c1/c1_globals.hpp"
  70 #endif
  71 
  72 template <typename E>
  73 static void set_current_safepoint_id(E* event, int adjustment = 0) {
  74   assert(event != NULL, "invariant");
  75   event->set_safepointId(SafepointSynchronize::safepoint_counter() + adjustment);
  76 }
  77 
  78 static void post_safepoint_begin_event(EventSafepointBegin* event,
  79                                        int thread_count,
  80                                        int critical_thread_count) {
  81   assert(event != NULL, "invariant");
  82   assert(event->should_commit(), "invariant");
  83   set_current_safepoint_id(event);
  84   event->set_totalThreadCount(thread_count);
  85   event->set_jniCriticalThreadCount(critical_thread_count);
  86   event->commit();
  87 }
  88 
  89 static void post_safepoint_cleanup_event(EventSafepointCleanup* event) {
  90   assert(event != NULL, "invariant");
  91   assert(event->should_commit(), "invariant");
  92   set_current_safepoint_id(event);
  93   event->commit();
  94 }
  95 
  96 static void post_safepoint_synchronize_event(EventSafepointStateSynchronization* event,
  97                                              int initial_number_of_threads,
  98                                              int threads_waiting_to_block,
  99                                              unsigned int iterations) {
 100   assert(event != NULL, "invariant");
 101   if (event->should_commit()) {
 102     // Group this event together with the ones committed after the counter is increased
 103     set_current_safepoint_id(event, 1);
 104     event->set_initialThreadCount(initial_number_of_threads);
 105     event->set_runningThreadCount(threads_waiting_to_block);
 106     event->set_iterations(iterations);
 107     event->commit();
 108   }
 109 }
 110 
 111 static void post_safepoint_wait_blocked_event(EventSafepointWaitBlocked* event,
 112                                               int initial_threads_waiting_to_block) {
 113   assert(event != NULL, "invariant");
 114   assert(event->should_commit(), "invariant");
 115   set_current_safepoint_id(event);
 116   event->set_runningThreadCount(initial_threads_waiting_to_block);
 117   event->commit();
 118 }
 119 
 120 static void post_safepoint_cleanup_task_event(EventSafepointCleanupTask* event,
 121                                               const char* name) {
 122   assert(event != NULL, "invariant");
 123   if (event->should_commit()) {
 124     set_current_safepoint_id(event);
 125     event->set_name(name);
 126     event->commit();
 127   }
 128 }
 129 
 130 static void post_safepoint_end_event(EventSafepointEnd* event) {
 131   assert(event != NULL, "invariant");
 132   if (event->should_commit()) {
 133     // Group this event together with the ones committed before the counter increased
 134     set_current_safepoint_id(event, -1);
 135     event->commit();
 136   }
 137 }
 138 
 139 // --------------------------------------------------------------------------------------------------
 140 // Implementation of Safepoint begin/end
 141 
 142 SafepointSynchronize::SynchronizeState volatile SafepointSynchronize::_state = SafepointSynchronize::_not_synchronized;
 143 volatile int  SafepointSynchronize::_waiting_to_block = 0;
 144 volatile int SafepointSynchronize::_safepoint_counter = 0;
 145 int SafepointSynchronize::_current_jni_active_count = 0;
 146 long  SafepointSynchronize::_end_of_last_safepoint = 0;
 147 int SafepointSynchronize::_defer_thr_suspend_loop_count = 4000;
 148 static const int safepoint_spin_before_yield = 2000;
 149 static volatile int PageArmed = 0 ;        // safepoint polling page is RO|RW vs PROT_NONE
 150 static volatile int TryingToBlock = 0 ;    // proximate value -- for advisory use only
 151 static bool timeout_error_printed = false;
 152 
 153 // Roll all threads forward to a safepoint and suspend them all
 154 void SafepointSynchronize::begin() {
 155   EventSafepointBegin begin_event;
 156   Thread* myThread = Thread::current();
 157   assert(myThread->is_VM_thread(), "Only VM thread may execute a safepoint");
 158 
 159   if (PrintSafepointStatistics || PrintSafepointStatisticsTimeout > 0) {
 160     _safepoint_begin_time = os::javaTimeNanos();
 161     _ts_of_current_safepoint = tty->time_stamp().seconds();
 162   }
 163 
 164   Universe::heap()->safepoint_synchronize_begin();
 165 
 166   // By getting the Threads_lock, we assure that no threads are about to start or
 167   // exit. It is released again in SafepointSynchronize::end().
 168   Threads_lock->lock();
 169 
 170   assert( _state == _not_synchronized, "trying to safepoint synchronize with wrong state");
 171 
 172   int nof_threads = Threads::number_of_threads();
 173 
 174   log_debug(safepoint)("Safepoint synchronization initiated. (%d threads)", nof_threads);
 175 
 176   RuntimeService::record_safepoint_begin();
 177 
 178   MutexLocker mu(Safepoint_lock);
 179 
 180   // Reset the count of active JNI critical threads
 181   _current_jni_active_count = 0;
 182 
 183   // Set number of threads to wait for, before we initiate the callbacks
 184   _waiting_to_block = nof_threads;
 185   TryingToBlock     = 0 ;
 186   int still_running = nof_threads;
 187 
 188   // Save the starting time, so that it can be compared to see if this has taken
 189   // too long to complete.
 190   jlong safepoint_limit_time = 0;
 191   timeout_error_printed = false;
 192 
 193   // PrintSafepointStatisticsTimeout can be specified separately. When
 194   // specified, PrintSafepointStatistics will be set to true in
 195   // deferred_initialize_stat method. The initialization has to be done
 196   // early enough to avoid any races. See bug 6880029 for details.
 197   if (PrintSafepointStatistics || PrintSafepointStatisticsTimeout > 0) {
 198     deferred_initialize_stat();
 199   }
 200 
 201   // Begin the process of bringing the system to a safepoint.
 202   // Java threads can be in several different states and are
 203   // stopped by different mechanisms:
 204   //
 205   //  1. Running interpreted
 206   //     The interpreter dispatch table is changed to force it to
 207   //     check for a safepoint condition between bytecodes.
 208   //  2. Running in native code
 209   //     When returning from the native code, a Java thread must check
 210   //     the safepoint _state to see if we must block.  If the
 211   //     VM thread sees a Java thread in native, it does
 212   //     not wait for this thread to block.  The order of the memory
 213   //     writes and reads of both the safepoint state and the Java
 214   //     threads state is critical.  In order to guarantee that the
 215   //     memory writes are serialized with respect to each other,
 216   //     the VM thread issues a memory barrier instruction
 217   //     (on MP systems).  In order to avoid the overhead of issuing
 218   //     a memory barrier for each Java thread making native calls, each Java
 219   //     thread performs a write to a single memory page after changing
 220   //     the thread state.  The VM thread performs a sequence of
 221   //     mprotect OS calls which forces all previous writes from all
 222   //     Java threads to be serialized.  This is done in the
 223   //     os::serialize_thread_states() call.  This has proven to be
 224   //     much more efficient than executing a membar instruction
 225   //     on every call to native code.
 226   //  3. Running compiled Code
 227   //     Compiled code reads a global (Safepoint Polling) page that
 228   //     is set to fault if we are trying to get to a safepoint.
 229   //  4. Blocked
 230   //     A thread which is blocked will not be allowed to return from the
 231   //     block condition until the safepoint operation is complete.
