1 /*
   2  * Copyright (c) 1997, 2015, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "classfile/stringTable.hpp"
  27 #include "classfile/systemDictionary.hpp"
  28 #include "code/codeCache.hpp"
  29 #include "code/icBuffer.hpp"
  30 #include "code/nmethod.hpp"
  31 #include "code/pcDesc.hpp"
  32 #include "code/scopeDesc.hpp"
  33 #include "gc/shared/collectedHeap.hpp"
  34 #include "gc/shared/gcLocker.inline.hpp"
  35 #include "interpreter/interpreter.hpp"
  36 #include "memory/resourceArea.hpp"
  37 #include "memory/universe.inline.hpp"
  38 #include "oops/oop.inline.hpp"
  39 #include "oops/symbol.hpp"
  40 #include "runtime/atomic.inline.hpp"
  41 #include "runtime/compilationPolicy.hpp"
  42 #include "runtime/deoptimization.hpp"
  43 #include "runtime/frame.inline.hpp"
  44 #include "runtime/interfaceSupport.hpp"
  45 #include "runtime/mutexLocker.hpp"
  46 #include "runtime/orderAccess.inline.hpp"
  47 #include "runtime/osThread.hpp"
  48 #include "runtime/safepoint.hpp"
  49 #include "runtime/signature.hpp"
  50 #include "runtime/stubCodeGenerator.hpp"
  51 #include "runtime/stubRoutines.hpp"
  52 #include "runtime/sweeper.hpp"
  53 #include "runtime/synchronizer.hpp"
  54 #include "runtime/thread.inline.hpp"
  55 #include "services/runtimeService.hpp"
  56 #include "utilities/events.hpp"
  57 #include "utilities/macros.hpp"
  58 #if INCLUDE_ALL_GCS
  59 #include "gc/cms/concurrentMarkSweepThread.hpp"
  60 #include "gc/g1/suspendibleThreadSet.hpp"
  61 #endif // INCLUDE_ALL_GCS
  62 #ifdef COMPILER1
  63 #include "c1/c1_globals.hpp"
  64 #endif
  65 
  66 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
  67 
  68 // --------------------------------------------------------------------------------------------------
  69 // Implementation of Safepoint begin/end
  70 
  71 SafepointSynchronize::SynchronizeState volatile SafepointSynchronize::_state = SafepointSynchronize::_not_synchronized;
  72 volatile int  SafepointSynchronize::_waiting_to_block = 0;
  73 volatile int SafepointSynchronize::_safepoint_counter = 0;
  74 int SafepointSynchronize::_current_jni_active_count = 0;
  75 long  SafepointSynchronize::_end_of_last_safepoint = 0;
  76 static volatile int PageArmed = 0 ;        // safepoint polling page is RO|RW vs PROT_NONE
  77 static volatile int TryingToBlock = 0 ;    // proximate value -- for advisory use only
  78 static bool timeout_error_printed = false;
  79 
  80 // Roll all threads forward to a safepoint and suspend them all
  81 void SafepointSynchronize::begin() {
  82 
  83   Thread* myThread = Thread::current();
  84   assert(myThread->is_VM_thread(), "Only VM thread may execute a safepoint");
  85 
  86   if (PrintSafepointStatistics || PrintSafepointStatisticsTimeout > 0) {
  87     _safepoint_begin_time = os::javaTimeNanos();
  88     _ts_of_current_safepoint = tty->time_stamp().seconds();
  89   }
  90 
  91 #if INCLUDE_ALL_GCS
  92   if (UseConcMarkSweepGC) {
  93     // In the future we should investigate whether CMS can use the
  94     // more-general mechanism below.  DLD (01/05).
  95     ConcurrentMarkSweepThread::synchronize(false);
  96   } else if (UseG1GC) {
  97     SuspendibleThreadSet::synchronize();
  98   }
  99 #endif // INCLUDE_ALL_GCS
 100 
 101   // By getting the Threads_lock, we assure that no threads are about to start or
 102   // exit. It is released again in SafepointSynchronize::end().
 103   Threads_lock->lock();
 104 
 105   assert( _state == _not_synchronized, "trying to safepoint synchronize with wrong state");
 106 
 107   int nof_threads = Threads::number_of_threads();
 108 
 109   if (TraceSafepoint) {
 110     tty->print_cr("Safepoint synchronization initiated. (%d)", nof_threads);
 111   }
 112 
 113   RuntimeService::record_safepoint_begin();
 114 
 115   MutexLocker mu(Safepoint_lock);
 116 
 117   // Reset the count of active JNI critical threads
 118   _current_jni_active_count = 0;
 119 
 120   // Set number of threads to wait for, before we initiate the callbacks
 121   _waiting_to_block = nof_threads;
 122   TryingToBlock     = 0 ;
 123   int still_running = nof_threads;
 124 
 125   // Save the starting time, so that it can be compared to see if this has taken
 126   // too long to complete.
 127   jlong safepoint_limit_time;
 128   timeout_error_printed = false;
 129 
 130   // PrintSafepointStatisticsTimeout can be specified separately. When
 131   // specified, PrintSafepointStatistics will be set to true in
 132   // deferred_initialize_stat method. The initialization has to be done
 133   // early enough to avoid any races. See bug 6880029 for details.
 134   if (PrintSafepointStatistics || PrintSafepointStatisticsTimeout > 0) {
 135     deferred_initialize_stat();
 136   }
 137 
 138   // Begin the process of bringing the system to a safepoint.
 139   // Java threads can be in several different states and are
 140   // stopped by different mechanisms:
 141   //
 142   //  1. Running interpreted
 143   //     The interpreter dispatch table is changed to force it to
 144   //     check for a safepoint condition between bytecodes.
 145   //  2. Running in native code
 146   //     When returning from the native code, a Java thread must check
 147   //     the safepoint _state to see if we must block.  If the
 148   //     VM thread sees a Java thread in native, it does
 149   //     not wait for this thread to block.  The order of the memory
 150   //     writes and reads of both the safepoint state and the Java
 151   //     threads state is critical.  In order to guarantee that the
 152   //     memory writes are serialized with respect to each other,
 153   //     the VM thread issues a memory barrier instruction
 154   //     (on MP systems).  In order to avoid the overhead of issuing
 155   //     a memory barrier for each Java thread making native calls, each Java
 156   //     thread performs a write to a single memory page after changing
 157   //     the thread state.  The VM thread performs a sequence of
 158   //     mprotect OS calls which forces all previous writes from all
 159   //     Java threads to be serialized.  This is done in the
 160   //     os::serialize_thread_states() call.  This has proven to be
 161   //     much more efficient than executing a membar instruction
 162   //     on every call to native code.
 163   //  3. Running compiled Code
 164   //     Compiled code reads a global (Safepoint Polling) page that
 165   //     is set to fault if we are trying to get to a safepoint.
