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 /*

  * Copyright (c) 1997, 2014, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

  * or visit www.oracle.com if you need additional information or have any

  * questions.

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  */

 #include "precompiled.hpp"

 #include "classfile/symbolTable.hpp"

 #include "classfile/systemDictionary.hpp"

 #include "code/codeCache.hpp"

 #include "code/icBuffer.hpp"

 #include "code/nmethod.hpp"

 #include "code/pcDesc.hpp"

 #include "code/scopeDesc.hpp"

 #include "gc_interface/collectedHeap.hpp"

 #include "interpreter/interpreter.hpp"

 #include "memory/resourceArea.hpp"

 #include "memory/universe.inline.hpp"

 #include "oops/oop.inline.hpp"

 #include "oops/symbol.hpp"

 #include "runtime/compilationPolicy.hpp"

 #include "runtime/deoptimization.hpp"

 #include "runtime/frame.inline.hpp"

 #include "runtime/interfaceSupport.hpp"

 #include "runtime/mutexLocker.hpp"

 #include "runtime/orderAccess.inline.hpp"

 #include "runtime/osThread.hpp"

 #include "runtime/safepoint.hpp"

 #include "runtime/signature.hpp"

 #include "runtime/stubCodeGenerator.hpp"

 #include "runtime/stubRoutines.hpp"

 #include "runtime/sweeper.hpp"

 #include "runtime/synchronizer.hpp"

 #include "runtime/thread.inline.hpp"

 #include "services/runtimeService.hpp"

 #include "utilities/events.hpp"

 #include "utilities/macros.hpp"

 #ifdef TARGET_ARCH_x86

 # include "nativeInst_x86.hpp"

 # include "vmreg_x86.inline.hpp"

 #endif

 #ifdef TARGET_ARCH_sparc

 # include "nativeInst_sparc.hpp"

 # include "vmreg_sparc.inline.hpp"

 #endif

 #ifdef TARGET_ARCH_zero

 # include "nativeInst_zero.hpp"

 # include "vmreg_zero.inline.hpp"

 #endif

 #ifdef TARGET_ARCH_arm

 # include "nativeInst_arm.hpp"

 # include "vmreg_arm.inline.hpp"

 #endif

 #ifdef TARGET_ARCH_ppc

 # include "nativeInst_ppc.hpp"

 # include "vmreg_ppc.inline.hpp"

 #endif

 #if INCLUDE_ALL_GCS

 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"

 #include "gc_implementation/shared/suspendibleThreadSet.hpp"

 #endif // INCLUDE_ALL_GCS

 #ifdef COMPILER1

 #include "c1/c1_globals.hpp"

 #endif

 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC

 // --------------------------------------------------------------------------------------------------

 // Implementation of Safepoint begin/end

 SafepointSynchronize::SynchronizeState volatile SafepointSynchronize::_state = SafepointSynchronize::_not_synchronized;

 volatile int  SafepointSynchronize::_waiting_to_block = 0;

 volatile int SafepointSynchronize::_safepoint_counter = 0;

 int SafepointSynchronize::_current_jni_active_count = 0;

 long  SafepointSynchronize::_end_of_last_safepoint = 0;

 static volatile int PageArmed = 0 ;        // safepoint polling page is RO|RW vs PROT_NONE

 static volatile int TryingToBlock = 0 ;    // proximate value -- for advisory use only

 static bool timeout_error_printed = false;

 // Roll all threads forward to a safepoint and suspend them all

 void SafepointSynchronize::begin() {

   Thread* myThread = Thread::current();

   assert(myThread->is_VM_thread(), "Only VM thread may execute a safepoint");

   if (PrintSafepointStatistics || PrintSafepointStatisticsTimeout > 0) {

     _safepoint_begin_time = os::javaTimeNanos();

     _ts_of_current_safepoint = tty->time_stamp().seconds();

   }

 #if INCLUDE_ALL_GCS

   if (UseConcMarkSweepGC) {

     // In the future we should investigate whether CMS can use the

     // more-general mechanism below.  DLD (01/05).

     ConcurrentMarkSweepThread::synchronize(false);

   } else if (UseG1GC) {

     SuspendibleThreadSet::synchronize();

   }

 #endif // INCLUDE_ALL_GCS

   // By getting the Threads_lock, we assure that no threads are about to start or

   // exit. It is released again in SafepointSynchronize::end().

   Threads_lock->lock();

   assert( _state == _not_synchronized, "trying to safepoint synchronize with wrong state");

   int nof_threads = Threads::number_of_threads();

   if (TraceSafepoint) {

     tty->print_cr("Safepoint synchronization initiated. (%d)", nof_threads);

   }

   RuntimeService::record_safepoint_begin();

   MutexLocker mu(Safepoint_lock);

   // Reset the count of active JNI critical threads

   _current_jni_active_count = 0;

   // Set number of threads to wait for, before we initiate the callbacks

   _waiting_to_block = nof_threads;

   TryingToBlock     = 0 ;

   int still_running = nof_threads;

   // Save the starting time, so that it can be compared to see if this has taken

   // too long to complete.

   jlong safepoint_limit_time;

   timeout_error_printed = false;

   // PrintSafepointStatisticsTimeout can be specified separately. When

   // specified, PrintSafepointStatistics will be set to true in

   // deferred_initialize_stat method. The initialization has to be done

   // early enough to avoid any races. See bug 6880029 for details.

   if (PrintSafepointStatistics || PrintSafepointStatisticsTimeout > 0) {

     deferred_initialize_stat();

   }

   // Begin the process of bringing the system to a safepoint.

   // Java threads can be in several different states and are

   // stopped by different mechanisms:

   //

   //  1. Running interpreted

   //     The interpeter dispatch table is changed to force it to

   //     check for a safepoint condition between bytecodes.

   //  2. Running in native code

   //     When returning from the native code, a Java thread must check

   //     the safepoint _state to see if we must block.  If the

   //     VM thread sees a Java thread in native, it does

   //     not wait for this thread to block.  The order of the memory

   //     writes and reads of both the safepoint state and the Java

   //     threads state is critical.  In order to guarantee that the

   //     memory writes are serialized with respect to each other,

   //     the VM thread issues a memory barrier instruction

   //     (on MP systems).  In order to avoid the overhead of issuing

   //     a memory barrier for each Java thread making native calls, each Java

   //     thread performs a write to a single memory page after changing

   //     the thread state.  The VM thread performs a sequence of

   //     mprotect OS calls which forces all previous writes from all

   //     Java threads to be serialized.  This is done in the

   //     os::serialize_thread_states() call.  This has proven to be

   //     much more efficient than executing a membar instruction

   //     on every call to native code.

