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