vm/runtime/thread.cpp

/*
 * Copyright (c) 1997, 2010, 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.
 *
 */

#include "precompiled.hpp"
#include "classfile/classLoader.hpp"
#include "classfile/javaClasses.hpp"
#include "classfile/systemDictionary.hpp"
#include "classfile/vmSymbols.hpp"
#include "code/scopeDesc.hpp"
#include "compiler/compileBroker.hpp"
#include "interpreter/interpreter.hpp"
#include "interpreter/linkResolver.hpp"
#include "memory/oopFactory.hpp"
#include "memory/universe.inline.hpp"
#include "oops/instanceKlass.hpp"
#include "oops/objArrayOop.hpp"
#include "oops/oop.inline.hpp"
#include "oops/symbolOop.hpp"
#include "prims/jvm_misc.hpp"
#include "prims/jvmtiExport.hpp"
#include "prims/jvmtiThreadState.hpp"
#include "prims/privilegedStack.hpp"
#include "runtime/aprofiler.hpp"
#include "runtime/arguments.hpp"
#include "runtime/biasedLocking.hpp"
#include "runtime/deoptimization.hpp"
#include "runtime/fprofiler.hpp"
#include "runtime/frame.inline.hpp"
#include "runtime/init.hpp"
#include "runtime/interfaceSupport.hpp"
#include "runtime/java.hpp"
#include "runtime/javaCalls.hpp"
#include "runtime/jniPeriodicChecker.hpp"
#include "runtime/memprofiler.hpp"
#include "runtime/mutexLocker.hpp"
#include "runtime/objectMonitor.hpp"
#include "runtime/osThread.hpp"
#include "runtime/safepoint.hpp"
#include "runtime/sharedRuntime.hpp"
#include "runtime/statSampler.hpp"
#include "runtime/stubRoutines.hpp"
#include "runtime/task.hpp"
#include "runtime/threadCritical.hpp"
#include "runtime/threadLocalStorage.hpp"
#include "runtime/vframe.hpp"
#include "runtime/vframeArray.hpp"
#include "runtime/vframe_hp.hpp"
#include "runtime/vmThread.hpp"
#include "runtime/vm_operations.hpp"
#include "services/attachListener.hpp"
#include "services/management.hpp"
#include "services/threadService.hpp"
#include "utilities/defaultStream.hpp"
#include "utilities/dtrace.hpp"
#include "utilities/events.hpp"
#include "utilities/preserveException.hpp"
#ifdef TARGET_OS_FAMILY_linux
# include "os_linux.inline.hpp"
# include "thread_linux.inline.hpp"
#endif
#ifdef TARGET_OS_FAMILY_solaris
# include "os_solaris.inline.hpp"
# include "thread_solaris.inline.hpp"
#endif
#ifdef TARGET_OS_FAMILY_windows
# include "os_windows.inline.hpp"
# include "thread_windows.inline.hpp"
#endif
#ifndef SERIALGC
#include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
#include "gc_implementation/g1/concurrentMarkThread.inline.hpp"
#include "gc_implementation/parallelScavenge/pcTasks.hpp"
#endif
#ifdef COMPILER1
#include "c1/c1_Compiler.hpp"
#endif
#ifdef COMPILER2
#include "opto/c2compiler.hpp"
#include "opto/idealGraphPrinter.hpp"
#endif

#ifdef DTRACE_ENABLED

// Only bother with this argument setup if dtrace is available

HS_DTRACE_PROBE_DECL(hotspot, vm__init__begin);
HS_DTRACE_PROBE_DECL(hotspot, vm__init__end);
HS_DTRACE_PROBE_DECL5(hotspot, thread__start, char*, intptr_t,
  intptr_t, intptr_t, bool);
HS_DTRACE_PROBE_DECL5(hotspot, thread__stop, char*, intptr_t,
  intptr_t, intptr_t, bool);

#define DTRACE_THREAD_PROBE(probe, javathread)                             \
  {                                                                        \
    ResourceMark rm(this);                                                 \
    int len = 0;                                                           \
    const char* name = (javathread)->get_thread_name();                    \
    len = strlen(name);                                                    \
    HS_DTRACE_PROBE5(hotspot, thread__##probe,                             \
      name, len,                                                           \
      java_lang_Thread::thread_id((javathread)->threadObj()),              \
      (javathread)->osthread()->thread_id(),                               \
      java_lang_Thread::is_daemon((javathread)->threadObj()));             \
  }