 232   //  5. In VM or Transitioning between states
 233   //     If a Java thread is currently running in the VM or transitioning
 234   //     between states, the safepointing code will wait for the thread to
 235   //     block itself when it attempts transitions to a new state.
 236   //
 237   {
 238     EventSafepointStateSynchronization sync_event;
 239     int initial_running = 0;
 240 
 241     _state            = _synchronizing;
 242 
 243     if (SafepointMechanism::uses_thread_local_poll()) {
 244       // Arming the per thread poll while having _state != _not_synchronized means safepointing
 245       log_trace(safepoint)("Setting thread local yield flag for threads");
 246       OrderAccess::storestore(); // storestore, global state -> local state
 247       for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
 248         // Make sure the threads start polling, it is time to yield.
 249         SafepointMechanism::arm_local_poll(cur);
 250       }
 251     }
 252     OrderAccess::fence(); // storestore|storeload, global state -> local state
 253 
 254     // Flush all thread states to memory
 255     if (!UseMembar) {
 256       os::serialize_thread_states();
 257     }
 258 
 259     if (SafepointMechanism::uses_global_page_poll()) {
 260       // Make interpreter safepoint aware
 261       Interpreter::notice_safepoints();
 262 
 263       // Make polling safepoint aware
 264       guarantee (PageArmed == 0, "invariant") ;
 265       PageArmed = 1 ;
 266       os::make_polling_page_unreadable();
 267     }
 268 
 269     // Consider using active_processor_count() ... but that call is expensive.
 270     int ncpus = os::processor_count() ;
 271     unsigned int iterations = 0;
 272 
 273     {
 274       JavaThreadIteratorWithHandle jtiwh;
 275 #ifdef ASSERT
 276       for (; JavaThread *cur = jtiwh.next(); ) {
 277         assert(cur->safepoint_state()->is_running(), "Illegal initial state");
 278         // Clear the visited flag to ensure that the critical counts are collected properly.
 279         cur->set_visited_for_critical_count(false);
 280       }
 281 #endif // ASSERT
 282 
 283       if (SafepointTimeout)
 284         safepoint_limit_time = os::javaTimeNanos() + (jlong)SafepointTimeoutDelay * MICROUNITS;
 285 
 286       // Iterate through all threads until it have been determined how to stop them all at a safepoint
 287       int steps = 0 ;
 288       while(still_running > 0) {
 289         jtiwh.rewind();
 290         for (; JavaThread *cur = jtiwh.next(); ) {
 291           assert(!cur->is_ConcurrentGC_thread(), "A concurrent GC thread is unexpectly being suspended");
 292           ThreadSafepointState *cur_state = cur->safepoint_state();
 293           if (cur_state->is_running()) {
 294             cur_state->examine_state_of_thread();
 295             if (!cur_state->is_running()) {
 296               still_running--;
 297               // consider adjusting steps downward:
 298               //   steps = 0
 299               //   steps -= NNN
 300               //   steps >>= 1
 301               //   steps = MIN(steps, 2000-100)
 302               //   if (iterations != 0) steps -= NNN
 303             }
 304             LogTarget(Trace, safepoint) lt;
 305             if (lt.is_enabled()) {
 306               ResourceMark rm;
 307               LogStream ls(lt);
 308               cur_state->print_on(&ls);
 309             }
 310           }
 311         }
 312 
 313         if (iterations == 0) {
 314           initial_running = still_running;
 315           if (PrintSafepointStatistics) {
 316             begin_statistics(nof_threads, still_running);
 317           }
 318         }
 319 
 320         if (still_running > 0) {
 321           // Check for if it takes to long
 322           if (SafepointTimeout && safepoint_limit_time < os::javaTimeNanos()) {
 323             print_safepoint_timeout(_spinning_timeout);
 324           }
 325 
 326           // Spin to avoid context switching.
 327           // There's a tension between allowing the mutators to run (and rendezvous)
 328           // vs spinning.  As the VM thread spins, wasting cycles, it consumes CPU that
 329           // a mutator might otherwise use profitably to reach a safepoint.  Excessive
 330           // spinning by the VM thread on a saturated system can increase rendezvous latency.
 331           // Blocking or yielding incur their own penalties in the form of context switching
 332           // and the resultant loss of $ residency.
 333           //
 334           // Further complicating matters is that yield() does not work as naively expected
 335           // on many platforms -- yield() does not guarantee that any other ready threads
 336           // will run.   As such we revert to naked_short_sleep() after some number of iterations.
 337           // nakes_short_sleep() is implemented as a short unconditional sleep.
 338           // Typical operating systems round a "short" sleep period up to 10 msecs, so sleeping
 339           // can actually increase the time it takes the VM thread to detect that a system-wide
 340           // stop-the-world safepoint has been reached.  In a pathological scenario such as that
 341           // described in CR6415670 the VMthread may sleep just before the mutator(s) become safe.
 342           // In that case the mutators will be stalled waiting for the safepoint to complete and the
 343           // the VMthread will be sleeping, waiting for the mutators to rendezvous.  The VMthread
 344           // will eventually wake up and detect that all mutators are safe, at which point
 345           // we'll again make progress.
 346           //
 347           // Beware too that that the VMThread typically runs at elevated priority.
 348           // Its default priority is higher than the default mutator priority.
 349           // Obviously, this complicates spinning.
 350           //
 351           // Note too that on Windows XP SwitchThreadTo() has quite different behavior than Sleep(0).
 352           // Sleep(0) will _not yield to lower priority threads, while SwitchThreadTo() will.
 353           //
 354           // See the comments in synchronizer.cpp for additional remarks on spinning.
 355           //
 356           // In the future we might:
 357           // 1. Modify the safepoint scheme to avoid potentially unbounded spinning.
 358           //    This is tricky as the path used by a thread exiting the JVM (say on
 359           //    on JNI call-out) simply stores into its state field.  The burden
 360           //    is placed on the VM thread, which must poll (spin).
 361           // 2. Find something useful to do while spinning.  If the safepoint is GC-related
 362           //    we might aggressively scan the stacks of threads that are already safe.
 363           // 3. Use Solaris schedctl to examine the state of the still-running mutators.
 364           //    If all the mutators are ONPROC there's no reason to sleep or yield.
 365           // 4. YieldTo() any still-running mutators that are ready but OFFPROC.
 366           // 5. Check system saturation.  If the system is not fully saturated then
 367           //    simply spin and avoid sleep/yield.
 368           // 6. As still-running mutators rendezvous they could unpark the sleeping
 369           //    VMthread.  This works well for still-running mutators that become
 370           //    safe.  The VMthread must still poll for mutators that call-out.
 371           // 7. Drive the policy on time-since-begin instead of iterations.
 372           // 8. Consider making the spin duration a function of the # of CPUs:
 373           //    Spin = (((ncpus-1) * M) + K) + F(still_running)
 374           //    Alternately, instead of counting iterations of the outer loop
 375           //    we could count the # of threads visited in the inner loop, above.
 376           // 9. On windows consider using the return value from SwitchThreadTo()
 377           //    to drive subsequent spin/SwitchThreadTo()/Sleep(N) decisions.
 378 
 379           if (int(iterations) == -1) { // overflow - something is wrong.
 380             // We can only overflow here when we are using global
 381             // polling pages. We keep this guarantee in its original
 382             // form so that searches of the bug database for this
 383             // failure mode find the right bugs.