 166   //  4. Blocked
 167   //     A thread which is blocked will not be allowed to return from the
 168   //     block condition until the safepoint operation is complete.
 169   //  5. In VM or Transitioning between states
 170   //     If a Java thread is currently running in the VM or transitioning
 171   //     between states, the safepointing code will wait for the thread to
 172   //     block itself when it attempts transitions to a new state.
 173   //
 174   _state            = _synchronizing;
 175   OrderAccess::fence();
 176 
 177   // Flush all thread states to memory
 178   if (!UseMembar) {
 179     os::serialize_thread_states();
 180   }
 181 
 182   // Make interpreter safepoint aware
 183   Interpreter::notice_safepoints();
 184 
 185   if (DeferPollingPageLoopCount < 0) {
 186     // Make polling safepoint aware
 187     guarantee (PageArmed == 0, "invariant") ;
 188     PageArmed = 1 ;
 189     os::make_polling_page_unreadable();
 190   }
 191 
 192   // Consider using active_processor_count() ... but that call is expensive.
 193   int ncpus = os::processor_count() ;
 194 
 195 #ifdef ASSERT
 196   for (JavaThread *cur = Threads::first(); cur != NULL; cur = cur->next()) {
 197     assert(cur->safepoint_state()->is_running(), "Illegal initial state");
 198     // Clear the visited flag to ensure that the critical counts are collected properly.
 199     cur->set_visited_for_critical_count(false);
 200   }
 201 #endif // ASSERT
 202 
 203   if (SafepointTimeout)
 204     safepoint_limit_time = os::javaTimeNanos() + (jlong)SafepointTimeoutDelay * MICROUNITS;
 205 
 206   // Iterate through all threads until it have been determined how to stop them all at a safepoint
 207   unsigned int iterations = 0;
 208   int steps = 0 ;
 209   while(still_running > 0) {
 210     for (JavaThread *cur = Threads::first(); cur != NULL; cur = cur->next()) {
 211       assert(!cur->is_ConcurrentGC_thread(), "A concurrent GC thread is unexpectly being suspended");
 212       ThreadSafepointState *cur_state = cur->safepoint_state();
 213       if (cur_state->is_running()) {
 214         cur_state->examine_state_of_thread();
 215         if (!cur_state->is_running()) {
 216            still_running--;
 217            // consider adjusting steps downward:
 218            //   steps = 0
 219            //   steps -= NNN
 220            //   steps >>= 1
 221            //   steps = MIN(steps, 2000-100)
 222            //   if (iterations != 0) steps -= NNN
 223         }
 224         if (TraceSafepoint && Verbose) cur_state->print();
 225       }
 226     }
 227 
 228     if (PrintSafepointStatistics && iterations == 0) {
 229       begin_statistics(nof_threads, still_running);
 230     }
 231 
 232     if (still_running > 0) {
 233       // Check for if it takes to long
 234       if (SafepointTimeout && safepoint_limit_time < os::javaTimeNanos()) {
 235         print_safepoint_timeout(_spinning_timeout);
 236       }
 237 
 238       // Spin to avoid context switching.
 239       // There's a tension between allowing the mutators to run (and rendezvous)
 240       // vs spinning.  As the VM thread spins, wasting cycles, it consumes CPU that
 241       // a mutator might otherwise use profitably to reach a safepoint.  Excessive
 242       // spinning by the VM thread on a saturated system can increase rendezvous latency.
 243       // Blocking or yielding incur their own penalties in the form of context switching
 244       // and the resultant loss of $ residency.
 245       //
 246       // Further complicating matters is that yield() does not work as naively expected
 247       // on many platforms -- yield() does not guarantee that any other ready threads
 248       // will run.   As such we revert to naked_short_sleep() after some number of iterations.
 249       // nakes_short_sleep() is implemented as a short unconditional sleep.
 250       // Typical operating systems round a "short" sleep period up to 10 msecs, so sleeping
 251       // can actually increase the time it takes the VM thread to detect that a system-wide
 252       // stop-the-world safepoint has been reached.  In a pathological scenario such as that
 253       // described in CR6415670 the VMthread may sleep just before the mutator(s) become safe.
 254       // In that case the mutators will be stalled waiting for the safepoint to complete and the
 255       // the VMthread will be sleeping, waiting for the mutators to rendezvous.  The VMthread
 256       // will eventually wake up and detect that all mutators are safe, at which point
 257       // we'll again make progress.
 258       //
 259       // Beware too that that the VMThread typically runs at elevated priority.
 260       // Its default priority is higher than the default mutator priority.
 261       // Obviously, this complicates spinning.
 262       //
 263       // Note too that on Windows XP SwitchThreadTo() has quite different behavior than Sleep(0).
 264       // Sleep(0) will _not yield to lower priority threads, while SwitchThreadTo() will.
 265       //
 266       // See the comments in synchronizer.cpp for additional remarks on spinning.
 267       //
 268       // In the future we might:
 269       // 1. Modify the safepoint scheme to avoid potentially unbounded spinning.
 270       //    This is tricky as the path used by a thread exiting the JVM (say on
 271       //    on JNI call-out) simply stores into its state field.  The burden
 272       //    is placed on the VM thread, which must poll (spin).
 273       // 2. Find something useful to do while spinning.  If the safepoint is GC-related
 274       //    we might aggressively scan the stacks of threads that are already safe.
 275       // 3. Use Solaris schedctl to examine the state of the still-running mutators.
 276       //    If all the mutators are ONPROC there's no reason to sleep or yield.
 277       // 4. YieldTo() any still-running mutators that are ready but OFFPROC.
 278       // 5. Check system saturation.  If the system is not fully saturated then
 279       //    simply spin and avoid sleep/yield.
 280       // 6. As still-running mutators rendezvous they could unpark the sleeping
 281       //    VMthread.  This works well for still-running mutators that become
 282       //    safe.  The VMthread must still poll for mutators that call-out.
 283       // 7. Drive the policy on time-since-begin instead of iterations.
 284       // 8. Consider making the spin duration a function of the # of CPUs:
 285       //    Spin = (((ncpus-1) * M) + K) + F(still_running)
 286       //    Alternately, instead of counting iterations of the outer loop
 287       //    we could count the # of threads visited in the inner loop, above.
 288       // 9. On windows consider using the return value from SwitchThreadTo()
 289       //    to drive subsequent spin/SwitchThreadTo()/Sleep(N) decisions.