#else //  ndef DTRACE_ENABLED

#define DTRACE_THREAD_PROBE(probe, javathread)

#endif // ndef DTRACE_ENABLED

// Class hierarchy
// - Thread
//   - VMThread
//   - WatcherThread
//   - ConcurrentMarkSweepThread
//   - JavaThread
//     - CompilerThread

// ======= Thread ========

// Support for forcing alignment of thread objects for biased locking
void* Thread::operator new(size_t size) {
  if (UseBiasedLocking) {
    const int alignment = markOopDesc::biased_lock_alignment;
    size_t aligned_size = size + (alignment - sizeof(intptr_t));
    void* real_malloc_addr = CHeapObj::operator new(aligned_size);
    void* aligned_addr     = (void*) align_size_up((intptr_t) real_malloc_addr, alignment);
    assert(((uintptr_t) aligned_addr + (uintptr_t) size) <=
           ((uintptr_t) real_malloc_addr + (uintptr_t) aligned_size),
           "JavaThread alignment code overflowed allocated storage");
    if (TraceBiasedLocking) {
      if (aligned_addr != real_malloc_addr)
        tty->print_cr("Aligned thread " INTPTR_FORMAT " to " INTPTR_FORMAT,
                      real_malloc_addr, aligned_addr);
    }
    ((Thread*) aligned_addr)->_real_malloc_address = real_malloc_addr;
    return aligned_addr;
  } else {
    return CHeapObj::operator new(size);
  }
}

void Thread::operator delete(void* p) {
  if (UseBiasedLocking) {
    void* real_malloc_addr = ((Thread*) p)->_real_malloc_address;
    CHeapObj::operator delete(real_malloc_addr);
  } else {
    CHeapObj::operator delete(p);
  }
}


// Base class for all threads: VMThread, WatcherThread, ConcurrentMarkSweepThread,
// JavaThread


Thread::Thread() {
  // stack
  _stack_base   = NULL;
  _stack_size   = 0;
  _self_raw_id  = 0;
  _lgrp_id      = -1;
  _osthread     = NULL;

  // allocated data structures
  set_resource_area(new ResourceArea());
  set_handle_area(new HandleArea(NULL));
  set_active_handles(NULL);
  set_free_handle_block(NULL);
  set_last_handle_mark(NULL);
  set_osthread(NULL);

  // This initial value ==> never claimed.
  _oops_do_parity = 0;

  // the handle mark links itself to last_handle_mark
  new HandleMark(this);

  // plain initialization
  debug_only(_owned_locks = NULL;)
  debug_only(_allow_allocation_count = 0;)
  NOT_PRODUCT(_allow_safepoint_count = 0;)
  NOT_PRODUCT(_skip_gcalot = false;)
  CHECK_UNHANDLED_OOPS_ONLY(_gc_locked_out_count = 0;)
  _jvmti_env_iteration_count = 0;
  _vm_operation_started_count = 0;
  _vm_operation_completed_count = 0;
  _current_pending_monitor = NULL;
  _current_pending_monitor_is_from_java = true;
  _current_waiting_monitor = NULL;
  _num_nested_signal = 0;
  omFreeList = NULL ;
  omFreeCount = 0 ;
  omFreeProvision = 32 ;
  omInUseList = NULL ;
  omInUseCount = 0 ;

  _SR_lock = new Monitor(Mutex::suspend_resume, "SR_lock", true);
  _suspend_flags = 0;

  // thread-specific hashCode stream generator state - Marsaglia shift-xor form
  _hashStateX = os::random() ;
  _hashStateY = 842502087 ;
  _hashStateZ = 0x8767 ;    // (int)(3579807591LL & 0xffff) ;
  _hashStateW = 273326509 ;

  _OnTrap   = 0 ;
  _schedctl = NULL ;
  _Stalled  = 0 ;
  _TypeTag  = 0x2BAD ;