 384             guarantee (PageArmed == 0, "invariant");
 385           }
 386 
 387           // Instead of (ncpus > 1) consider either (still_running < (ncpus + EPSILON)) or
 388           // ((still_running + _waiting_to_block - TryingToBlock)) < ncpus)
 389           ++steps ;
 390           if (ncpus > 1 && steps < safepoint_spin_before_yield) {
 391             SpinPause() ;     // MP-Polite spin
 392           } else
 393             if (steps < _defer_thr_suspend_loop_count) {
 394               os::naked_yield() ;
 395             } else {
 396               os::naked_short_sleep(1);
 397             }
 398 
 399           iterations ++ ;
 400         }
 401         assert(iterations < (uint)max_jint, "We have been iterating in the safepoint loop too long");
 402       }
 403     } // ThreadsListHandle destroyed here.
 404     assert(still_running == 0, "sanity check");
 405 
 406     if (PrintSafepointStatistics) {
 407       update_statistics_on_spin_end();
 408     }
 409     if (sync_event.should_commit()) {
 410       post_safepoint_synchronize_event(&sync_event, initial_running, _waiting_to_block, iterations);
 411     }
 412   }
 413 
 414   // wait until all threads are stopped
 415   {
 416     EventSafepointWaitBlocked wait_blocked_event;
 417     int initial_waiting_to_block = _waiting_to_block;
 418 
 419     while (_waiting_to_block > 0) {
 420       log_debug(safepoint)("Waiting for %d thread(s) to block", _waiting_to_block);
 421       if (!SafepointTimeout || timeout_error_printed) {
 422         Safepoint_lock->wait(true);  // true, means with no safepoint checks
 423       } else {
 424         // Compute remaining time
 425         jlong remaining_time = safepoint_limit_time - os::javaTimeNanos();
 426 
 427         // If there is no remaining time, then there is an error
 428         if (remaining_time < 0 || Safepoint_lock->wait(true, remaining_time / MICROUNITS)) {
 429           print_safepoint_timeout(_blocking_timeout);
 430         }
 431       }
 432     }
 433     assert(_waiting_to_block == 0, "sanity check");
 434 
 435 #ifndef PRODUCT
 436     if (SafepointTimeout) {
 437       jlong current_time = os::javaTimeNanos();
 438       if (safepoint_limit_time < current_time) {
 439         tty->print_cr("# SafepointSynchronize: Finished after "
 440                       INT64_FORMAT_W(6) " ms",
 441                       (int64_t)((current_time - safepoint_limit_time) / MICROUNITS +
 442                                 (jlong)SafepointTimeoutDelay));
 443       }
 444     }
 445 #endif
 446 
 447     assert((_safepoint_counter & 0x1) == 0, "must be even");
 448     assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
 449     _safepoint_counter ++;
 450 
 451     // Record state
 452     _state = _synchronized;
 453 
 454     OrderAccess::fence();
 455     if (wait_blocked_event.should_commit()) {
 456       post_safepoint_wait_blocked_event(&wait_blocked_event, initial_waiting_to_block);
 457     }
 458   }
 459 
 460 #ifdef ASSERT
 461   // Make sure all the threads were visited.
 462   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
 463     assert(cur->was_visited_for_critical_count(), "missed a thread");
 464   }
 465 #endif // ASSERT
 466 
 467   // Update the count of active JNI critical regions
 468   GCLocker::set_jni_lock_count(_current_jni_active_count);
 469 
 470   log_info(safepoint)("Entering safepoint region: %s", VMThread::vm_safepoint_description());
 471 
 472   RuntimeService::record_safepoint_synchronized();
 473   if (PrintSafepointStatistics) {
 474     update_statistics_on_sync_end(os::javaTimeNanos());
 475   }
 476 
 477   // Call stuff that needs to be run when a safepoint is just about to be completed
 478   {
 479     EventSafepointCleanup cleanup_event;
 480     do_cleanup_tasks();
 481     if (cleanup_event.should_commit()) {
 482       post_safepoint_cleanup_event(&cleanup_event);
 483     }
 484   }
 485 
 486   if (PrintSafepointStatistics) {
 487     // Record how much time spend on the above cleanup tasks
 488     update_statistics_on_cleanup_end(os::javaTimeNanos());
 489   }
 490 
 491   if (begin_event.should_commit()) {
 492     post_safepoint_begin_event(&begin_event, nof_threads, _current_jni_active_count);
 493   }
 494 }
 495 
 496 // Wake up all threads, so they are ready to resume execution after the safepoint
 497 // operation has been carried out
 498 void SafepointSynchronize::end() {
 499   assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
 500   assert((_safepoint_counter & 0x1) == 1, "must be odd");
 501   EventSafepointEnd event;
 502   _safepoint_counter ++;
 503   // memory fence isn't required here since an odd _safepoint_counter
 504   // value can do no harm and a fence is issued below anyway.
 505 
 506   DEBUG_ONLY(Thread* myThread = Thread::current();)
 507   assert(myThread->is_VM_thread(), "Only VM thread can execute a safepoint");
 508 
 509   if (PrintSafepointStatistics) {
 510     end_statistics(os::javaTimeNanos());
 511   }
 512 
 513   {
 514     JavaThreadIteratorWithHandle jtiwh;
 515 #ifdef ASSERT
 516     // A pending_exception cannot be installed during a safepoint.  The threads
 517     // may install an async exception after they come back from a safepoint into
 518     // pending_exception after they unblock.  But that should happen later.
 519     for (; JavaThread *cur = jtiwh.next(); ) {
 520       assert (!(cur->has_pending_exception() &&
 521                 cur->safepoint_state()->is_at_poll_safepoint()),
 522               "safepoint installed a pending exception");
 523     }
 524 #endif // ASSERT
 525 
 526     if (PageArmed) {
 527       assert(SafepointMechanism::uses_global_page_poll(), "sanity");
 528       // Make polling safepoint aware
 529       os::make_polling_page_readable();
 530       PageArmed = 0 ;
 531     }
 532 
 533     if (SafepointMechanism::uses_global_page_poll()) {
 534       // Remove safepoint check from interpreter
 535       Interpreter::ignore_safepoints();
 536     }
 537 
 538     {
 539       MutexLocker mu(Safepoint_lock);
 540 
 541       assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization");
 542 
 543       if (SafepointMechanism::uses_thread_local_poll()) {
 544         _state = _not_synchronized;
 545         OrderAccess::storestore(); // global state -> local state
 546         jtiwh.rewind();
 547         for (; JavaThread *current = jtiwh.next(); ) {
 548           ThreadSafepointState* cur_state = current->safepoint_state();
 549           cur_state->restart(); // TSS _running
 550           SafepointMechanism::disarm_local_poll(current);
 551         }
 552         log_info(safepoint)("Leaving safepoint region");
 553       } else {
 554         // Set to not synchronized, so the threads will not go into the signal_thread_blocked method
 555         // when they get restarted.
 556         _state = _not_synchronized;
 557         OrderAccess::fence();
 558 
 559         log_info(safepoint)("Leaving safepoint region");
 560 
 561         // Start suspended threads
 562         jtiwh.rewind();
 563         for (; JavaThread *current = jtiwh.next(); ) {
 564           // A problem occurring on Solaris is when attempting to restart threads
 565           // the first #cpus - 1 go well, but then the VMThread is preempted when we get
 566           // to the next one (since it has been running the longest).  We then have
 567           // to wait for a cpu to become available before we can continue restarting
 568           // threads.
 569           // FIXME: This causes the performance of the VM to degrade when active and with
 570           // large numbers of threads.  Apparently this is due to the synchronous nature
 571           // of suspending threads.