   //  3. Running compiled Code

   //     Compiled code reads a global (Safepoint Polling) page that

   //     is set to fault if we are trying to get to a safepoint.

   //  4. Blocked

   //     A thread which is blocked will not be allowed to return from the

   //     block condition until the safepoint operation is complete.

   //  5. In VM or Transitioning between states

   //     If a Java thread is currently running in the VM or transitioning

   //     between states, the safepointing code will wait for the thread to

   //     block itself when it attempts transitions to a new state.

   //

   _state            = _synchronizing;

   OrderAccess::fence();

   // Flush all thread states to memory

   if (!UseMembar) {

     os::serialize_thread_states();

   }

   // Make interpreter safepoint aware

   Interpreter::notice_safepoints();

   if (UseCompilerSafepoints && DeferPollingPageLoopCount < 0) {

     // Make polling safepoint aware

     guarantee (PageArmed == 0, "invariant") ;

     PageArmed = 1 ;

     os::make_polling_page_unreadable();

   }

   // Consider using active_processor_count() ... but that call is expensive.

   int ncpus = os::processor_count() ;

 #ifdef ASSERT

   for (JavaThread *cur = Threads::first(); cur != NULL; cur = cur->next()) {

     assert(cur->safepoint_state()->is_running(), "Illegal initial state");

     // Clear the visited flag to ensure that the critical counts are collected properly.

     cur->set_visited_for_critical_count(false);

   }

 #endif // ASSERT

   if (SafepointTimeout)

     safepoint_limit_time = os::javaTimeNanos() + (jlong)SafepointTimeoutDelay * MICROUNITS;

   // Iterate through all threads until it have been determined how to stop them all at a safepoint

   unsigned int iterations = 0;

   int steps = 0 ;

   while(still_running > 0) {

     for (JavaThread *cur = Threads::first(); cur != NULL; cur = cur->next()) {

       assert(!cur->is_ConcurrentGC_thread(), "A concurrent GC thread is unexpectly being suspended");

       ThreadSafepointState *cur_state = cur->safepoint_state();

       if (cur_state->is_running()) {

         cur_state->examine_state_of_thread();

         if (!cur_state->is_running()) {

            still_running--;

            // consider adjusting steps downward:

            //   steps = 0

            //   steps -= NNN

            //   steps >>= 1

            //   steps = MIN(steps, 2000-100)

            //   if (iterations != 0) steps -= NNN

         }

         if (TraceSafepoint && Verbose) cur_state->print();

       }

     }

     if (PrintSafepointStatistics && iterations == 0) {

       begin_statistics(nof_threads, still_running);

     }

     if (still_running > 0) {

       // Check for if it takes to long

       if (SafepointTimeout && safepoint_limit_time < os::javaTimeNanos()) {

         print_safepoint_timeout(_spinning_timeout);

       }

       // Spin to avoid context switching.

       // There's a tension between allowing the mutators to run (and rendezvous)

       // vs spinning.  As the VM thread spins, wasting cycles, it consumes CPU that

       // a mutator might otherwise use profitably to reach a safepoint.  Excessive

       // spinning by the VM thread on a saturated system can increase rendezvous latency.

       // Blocking or yielding incur their own penalties in the form of context switching

       // and the resultant loss of $ residency.

       //

       // Further complicating matters is that yield() does not work as naively expected

       // on many platforms -- yield() does not guarantee that any other ready threads

       // will run.   As such we revert yield_all() after some number of iterations.

       // Yield_all() is implemented as a short unconditional sleep on some platforms.

       // Typical operating systems round a "short" sleep period up to 10 msecs, so sleeping

       // can actually increase the time it takes the VM thread to detect that a system-wide

       // stop-the-world safepoint has been reached.  In a pathological scenario such as that

       // described in CR6415670 the VMthread may sleep just before the mutator(s) become safe.

       // In that case the mutators will be stalled waiting for the safepoint to complete and the

       // the VMthread will be sleeping, waiting for the mutators to rendezvous.  The VMthread

       // will eventually wake up and detect that all mutators are safe, at which point

       // we'll again make progress.

       //

       // Beware too that that the VMThread typically runs at elevated priority.

       // Its default priority is higher than the default mutator priority.

       // Obviously, this complicates spinning.

       //

       // Note too that on Windows XP SwitchThreadTo() has quite different behavior than Sleep(0).

       // Sleep(0) will _not yield to lower priority threads, while SwitchThreadTo() will.

       //

       // See the comments in synchronizer.cpp for additional remarks on spinning.

       //

       // In the future we might:

       // 1. Modify the safepoint scheme to avoid potentally unbounded spinning.

       //    This is tricky as the path used by a thread exiting the JVM (say on

       //    on JNI call-out) simply stores into its state field.  The burden

       //    is placed on the VM thread, which must poll (spin).

       // 2. Find something useful to do while spinning.  If the safepoint is GC-related

       //    we might aggressively scan the stacks of threads that are already safe.

       // 3. Use Solaris schedctl to examine the state of the still-running mutators.

       //    If all the mutators are ONPROC there's no reason to sleep or yield.

       // 4. YieldTo() any still-running mutators that are ready but OFFPROC.

       // 5. Check system saturation.  If the system is not fully saturated then

       //    simply spin and avoid sleep/yield.

       // 6. As still-running mutators rendezvous they could unpark the sleeping

       //    VMthread.  This works well for still-running mutators that become

       //    safe.  The VMthread must still poll for mutators that call-out.

       // 7. Drive the policy on time-since-begin instead of iterations.

       // 8. Consider making the spin duration a function of the # of CPUs:

       //    Spin = (((ncpus-1) * M) + K) + F(still_running)

       //    Alternately, instead of counting iterations of the outer loop

       //    we could count the # of threads visited in the inner loop, above.

       // 9. On windows consider using the return value from SwitchThreadTo()

       //    to drive subsequent spin/SwitchThreadTo()/Sleep(N) decisions.

       if (UseCompilerSafepoints && int(iterations) == DeferPollingPageLoopCount) {

          guarantee (PageArmed == 0, "invariant") ;

          PageArmed = 1 ;

          os::make_polling_page_unreadable();

       }

       // Instead of (ncpus > 1) consider either (still_running < (ncpus + EPSILON)) or

       // ((still_running + _waiting_to_block - TryingToBlock)) < ncpus)

       ++steps ;

       if (ncpus > 1 && steps < SafepointSpinBeforeYield) {

         SpinPause() ;     // MP-Polite spin

       } else

       if (steps < DeferThrSuspendLoopCount) {

         os::NakedYield() ;

       } else {

         os::yield_all(steps) ;

         // Alternately, the VM thread could transiently depress its scheduling priority or

         // transiently increase the priority of the tardy mutator(s).