  // Many of the following fields are effectively final - immutable
  // Note that nascent threads can't use the Native Monitor-Mutex
  // construct until the _MutexEvent is initialized ...
  // CONSIDER: instead of using a fixed set of purpose-dedicated ParkEvents
  // we might instead use a stack of ParkEvents that we could provision on-demand.
  // The stack would act as a cache to avoid calls to ParkEvent::Allocate()
  // and ::Release()
  _ParkEvent   = ParkEvent::Allocate (this) ;
  _SleepEvent  = ParkEvent::Allocate (this) ;
  _MutexEvent  = ParkEvent::Allocate (this) ;
  _MuxEvent    = ParkEvent::Allocate (this) ;

#ifdef CHECK_UNHANDLED_OOPS
  if (CheckUnhandledOops) {
    _unhandled_oops = new UnhandledOops(this);
  }
#endif // CHECK_UNHANDLED_OOPS
#ifdef ASSERT
  if (UseBiasedLocking) {
    assert((((uintptr_t) this) & (markOopDesc::biased_lock_alignment - 1)) == 0, "forced alignment of thread object failed");
    assert(this == _real_malloc_address ||
           this == (void*) align_size_up((intptr_t) _real_malloc_address, markOopDesc::biased_lock_alignment),
           "bug in forced alignment of thread objects");
  }
#endif /* ASSERT */
}

void Thread::initialize_thread_local_storage() {
  // Note: Make sure this method only calls
  // non-blocking operations. Otherwise, it might not work
  // with the thread-startup/safepoint interaction.

  // During Java thread startup, safepoint code should allow this
  // method to complete because it may need to allocate memory to
  // store information for the new thread.

  // initialize structure dependent on thread local storage
  ThreadLocalStorage::set_thread(this);

  // set up any platform-specific state.
  os::initialize_thread();

}

void Thread::record_stack_base_and_size() {
  set_stack_base(os::current_stack_base());
  set_stack_size(os::current_stack_size());
}


Thread::~Thread() {
  // Reclaim the objectmonitors from the omFreeList of the moribund thread.
  ObjectSynchronizer::omFlush (this) ;

  // deallocate data structures
  delete resource_area();
  // since the handle marks are using the handle area, we have to deallocated the root
  // handle mark before deallocating the thread's handle area,
  assert(last_handle_mark() != NULL, "check we have an element");
  delete last_handle_mark();
  assert(last_handle_mark() == NULL, "check we have reached the end");

  // It's possible we can encounter a null _ParkEvent, etc., in stillborn threads.
  // We NULL out the fields for good hygiene.
  ParkEvent::Release (_ParkEvent)   ; _ParkEvent   = NULL ;
  ParkEvent::Release (_SleepEvent)  ; _SleepEvent  = NULL ;
  ParkEvent::Release (_MutexEvent)  ; _MutexEvent  = NULL ;
  ParkEvent::Release (_MuxEvent)    ; _MuxEvent    = NULL ;

  delete handle_area();

  // osthread() can be NULL, if creation of thread failed.
  if (osthread() != NULL) os::free_thread(osthread());

  delete _SR_lock;

  // clear thread local storage if the Thread is deleting itself
  if (this == Thread::current()) {
    ThreadLocalStorage::set_thread(NULL);
  } else {
    // In the case where we're not the current thread, invalidate all the
    // caches in case some code tries to get the current thread or the
    // thread that was destroyed, and gets stale information.
    ThreadLocalStorage::invalidate_all();
  }
  CHECK_UNHANDLED_OOPS_ONLY(if (CheckUnhandledOops) delete unhandled_oops();)
}

// NOTE: dummy function for assertion purpose.
void Thread::run() {
  ShouldNotReachHere();
}

#ifdef ASSERT
// Private method to check for dangling thread pointer
void check_for_dangling_thread_pointer(Thread *thread) {
 assert(!thread->is_Java_thread() || Thread::current() == thread || Threads_lock->owned_by_self(),
         "possibility of dangling Thread pointer");
}
#endif