 572           //
 573           // TODO-FIXME: the comments above are vestigial and no longer apply.
 574           // Furthermore, using solaris' schedctl in this particular context confers no benefit
 575           if (VMThreadHintNoPreempt) {
 576             os::hint_no_preempt();
 577           }
 578           ThreadSafepointState* cur_state = current->safepoint_state();
 579           assert(cur_state->type() != ThreadSafepointState::_running, "Thread not suspended at safepoint");
 580           cur_state->restart();
 581           assert(cur_state->is_running(), "safepoint state has not been reset");
 582         }
 583       }
 584 
 585       RuntimeService::record_safepoint_end();
 586 
 587       // Release threads lock, so threads can be created/destroyed again.
 588       // It will also release all threads blocked in signal_thread_blocked.
 589       Threads_lock->unlock();
 590     }
 591   } // ThreadsListHandle destroyed here.
 592 
 593   Universe::heap()->safepoint_synchronize_end();
 594   // record this time so VMThread can keep track how much time has elapsed
 595   // since last safepoint.
 596   _end_of_last_safepoint = os::javaTimeMillis();
 597   if (event.should_commit()) {
 598     post_safepoint_end_event(&event);
 599   }
 600 }
 601 
 602 bool SafepointSynchronize::is_cleanup_needed() {
 603   // Need a safepoint if there are many monitors to deflate.
 604   if (ObjectSynchronizer::is_cleanup_needed()) return true;
 605   // Need a safepoint if some inline cache buffers is non-empty
 606   if (!InlineCacheBuffer::is_empty()) return true;
 607   return false;
 608 }
 609 
 610 class ParallelSPCleanupThreadClosure : public ThreadClosure {
 611 private:
 612   CodeBlobClosure* _nmethod_cl;
 613   DeflateMonitorCounters* _counters;
 614 
 615 public:
 616   ParallelSPCleanupThreadClosure(DeflateMonitorCounters* counters) :
 617     _counters(counters),
 618     _nmethod_cl(NMethodSweeper::prepare_mark_active_nmethods()) {}
 619 
 620   void do_thread(Thread* thread) {
 621     ObjectSynchronizer::deflate_thread_local_monitors(thread, _counters);
 622     if (_nmethod_cl != NULL && thread->is_Java_thread() &&
 623         ! thread->is_Code_cache_sweeper_thread()) {
 624       JavaThread* jt = (JavaThread*) thread;
 625       jt->nmethods_do(_nmethod_cl);
 626     }
 627   }
 628 };
 629 
 630 class ParallelSPCleanupTask : public AbstractGangTask {
 631 private:
 632   SubTasksDone _subtasks;
 633   ParallelSPCleanupThreadClosure _cleanup_threads_cl;
 634   uint _num_workers;
 635   DeflateMonitorCounters* _counters;
 636 public:
 637   ParallelSPCleanupTask(uint num_workers, DeflateMonitorCounters* counters) :
 638     AbstractGangTask("Parallel Safepoint Cleanup"),
 639     _cleanup_threads_cl(ParallelSPCleanupThreadClosure(counters)),
 640     _num_workers(num_workers),
 641     _subtasks(SubTasksDone(SafepointSynchronize::SAFEPOINT_CLEANUP_NUM_TASKS)),
 642     _counters(counters) {}
 643 
 644   void work(uint worker_id) {
 645     // All threads deflate monitors and mark nmethods (if necessary).
 646     Threads::possibly_parallel_threads_do(true, &_cleanup_threads_cl);
 647 
 648     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_DEFLATE_MONITORS)) {
 649       const char* name = "deflating idle monitors";
 650       EventSafepointCleanupTask event;
 651       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 652       ObjectSynchronizer::deflate_idle_monitors(_counters);
 653       if (event.should_commit()) {
 654         post_safepoint_cleanup_task_event(&event, name);
 655       }
 656     }
 657 
 658     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_UPDATE_INLINE_CACHES)) {
 659       const char* name = "updating inline caches";
 660       EventSafepointCleanupTask event;
 661       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 662       InlineCacheBuffer::update_inline_caches();
 663       if (event.should_commit()) {
 664         post_safepoint_cleanup_task_event(&event, name);
 665       }
 666     }
 667 
 668     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_COMPILATION_POLICY)) {
 669       const char* name = "compilation policy safepoint handler";
 670       EventSafepointCleanupTask event;
 671       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 672       CompilationPolicy::policy()->do_safepoint_work();
 673       if (event.should_commit()) {
 674         post_safepoint_cleanup_task_event(&event, name);
 675       }
 676     }
 677 
 678     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_SYMBOL_TABLE_REHASH)) {
 679       if (SymbolTable::needs_rehashing()) {
 680         const char* name = "rehashing symbol table";
 681         EventSafepointCleanupTask event;
 682         TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 683         SymbolTable::rehash_table();
 684         if (event.should_commit()) {
 685           post_safepoint_cleanup_task_event(&event, name);
 686         }
 687       }
 688     }
 689 
 690     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_STRING_TABLE_REHASH)) {
 691       if (StringTable::needs_rehashing()) {
 692         const char* name = "rehashing string table";
 693         EventSafepointCleanupTask event;
 694         TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 695         StringTable::rehash_table();
 696         if (event.should_commit()) {
 697           post_safepoint_cleanup_task_event(&event, name);
 698         }
 699       }
 700     }
 701 
 702     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_CLD_PURGE)) {
 703       // CMS delays purging the CLDG until the beginning of the next safepoint and to
 704       // make sure concurrent sweep is done
 705       const char* name = "purging class loader data graph";
 706       EventSafepointCleanupTask event;
 707       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 708       ClassLoaderDataGraph::purge_if_needed();
 709       if (event.should_commit()) {
 710         post_safepoint_cleanup_task_event(&event, name);
 711       }
 712     }
 713 
 714     if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_SYSTEM_DICTIONARY_RESIZE)) {
 715       const char* name = "resizing system dictionaries";
 716       EventSafepointCleanupTask event;
 717       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 718       ClassLoaderDataGraph::resize_if_needed();
 719       if (event.should_commit()) {
 720         post_safepoint_cleanup_task_event(&event, name);
 721       }
 722     }
 723     _subtasks.all_tasks_completed(_num_workers);
 724   }
 725 };
 726 
 727 // Various cleaning tasks that should be done periodically at safepoints.
 728 void SafepointSynchronize::do_cleanup_tasks() {
 729 
 730   TraceTime timer("safepoint cleanup tasks", TRACETIME_LOG(Info, safepoint, cleanup));
 731 
 732   // Prepare for monitor deflation.
 733   DeflateMonitorCounters deflate_counters;
 734   ObjectSynchronizer::prepare_deflate_idle_monitors(&deflate_counters);
 735 
 736   CollectedHeap* heap = Universe::heap();
 737   assert(heap != NULL, "heap not initialized yet?");
 738   WorkGang* cleanup_workers = heap->get_safepoint_workers();
 739   if (cleanup_workers != NULL) {
 740     // Parallel cleanup using GC provided thread pool.
 741     uint num_cleanup_workers = cleanup_workers->active_workers();
 742     ParallelSPCleanupTask cleanup(num_cleanup_workers, &deflate_counters);
 743     StrongRootsScope srs(num_cleanup_workers);
 744     cleanup_workers->run_task(&cleanup);
 745   } else {
 746     // Serial cleanup using VMThread.
 747     ParallelSPCleanupTask cleanup(1, &deflate_counters);
 748     StrongRootsScope srs(1);
 749     cleanup.work(0);
 750   }
 751 
 752   // Finish monitor deflation.