       }

       iterations ++ ;

     }

     assert(iterations < (uint)max_jint, "We have been iterating in the safepoint loop too long");

   }

   assert(still_running == 0, "sanity check");

   if (PrintSafepointStatistics) {

     update_statistics_on_spin_end();

   }

   // wait until all threads are stopped

   while (_waiting_to_block > 0) {

     if (TraceSafepoint) tty->print_cr("Waiting for %d thread(s) to block", _waiting_to_block);

     if (!SafepointTimeout || timeout_error_printed) {

       Safepoint_lock->wait(true);  // true, means with no safepoint checks

     } else {

       // Compute remaining time

       jlong remaining_time = safepoint_limit_time - os::javaTimeNanos();

       // If there is no remaining time, then there is an error

       if (remaining_time < 0 || Safepoint_lock->wait(true, remaining_time / MICROUNITS)) {

         print_safepoint_timeout(_blocking_timeout);

       }

     }

   }

   assert(_waiting_to_block == 0, "sanity check");

 #ifndef PRODUCT

   if (SafepointTimeout) {

     jlong current_time = os::javaTimeNanos();

     if (safepoint_limit_time < current_time) {

       tty->print_cr("# SafepointSynchronize: Finished after "

                     INT64_FORMAT_W(6) " ms",

                     ((current_time - safepoint_limit_time) / MICROUNITS +

                      SafepointTimeoutDelay));

     }

   }

 #endif

   assert((_safepoint_counter & 0x1) == 0, "must be even");

   assert(Threads_lock->owned_by_self(), "must hold Threads_lock");

   _safepoint_counter ++;

   // Record state

   _state = _synchronized;

   OrderAccess::fence();

 #ifdef ASSERT

   for (JavaThread *cur = Threads::first(); cur != NULL; cur = cur->next()) {

     // make sure all the threads were visited

     assert(cur->was_visited_for_critical_count(), "missed a thread");

   }

 #endif // ASSERT

   // Update the count of active JNI critical regions

   GC_locker::set_jni_lock_count(_current_jni_active_count);

   if (TraceSafepoint) {

     VM_Operation *op = VMThread::vm_operation();

     tty->print_cr("Entering safepoint region: %s", (op != NULL) ? op->name() : "no vm operation");

   }

   RuntimeService::record_safepoint_synchronized();

   if (PrintSafepointStatistics) {

     update_statistics_on_sync_end(os::javaTimeNanos());

   }

   // Call stuff that needs to be run when a safepoint is just about to be completed

   do_cleanup_tasks();

   if (PrintSafepointStatistics) {

     // Record how much time spend on the above cleanup tasks

     update_statistics_on_cleanup_end(os::javaTimeNanos());

   }

 }

 // Wake up all threads, so they are ready to resume execution after the safepoint

 // operation has been carried out

 void SafepointSynchronize::end() {

   assert(Threads_lock->owned_by_self(), "must hold Threads_lock");

   assert((_safepoint_counter & 0x1) == 1, "must be odd");

   _safepoint_counter ++;

   // memory fence isn't required here since an odd _safepoint_counter

   // value can do no harm and a fence is issued below anyway.

   DEBUG_ONLY(Thread* myThread = Thread::current();)

   assert(myThread->is_VM_thread(), "Only VM thread can execute a safepoint");

   if (PrintSafepointStatistics) {

     end_statistics(os::javaTimeNanos());

   }

 #ifdef ASSERT

   // A pending_exception cannot be installed during a safepoint.  The threads

   // may install an async exception after they come back from a safepoint into

   // pending_exception after they unblock.  But that should happen later.

   for(JavaThread *cur = Threads::first(); cur; cur = cur->next()) {

     assert (!(cur->has_pending_exception() &&

               cur->safepoint_state()->is_at_poll_safepoint()),

             "safepoint installed a pending exception");

   }

 #endif // ASSERT

   if (PageArmed) {

     // Make polling safepoint aware

     os::make_polling_page_readable();

     PageArmed = 0 ;

   }

   // Remove safepoint check from interpreter

   Interpreter::ignore_safepoints();

   {

     MutexLocker mu(Safepoint_lock);

     assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization");

     // Set to not synchronized, so the threads will not go into the signal_thread_blocked method

     // when they get restarted.

     _state = _not_synchronized;

     OrderAccess::fence();

     if (TraceSafepoint) {

        tty->print_cr("Leaving safepoint region");

     }

     // Start suspended threads

     for(JavaThread *current = Threads::first(); current; current = current->next()) {

       // A problem occurring on Solaris is when attempting to restart threads

       // the first #cpus - 1 go well, but then the VMThread is preempted when we get

       // to the next one (since it has been running the longest).  We then have

       // to wait for a cpu to become available before we can continue restarting

       // threads.

       // FIXME: This causes the performance of the VM to degrade when active and with

       // large numbers of threads.  Apparently this is due to the synchronous nature

       // of suspending threads.

       //

       // TODO-FIXME: the comments above are vestigial and no longer apply.

       // Furthermore, using solaris' schedctl in this particular context confers no benefit

       if (VMThreadHintNoPreempt) {

         os::hint_no_preempt();

       }

       ThreadSafepointState* cur_state = current->safepoint_state();

       assert(cur_state->type() != ThreadSafepointState::_running, "Thread not suspended at safepoint");

       cur_state->restart();

       assert(cur_state->is_running(), "safepoint state has not been reset");

     }

     RuntimeService::record_safepoint_end();

     // Release threads lock, so threads can be created/destroyed again. It will also starts all threads

     // blocked in signal_thread_blocked

     Threads_lock->unlock();

   }

 #if INCLUDE_ALL_GCS

   // If there are any concurrent GC threads resume them.

   if (UseConcMarkSweepGC) {

     ConcurrentMarkSweepThread::desynchronize(false);

   } else if (UseG1GC) {

     SuspendibleThreadSet::desynchronize();

   }

 #endif // INCLUDE_ALL_GCS

   // record this time so VMThread can keep track how much time has elasped

   // since last safepoint.