#ifndef PRODUCT
// Tracing method for basic thread operations
void Thread::trace(const char* msg, const Thread* const thread) {
  if (!TraceThreadEvents) return;
  ResourceMark rm;
  ThreadCritical tc;
  const char *name = "non-Java thread";
  int prio = -1;
  if (thread->is_Java_thread()
      && !thread->is_Compiler_thread()) {
    // The Threads_lock must be held to get information about
    // this thread but may not be in some situations when
    // tracing  thread events.
    bool release_Threads_lock = false;
    if (!Threads_lock->owned_by_self()) {
      Threads_lock->lock();
      release_Threads_lock = true;
    }
    JavaThread* jt = (JavaThread *)thread;
    name = (char *)jt->get_thread_name();
    oop thread_oop = jt->threadObj();
    if (thread_oop != NULL) {
      prio = java_lang_Thread::priority(thread_oop);
    }
    if (release_Threads_lock) {
      Threads_lock->unlock();
    }
  }
  tty->print_cr("Thread::%s " INTPTR_FORMAT " [%lx] %s (prio: %d)", msg, thread, thread->osthread()->thread_id(), name, prio);
}
#endif


ThreadPriority Thread::get_priority(const Thread* const thread) {
  trace("get priority", thread);
  ThreadPriority priority;
  // Can return an error!
  (void)os::get_priority(thread, priority);
  assert(MinPriority <= priority && priority <= MaxPriority, "non-Java priority found");
  return priority;
}

void Thread::set_priority(Thread* thread, ThreadPriority priority) {
  trace("set priority", thread);
  debug_only(check_for_dangling_thread_pointer(thread);)
  // Can return an error!
  (void)os::set_priority(thread, priority);
}


void Thread::start(Thread* thread) {
  trace("start", thread);
  // Start is different from resume in that its safety is guaranteed by context or
  // being called from a Java method synchronized on the Thread object.
  if (!DisableStartThread) {
    if (thread->is_Java_thread()) {
      // Initialize the thread state to RUNNABLE before starting this thread.
      // Can not set it after the thread started because we do not know the
      // exact thread state at that time. It could be in MONITOR_WAIT or
      // in SLEEPING or some other state.
      java_lang_Thread::set_thread_status(((JavaThread*)thread)->threadObj(),
                                          java_lang_Thread::RUNNABLE);
    }
    os::start_thread(thread);
  }
}

// Enqueue a VM_Operation to do the job for us - sometime later
void Thread::send_async_exception(oop java_thread, oop java_throwable) {
  VM_ThreadStop* vm_stop = new VM_ThreadStop(java_thread, java_throwable);
  VMThread::execute(vm_stop);
}


//
// Check if an external suspend request has completed (or has been
// cancelled). Returns true if the thread is externally suspended and
// false otherwise.
//
// The bits parameter returns information about the code path through
// the routine. Useful for debugging:
//
// set in is_ext_suspend_completed():
// 0x00000001 - routine was entered
// 0x00000010 - routine return false at end
// 0x00000100 - thread exited (return false)
// 0x00000200 - suspend request cancelled (return false)
// 0x00000400 - thread suspended (return true)
// 0x00001000 - thread is in a suspend equivalent state (return true)
// 0x00002000 - thread is native and walkable (return true)
// 0x00004000 - thread is native_trans and walkable (needed retry)
//
// set in wait_for_ext_suspend_completion():
// 0x00010000 - routine was entered
// 0x00020000 - suspend request cancelled before loop (return false)
// 0x00040000 - thread suspended before loop (return true)
// 0x00080000 - suspend request cancelled in loop (return false)
// 0x00100000 - thread suspended in loop (return true)
// 0x00200000 - suspend not completed during retry loop (return false)
//

// Helper class for tracing suspend wait debug bits.
//
// 0x00000100 indicates that the target thread exited before it could
// self-suspend which is not a wait failure. 0x00000200, 0x00020000 and
// 0x00080000 each indicate a cancelled suspend request so they don't
// count as wait failures either.
#define DEBUG_FALSE_BITS (0x00000010 | 0x00200000)

class TraceSuspendDebugBits : public StackObj {
 private:
  JavaThread * jt;
  bool         is_wait;
  bool         called_by_wait;  // meaningful when !is_wait
  uint32_t *   bits;

 public:
  TraceSuspendDebugBits(JavaThread *_jt, bool _is_wait, bool _called_by_wait,
                        uint32_t *_bits) {
    jt             = _jt;
    is_wait        = _is_wait;
    called_by_wait = _called_by_wait;
    bits           = _bits;
  }