 753   ObjectSynchronizer::finish_deflate_idle_monitors(&deflate_counters);
 754 }
 755 
 756 
 757 bool SafepointSynchronize::safepoint_safe(JavaThread *thread, JavaThreadState state) {
 758   switch(state) {
 759   case _thread_in_native:
 760     // native threads are safe if they have no java stack or have walkable stack
 761     return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable();
 762 
 763    // blocked threads should have already have walkable stack
 764   case _thread_blocked:
 765     assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable");
 766     return true;
 767 
 768   default:
 769     return false;
 770   }
 771 }
 772 
 773 
 774 // See if the thread is running inside a lazy critical native and
 775 // update the thread critical count if so.  Also set a suspend flag to
 776 // cause the native wrapper to return into the JVM to do the unlock
 777 // once the native finishes.
 778 void SafepointSynchronize::check_for_lazy_critical_native(JavaThread *thread, JavaThreadState state) {
 779   if (state == _thread_in_native &&
 780       thread->has_last_Java_frame() &&
 781       thread->frame_anchor()->walkable()) {
 782     // This thread might be in a critical native nmethod so look at
 783     // the top of the stack and increment the critical count if it
 784     // is.
 785     frame wrapper_frame = thread->last_frame();
 786     CodeBlob* stub_cb = wrapper_frame.cb();
 787     if (stub_cb != NULL &&
 788         stub_cb->is_nmethod() &&
 789         stub_cb->as_nmethod_or_null()->is_lazy_critical_native()) {
 790       // A thread could potentially be in a critical native across
 791       // more than one safepoint, so only update the critical state on
 792       // the first one.  When it returns it will perform the unlock.
 793       if (!thread->do_critical_native_unlock()) {
 794 #ifdef ASSERT
 795         if (!thread->in_critical()) {
 796           GCLocker::increment_debug_jni_lock_count();
 797         }
 798 #endif
 799         thread->enter_critical();
 800         // Make sure the native wrapper calls back on return to
 801         // perform the needed critical unlock.
 802         thread->set_critical_native_unlock();
 803       }
 804     }
 805   }
 806 }
 807 
 808 
 809 
 810 // -------------------------------------------------------------------------------------------------------
 811 // Implementation of Safepoint callback point
 812 
 813 void SafepointSynchronize::block(JavaThread *thread) {
 814   assert(thread != NULL, "thread must be set");
 815   assert(thread->is_Java_thread(), "not a Java thread");
 816 
 817   // Threads shouldn't block if they are in the middle of printing, but...
 818   ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id());
 819 
 820   // Only bail from the block() call if the thread is gone from the
 821   // thread list; starting to exit should still block.
 822   if (thread->is_terminated()) {
 823      // block current thread if we come here from native code when VM is gone
 824      thread->block_if_vm_exited();
 825 
 826      // otherwise do nothing
 827      return;
 828   }
 829 
 830   JavaThreadState state = thread->thread_state();
 831   thread->frame_anchor()->make_walkable(thread);
 832 
 833   // Check that we have a valid thread_state at this point
 834   switch(state) {
 835     case _thread_in_vm_trans:
 836     case _thread_in_Java:        // From compiled code
 837 
 838       // We are highly likely to block on the Safepoint_lock. In order to avoid blocking in this case,
 839       // we pretend we are still in the VM.
 840       thread->set_thread_state(_thread_in_vm);
 841 
 842       if (is_synchronizing()) {
 843          Atomic::inc (&TryingToBlock) ;
 844       }
 845 
 846       // We will always be holding the Safepoint_lock when we are examine the state
 847       // of a thread. Hence, the instructions between the Safepoint_lock->lock() and
 848       // Safepoint_lock->unlock() are happening atomic with regards to the safepoint code
 849       Safepoint_lock->lock_without_safepoint_check();
 850       if (is_synchronizing()) {
 851         // Decrement the number of threads to wait for and signal vm thread
 852         assert(_waiting_to_block > 0, "sanity check");
 853         _waiting_to_block--;
 854         thread->safepoint_state()->set_has_called_back(true);
 855 
 856         DEBUG_ONLY(thread->set_visited_for_critical_count(true));
 857         if (thread->in_critical()) {
 858           // Notice that this thread is in a critical section
 859           increment_jni_active_count();
 860         }
 861 
 862         // Consider (_waiting_to_block < 2) to pipeline the wakeup of the VM thread
 863         if (_waiting_to_block == 0) {
 864           Safepoint_lock->notify_all();
 865         }
 866       }
 867 
 868       // We transition the thread to state _thread_blocked here, but
 869       // we can't do our usual check for external suspension and then
 870       // self-suspend after the lock_without_safepoint_check() call
 871       // below because we are often called during transitions while
 872       // we hold different locks. That would leave us suspended while
 873       // holding a resource which results in deadlocks.
 874       thread->set_thread_state(_thread_blocked);
 875       Safepoint_lock->unlock();
 876 
 877       // We now try to acquire the threads lock. Since this lock is hold by the VM thread during
 878       // the entire safepoint, the threads will all line up here during the safepoint.
 879       Threads_lock->lock_without_safepoint_check();
 880       // restore original state. This is important if the thread comes from compiled code, so it
 881       // will continue to execute with the _thread_in_Java state.
 882       thread->set_thread_state(state);
 883       Threads_lock->unlock();
 884       break;
 885 
 886     case _thread_in_native_trans:
 887     case _thread_blocked_trans:
 888     case _thread_new_trans:
 889       if (thread->safepoint_state()->type() == ThreadSafepointState::_call_back) {
 890         thread->print_thread_state();
 891         fatal("Deadlock in safepoint code.  "
 892               "Should have called back to the VM before blocking.");
 893       }
 894 
 895       // We transition the thread to state _thread_blocked here, but
 896       // we can't do our usual check for external suspension and then
 897       // self-suspend after the lock_without_safepoint_check() call
 898       // below because we are often called during transitions while
 899       // we hold different locks. That would leave us suspended while
 900       // holding a resource which results in deadlocks.
 901       thread->set_thread_state(_thread_blocked);
 902 
 903       // It is not safe to suspend a thread if we discover it is in _thread_in_native_trans. Hence,
 904       // the safepoint code might still be waiting for it to block. We need to change the state here,
 905       // so it can see that it is at a safepoint.
 906 
 907       // Block until the safepoint operation is completed.
 908       Threads_lock->lock_without_safepoint_check();
 909 
 910       // Restore state
 911       thread->set_thread_state(state);
 912 
 913       Threads_lock->unlock();
 914       break;
 915 
 916     default:
 917      fatal("Illegal threadstate encountered: %d", state);
 918   }
 919 
 920   // Check for pending. async. exceptions or suspends - except if the
 921   // thread was blocked inside the VM. has_special_runtime_exit_condition()
 922   // is called last since it grabs a lock and we only want to do that when
 923   // we must.
 924   //
 925   // Note: we never deliver an async exception at a polling point as the
 926   // compiler may not have an exception handler for it. The polling
 927   // code will notice the async and deoptimize and the exception will
 928   // be delivered. (Polling at a return point is ok though). Sure is
 929   // a lot of bother for a deprecated feature...
 930   //
 931   // We don't deliver an async exception if the thread state is
 932   // _thread_in_native_trans so JNI functions won't be called with
 933   // a surprising pending exception. If the thread state is going back to java,
 934   // async exception is checked in check_special_condition_for_native_trans().