   _end_of_last_safepoint = os::javaTimeMillis();

 }

 bool SafepointSynchronize::is_cleanup_needed() {

   // Need a safepoint if some inline cache buffers is non-empty

   if (!InlineCacheBuffer::is_empty()) return true;

   return false;

 }

 // Various cleaning tasks that should be done periodically at safepoints

 void SafepointSynchronize::do_cleanup_tasks() {

   {

     TraceTime t1("deflating idle monitors", TraceSafepointCleanupTime);

     ObjectSynchronizer::deflate_idle_monitors();

   }

   {

     TraceTime t2("updating inline caches", TraceSafepointCleanupTime);

     InlineCacheBuffer::update_inline_caches();

   }

   {

     TraceTime t3("compilation policy safepoint handler", TraceSafepointCleanupTime);

     CompilationPolicy::policy()->do_safepoint_work();

   }

   {

     TraceTime t4("mark nmethods", TraceSafepointCleanupTime);

     NMethodSweeper::mark_active_nmethods();

   }

   if (SymbolTable::needs_rehashing()) {

     TraceTime t5("rehashing symbol table", TraceSafepointCleanupTime);

     SymbolTable::rehash_table();

   }

   if (StringTable::needs_rehashing()) {

     TraceTime t6("rehashing string table", TraceSafepointCleanupTime);

     StringTable::rehash_table();

   }

   // rotate log files?

   if (UseGCLogFileRotation) {

     gclog_or_tty->rotate_log(false);

   }

   {

     // CMS delays purging the CLDG until the beginning of the next safepoint and to

     // make sure concurrent sweep is done

     TraceTime t7("purging class loader data graph", TraceSafepointCleanupTime);

     ClassLoaderDataGraph::purge_if_needed();

   }

 }

 bool SafepointSynchronize::safepoint_safe(JavaThread *thread, JavaThreadState state) {

   switch(state) {

   case _thread_in_native:

     // native threads are safe if they have no java stack or have walkable stack

     return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable();

    // blocked threads should have already have walkable stack

   case _thread_blocked:

     assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable");

     return true;

   default:

     return false;

   }

 }

 // See if the thread is running inside a lazy critical native and

 // update the thread critical count if so.  Also set a suspend flag to

 // cause the native wrapper to return into the JVM to do the unlock

 // once the native finishes.

 void SafepointSynchronize::check_for_lazy_critical_native(JavaThread *thread, JavaThreadState state) {

   if (state == _thread_in_native &&

       thread->has_last_Java_frame() &&

       thread->frame_anchor()->walkable()) {

     // This thread might be in a critical native nmethod so look at

     // the top of the stack and increment the critical count if it

     // is.

     frame wrapper_frame = thread->last_frame();

     CodeBlob* stub_cb = wrapper_frame.cb();

     if (stub_cb != NULL &&

         stub_cb->is_nmethod() &&

         stub_cb->as_nmethod_or_null()->is_lazy_critical_native()) {

       // A thread could potentially be in a critical native across

       // more than one safepoint, so only update the critical state on

       // the first one.  When it returns it will perform the unlock.

       if (!thread->do_critical_native_unlock()) {

 #ifdef ASSERT

         if (!thread->in_critical()) {

           GC_locker::increment_debug_jni_lock_count();

         }

 #endif

         thread->enter_critical();

         // Make sure the native wrapper calls back on return to

         // perform the needed critical unlock.

         thread->set_critical_native_unlock();

       }

     }

   }

 }

 // -------------------------------------------------------------------------------------------------------

 // Implementation of Safepoint callback point

 void SafepointSynchronize::block(JavaThread *thread) {

   assert(thread != NULL, "thread must be set");

   assert(thread->is_Java_thread(), "not a Java thread");

   // Threads shouldn't block if they are in the middle of printing, but...

   ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id());

   // Only bail from the block() call if the thread is gone from the

   // thread list; starting to exit should still block.

   if (thread->is_terminated()) {

      // block current thread if we come here from native code when VM is gone

      thread->block_if_vm_exited();

      // otherwise do nothing

      return;

   }

   JavaThreadState state = thread->thread_state();

   thread->frame_anchor()->make_walkable(thread);

   // Check that we have a valid thread_state at this point

   switch(state) {

     case _thread_in_vm_trans:

     case _thread_in_Java:        // From compiled code

       // We are highly likely to block on the Safepoint_lock. In order to avoid blocking in this case,

       // we pretend we are still in the VM.

       thread->set_thread_state(_thread_in_vm);

       if (is_synchronizing()) {

          Atomic::inc (&TryingToBlock) ;

       }

       // We will always be holding the Safepoint_lock when we are examine the state

       // of a thread. Hence, the instructions between the Safepoint_lock->lock() and

       // Safepoint_lock->unlock() are happening atomic with regards to the safepoint code

       Safepoint_lock->lock_without_safepoint_check();

       if (is_synchronizing()) {

         // Decrement the number of threads to wait for and signal vm thread

         assert(_waiting_to_block > 0, "sanity check");

         _waiting_to_block--;

         thread->safepoint_state()->set_has_called_back(true);

         DEBUG_ONLY(thread->set_visited_for_critical_count(true));

         if (thread->in_critical()) {

           // Notice that this thread is in a critical section

           increment_jni_active_count();

         }

         // Consider (_waiting_to_block < 2) to pipeline the wakeup of the VM thread

         if (_waiting_to_block == 0) {

           Safepoint_lock->notify_all();

         }

       }

       // We transition the thread to state _thread_blocked here, but

       // we can't do our usual check for external suspension and then

       // self-suspend after the lock_without_safepoint_check() call

       // below because we are often called during transitions while

       // we hold different locks. That would leave us suspended while

       // holding a resource which results in deadlocks.

       thread->set_thread_state(_thread_blocked);

       Safepoint_lock->unlock();

       // We now try to acquire the threads lock. Since this lock is hold by the VM thread during

       // the entire safepoint, the threads will all line up here during the safepoint.

       Threads_lock->lock_without_safepoint_check();

       // restore original state. This is important if the thread comes from compiled code, so it

       // will continue to execute with the _thread_in_Java state.

       thread->set_thread_state(state);

       Threads_lock->unlock();

       break;

     case _thread_in_native_trans:

     case _thread_blocked_trans:

     case _thread_new_trans:

       if (thread->safepoint_state()->type() == ThreadSafepointState::_call_back) {

         thread->print_thread_state();

         fatal("Deadlock in safepoint code.  "

               "Should have called back to the VM before blocking.");

       }

       // We transition the thread to state _thread_blocked here, but

       // we can't do our usual check for external suspension and then

       // self-suspend after the lock_without_safepoint_check() call

       // below because we are often called during transitions while

       // we hold different locks. That would leave us suspended while

       // holding a resource which results in deadlocks.

       thread->set_thread_state(_thread_blocked);

       // It is not safe to suspend a thread if we discover it is in _thread_in_native_trans. Hence,

       // the safepoint code might still be waiting for it to block. We need to change the state here,

       // so it can see that it is at a safepoint.