  ~TraceSuspendDebugBits() {
    if (!is_wait) {
#if 1
      // By default, don't trace bits for is_ext_suspend_completed() calls.
      // That trace is very chatty.
      return;
#else
      if (!called_by_wait) {
        // If tracing for is_ext_suspend_completed() is enabled, then only
        // trace calls to it from wait_for_ext_suspend_completion()
        return;
      }
#endif
    }

    if (AssertOnSuspendWaitFailure || TraceSuspendWaitFailures) {
      if (bits != NULL && (*bits & DEBUG_FALSE_BITS) != 0) {
        MutexLocker ml(Threads_lock);  // needed for get_thread_name()
        ResourceMark rm;

        tty->print_cr(
            "Failed wait_for_ext_suspend_completion(thread=%s, debug_bits=%x)",
            jt->get_thread_name(), *bits);

        guarantee(!AssertOnSuspendWaitFailure, "external suspend wait failed");
      }
    }
  }
};
#undef DEBUG_FALSE_BITS


bool JavaThread::is_ext_suspend_completed(bool called_by_wait, int delay, uint32_t *bits) {
  TraceSuspendDebugBits tsdb(this, false /* !is_wait */, called_by_wait, bits);

  bool did_trans_retry = false;  // only do thread_in_native_trans retry once
  bool do_trans_retry;           // flag to force the retry

  *bits |= 0x00000001;

  do {
    do_trans_retry = false;

    if (is_exiting()) {
      // Thread is in the process of exiting. This is always checked
      // first to reduce the risk of dereferencing a freed JavaThread.
      *bits |= 0x00000100;
      return false;
    }

    if (!is_external_suspend()) {
      // Suspend request is cancelled. This is always checked before
      // is_ext_suspended() to reduce the risk of a rogue resume
      // confusing the thread that made the suspend request.
      *bits |= 0x00000200;
      return false;
    }

    if (is_ext_suspended()) {
      // thread is suspended
      *bits |= 0x00000400;
      return true;
    }

    // Now that we no longer do hard suspends of threads running
    // native code, the target thread can be changing thread state
    // while we are in this routine:
    //
    //   _thread_in_native -> _thread_in_native_trans -> _thread_blocked
    //
    // We save a copy of the thread state as observed at this moment
    // and make our decision about suspend completeness based on the
    // copy. This closes the race where the thread state is seen as
    // _thread_in_native_trans in the if-thread_blocked check, but is
    // seen as _thread_blocked in if-thread_in_native_trans check.
    JavaThreadState save_state = thread_state();

    if (save_state == _thread_blocked && is_suspend_equivalent()) {
      // If the thread's state is _thread_blocked and this blocking
      // condition is known to be equivalent to a suspend, then we can
      // consider the thread to be externally suspended. This means that
      // the code that sets _thread_blocked has been modified to do
      // self-suspension if the blocking condition releases. We also
      // used to check for CONDVAR_WAIT here, but that is now covered by
      // the _thread_blocked with self-suspension check.
      //
      // Return true since we wouldn't be here unless there was still an
      // external suspend request.
      *bits |= 0x00001000;
      return true;
    } else if (save_state == _thread_in_native && frame_anchor()->walkable()) {
      // Threads running native code will self-suspend on native==>VM/Java
      // transitions. If its stack is walkable (should always be the case
      // unless this function is called before the actual java_suspend()
      // call), then the wait is done.
      *bits |= 0x00002000;
      return true;
    } else if (!called_by_wait && !did_trans_retry &&
               save_state == _thread_in_native_trans &&
               frame_anchor()->walkable()) {
      // The thread is transitioning from thread_in_native to another
      // thread state. check_safepoint_and_suspend_for_native_trans()
      // will force the thread to self-suspend. If it hasn't gotten
      // there yet we may have caught the thread in-between the native
      // code check above and the self-suspend. Lucky us. If we were
      // called by wait_for_ext_suspend_completion(), then it
      // will be doing the retries so we don't have to.
      //
      // Since we use the saved thread state in the if-statement above,
      // there is a chance that the thread has already transitioned to
      // _thread_blocked by the time we get here. In that case, we will
      // make a single unnecessary pass through the logic below. This
      // doesn't hurt anything since we still do the trans retry.