 290 
 291       if (int(iterations) == DeferPollingPageLoopCount) {
 292          guarantee (PageArmed == 0, "invariant") ;
 293          PageArmed = 1 ;
 294          os::make_polling_page_unreadable();
 295       }
 296 
 297       // Instead of (ncpus > 1) consider either (still_running < (ncpus + EPSILON)) or
 298       // ((still_running + _waiting_to_block - TryingToBlock)) < ncpus)
 299       ++steps ;
 300       if (ncpus > 1 && steps < SafepointSpinBeforeYield) {
 301         SpinPause() ;     // MP-Polite spin
 302       } else
 303       if (steps < DeferThrSuspendLoopCount) {
 304         os::naked_yield() ;
 305       } else {
 306         os::naked_short_sleep(1);
 307       }
 308 
 309       iterations ++ ;
 310     }
 311     assert(iterations < (uint)max_jint, "We have been iterating in the safepoint loop too long");
 312   }
 313   assert(still_running == 0, "sanity check");
 314 
 315   if (PrintSafepointStatistics) {
 316     update_statistics_on_spin_end();
 317   }
 318 
 319   // wait until all threads are stopped
 320   while (_waiting_to_block > 0) {
 321     if (TraceSafepoint) tty->print_cr("Waiting for %d thread(s) to block", _waiting_to_block);
 322     if (!SafepointTimeout || timeout_error_printed) {
 323       Safepoint_lock->wait(true);  // true, means with no safepoint checks
 324     } else {
 325       // Compute remaining time
 326       jlong remaining_time = safepoint_limit_time - os::javaTimeNanos();
 327 
 328       // If there is no remaining time, then there is an error
 329       if (remaining_time < 0 || Safepoint_lock->wait(true, remaining_time / MICROUNITS)) {
 330         print_safepoint_timeout(_blocking_timeout);
 331       }
 332     }
 333   }
 334   assert(_waiting_to_block == 0, "sanity check");
 335 
 336 #ifndef PRODUCT
 337   if (SafepointTimeout) {
 338     jlong current_time = os::javaTimeNanos();
 339     if (safepoint_limit_time < current_time) {
 340       tty->print_cr("# SafepointSynchronize: Finished after "
 341                     INT64_FORMAT_W(6) " ms",
 342                     ((current_time - safepoint_limit_time) / MICROUNITS +
 343                      SafepointTimeoutDelay));
 344     }
 345   }
 346 #endif
 347 
 348   assert((_safepoint_counter & 0x1) == 0, "must be even");
 349   assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
 350   _safepoint_counter ++;
 351 
 352   // Record state
 353   _state = _synchronized;
 354 
 355   OrderAccess::fence();
 356 
 357 #ifdef ASSERT
 358   for (JavaThread *cur = Threads::first(); cur != NULL; cur = cur->next()) {
 359     // make sure all the threads were visited
 360     assert(cur->was_visited_for_critical_count(), "missed a thread");
 361   }
 362 #endif // ASSERT
 363 
 364   // Update the count of active JNI critical regions
 365   GC_locker::set_jni_lock_count(_current_jni_active_count);
 366 
 367   if (TraceSafepoint) {
 368     VM_Operation *op = VMThread::vm_operation();
 369     tty->print_cr("Entering safepoint region: %s", (op != NULL) ? op->name() : "no vm operation");
 370   }
 371 
 372   RuntimeService::record_safepoint_synchronized();
 373   if (PrintSafepointStatistics) {
 374     update_statistics_on_sync_end(os::javaTimeNanos());
 375   }
 376 
 377   // Call stuff that needs to be run when a safepoint is just about to be completed
 378   do_cleanup_tasks();
 379 
 380   if (PrintSafepointStatistics) {
 381     // Record how much time spend on the above cleanup tasks
 382     update_statistics_on_cleanup_end(os::javaTimeNanos());
 383   }
 384 }
 385 
 386 // Wake up all threads, so they are ready to resume execution after the safepoint
 387 // operation has been carried out
 388 void SafepointSynchronize::end() {
 389 
 390   assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
 391   assert((_safepoint_counter & 0x1) == 1, "must be odd");
 392   _safepoint_counter ++;
 393   // memory fence isn't required here since an odd _safepoint_counter
 394   // value can do no harm and a fence is issued below anyway.
 395 
 396   DEBUG_ONLY(Thread* myThread = Thread::current();)
 397   assert(myThread->is_VM_thread(), "Only VM thread can execute a safepoint");
 398 
 399   if (PrintSafepointStatistics) {
 400     end_statistics(os::javaTimeNanos());
 401   }
 402 
 403 #ifdef ASSERT
 404   // A pending_exception cannot be installed during a safepoint.  The threads
 405   // may install an async exception after they come back from a safepoint into
 406   // pending_exception after they unblock.  But that should happen later.
 407   for(JavaThread *cur = Threads::first(); cur; cur = cur->next()) {
 408     assert (!(cur->has_pending_exception() &&
 409               cur->safepoint_state()->is_at_poll_safepoint()),
 410             "safepoint installed a pending exception");
 411   }
 412 #endif // ASSERT
 413 
 414   if (PageArmed) {
 415     // Make polling safepoint aware
 416     os::make_polling_page_readable();
 417     PageArmed = 0 ;
 418   }
 419 
 420   // Remove safepoint check from interpreter
 421   Interpreter::ignore_safepoints();
 422 
 423   {
 424     MutexLocker mu(Safepoint_lock);
 425 
 426     assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization");
 427 
 428     // Set to not synchronized, so the threads will not go into the signal_thread_blocked method
 429     // when they get restarted.
 430     _state = _not_synchronized;
 431     OrderAccess::fence();
 432 
 433     if (TraceSafepoint) {
 434        tty->print_cr("Leaving safepoint region");
 435     }
 436 
 437     // Start suspended threads
 438     for(JavaThread *current = Threads::first(); current; current = current->next()) {
 439       // A problem occurring on Solaris is when attempting to restart threads
 440       // the first #cpus - 1 go well, but then the VMThread is preempted when we get
 441       // to the next one (since it has been running the longest).  We then have
 442       // to wait for a cpu to become available before we can continue restarting
 443       // threads.
 444       // FIXME: This causes the performance of the VM to degrade when active and with
 445       // large numbers of threads.  Apparently this is due to the synchronous nature
 446       // of suspending threads.
 447       //
 448       // TODO-FIXME: the comments above are vestigial and no longer apply.
 449       // Furthermore, using solaris' schedctl in this particular context confers no benefit
 450       if (VMThreadHintNoPreempt) {
 451         os::hint_no_preempt();
 452       }
 453       ThreadSafepointState* cur_state = current->safepoint_state();
 454       assert(cur_state->type() != ThreadSafepointState::_running, "Thread not suspended at safepoint");
 455       cur_state->restart();
 456       assert(cur_state->is_running(), "safepoint state has not been reset");
 457     }
 458 
 459     RuntimeService::record_safepoint_end();
 460 
 461     // Release threads lock, so threads can be created/destroyed again. It will also starts all threads
 462     // blocked in signal_thread_blocked
 463     Threads_lock->unlock();
 464 
 465   }
 466 #if INCLUDE_ALL_GCS
 467   // If there are any concurrent GC threads resume them.