       // Block until the safepoint operation is completed.

       Threads_lock->lock_without_safepoint_check();

       // Restore state

       thread->set_thread_state(state);

       Threads_lock->unlock();

       break;

     default:

      fatal(err_msg("Illegal threadstate encountered: %d", state));

   }

   // Check for pending. async. exceptions or suspends - except if the

   // thread was blocked inside the VM. has_special_runtime_exit_condition()

   // is called last since it grabs a lock and we only want to do that when

   // we must.

   //

   // Note: we never deliver an async exception at a polling point as the

   // compiler may not have an exception handler for it. The polling

   // code will notice the async and deoptimize and the exception will

   // be delivered. (Polling at a return point is ok though). Sure is

   // a lot of bother for a deprecated feature...

   //

   // We don't deliver an async exception if the thread state is

   // _thread_in_native_trans so JNI functions won't be called with

   // a surprising pending exception. If the thread state is going back to java,

   // async exception is checked in check_special_condition_for_native_trans().

   if (state != _thread_blocked_trans &&

       state != _thread_in_vm_trans &&

       thread->has_special_runtime_exit_condition()) {

     thread->handle_special_runtime_exit_condition(

       !thread->is_at_poll_safepoint() && (state != _thread_in_native_trans));

   }

 }

 // ------------------------------------------------------------------------------------------------------

 // Exception handlers

 #ifndef PRODUCT

 #ifdef SPARC

 #ifdef _LP64

 #define PTR_PAD ""

 #else

 #define PTR_PAD "        "

 #endif

 static void print_ptrs(intptr_t oldptr, intptr_t newptr, bool wasoop) {

   bool is_oop = newptr ? (cast_to_oop(newptr))->is_oop() : false;

   tty->print_cr(PTR_FORMAT PTR_PAD " %s %c " PTR_FORMAT PTR_PAD " %s %s",

                 oldptr, wasoop?"oop":"   ", oldptr == newptr ? ' ' : '!',

                 newptr, is_oop?"oop":"   ", (wasoop && !is_oop) ? "STALE" : ((wasoop==false&&is_oop==false&&oldptr !=newptr)?"STOMP":"     "));

 }

 static void print_longs(jlong oldptr, jlong newptr, bool wasoop) {

   bool is_oop = newptr ? (cast_to_oop(newptr))->is_oop() : false;

   tty->print_cr(PTR64_FORMAT " %s %c " PTR64_FORMAT " %s %s",

                 oldptr, wasoop?"oop":"   ", oldptr == newptr ? ' ' : '!',

                 newptr, is_oop?"oop":"   ", (wasoop && !is_oop) ? "STALE" : ((wasoop==false&&is_oop==false&&oldptr !=newptr)?"STOMP":"     "));

 }

 static void print_me(intptr_t *new_sp, intptr_t *old_sp, bool *was_oops) {

 #ifdef _LP64

   tty->print_cr("--------+------address-----+------before-----------+-------after----------+");

   const int incr = 1;           // Increment to skip a long, in units of intptr_t

 #else

   tty->print_cr("--------+--address-+------before-----------+-------after----------+");

   const int incr = 2;           // Increment to skip a long, in units of intptr_t

 #endif

   tty->print_cr("---SP---|");

   for( int i=0; i<16; i++ ) {

     tty->print("blob %c%d |"PTR_FORMAT" ","LO"[i>>3],i&7,new_sp); print_ptrs(*old_sp++,*new_sp++,*was_oops++); }

   tty->print_cr("--------|");

   for( int i1=0; i1<frame::memory_parameter_word_sp_offset-16; i1++ ) {

     tty->print("argv pad|"PTR_FORMAT" ",new_sp); print_ptrs(*old_sp++,*new_sp++,*was_oops++); }

   tty->print("     pad|"PTR_FORMAT" ",new_sp); print_ptrs(*old_sp++,*new_sp++,*was_oops++);

   tty->print_cr("--------|");

   tty->print(" G1     |"PTR_FORMAT" ",new_sp); print_longs(*(jlong*)old_sp,*(jlong*)new_sp,was_oops[incr-1]); old_sp += incr; new_sp += incr; was_oops += incr;

   tty->print(" G3     |"PTR_FORMAT" ",new_sp); print_longs(*(jlong*)old_sp,*(jlong*)new_sp,was_oops[incr-1]); old_sp += incr; new_sp += incr; was_oops += incr;

   tty->print(" G4     |"PTR_FORMAT" ",new_sp); print_longs(*(jlong*)old_sp,*(jlong*)new_sp,was_oops[incr-1]); old_sp += incr; new_sp += incr; was_oops += incr;

   tty->print(" G5     |"PTR_FORMAT" ",new_sp); print_longs(*(jlong*)old_sp,*(jlong*)new_sp,was_oops[incr-1]); old_sp += incr; new_sp += incr; was_oops += incr;

   tty->print_cr(" FSR    |"PTR_FORMAT" "PTR64_FORMAT"       "PTR64_FORMAT,new_sp,*(jlong*)old_sp,*(jlong*)new_sp);

   old_sp += incr; new_sp += incr; was_oops += incr;

   // Skip the floats

   tty->print_cr("--Float-|"PTR_FORMAT,new_sp);

   tty->print_cr("---FP---|");

   old_sp += incr*32;  new_sp += incr*32;  was_oops += incr*32;

   for( int i2=0; i2<16; i2++ ) {

     tty->print("call %c%d |"PTR_FORMAT" ","LI"[i2>>3],i2&7,new_sp); print_ptrs(*old_sp++,*new_sp++,*was_oops++); }

   tty->cr();

 }

 #endif  // SPARC

 #endif  // PRODUCT

 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) {

   assert(thread->is_Java_thread(), "polling reference encountered by VM thread");

   assert(thread->thread_state() == _thread_in_Java, "should come from Java code");

   assert(SafepointSynchronize::is_synchronizing(), "polling encountered outside safepoint synchronization");

   // Uncomment this to get some serious before/after printing of the

   // Sparc safepoint-blob frame structure.