 935 
 936   if (state != _thread_blocked_trans &&
 937       state != _thread_in_vm_trans &&
 938       thread->has_special_runtime_exit_condition()) {
 939     thread->handle_special_runtime_exit_condition(
 940       !thread->is_at_poll_safepoint() && (state != _thread_in_native_trans));
 941   }
 942 }
 943 
 944 // ------------------------------------------------------------------------------------------------------
 945 // Exception handlers
 946 
 947 
 948 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) {
 949   assert(thread->is_Java_thread(), "polling reference encountered by VM thread");
 950   assert(thread->thread_state() == _thread_in_Java, "should come from Java code");
 951   if (!ThreadLocalHandshakes) {
 952     assert(SafepointSynchronize::is_synchronizing(), "polling encountered outside safepoint synchronization");
 953   }
 954 
 955   if (PrintSafepointStatistics) {
 956     inc_page_trap_count();
 957   }
 958 
 959   ThreadSafepointState* state = thread->safepoint_state();
 960 
 961   state->handle_polling_page_exception();
 962 }
 963 
 964 
 965 void SafepointSynchronize::print_safepoint_timeout(SafepointTimeoutReason reason) {
 966   if (!timeout_error_printed) {
 967     timeout_error_printed = true;
 968     // Print out the thread info which didn't reach the safepoint for debugging
 969     // purposes (useful when there are lots of threads in the debugger).
 970     tty->cr();
 971     tty->print_cr("# SafepointSynchronize::begin: Timeout detected:");
 972     if (reason ==  _spinning_timeout) {
 973       tty->print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint.");
 974     } else if (reason == _blocking_timeout) {
 975       tty->print_cr("# SafepointSynchronize::begin: Timed out while waiting for threads to stop.");
 976     }
 977 
 978     tty->print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:");
 979     ThreadSafepointState *cur_state;
 980     ResourceMark rm;
 981     for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
 982       cur_state = cur_thread->safepoint_state();
 983 
 984       if (cur_thread->thread_state() != _thread_blocked &&
 985         ((reason == _spinning_timeout && cur_state->is_running()) ||
 986            (reason == _blocking_timeout && !cur_state->has_called_back()))) {
 987         tty->print("# ");
 988         cur_thread->print();
 989         tty->cr();
 990       }
 991     }
 992     tty->print_cr("# SafepointSynchronize::begin: (End of list)");
 993   }
 994 
 995   // To debug the long safepoint, specify both AbortVMOnSafepointTimeout &
 996   // ShowMessageBoxOnError.
 997   if (AbortVMOnSafepointTimeout) {
 998     // Send the blocking thread a signal to terminate and write an error file.
 999     for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
1000       ThreadSafepointState *cur_state = cur_thread->safepoint_state();
1001       if (cur_thread->thread_state() != _thread_blocked &&
1002           ((reason == _spinning_timeout && cur_state->is_running()) ||
1003              (reason == _blocking_timeout && !cur_state->has_called_back()))) {
1004         if (!os::signal_thread(cur_thread, SIGILL, "blocking a safepoint")) {
1005           break; // Could not send signal. Report fatal error.
1006         }
1007         // Give cur_thread a chance to report the error and terminate the VM.
1008         os::sleep(Thread::current(), 3000, false);
1009       }
1010     }
1011     fatal("Safepoint sync time longer than " INTX_FORMAT "ms detected when executing %s.",
1012           SafepointTimeoutDelay, VMThread::vm_safepoint_description());
1013   }
1014 }
1015 
1016 
1017 // -------------------------------------------------------------------------------------------------------
1018 // Implementation of ThreadSafepointState
1019 
1020 ThreadSafepointState::ThreadSafepointState(JavaThread *thread) {
1021   _thread = thread;
1022   _type   = _running;
1023   _has_called_back = false;
1024   _at_poll_safepoint = false;
1025 }
1026 
1027 void ThreadSafepointState::create(JavaThread *thread) {
1028   ThreadSafepointState *state = new ThreadSafepointState(thread);
1029   thread->set_safepoint_state(state);
1030 }
1031 
1032 void ThreadSafepointState::destroy(JavaThread *thread) {
1033   if (thread->safepoint_state()) {
1034     delete(thread->safepoint_state());
1035     thread->set_safepoint_state(NULL);
1036   }
1037 }
1038 
1039 void ThreadSafepointState::examine_state_of_thread() {
1040   assert(is_running(), "better be running or just have hit safepoint poll");
1041 
1042   JavaThreadState state = _thread->thread_state();
1043 
1044   // Save the state at the start of safepoint processing.
1045   _orig_thread_state = state;
1046 
1047   // Check for a thread that is suspended. Note that thread resume tries
1048   // to grab the Threads_lock which we own here, so a thread cannot be
1049   // resumed during safepoint synchronization.
1050 
1051   // We check to see if this thread is suspended without locking to
1052   // avoid deadlocking with a third thread that is waiting for this
1053   // thread to be suspended. The third thread can notice the safepoint
1054   // that we're trying to start at the beginning of its SR_lock->wait()
1055   // call. If that happens, then the third thread will block on the
1056   // safepoint while still holding the underlying SR_lock. We won't be
1057   // able to get the SR_lock and we'll deadlock.
1058   //
1059   // We don't need to grab the SR_lock here for two reasons:
1060   // 1) The suspend flags are both volatile and are set with an
1061   //    Atomic::cmpxchg() call so we should see the suspended
1062   //    state right away.
1063   // 2) We're being called from the safepoint polling loop; if
1064   //    we don't see the suspended state on this iteration, then
1065   //    we'll come around again.
1066   //
1067   bool is_suspended = _thread->is_ext_suspended();
1068   if (is_suspended) {
1069     roll_forward(_at_safepoint);
1070     return;
1071   }
1072 
1073   // Some JavaThread states have an initial safepoint state of
1074   // running, but are actually at a safepoint. We will happily
1075   // agree and update the safepoint state here.
1076   if (SafepointSynchronize::safepoint_safe(_thread, state)) {
1077     SafepointSynchronize::check_for_lazy_critical_native(_thread, state);
1078     roll_forward(_at_safepoint);
1079     return;
1080   }
1081 
1082   if (state == _thread_in_vm) {
1083     roll_forward(_call_back);
1084     return;
1085   }
1086 
1087   // All other thread states will continue to run until they
1088   // transition and self-block in state _blocked
1089   // Safepoint polling in compiled code causes the Java threads to do the same.
1090   // Note: new threads may require a malloc so they must be allowed to finish
1091 
1092   assert(is_running(), "examine_state_of_thread on non-running thread");
1093   return;
1094 }
1095 
1096 // Returns true is thread could not be rolled forward at present position.