 468   if (UseConcMarkSweepGC) {
 469     ConcurrentMarkSweepThread::desynchronize(false);
 470   } else if (UseG1GC) {
 471     SuspendibleThreadSet::desynchronize();
 472   }
 473 #endif // INCLUDE_ALL_GCS
 474   // record this time so VMThread can keep track how much time has elapsed
 475   // since last safepoint.
 476   _end_of_last_safepoint = os::javaTimeMillis();
 477 }
 478 
 479 bool SafepointSynchronize::is_cleanup_needed() {
 480   // Need a safepoint if some inline cache buffers is non-empty
 481   if (!InlineCacheBuffer::is_empty()) return true;
 482   return false;
 483 }
 484 
 485 
 486 
 487 // Various cleaning tasks that should be done periodically at safepoints
 488 void SafepointSynchronize::do_cleanup_tasks() {
 489   {
 490     TraceTime t1("deflating idle monitors", TraceSafepointCleanupTime);
 491     ObjectSynchronizer::deflate_idle_monitors();
 492   }
 493 
 494   {
 495     TraceTime t2("updating inline caches", TraceSafepointCleanupTime);
 496     InlineCacheBuffer::update_inline_caches();
 497   }
 498   {
 499     TraceTime t3("compilation policy safepoint handler", TraceSafepointCleanupTime);
 500     CompilationPolicy::policy()->do_safepoint_work();
 501   }
 502 
 503   {
 504     TraceTime t4("mark nmethods", TraceSafepointCleanupTime);
 505     NMethodSweeper::mark_active_nmethods();
 506   }
 507 
 508   if (SymbolTable::needs_rehashing()) {
 509     TraceTime t5("rehashing symbol table", TraceSafepointCleanupTime);
 510     SymbolTable::rehash_table();
 511   }
 512 
 513   if (StringTable::needs_rehashing()) {
 514     TraceTime t6("rehashing string table", TraceSafepointCleanupTime);
 515     StringTable::rehash_table();
 516   }
 517 
 518   // rotate log files?
 519   if (UseGCLogFileRotation) {
 520     gclog_or_tty->rotate_log(false);
 521   }
 522 
 523   {
 524     // CMS delays purging the CLDG until the beginning of the next safepoint and to
 525     // make sure concurrent sweep is done
 526     TraceTime t7("purging class loader data graph", TraceSafepointCleanupTime);
 527     ClassLoaderDataGraph::purge_if_needed();
 528   }
 529 }
 530 
 531 
 532 bool SafepointSynchronize::safepoint_safe(JavaThread *thread, JavaThreadState state) {
 533   switch(state) {
 534   case _thread_in_native:
 535     // native threads are safe if they have no java stack or have walkable stack
 536     return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable();
 537 
 538    // blocked threads should have already have walkable stack
 539   case _thread_blocked:
 540     assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable");
 541     return true;
 542 
 543   default:
 544     return false;
 545   }
 546 }
 547 
 548 
 549 // See if the thread is running inside a lazy critical native and
 550 // update the thread critical count if so.  Also set a suspend flag to
 551 // cause the native wrapper to return into the JVM to do the unlock
 552 // once the native finishes.
 553 void SafepointSynchronize::check_for_lazy_critical_native(JavaThread *thread, JavaThreadState state) {
 554   if (state == _thread_in_native &&
 555       thread->has_last_Java_frame() &&
 556       thread->frame_anchor()->walkable()) {
 557     // This thread might be in a critical native nmethod so look at
 558     // the top of the stack and increment the critical count if it
 559     // is.
 560     frame wrapper_frame = thread->last_frame();
 561     CodeBlob* stub_cb = wrapper_frame.cb();
 562     if (stub_cb != NULL &&
 563         stub_cb->is_nmethod() &&
 564         stub_cb->as_nmethod_or_null()->is_lazy_critical_native()) {
 565       // A thread could potentially be in a critical native across
 566       // more than one safepoint, so only update the critical state on
 567       // the first one.  When it returns it will perform the unlock.
 568       if (!thread->do_critical_native_unlock()) {
 569 #ifdef ASSERT
 570         if (!thread->in_critical()) {
 571           GC_locker::increment_debug_jni_lock_count();
 572         }
 573 #endif
 574         thread->enter_critical();
 575         // Make sure the native wrapper calls back on return to
 576         // perform the needed critical unlock.
 577         thread->set_critical_native_unlock();
 578       }
 579     }
 580   }
 581 }
 582 
 583 
 584 
 585 // -------------------------------------------------------------------------------------------------------
 586 // Implementation of Safepoint callback point
 587 
 588 void SafepointSynchronize::block(JavaThread *thread) {
 589   assert(thread != NULL, "thread must be set");
 590   assert(thread->is_Java_thread(), "not a Java thread");
 591 
 592   // Threads shouldn't block if they are in the middle of printing, but...
 593   ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id());
 594 
 595   // Only bail from the block() call if the thread is gone from the
 596   // thread list; starting to exit should still block.
 597   if (thread->is_terminated()) {
 598      // block current thread if we come here from native code when VM is gone
 599      thread->block_if_vm_exited();
 600 
 601      // otherwise do nothing
 602      return;
 603   }
 604 
 605   JavaThreadState state = thread->thread_state();
 606   thread->frame_anchor()->make_walkable(thread);
 607 
 608   // Check that we have a valid thread_state at this point
 609   switch(state) {
 610     case _thread_in_vm_trans:
 611     case _thread_in_Java:        // From compiled code
 612 
 613       // We are highly likely to block on the Safepoint_lock. In order to avoid blocking in this case,
 614       // we pretend we are still in the VM.
 615       thread->set_thread_state(_thread_in_vm);
 616 
 617       if (is_synchronizing()) {
 618          Atomic::inc (&TryingToBlock) ;
 619       }
 620 
 621       // We will always be holding the Safepoint_lock when we are examine the state
 622       // of a thread. Hence, the instructions between the Safepoint_lock->lock() and
 623       // Safepoint_lock->unlock() are happening atomic with regards to the safepoint code
 624       Safepoint_lock->lock_without_safepoint_check();
 625       if (is_synchronizing()) {
 626         // Decrement the number of threads to wait for and signal vm thread
 627         assert(_waiting_to_block > 0, "sanity check");
 628         _waiting_to_block--;
 629         thread->safepoint_state()->set_has_called_back(true);
 630 
 631         DEBUG_ONLY(thread->set_visited_for_critical_count(true));
 632         if (thread->in_critical()) {
 633           // Notice that this thread is in a critical section
 634           increment_jni_active_count();
 635         }
 636 
 637         // Consider (_waiting_to_block < 2) to pipeline the wakeup of the VM thread
 638         if (_waiting_to_block == 0) {
 639           Safepoint_lock->notify_all();
 640         }
 641       }
 642 
 643       // We transition the thread to state _thread_blocked here, but
 644       // we can't do our usual check for external suspension and then
 645       // self-suspend after the lock_without_safepoint_check() call
 646       // below because we are often called during transitions while
 647       // we hold different locks. That would leave us suspended while
 648       // holding a resource which results in deadlocks.