   /*

   intptr_t* sp = thread->last_Java_sp();

   intptr_t stack_copy[150];

   for( int i=0; i<150; i++ ) stack_copy[i] = sp[i];

   bool was_oops[150];

   for( int i=0; i<150; i++ )

     was_oops[i] = stack_copy[i] ? ((oop)stack_copy[i])->is_oop() : false;

   */

   if (ShowSafepointMsgs) {

     tty->print("handle_polling_page_exception: ");

   }

   if (PrintSafepointStatistics) {

     inc_page_trap_count();

   }

   ThreadSafepointState* state = thread->safepoint_state();

   state->handle_polling_page_exception();

   // print_me(sp,stack_copy,was_oops);

 }

 void SafepointSynchronize::print_safepoint_timeout(SafepointTimeoutReason reason) {

   if (!timeout_error_printed) {

     timeout_error_printed = true;

     // Print out the thread infor which didn't reach the safepoint for debugging

     // purposes (useful when there are lots of threads in the debugger).

     tty->cr();

     tty->print_cr("# SafepointSynchronize::begin: Timeout detected:");

     if (reason ==  _spinning_timeout) {

       tty->print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint.");

     } else if (reason == _blocking_timeout) {

       tty->print_cr("# SafepointSynchronize::begin: Timed out while waiting for threads to stop.");

     }

     tty->print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:");

     ThreadSafepointState *cur_state;

     ResourceMark rm;

     for(JavaThread *cur_thread = Threads::first(); cur_thread;

         cur_thread = cur_thread->next()) {

       cur_state = cur_thread->safepoint_state();

       if (cur_thread->thread_state() != _thread_blocked &&

           ((reason == _spinning_timeout && cur_state->is_running()) ||

            (reason == _blocking_timeout && !cur_state->has_called_back()))) {

         tty->print("# ");

         cur_thread->print();

         tty->cr();

       }

     }

     tty->print_cr("# SafepointSynchronize::begin: (End of list)");

   }

   // To debug the long safepoint, specify both DieOnSafepointTimeout &

   // ShowMessageBoxOnError.

   if (DieOnSafepointTimeout) {

     char msg[1024];

     VM_Operation *op = VMThread::vm_operation();

     sprintf(msg, "Safepoint sync time longer than " INTX_FORMAT "ms detected when executing %s.",

             SafepointTimeoutDelay,

             op != NULL ? op->name() : "no vm operation");

     fatal(msg);

   }

 }

 // -------------------------------------------------------------------------------------------------------

 // Implementation of ThreadSafepointState

 ThreadSafepointState::ThreadSafepointState(JavaThread *thread) {

   _thread = thread;

   _type   = _running;

   _has_called_back = false;

   _at_poll_safepoint = false;

 }

 void ThreadSafepointState::create(JavaThread *thread) {

   ThreadSafepointState *state = new ThreadSafepointState(thread);

   thread->set_safepoint_state(state);

 }

 void ThreadSafepointState::destroy(JavaThread *thread) {

   if (thread->safepoint_state()) {

     delete(thread->safepoint_state());

     thread->set_safepoint_state(NULL);

   }

 }

 void ThreadSafepointState::examine_state_of_thread() {

   assert(is_running(), "better be running or just have hit safepoint poll");

   JavaThreadState state = _thread->thread_state();

   // Save the state at the start of safepoint processing.

   _orig_thread_state = state;

   // Check for a thread that is suspended. Note that thread resume tries

   // to grab the Threads_lock which we own here, so a thread cannot be

   // resumed during safepoint synchronization.

   // We check to see if this thread is suspended without locking to

   // avoid deadlocking with a third thread that is waiting for this

   // thread to be suspended. The third thread can notice the safepoint

   // that we're trying to start at the beginning of its SR_lock->wait()

   // call. If that happens, then the third thread will block on the

   // safepoint while still holding the underlying SR_lock. We won't be

   // able to get the SR_lock and we'll deadlock.

   //

   // We don't need to grab the SR_lock here for two reasons:

   // 1) The suspend flags are both volatile and are set with an

   //    Atomic::cmpxchg() call so we should see the suspended

   //    state right away.

   // 2) We're being called from the safepoint polling loop; if

   //    we don't see the suspended state on this iteration, then

   //    we'll come around again.

   //

   bool is_suspended = _thread->is_ext_suspended();

   if (is_suspended) {

     roll_forward(_at_safepoint);

     return;

   }

   // Some JavaThread states have an initial safepoint state of

   // running, but are actually at a safepoint. We will happily

   // agree and update the safepoint state here.

   if (SafepointSynchronize::safepoint_safe(_thread, state)) {

     SafepointSynchronize::check_for_lazy_critical_native(_thread, state);

     roll_forward(_at_safepoint);

     return;

   }

   if (state == _thread_in_vm) {

     roll_forward(_call_back);

     return;

   }

   // All other thread states will continue to run until they

   // transition and self-block in state _blocked

   // Safepoint polling in compiled code causes the Java threads to do the same.

   // Note: new threads may require a malloc so they must be allowed to finish

   assert(is_running(), "examine_state_of_thread on non-running thread");

   return;

 }

 // Returns true is thread could not be rolled forward at present position.

 void ThreadSafepointState::roll_forward(suspend_type type) {

   _type = type;

   switch(_type) {

     case _at_safepoint:

       SafepointSynchronize::signal_thread_at_safepoint();

       DEBUG_ONLY(_thread->set_visited_for_critical_count(true));

       if (_thread->in_critical()) {

         // Notice that this thread is in a critical section

         SafepointSynchronize::increment_jni_active_count();

       }

       break;

     case _call_back:

       set_has_called_back(false);

       break;

     case _running:

     default:

       ShouldNotReachHere();

   }

 }

 void ThreadSafepointState::restart() {

   switch(type()) {

     case _at_safepoint:

     case _call_back:

       break;

     case _running:

     default:

        tty->print_cr("restart thread "INTPTR_FORMAT" with state %d",

                       _thread, _type);

        _thread->print();

       ShouldNotReachHere();

   }

   _type = _running;

   set_has_called_back(false);

 }

 void ThreadSafepointState::print_on(outputStream *st) const {

   const char *s;

   switch(_type) {

     case _running                : s = "_running";              break;

     case _at_safepoint           : s = "_at_safepoint";         break;

     case _call_back              : s = "_call_back";            break;

     default:

       ShouldNotReachHere();

   }

   st->print_cr("Thread: " INTPTR_FORMAT

               "  [0x%2x] State: %s _has_called_back %d _at_poll_safepoint %d",

                _thread, _thread->osthread()->thread_id(), s, _has_called_back,

                _at_poll_safepoint);

   _thread->print_thread_state_on(st);

 }

 // ---------------------------------------------------------------------------------------------------------------------

 // Block the thread at the safepoint poll or poll return.

 void ThreadSafepointState::handle_polling_page_exception() {

   // Check state.  block() will set thread state to thread_in_vm which will

   // cause the safepoint state _type to become _call_back.

   assert(type() == ThreadSafepointState::_running,

          "polling page exception on thread not running state");