      *bits |= 0x00004000;

      // Once the thread leaves thread_in_native_trans for another
      // thread state, we break out of this retry loop. We shouldn't
      // need this flag to prevent us from getting back here, but
      // sometimes paranoia is good.
      did_trans_retry = true;

      // We wait for the thread to transition to a more usable state.
      for (int i = 1; i <= SuspendRetryCount; i++) {
        // We used to do an "os::yield_all(i)" call here with the intention
        // that yielding would increase on each retry. However, the parameter
        // is ignored on Linux which means the yield didn't scale up. Waiting
        // on the SR_lock below provides a much more predictable scale up for
        // the delay. It also provides a simple/direct point to check for any
        // safepoint requests from the VMThread

        // temporarily drops SR_lock while doing wait with safepoint check
        // (if we're a JavaThread - the WatcherThread can also call this)
        // and increase delay with each retry
        SR_lock()->wait(!Thread::current()->is_Java_thread(), i * delay);

        // check the actual thread state instead of what we saved above
        if (thread_state() != _thread_in_native_trans) {
          // the thread has transitioned to another thread state so
          // try all the checks (except this one) one more time.
          do_trans_retry = true;
          break;
        }
      } // end retry loop


    }
  } while (do_trans_retry);

  *bits |= 0x00000010;
  return false;
}

//
// Wait for an external suspend request to complete (or be cancelled).
// Returns true if the thread is externally suspended and false otherwise.
//
bool JavaThread::wait_for_ext_suspend_completion(int retries, int delay,
       uint32_t *bits) {
  TraceSuspendDebugBits tsdb(this, true /* is_wait */,
                             false /* !called_by_wait */, bits);

  // local flag copies to minimize SR_lock hold time
  bool is_suspended;
  bool pending;
  uint32_t reset_bits;

  // set a marker so is_ext_suspend_completed() knows we are the caller
  *bits |= 0x00010000;

  // We use reset_bits to reinitialize the bits value at the top of
  // each retry loop. This allows the caller to make use of any
  // unused bits for their own marking purposes.
  reset_bits = *bits;

  {
    MutexLockerEx ml(SR_lock(), Mutex::_no_safepoint_check_flag);
    is_suspended = is_ext_suspend_completed(true /* called_by_wait */,
                                            delay, bits);
    pending = is_external_suspend();
  }
  // must release SR_lock to allow suspension to complete

  if (!pending) {
    // A cancelled suspend request is the only false return from
    // is_ext_suspend_completed() that keeps us from entering the
    // retry loop.
    *bits |= 0x00020000;
    return false;
  }

  if (is_suspended) {
    *bits |= 0x00040000;
    return true;
  }

  for (int i = 1; i <= retries; i++) {
    *bits = reset_bits;  // reinit to only track last retry

    // We used to do an "os::yield_all(i)" call here with the intention
    // that yielding would increase on each retry. However, the parameter
    // is ignored on Linux which means the yield didn't scale up. Waiting
    // on the SR_lock below provides a much more predictable scale up for
    // the delay. It also provides a simple/direct point to check for any
    // safepoint requests from the VMThread

    {
      MutexLocker ml(SR_lock());
      // wait with safepoint check (if we're a JavaThread - the WatcherThread
      // can also call this)  and increase delay with each retry
      SR_lock()->wait(!Thread::current()->is_Java_thread(), i * delay);

      is_suspended = is_ext_suspend_completed(true /* called_by_wait */,
                                              delay, bits);

      // It is possible for the external suspend request to be cancelled
      // (by a resume) before the actual suspend operation is completed.
      // Refresh our local copy to see if we still need to wait.
      pending = is_external_suspend();
    }

    if (!pending) {
      // A cancelled suspend request is the only false return from
      // is_ext_suspend_completed() that keeps us from staying in the
      // retry loop.
      *bits |= 0x00080000;
      return false;
    }

    if (is_suspended) {
      *bits |= 0x00100000;
      return true;
    }
  } // end retry loop