 649       thread->set_thread_state(_thread_blocked);
 650       Safepoint_lock->unlock();
 651 
 652       // We now try to acquire the threads lock. Since this lock is hold by the VM thread during
 653       // the entire safepoint, the threads will all line up here during the safepoint.
 654       Threads_lock->lock_without_safepoint_check();
 655       // restore original state. This is important if the thread comes from compiled code, so it
 656       // will continue to execute with the _thread_in_Java state.
 657       thread->set_thread_state(state);
 658       Threads_lock->unlock();
 659       break;
 660 
 661     case _thread_in_native_trans:
 662     case _thread_blocked_trans:
 663     case _thread_new_trans:
 664       if (thread->safepoint_state()->type() == ThreadSafepointState::_call_back) {
 665         thread->print_thread_state();
 666         fatal("Deadlock in safepoint code.  "
 667               "Should have called back to the VM before blocking.");
 668       }
 669 
 670       // We transition the thread to state _thread_blocked here, but
 671       // we can't do our usual check for external suspension and then
 672       // self-suspend after the lock_without_safepoint_check() call
 673       // below because we are often called during transitions while
 674       // we hold different locks. That would leave us suspended while
 675       // holding a resource which results in deadlocks.
 676       thread->set_thread_state(_thread_blocked);
 677 
 678       // It is not safe to suspend a thread if we discover it is in _thread_in_native_trans. Hence,
 679       // the safepoint code might still be waiting for it to block. We need to change the state here,
 680       // so it can see that it is at a safepoint.
 681 
 682       // Block until the safepoint operation is completed.
 683       Threads_lock->lock_without_safepoint_check();
 684 
 685       // Restore state
 686       thread->set_thread_state(state);
 687 
 688       Threads_lock->unlock();
 689       break;
 690 
 691     default:
 692      fatal(err_msg("Illegal threadstate encountered: %d", state));
 693   }
 694 
 695   // Check for pending. async. exceptions or suspends - except if the
 696   // thread was blocked inside the VM. has_special_runtime_exit_condition()
 697   // is called last since it grabs a lock and we only want to do that when
 698   // we must.
 699   //
 700   // Note: we never deliver an async exception at a polling point as the
 701   // compiler may not have an exception handler for it. The polling
 702   // code will notice the async and deoptimize and the exception will
 703   // be delivered. (Polling at a return point is ok though). Sure is
 704   // a lot of bother for a deprecated feature...
 705   //
 706   // We don't deliver an async exception if the thread state is
 707   // _thread_in_native_trans so JNI functions won't be called with
 708   // a surprising pending exception. If the thread state is going back to java,
 709   // async exception is checked in check_special_condition_for_native_trans().
 710 
 711   if (state != _thread_blocked_trans &&
 712       state != _thread_in_vm_trans &&
 713       thread->has_special_runtime_exit_condition()) {
 714     thread->handle_special_runtime_exit_condition(
 715       !thread->is_at_poll_safepoint() && (state != _thread_in_native_trans));
 716   }
 717 }
 718 
 719 // ------------------------------------------------------------------------------------------------------
 720 // Exception handlers
 721 
 722 
 723 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) {
 724   assert(thread->is_Java_thread(), "polling reference encountered by VM thread");
 725   assert(thread->thread_state() == _thread_in_Java, "should come from Java code");
 726   assert(SafepointSynchronize::is_synchronizing(), "polling encountered outside safepoint synchronization");
 727 
 728   if (ShowSafepointMsgs) {
 729     tty->print("handle_polling_page_exception: ");
 730   }
 731 
 732   if (PrintSafepointStatistics) {
 733     inc_page_trap_count();
 734   }
 735 
 736   ThreadSafepointState* state = thread->safepoint_state();
 737 
 738   state->handle_polling_page_exception();
 739 }
 740 
 741 
 742 void SafepointSynchronize::print_safepoint_timeout(SafepointTimeoutReason reason) {
 743   if (!timeout_error_printed) {
 744     timeout_error_printed = true;
 745     // Print out the thread info which didn't reach the safepoint for debugging
 746     // purposes (useful when there are lots of threads in the debugger).
 747     tty->cr();
 748     tty->print_cr("# SafepointSynchronize::begin: Timeout detected:");
 749     if (reason ==  _spinning_timeout) {
 750       tty->print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint.");
 751     } else if (reason == _blocking_timeout) {
 752       tty->print_cr("# SafepointSynchronize::begin: Timed out while waiting for threads to stop.");
 753     }
 754 
 755     tty->print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:");
 756     ThreadSafepointState *cur_state;
 757     ResourceMark rm;
 758     for(JavaThread *cur_thread = Threads::first(); cur_thread;
 759         cur_thread = cur_thread->next()) {
 760       cur_state = cur_thread->safepoint_state();
 761 
 762       if (cur_thread->thread_state() != _thread_blocked &&
 763           ((reason == _spinning_timeout && cur_state->is_running()) ||
 764            (reason == _blocking_timeout && !cur_state->has_called_back()))) {
 765         tty->print("# ");
 766         cur_thread->print();
 767         tty->cr();
 768       }
 769     }
 770     tty->print_cr("# SafepointSynchronize::begin: (End of list)");
 771   }
 772 
 773   // To debug the long safepoint, specify both DieOnSafepointTimeout &
 774   // ShowMessageBoxOnError.
 775   if (DieOnSafepointTimeout) {
 776     char msg[1024];
 777     VM_Operation *op = VMThread::vm_operation();
 778     sprintf(msg, "Safepoint sync time longer than " INTX_FORMAT "ms detected when executing %s.",
 779             SafepointTimeoutDelay,
 780             op != NULL ? op->name() : "no vm operation");
 781     fatal(msg);
 782   }
 783 }
 784 
 785 
 786 // -------------------------------------------------------------------------------------------------------
 787 // Implementation of ThreadSafepointState
 788 
 789 ThreadSafepointState::ThreadSafepointState(JavaThread *thread) {
 790   _thread = thread;
 791   _type   = _running;
 792   _has_called_back = false;
 793   _at_poll_safepoint = false;
 794 }
 795 
 796 void ThreadSafepointState::create(JavaThread *thread) {
 797   ThreadSafepointState *state = new ThreadSafepointState(thread);
 798   thread->set_safepoint_state(state);
 799 }
 800 
 801 void ThreadSafepointState::destroy(JavaThread *thread) {
 802   if (thread->safepoint_state()) {
 803     delete(thread->safepoint_state());
 804     thread->set_safepoint_state(NULL);
 805   }
 806 }
 807 
 808 void ThreadSafepointState::examine_state_of_thread() {
 809   assert(is_running(), "better be running or just have hit safepoint poll");
 810 
 811   JavaThreadState state = _thread->thread_state();
 812 
 813   // Save the state at the start of safepoint processing.