   // Step 1: Find the nmethod from the return address

   if (ShowSafepointMsgs && Verbose) {

     tty->print_cr("Polling page exception at " INTPTR_FORMAT, thread()->saved_exception_pc());

   }

   address real_return_addr = thread()->saved_exception_pc();

   CodeBlob *cb = CodeCache::find_blob(real_return_addr);

   assert(cb != NULL && cb->is_nmethod(), "return address should be in nmethod");

   nmethod* nm = (nmethod*)cb;

   // Find frame of caller

   frame stub_fr = thread()->last_frame();

   CodeBlob* stub_cb = stub_fr.cb();

   assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub");

   RegisterMap map(thread(), true);

   frame caller_fr = stub_fr.sender(&map);

   // Should only be poll_return or poll

   assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" );

   // This is a poll immediately before a return. The exception handling code

   // has already had the effect of causing the return to occur, so the execution

   // will continue immediately after the call. In addition, the oopmap at the

   // return point does not mark the return value as an oop (if it is), so

   // it needs a handle here to be updated.

   if( nm->is_at_poll_return(real_return_addr) ) {

     // See if return type is an oop.

     bool return_oop = nm->method()->is_returning_oop();

     Handle return_value;

     if (return_oop) {

       // The oop result has been saved on the stack together with all

       // the other registers. In order to preserve it over GCs we need

       // to keep it in a handle.

       oop result = caller_fr.saved_oop_result(&map);

       assert(result == NULL || result->is_oop(), "must be oop");

       return_value = Handle(thread(), result);

       assert(Universe::heap()->is_in_or_null(result), "must be heap pointer");

     }

     // Block the thread

     SafepointSynchronize::block(thread());

     // restore oop result, if any

     if (return_oop) {

       caller_fr.set_saved_oop_result(&map, return_value());

     }

   }

   // This is a safepoint poll. Verify the return address and block.

   else {

     set_at_poll_safepoint(true);

     // verify the blob built the "return address" correctly

     assert(real_return_addr == caller_fr.pc(), "must match");

     // Block the thread

     SafepointSynchronize::block(thread());

     set_at_poll_safepoint(false);

     // If we have a pending async exception deoptimize the frame

     // as otherwise we may never deliver it.

     if (thread()->has_async_condition()) {

       ThreadInVMfromJavaNoAsyncException __tiv(thread());

       Deoptimization::deoptimize_frame(thread(), caller_fr.id());

     }

     // If an exception has been installed we must check for a pending deoptimization

     // Deoptimize frame if exception has been thrown.

     if (thread()->has_pending_exception() ) {

       RegisterMap map(thread(), true);

       frame caller_fr = stub_fr.sender(&map);

       if (caller_fr.is_deoptimized_frame()) {

         // The exception patch will destroy registers that are still

         // live and will be needed during deoptimization. Defer the

         // Async exception should have defered the exception until the

         // next safepoint which will be detected when we get into

         // the interpreter so if we have an exception now things

         // are messed up.

         fatal("Exception installed and deoptimization is pending");

       }

     }

   }

 }

 //

 //                     Statistics & Instrumentations

 //

 SafepointSynchronize::SafepointStats*  SafepointSynchronize::_safepoint_stats = NULL;

 jlong  SafepointSynchronize::_safepoint_begin_time = 0;

 int    SafepointSynchronize::_cur_stat_index = 0;

 julong SafepointSynchronize::_safepoint_reasons[VM_Operation::VMOp_Terminating];

 julong SafepointSynchronize::_coalesced_vmop_count = 0;

 jlong  SafepointSynchronize::_max_sync_time = 0;

 jlong  SafepointSynchronize::_max_vmop_time = 0;

 float  SafepointSynchronize::_ts_of_current_safepoint = 0.0f;

 static jlong  cleanup_end_time = 0;

 static bool   need_to_track_page_armed_status = false;

 static bool   init_done = false;

 // Helper method to print the header.

 static void print_header() {

   tty->print("         vmop                    "

              "[threads: total initially_running wait_to_block]    ");

   tty->print("[time: spin block sync cleanup vmop] ");

   // no page armed status printed out if it is always armed.

   if (need_to_track_page_armed_status) {

     tty->print("page_armed ");

   }

   tty->print_cr("page_trap_count");

 }

 void SafepointSynchronize::deferred_initialize_stat() {

   if (init_done) return;

   if (PrintSafepointStatisticsCount <= 0) {

     fatal("Wrong PrintSafepointStatisticsCount");

   }

   // If PrintSafepointStatisticsTimeout is specified, the statistics data will

   // be printed right away, in which case, _safepoint_stats will regress to

   // a single element array. Otherwise, it is a circular ring buffer with default

   // size of PrintSafepointStatisticsCount.

   int stats_array_size;

   if (PrintSafepointStatisticsTimeout > 0) {

     stats_array_size = 1;

     PrintSafepointStatistics = true;

   } else {

     stats_array_size = PrintSafepointStatisticsCount;

   }

   _safepoint_stats = (SafepointStats*)os::malloc(stats_array_size

                                                  * sizeof(SafepointStats), mtInternal);

   guarantee(_safepoint_stats != NULL,

             "not enough memory for safepoint instrumentation data");

   if (UseCompilerSafepoints && DeferPollingPageLoopCount >= 0) {

     need_to_track_page_armed_status = true;

   }

   init_done = true;

 }

 void SafepointSynchronize::begin_statistics(int nof_threads, int nof_running) {

   assert(init_done, "safepoint statistics array hasn't been initialized");

   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];

   spstat->_time_stamp = _ts_of_current_safepoint;

   VM_Operation *op = VMThread::vm_operation();

   spstat->_vmop_type = (op != NULL ? op->type() : -1);

   if (op != NULL) {

     _safepoint_reasons[spstat->_vmop_type]++;

   }

   spstat->_nof_total_threads = nof_threads;

   spstat->_nof_initial_running_threads = nof_running;

   spstat->_nof_threads_hit_page_trap = 0;

   // Records the start time of spinning. The real time spent on spinning

   // will be adjusted when spin is done. Same trick is applied for time

   // spent on waiting for threads to block.

   if (nof_running != 0) {

     spstat->_time_to_spin = os::javaTimeNanos();

   }  else {

     spstat->_time_to_spin = 0;

   }

 }

 void SafepointSynchronize::update_statistics_on_spin_end() {

   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];

   jlong cur_time = os::javaTimeNanos();

   spstat->_nof_threads_wait_to_block = _waiting_to_block;

   if (spstat->_nof_initial_running_threads != 0) {

     spstat->_time_to_spin = cur_time - spstat->_time_to_spin;