1097 void ThreadSafepointState::roll_forward(suspend_type type) {
1098   _type = type;
1099 
1100   switch(_type) {
1101     case _at_safepoint:
1102       SafepointSynchronize::signal_thread_at_safepoint();
1103       DEBUG_ONLY(_thread->set_visited_for_critical_count(true));
1104       if (_thread->in_critical()) {
1105         // Notice that this thread is in a critical section
1106         SafepointSynchronize::increment_jni_active_count();
1107       }
1108       break;
1109 
1110     case _call_back:
1111       set_has_called_back(false);
1112       break;
1113 
1114     case _running:
1115     default:
1116       ShouldNotReachHere();
1117   }
1118 }
1119 
1120 void ThreadSafepointState::restart() {
1121   switch(type()) {
1122     case _at_safepoint:
1123     case _call_back:
1124       break;
1125 
1126     case _running:
1127     default:
1128        tty->print_cr("restart thread " INTPTR_FORMAT " with state %d",
1129                      p2i(_thread), _type);
1130        _thread->print();
1131       ShouldNotReachHere();
1132   }
1133   _type = _running;
1134   set_has_called_back(false);
1135 }
1136 
1137 
1138 void ThreadSafepointState::print_on(outputStream *st) const {
1139   const char *s = NULL;
1140 
1141   switch(_type) {
1142     case _running                : s = "_running";              break;
1143     case _at_safepoint           : s = "_at_safepoint";         break;
1144     case _call_back              : s = "_call_back";            break;
1145     default:
1146       ShouldNotReachHere();
1147   }
1148 
1149   st->print_cr("Thread: " INTPTR_FORMAT
1150               "  [0x%2x] State: %s _has_called_back %d _at_poll_safepoint %d",
1151                p2i(_thread), _thread->osthread()->thread_id(), s, _has_called_back,
1152                _at_poll_safepoint);
1153 
1154   _thread->print_thread_state_on(st);
1155 }
1156 
1157 // ---------------------------------------------------------------------------------------------------------------------
1158 
1159 // Block the thread at poll or poll return for safepoint/handshake.
1160 void ThreadSafepointState::handle_polling_page_exception() {
1161 
1162   // Check state.  block() will set thread state to thread_in_vm which will
1163   // cause the safepoint state _type to become _call_back.
1164   suspend_type t = type();
1165   assert(!SafepointMechanism::uses_global_page_poll() || t == ThreadSafepointState::_running,
1166          "polling page exception on thread not running state: %u", uint(t));
1167 
1168   // Step 1: Find the nmethod from the return address
1169   address real_return_addr = thread()->saved_exception_pc();
1170 
1171   CodeBlob *cb = CodeCache::find_blob(real_return_addr);
1172   assert(cb != NULL && cb->is_compiled(), "return address should be in nmethod");
1173   CompiledMethod* nm = (CompiledMethod*)cb;
1174 
1175   // Find frame of caller
1176   frame stub_fr = thread()->last_frame();
1177   CodeBlob* stub_cb = stub_fr.cb();
1178   assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub");
1179   RegisterMap map(thread(), true);
1180   frame caller_fr = stub_fr.sender(&map);
1181 
1182   // Should only be poll_return or poll
1183   assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" );
1184 
1185   // This is a poll immediately before a return. The exception handling code
1186   // has already had the effect of causing the return to occur, so the execution
1187   // will continue immediately after the call. In addition, the oopmap at the
1188   // return point does not mark the return value as an oop (if it is), so
1189   // it needs a handle here to be updated.
1190   if( nm->is_at_poll_return(real_return_addr) ) {
1191     // See if return type is an oop.
1192     bool return_oop = nm->method()->is_returning_oop();
1193     Handle return_value;
1194     if (return_oop) {
1195       // The oop result has been saved on the stack together with all
1196       // the other registers. In order to preserve it over GCs we need
1197       // to keep it in a handle.
1198       oop result = caller_fr.saved_oop_result(&map);
1199       assert(oopDesc::is_oop_or_null(result), "must be oop");
1200       return_value = Handle(thread(), result);
1201       assert(Universe::heap()->is_in_or_null(result), "must be heap pointer");
1202     }
1203 
1204     // Block the thread
1205     SafepointMechanism::block_if_requested(thread());
1206 
1207     // restore oop result, if any
1208     if (return_oop) {
1209       caller_fr.set_saved_oop_result(&map, return_value());
1210     }
1211   }
1212 
1213   // This is a safepoint poll. Verify the return address and block.
1214   else {
1215     set_at_poll_safepoint(true);
1216 
1217     // verify the blob built the "return address" correctly
1218     assert(real_return_addr == caller_fr.pc(), "must match");
1219 
1220     // Block the thread
1221     SafepointMechanism::block_if_requested(thread());
1222     set_at_poll_safepoint(false);
1223 
1224     // If we have a pending async exception deoptimize the frame
1225     // as otherwise we may never deliver it.
1226     if (thread()->has_async_condition()) {
1227       ThreadInVMfromJavaNoAsyncException __tiv(thread());
1228       Deoptimization::deoptimize_frame(thread(), caller_fr.id());
1229     }
1230 
1231     // If an exception has been installed we must check for a pending deoptimization
1232     // Deoptimize frame if exception has been thrown.
1233 
1234     if (thread()->has_pending_exception() ) {
1235       RegisterMap map(thread(), true);
1236       frame caller_fr = stub_fr.sender(&map);
1237       if (caller_fr.is_deoptimized_frame()) {
1238         // The exception patch will destroy registers that are still
1239         // live and will be needed during deoptimization. Defer the
1240         // Async exception should have deferred the exception until the
1241         // next safepoint which will be detected when we get into
1242         // the interpreter so if we have an exception now things
1243         // are messed up.
1244 
1245         fatal("Exception installed and deoptimization is pending");
1246       }
1247     }
1248   }
1249 }
1250 
1251 
1252 //
1253 //                     Statistics & Instrumentations
1254 //
1255 SafepointSynchronize::SafepointStats*  SafepointSynchronize::_safepoint_stats = NULL;
1256 jlong  SafepointSynchronize::_safepoint_begin_time = 0;
1257 int    SafepointSynchronize::_cur_stat_index = 0;
1258 julong SafepointSynchronize::_safepoint_reasons[VM_Operation::VMOp_Terminating];
1259 julong SafepointSynchronize::_coalesced_vmop_count = 0;
1260 jlong  SafepointSynchronize::_max_sync_time = 0;
1261 jlong  SafepointSynchronize::_max_vmop_time = 0;
1262 float  SafepointSynchronize::_ts_of_current_safepoint = 0.0f;
1263 
1264 static jlong  cleanup_end_time = 0;
1265 static bool   init_done = false;
1266 
1267 // Helper method to print the header.
1268 static void print_header() {
1269   // The number of spaces is significant here, and should match the format
1270   // specifiers in print_statistics().
1271 
1272   tty->print("          vmop                            "
1273              "[ threads:    total initially_running wait_to_block ]"
1274              "[ time:    spin   block    sync cleanup    vmop ] ");
1275 
1276   tty->print_cr("page_trap_count");
1277 }
1278 
1279 void SafepointSynchronize::deferred_initialize_stat() {
1280   if (init_done) return;
1281 
1282   // If PrintSafepointStatisticsTimeout is specified, the statistics data will
1283   // be printed right away, in which case, _safepoint_stats will regress to
1284   // a single element array. Otherwise, it is a circular ring buffer with default
1285   // size of PrintSafepointStatisticsCount.