 814   _orig_thread_state = state;
 815 
 816   // Check for a thread that is suspended. Note that thread resume tries
 817   // to grab the Threads_lock which we own here, so a thread cannot be
 818   // resumed during safepoint synchronization.
 819 
 820   // We check to see if this thread is suspended without locking to
 821   // avoid deadlocking with a third thread that is waiting for this
 822   // thread to be suspended. The third thread can notice the safepoint
 823   // that we're trying to start at the beginning of its SR_lock->wait()
 824   // call. If that happens, then the third thread will block on the
 825   // safepoint while still holding the underlying SR_lock. We won't be
 826   // able to get the SR_lock and we'll deadlock.
 827   //
 828   // We don't need to grab the SR_lock here for two reasons:
 829   // 1) The suspend flags are both volatile and are set with an
 830   //    Atomic::cmpxchg() call so we should see the suspended
 831   //    state right away.
 832   // 2) We're being called from the safepoint polling loop; if
 833   //    we don't see the suspended state on this iteration, then
 834   //    we'll come around again.
 835   //
 836   bool is_suspended = _thread->is_ext_suspended();
 837   if (is_suspended) {
 838     roll_forward(_at_safepoint);
 839     return;
 840   }
 841 
 842   // Some JavaThread states have an initial safepoint state of
 843   // running, but are actually at a safepoint. We will happily
 844   // agree and update the safepoint state here.
 845   if (SafepointSynchronize::safepoint_safe(_thread, state)) {
 846     SafepointSynchronize::check_for_lazy_critical_native(_thread, state);
 847     roll_forward(_at_safepoint);
 848     return;
 849   }
 850 
 851   if (state == _thread_in_vm) {
 852     roll_forward(_call_back);
 853     return;
 854   }
 855 
 856   // All other thread states will continue to run until they
 857   // transition and self-block in state _blocked
 858   // Safepoint polling in compiled code causes the Java threads to do the same.
 859   // Note: new threads may require a malloc so they must be allowed to finish
 860 
 861   assert(is_running(), "examine_state_of_thread on non-running thread");
 862   return;
 863 }
 864 
 865 // Returns true is thread could not be rolled forward at present position.
 866 void ThreadSafepointState::roll_forward(suspend_type type) {
 867   _type = type;
 868 
 869   switch(_type) {
 870     case _at_safepoint:
 871       SafepointSynchronize::signal_thread_at_safepoint();
 872       DEBUG_ONLY(_thread->set_visited_for_critical_count(true));
 873       if (_thread->in_critical()) {
 874         // Notice that this thread is in a critical section
 875         SafepointSynchronize::increment_jni_active_count();
 876       }
 877       break;
 878 
 879     case _call_back:
 880       set_has_called_back(false);
 881       break;
 882 
 883     case _running:
 884     default:
 885       ShouldNotReachHere();
 886   }
 887 }
 888 
 889 void ThreadSafepointState::restart() {
 890   switch(type()) {
 891     case _at_safepoint:
 892     case _call_back:
 893       break;
 894 
 895     case _running:
 896     default:
 897        tty->print_cr("restart thread " INTPTR_FORMAT " with state %d",
 898                       _thread, _type);
 899        _thread->print();
 900       ShouldNotReachHere();
 901   }
 902   _type = _running;
 903   set_has_called_back(false);
 904 }
 905 
 906 
 907 void ThreadSafepointState::print_on(outputStream *st) const {
 908   const char *s;
 909 
 910   switch(_type) {
 911     case _running                : s = "_running";              break;
 912     case _at_safepoint           : s = "_at_safepoint";         break;
 913     case _call_back              : s = "_call_back";            break;
 914     default:
 915       ShouldNotReachHere();
 916   }
 917 
 918   st->print_cr("Thread: " INTPTR_FORMAT
 919               "  [0x%2x] State: %s _has_called_back %d _at_poll_safepoint %d",
 920                _thread, _thread->osthread()->thread_id(), s, _has_called_back,
 921                _at_poll_safepoint);
 922 
 923   _thread->print_thread_state_on(st);
 924 }
 925 
 926 
 927 // ---------------------------------------------------------------------------------------------------------------------
 928 
 929 // Block the thread at the safepoint poll or poll return.
 930 void ThreadSafepointState::handle_polling_page_exception() {
 931 
 932   // Check state.  block() will set thread state to thread_in_vm which will
 933   // cause the safepoint state _type to become _call_back.
 934   assert(type() == ThreadSafepointState::_running,
 935          "polling page exception on thread not running state");
 936 
 937   // Step 1: Find the nmethod from the return address
 938   if (ShowSafepointMsgs && Verbose) {
 939     tty->print_cr("Polling page exception at " INTPTR_FORMAT, thread()->saved_exception_pc());
 940   }
 941   address real_return_addr = thread()->saved_exception_pc();
 942 
 943   CodeBlob *cb = CodeCache::find_blob(real_return_addr);
 944   assert(cb != NULL && cb->is_nmethod(), "return address should be in nmethod");
 945   nmethod* nm = (nmethod*)cb;
 946 
 947   // Find frame of caller
 948   frame stub_fr = thread()->last_frame();
 949   CodeBlob* stub_cb = stub_fr.cb();
 950   assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub");
 951   RegisterMap map(thread(), true);
 952   frame caller_fr = stub_fr.sender(&map);
 953 
 954   // Should only be poll_return or poll
 955   assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" );
 956 
 957   // This is a poll immediately before a return. The exception handling code
 958   // has already had the effect of causing the return to occur, so the execution
 959   // will continue immediately after the call. In addition, the oopmap at the
 960   // return point does not mark the return value as an oop (if it is), so
 961   // it needs a handle here to be updated.
 962   if( nm->is_at_poll_return(real_return_addr) ) {
 963     // See if return type is an oop.
 964     bool return_oop = nm->method()->is_returning_oop();
 965     Handle return_value;
 966     if (return_oop) {
 967       // The oop result has been saved on the stack together with all
 968       // the other registers. In order to preserve it over GCs we need
 969       // to keep it in a handle.