   }

   if (need_to_track_page_armed_status) {

     spstat->_page_armed = (PageArmed == 1);

   }

   // Records the start time of waiting for to block. Updated when block is done.

   if (_waiting_to_block != 0) {

     spstat->_time_to_wait_to_block = cur_time;

   } else {

     spstat->_time_to_wait_to_block = 0;

   }

 }

 void SafepointSynchronize::update_statistics_on_sync_end(jlong end_time) {

   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];

   if (spstat->_nof_threads_wait_to_block != 0) {

     spstat->_time_to_wait_to_block = end_time -

       spstat->_time_to_wait_to_block;

   }

   // Records the end time of sync which will be used to calculate the total

   // vm operation time. Again, the real time spending in syncing will be deducted

   // from the start of the sync time later when end_statistics is called.

   spstat->_time_to_sync = end_time - _safepoint_begin_time;

   if (spstat->_time_to_sync > _max_sync_time) {

     _max_sync_time = spstat->_time_to_sync;

   }

   spstat->_time_to_do_cleanups = end_time;

 }

 void SafepointSynchronize::update_statistics_on_cleanup_end(jlong end_time) {

   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];

   // Record how long spent in cleanup tasks.

   spstat->_time_to_do_cleanups = end_time - spstat->_time_to_do_cleanups;

   cleanup_end_time = end_time;

 }

 void SafepointSynchronize::end_statistics(jlong vmop_end_time) {

   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];

   // Update the vm operation time.

   spstat->_time_to_exec_vmop = vmop_end_time -  cleanup_end_time;

   if (spstat->_time_to_exec_vmop > _max_vmop_time) {

     _max_vmop_time = spstat->_time_to_exec_vmop;

   }

   // Only the sync time longer than the specified

   // PrintSafepointStatisticsTimeout will be printed out right away.

   // By default, it is -1 meaning all samples will be put into the list.

   if ( PrintSafepointStatisticsTimeout > 0) {

     if (spstat->_time_to_sync > PrintSafepointStatisticsTimeout * MICROUNITS) {

       print_statistics();

     }

   } else {

     // The safepoint statistics will be printed out when the _safepoin_stats

     // array fills up.

     if (_cur_stat_index == PrintSafepointStatisticsCount - 1) {

       print_statistics();

       _cur_stat_index = 0;

     } else {

       _cur_stat_index++;

     }

   }

 }

 void SafepointSynchronize::print_statistics() {

   SafepointStats* sstats = _safepoint_stats;

   for (int index = 0; index <= _cur_stat_index; index++) {

     if (index % 30 == 0) {

       print_header();

     }

     sstats = &_safepoint_stats[index];

     tty->print("%.3f: ", sstats->_time_stamp);

     tty->print("%-26s       ["

                INT32_FORMAT_W(8)INT32_FORMAT_W(11)INT32_FORMAT_W(15)

                "    ]    ",

                sstats->_vmop_type == -1 ? "no vm operation" :

                VM_Operation::name(sstats->_vmop_type),

                sstats->_nof_total_threads,

                sstats->_nof_initial_running_threads,

                sstats->_nof_threads_wait_to_block);

     // "/ MICROUNITS " is to convert the unit from nanos to millis.

     tty->print("  ["

                INT64_FORMAT_W(6)INT64_FORMAT_W(6)

                INT64_FORMAT_W(6)INT64_FORMAT_W(6)

                INT64_FORMAT_W(6)"    ]  ",

                sstats->_time_to_spin / MICROUNITS,

                sstats->_time_to_wait_to_block / MICROUNITS,

                sstats->_time_to_sync / MICROUNITS,

                sstats->_time_to_do_cleanups / MICROUNITS,

                sstats->_time_to_exec_vmop / MICROUNITS);

     if (need_to_track_page_armed_status) {

       tty->print(INT32_FORMAT"         ", sstats->_page_armed);

     }

     tty->print_cr(INT32_FORMAT"   ", sstats->_nof_threads_hit_page_trap);

   }

 }

 // This method will be called when VM exits. It will first call

 // print_statistics to print out the rest of the sampling.  Then

 // it tries to summarize the sampling.

 void SafepointSynchronize::print_stat_on_exit() {

   if (_safepoint_stats == NULL) return;

   SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];

   // During VM exit, end_statistics may not get called and in that

   // case, if the sync time is less than PrintSafepointStatisticsTimeout,

   // don't print it out.

   // Approximate the vm op time.

   _safepoint_stats[_cur_stat_index]._time_to_exec_vmop =

     os::javaTimeNanos() - cleanup_end_time;

   if ( PrintSafepointStatisticsTimeout < 0 ||

        spstat->_time_to_sync > PrintSafepointStatisticsTimeout * MICROUNITS) {

     print_statistics();

   }

   tty->cr();

   // Print out polling page sampling status.

   if (!need_to_track_page_armed_status) {

     if (UseCompilerSafepoints) {

       tty->print_cr("Polling page always armed");

     }

   } else {

     tty->print_cr("Defer polling page loop count = %d\n",

                  DeferPollingPageLoopCount);

   }

   for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) {

     if (_safepoint_reasons[index] != 0) {

       tty->print_cr("%-26s"UINT64_FORMAT_W(10), VM_Operation::name(index),

                     _safepoint_reasons[index]);

     }

   }

   tty->print_cr(UINT64_FORMAT_W(5)" VM operations coalesced during safepoint",

                 _coalesced_vmop_count);

   tty->print_cr("Maximum sync time  "INT64_FORMAT_W(5)" ms",

                 _max_sync_time / MICROUNITS);

   tty->print_cr("Maximum vm operation time (except for Exit VM operation)  "

                 INT64_FORMAT_W(5)" ms",

                 _max_vmop_time / MICROUNITS);

 }

 // ------------------------------------------------------------------------------------------------

 // Non-product code

 #ifndef PRODUCT

 void SafepointSynchronize::print_state() {

   if (_state == _not_synchronized) {

     tty->print_cr("not synchronized");

   } else if (_state == _synchronizing || _state == _synchronized) {

     tty->print_cr("State: %s", (_state == _synchronizing) ? "synchronizing" :

                   "synchronized");

     for(JavaThread *cur = Threads::first(); cur; cur = cur->next()) {

        cur->safepoint_state()->print();

     }

   }

 }

 void SafepointSynchronize::safepoint_msg(const char* format, ...) {

   if (ShowSafepointMsgs) {

     va_list ap;

     va_start(ap, format);

     tty->vprint_cr(format, ap);

     va_end(ap);

   }

 }

 #endif // !PRODUCT