1286   int stats_array_size;
1287   if (PrintSafepointStatisticsTimeout > 0) {
1288     stats_array_size = 1;
1289     PrintSafepointStatistics = true;
1290   } else {
1291     stats_array_size = PrintSafepointStatisticsCount;
1292   }
1293   _safepoint_stats = (SafepointStats*)os::malloc(stats_array_size
1294                                                  * sizeof(SafepointStats), mtInternal);
1295   guarantee(_safepoint_stats != NULL,
1296             "not enough memory for safepoint instrumentation data");
1297 
1298   init_done = true;
1299 }
1300 
1301 void SafepointSynchronize::begin_statistics(int nof_threads, int nof_running) {
1302   assert(init_done, "safepoint statistics array hasn't been initialized");
1303   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1304 
1305   spstat->_time_stamp = _ts_of_current_safepoint;
1306 
1307   VM_Operation *op = VMThread::vm_operation();
1308   spstat->_vmop_type = (op != NULL ? op->type() : -1);
1309   if (op != NULL) {
1310     _safepoint_reasons[spstat->_vmop_type]++;
1311   }
1312 
1313   spstat->_nof_total_threads = nof_threads;
1314   spstat->_nof_initial_running_threads = nof_running;
1315   spstat->_nof_threads_hit_page_trap = 0;
1316 
1317   // Records the start time of spinning. The real time spent on spinning
1318   // will be adjusted when spin is done. Same trick is applied for time
1319   // spent on waiting for threads to block.
1320   if (nof_running != 0) {
1321     spstat->_time_to_spin = os::javaTimeNanos();
1322   }  else {
1323     spstat->_time_to_spin = 0;
1324   }
1325 }
1326 
1327 void SafepointSynchronize::update_statistics_on_spin_end() {
1328   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1329 
1330   jlong cur_time = os::javaTimeNanos();
1331 
1332   spstat->_nof_threads_wait_to_block = _waiting_to_block;
1333   if (spstat->_nof_initial_running_threads != 0) {
1334     spstat->_time_to_spin = cur_time - spstat->_time_to_spin;
1335   }
1336 
1337   // Records the start time of waiting for to block. Updated when block is done.
1338   if (_waiting_to_block != 0) {
1339     spstat->_time_to_wait_to_block = cur_time;
1340   } else {
1341     spstat->_time_to_wait_to_block = 0;
1342   }
1343 }
1344 
1345 void SafepointSynchronize::update_statistics_on_sync_end(jlong end_time) {
1346   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1347 
1348   if (spstat->_nof_threads_wait_to_block != 0) {
1349     spstat->_time_to_wait_to_block = end_time -
1350       spstat->_time_to_wait_to_block;
1351   }
1352 
1353   // Records the end time of sync which will be used to calculate the total
1354   // vm operation time. Again, the real time spending in syncing will be deducted
1355   // from the start of the sync time later when end_statistics is called.
1356   spstat->_time_to_sync = end_time - _safepoint_begin_time;
1357   if (spstat->_time_to_sync > _max_sync_time) {
1358     _max_sync_time = spstat->_time_to_sync;
1359   }
1360 
1361   spstat->_time_to_do_cleanups = end_time;
1362 }
1363 
1364 void SafepointSynchronize::update_statistics_on_cleanup_end(jlong end_time) {
1365   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1366 
1367   // Record how long spent in cleanup tasks.
1368   spstat->_time_to_do_cleanups = end_time - spstat->_time_to_do_cleanups;
1369 
1370   cleanup_end_time = end_time;
1371 }
1372 
1373 void SafepointSynchronize::end_statistics(jlong vmop_end_time) {
1374   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1375 
1376   // Update the vm operation time.
1377   spstat->_time_to_exec_vmop = vmop_end_time -  cleanup_end_time;
1378   if (spstat->_time_to_exec_vmop > _max_vmop_time) {
1379     _max_vmop_time = spstat->_time_to_exec_vmop;
1380   }
1381   // Only the sync time longer than the specified
1382   // PrintSafepointStatisticsTimeout will be printed out right away.
1383   // By default, it is -1 meaning all samples will be put into the list.
1384   if ( PrintSafepointStatisticsTimeout > 0) {
1385     if (spstat->_time_to_sync > (jlong)PrintSafepointStatisticsTimeout * MICROUNITS) {
1386       print_statistics();
1387     }
1388   } else {
1389     // The safepoint statistics will be printed out when the _safepoin_stats
1390     // array fills up.
1391     if (_cur_stat_index == PrintSafepointStatisticsCount - 1) {
1392       print_statistics();
1393       _cur_stat_index = 0;
1394     } else {
1395       _cur_stat_index++;
1396     }
1397   }
1398 }
1399 
1400 void SafepointSynchronize::print_statistics() {
1401   for (int index = 0; index <= _cur_stat_index; index++) {
1402     if (index % 30 == 0) {
1403       print_header();
1404     }
1405     SafepointStats* sstats = &_safepoint_stats[index];
1406     tty->print("%8.3f: ", sstats->_time_stamp);
1407     tty->print("%-30s  [          "
1408                INT32_FORMAT_W(8) " " INT32_FORMAT_W(17) " " INT32_FORMAT_W(13) " "
1409                "]",
1410                (sstats->_vmop_type == -1 ? "no vm operation" : VM_Operation::name(sstats->_vmop_type)),
1411                sstats->_nof_total_threads,
1412                sstats->_nof_initial_running_threads,
1413                sstats->_nof_threads_wait_to_block);
1414     // "/ MICROUNITS " is to convert the unit from nanos to millis.
1415     tty->print("[       "
1416                INT64_FORMAT_W(7) " " INT64_FORMAT_W(7) " "
1417                INT64_FORMAT_W(7) " " INT64_FORMAT_W(7) " "
1418                INT64_FORMAT_W(7) " ] ",
1419                (int64_t)(sstats->_time_to_spin / MICROUNITS),
1420                (int64_t)(sstats->_time_to_wait_to_block / MICROUNITS),
1421                (int64_t)(sstats->_time_to_sync / MICROUNITS),
1422                (int64_t)(sstats->_time_to_do_cleanups / MICROUNITS),
1423                (int64_t)(sstats->_time_to_exec_vmop / MICROUNITS));
1424 
1425     tty->print_cr(INT32_FORMAT_W(15) " ", sstats->_nof_threads_hit_page_trap);
1426   }
1427 }
1428 
1429 // This method will be called when VM exits. It will first call
1430 // print_statistics to print out the rest of the sampling.  Then
1431 // it tries to summarize the sampling.
1432 void SafepointSynchronize::print_stat_on_exit() {
1433   if (_safepoint_stats == NULL) return;
1434 
1435   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1436 
1437   // During VM exit, end_statistics may not get called and in that
1438   // case, if the sync time is less than PrintSafepointStatisticsTimeout,
1439   // don't print it out.
1440   // Approximate the vm op time.
1441   _safepoint_stats[_cur_stat_index]._time_to_exec_vmop =
1442     os::javaTimeNanos() - cleanup_end_time;
1443 
1444   if ( PrintSafepointStatisticsTimeout < 0 ||
1445        spstat->_time_to_sync > (jlong)PrintSafepointStatisticsTimeout * MICROUNITS) {
1446     print_statistics();
1447   }
1448   tty->cr();
1449 
1450   // Print out polling page sampling status.
1451   tty->print_cr("Polling page always armed");
1452 
1453   for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) {
1454     if (_safepoint_reasons[index] != 0) {
1455       tty->print_cr("%-26s" UINT64_FORMAT_W(10), VM_Operation::name(index),
1456                     _safepoint_reasons[index]);
1457     }
1458   }
1459 
1460   tty->print_cr(UINT64_FORMAT_W(5) " VM operations coalesced during safepoint",
1461                 _coalesced_vmop_count);
1462   tty->print_cr("Maximum sync time  " INT64_FORMAT_W(5) " ms",
1463                 (int64_t)(_max_sync_time / MICROUNITS));
1464   tty->print_cr("Maximum vm operation time (except for Exit VM operation)  "
1465                 INT64_FORMAT_W(5) " ms",
1466                 (int64_t)(_max_vmop_time / MICROUNITS));
1467 }