 970       oop result = caller_fr.saved_oop_result(&map);
 971       assert(result == NULL || result->is_oop(), "must be oop");
 972       return_value = Handle(thread(), result);
 973       assert(Universe::heap()->is_in_or_null(result), "must be heap pointer");
 974     }
 975 
 976     // Block the thread
 977     SafepointSynchronize::block(thread());
 978 
 979     // restore oop result, if any
 980     if (return_oop) {
 981       caller_fr.set_saved_oop_result(&map, return_value());
 982     }
 983   }
 984 
 985   // This is a safepoint poll. Verify the return address and block.
 986   else {
 987     set_at_poll_safepoint(true);
 988 
 989     // verify the blob built the "return address" correctly
 990     assert(real_return_addr == caller_fr.pc(), "must match");
 991 
 992     // Block the thread
 993     SafepointSynchronize::block(thread());
 994     set_at_poll_safepoint(false);
 995 
 996     // If we have a pending async exception deoptimize the frame
 997     // as otherwise we may never deliver it.
 998     if (thread()->has_async_condition()) {
 999       ThreadInVMfromJavaNoAsyncException __tiv(thread());
1000       Deoptimization::deoptimize_frame(thread(), caller_fr.id());
1001     }
1002 
1003     // If an exception has been installed we must check for a pending deoptimization
1004     // Deoptimize frame if exception has been thrown.
1005 
1006     if (thread()->has_pending_exception() ) {
1007       RegisterMap map(thread(), true);
1008       frame caller_fr = stub_fr.sender(&map);
1009       if (caller_fr.is_deoptimized_frame()) {
1010         // The exception patch will destroy registers that are still
1011         // live and will be needed during deoptimization. Defer the
1012         // Async exception should have deferred the exception until the
1013         // next safepoint which will be detected when we get into
1014         // the interpreter so if we have an exception now things
1015         // are messed up.
1016 
1017         fatal("Exception installed and deoptimization is pending");
1018       }
1019     }
1020   }
1021 }
1022 
1023 
1024 //
1025 //                     Statistics & Instrumentations
1026 //
1027 SafepointSynchronize::SafepointStats*  SafepointSynchronize::_safepoint_stats = NULL;
1028 jlong  SafepointSynchronize::_safepoint_begin_time = 0;
1029 int    SafepointSynchronize::_cur_stat_index = 0;
1030 julong SafepointSynchronize::_safepoint_reasons[VM_Operation::VMOp_Terminating];
1031 julong SafepointSynchronize::_coalesced_vmop_count = 0;
1032 jlong  SafepointSynchronize::_max_sync_time = 0;
1033 jlong  SafepointSynchronize::_max_vmop_time = 0;
1034 float  SafepointSynchronize::_ts_of_current_safepoint = 0.0f;
1035 
1036 static jlong  cleanup_end_time = 0;
1037 static bool   need_to_track_page_armed_status = false;
1038 static bool   init_done = false;
1039 
1040 // Helper method to print the header.
1041 static void print_header() {
1042   tty->print("         vmop                    "
1043              "[threads: total initially_running wait_to_block]    ");
1044   tty->print("[time: spin block sync cleanup vmop] ");
1045 
1046   // no page armed status printed out if it is always armed.
1047   if (need_to_track_page_armed_status) {
1048     tty->print("page_armed ");
1049   }
1050 
1051   tty->print_cr("page_trap_count");
1052 }
1053 
1054 void SafepointSynchronize::deferred_initialize_stat() {
1055   if (init_done) return;
1056 
1057   if (PrintSafepointStatisticsCount <= 0) {
1058     fatal("Wrong PrintSafepointStatisticsCount");
1059   }
1060 
1061   // If PrintSafepointStatisticsTimeout is specified, the statistics data will
1062   // be printed right away, in which case, _safepoint_stats will regress to
1063   // a single element array. Otherwise, it is a circular ring buffer with default
1064   // size of PrintSafepointStatisticsCount.
1065   int stats_array_size;
1066   if (PrintSafepointStatisticsTimeout > 0) {
1067     stats_array_size = 1;
1068     PrintSafepointStatistics = true;
1069   } else {
1070     stats_array_size = PrintSafepointStatisticsCount;
1071   }
1072   _safepoint_stats = (SafepointStats*)os::malloc(stats_array_size
1073                                                  * sizeof(SafepointStats), mtInternal);
1074   guarantee(_safepoint_stats != NULL,
1075             "not enough memory for safepoint instrumentation data");
1076 
1077   if (DeferPollingPageLoopCount >= 0) {
1078     need_to_track_page_armed_status = true;
1079   }
1080   init_done = true;
1081 }
1082 
1083 void SafepointSynchronize::begin_statistics(int nof_threads, int nof_running) {
1084   assert(init_done, "safepoint statistics array hasn't been initialized");
1085   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1086 
1087   spstat->_time_stamp = _ts_of_current_safepoint;
1088 
1089   VM_Operation *op = VMThread::vm_operation();
1090   spstat->_vmop_type = (op != NULL ? op->type() : -1);
1091   if (op != NULL) {
1092     _safepoint_reasons[spstat->_vmop_type]++;
1093   }
1094 
1095   spstat->_nof_total_threads = nof_threads;
1096   spstat->_nof_initial_running_threads = nof_running;
1097   spstat->_nof_threads_hit_page_trap = 0;
1098 
1099   // Records the start time of spinning. The real time spent on spinning
1100   // will be adjusted when spin is done. Same trick is applied for time
1101   // spent on waiting for threads to block.
1102   if (nof_running != 0) {
1103     spstat->_time_to_spin = os::javaTimeNanos();
1104   }  else {
1105     spstat->_time_to_spin = 0;
1106   }
1107 }
1108 
1109 void SafepointSynchronize::update_statistics_on_spin_end() {
1110   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1111 
1112   jlong cur_time = os::javaTimeNanos();
1113 
1114   spstat->_nof_threads_wait_to_block = _waiting_to_block;
1115   if (spstat->_nof_initial_running_threads != 0) {
1116     spstat->_time_to_spin = cur_time - spstat->_time_to_spin;
1117   }
1118 
1119   if (need_to_track_page_armed_status) {
1120     spstat->_page_armed = (PageArmed == 1);
1121   }
1122 
1123   // Records the start time of waiting for to block. Updated when block is done.
1124   if (_waiting_to_block != 0) {
1125     spstat->_time_to_wait_to_block = cur_time;
1126   } else {
1127     spstat->_time_to_wait_to_block = 0;
1128   }
1129 }
1130 
1131 void SafepointSynchronize::update_statistics_on_sync_end(jlong end_time) {
1132   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1133 
1134   if (spstat->_nof_threads_wait_to_block != 0) {
1135     spstat->_time_to_wait_to_block = end_time -
1136       spstat->_time_to_wait_to_block;
1137   }
1138 
1139   // Records the end time of sync which will be used to calculate the total
1140   // vm operation time. Again, the real time spending in syncing will be deducted
1141   // from the start of the sync time later when end_statistics is called.
1142   spstat->_time_to_sync = end_time - _safepoint_begin_time;
1143   if (spstat->_time_to_sync > _max_sync_time) {
1144     _max_sync_time = spstat->_time_to_sync;
1145   }
1146 
1147   spstat->_time_to_do_cleanups = end_time;
1148 }
1149 
1150 void SafepointSynchronize::update_statistics_on_cleanup_end(jlong end_time) {
1151   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1152 
1153   // Record how long spent in cleanup tasks.
1154   spstat->_time_to_do_cleanups = end_time - spstat->_time_to_do_cleanups;
1155 
1156   cleanup_end_time = end_time;
1157 }
1158 
1159 void SafepointSynchronize::end_statistics(jlong vmop_end_time) {
1160   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1161 
1162   // Update the vm operation time.
1163   spstat->_time_to_exec_vmop = vmop_end_time -  cleanup_end_time;
1164   if (spstat->_time_to_exec_vmop > _max_vmop_time) {
1165     _max_vmop_time = spstat->_time_to_exec_vmop;
1166   }
1167   // Only the sync time longer than the specified
1168   // PrintSafepointStatisticsTimeout will be printed out right away.
1169   // By default, it is -1 meaning all samples will be put into the list.
1170   if ( PrintSafepointStatisticsTimeout > 0) {
1171     if (spstat->_time_to_sync > PrintSafepointStatisticsTimeout * MICROUNITS) {
1172       print_statistics();
1173     }
1174   } else {
1175     // The safepoint statistics will be printed out when the _safepoin_stats
1176     // array fills up.
1177     if (_cur_stat_index == PrintSafepointStatisticsCount - 1) {
1178       print_statistics();
1179       _cur_stat_index = 0;
1180     } else {
1181       _cur_stat_index++;
1182     }
1183   }
1184 }
1185 
1186 void SafepointSynchronize::print_statistics() {
1187   SafepointStats* sstats = _safepoint_stats;
1188 
1189   for (int index = 0; index <= _cur_stat_index; index++) {
1190     if (index % 30 == 0) {
1191       print_header();
1192     }
1193     sstats = &_safepoint_stats[index];
1194     tty->print("%.3f: ", sstats->_time_stamp);
1195     tty->print("%-26s       ["
1196                INT32_FORMAT_W(8) INT32_FORMAT_W(11) INT32_FORMAT_W(15)
1197                "    ]    ",
1198                sstats->_vmop_type == -1 ? "no vm operation" :
1199                VM_Operation::name(sstats->_vmop_type),
1200                sstats->_nof_total_threads,
1201                sstats->_nof_initial_running_threads,
1202                sstats->_nof_threads_wait_to_block);
1203     // "/ MICROUNITS " is to convert the unit from nanos to millis.
1204     tty->print("  ["
1205                INT64_FORMAT_W(6) INT64_FORMAT_W(6)
1206                INT64_FORMAT_W(6) INT64_FORMAT_W(6)
1207                INT64_FORMAT_W(6) "    ]  ",
1208                sstats->_time_to_spin / MICROUNITS,
1209                sstats->_time_to_wait_to_block / MICROUNITS,
1210                sstats->_time_to_sync / MICROUNITS,
1211                sstats->_time_to_do_cleanups / MICROUNITS,
1212                sstats->_time_to_exec_vmop / MICROUNITS);
1213 
1214     if (need_to_track_page_armed_status) {
1215       tty->print(INT32_FORMAT "         ", sstats->_page_armed);
1216     }
1217     tty->print_cr(INT32_FORMAT "   ", sstats->_nof_threads_hit_page_trap);
1218   }
1219 }
1220 
1221 // This method will be called when VM exits. It will first call
1222 // print_statistics to print out the rest of the sampling.  Then
1223 // it tries to summarize the sampling.
1224 void SafepointSynchronize::print_stat_on_exit() {
1225   if (_safepoint_stats == NULL) return;
1226 
1227   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1228 
1229   // During VM exit, end_statistics may not get called and in that
1230   // case, if the sync time is less than PrintSafepointStatisticsTimeout,
1231   // don't print it out.
1232   // Approximate the vm op time.
1233   _safepoint_stats[_cur_stat_index]._time_to_exec_vmop =
1234     os::javaTimeNanos() - cleanup_end_time;
1235 
1236   if ( PrintSafepointStatisticsTimeout < 0 ||
1237        spstat->_time_to_sync > PrintSafepointStatisticsTimeout * MICROUNITS) {
1238     print_statistics();
1239   }
1240   tty->cr();
1241 
1242   // Print out polling page sampling status.
1243   if (!need_to_track_page_armed_status) {
1244     tty->print_cr("Polling page always armed");
1245   } else {
1246     tty->print_cr("Defer polling page loop count = %d\n",
1247                  DeferPollingPageLoopCount);
1248   }
1249 
1250   for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) {
1251     if (_safepoint_reasons[index] != 0) {
1252       tty->print_cr("%-26s" UINT64_FORMAT_W(10), VM_Operation::name(index),
1253                     _safepoint_reasons[index]);
1254     }
1255   }
1256 
1257   tty->print_cr(UINT64_FORMAT_W(5) " VM operations coalesced during safepoint",
1258                 _coalesced_vmop_count);
1259   tty->print_cr("Maximum sync time  " INT64_FORMAT_W(5) " ms",
1260                 _max_sync_time / MICROUNITS);
1261   tty->print_cr("Maximum vm operation time (except for Exit VM operation)  "
1262                 INT64_FORMAT_W(5) " ms",
1263                 _max_vmop_time / MICROUNITS);
1264 }
1265 
1266 // ------------------------------------------------------------------------------------------------
1267 // Non-product code
1268 
1269 #ifndef PRODUCT
1270 
1271 void SafepointSynchronize::print_state() {
1272   if (_state == _not_synchronized) {
1273     tty->print_cr("not synchronized");
1274   } else if (_state == _synchronizing || _state == _synchronized) {
1275     tty->print_cr("State: %s", (_state == _synchronizing) ? "synchronizing" :
1276                   "synchronized");
1277 
1278     for(JavaThread *cur = Threads::first(); cur; cur = cur->next()) {
1279        cur->safepoint_state()->print();
1280     }
1281   }
1282 }
1283 
1284 void SafepointSynchronize::safepoint_msg(const char* format, ...) {
1285   if (ShowSafepointMsgs) {
1286     va_list ap;
1287     va_start(ap, format);
1288     tty->vprint_cr(format, ap);
1289     va_end(ap);
1290   }
1291 }
1292 
1293 #endif // !PRODUCT
--- EOF ---