  // thread did not suspend after all our retries
  *bits |= 0x00200000;
  return false;
}

#ifndef PRODUCT
void JavaThread::record_jump(address target, address instr, const char* file, int line) {

  // This should not need to be atomic as the only way for simultaneous
  // updates is via interrupts. Even then this should be rare or non-existant
  // and we don't care that much anyway.

  int index = _jmp_ring_index;
  _jmp_ring_index = (index + 1 ) & (jump_ring_buffer_size - 1);
  _jmp_ring[index]._target = (intptr_t) target;
  _jmp_ring[index]._instruction = (intptr_t) instr;
  _jmp_ring[index]._file = file;
  _jmp_ring[index]._line = line;
}
#endif /* PRODUCT */

// Called by flat profiler
// Callers have already called wait_for_ext_suspend_completion
// The assertion for that is currently too complex to put here:
bool JavaThread::profile_last_Java_frame(frame* _fr) {
  bool gotframe = false;
  // self suspension saves needed state.
  if (has_last_Java_frame() && _anchor.walkable()) {
     *_fr = pd_last_frame();
     gotframe = true;
  }
  return gotframe;
}

void Thread::interrupt(Thread* thread) {
  trace("interrupt", thread);
  debug_only(check_for_dangling_thread_pointer(thread);)
  os::interrupt(thread);
}

bool Thread::is_interrupted(Thread* thread, bool clear_interrupted) {
  trace("is_interrupted", thread);
  debug_only(check_for_dangling_thread_pointer(thread);)
  // Note:  If clear_interrupted==false, this simply fetches and
  // returns the value of the field osthread()->interrupted().
  return os::is_interrupted(thread, clear_interrupted);
}


// GC Support
bool Thread::claim_oops_do_par_case(int strong_roots_parity) {
  jint thread_parity = _oops_do_parity;
  if (thread_parity != strong_roots_parity) {
    jint res = Atomic::cmpxchg(strong_roots_parity, &_oops_do_parity, thread_parity);
    if (res == thread_parity) return true;
    else {
      guarantee(res == strong_roots_parity, "Or else what?");
      assert(SharedHeap::heap()->n_par_threads() > 0,
             "Should only fail when parallel.");
      return false;
    }
  }
  assert(SharedHeap::heap()->n_par_threads() > 0,
         "Should only fail when parallel.");
  return false;
}

void Thread::oops_do(OopClosure* f, CodeBlobClosure* cf) {
  active_handles()->oops_do(f);
  // Do oop for ThreadShadow
  f->do_oop((oop*)&_pending_exception);
  handle_area()->oops_do(f);
}

void Thread::nmethods_do(CodeBlobClosure* cf) {
  // no nmethods in a generic thread...
}

void Thread::print_on(outputStream* st) const {
  // get_priority assumes osthread initialized
  if (osthread() != NULL) {
    st->print("prio=%d tid=" INTPTR_FORMAT " ", get_priority(this), this);
    osthread()->print_on(st);
  }
  debug_only(if (WizardMode) print_owned_locks_on(st);)
}

// Thread::print_on_error() is called by fatal error handler. Don't use
// any lock or allocate memory.
void Thread::print_on_error(outputStream* st, char* buf, int buflen) const {
  if      (is_VM_thread())                  st->print("VMThread");
  else if (is_Compiler_thread())            st->print("CompilerThread");
  else if (is_Java_thread())                st->print("JavaThread");
  else if (is_GC_task_thread())             st->print("GCTaskThread");
  else if (is_Watcher_thread())             st->print("WatcherThread");
  else if (is_ConcurrentGC_thread())        st->print("ConcurrentGCThread");
  else st->print("Thread");

  st->print(" [stack: " PTR_FORMAT "," PTR_FORMAT "]",
            _stack_base - _stack_size, _stack_base);

  if (osthread()) {
    st->print(" [id=%d]", osthread()->thread_id());
  }
}

#ifdef ASSERT
void Thread::print_owned_locks_on(outputStream* st) const {
  Monitor *cur = _owned_locks;
  if (cur == NULL) {
    st->print(" (no locks) ");
  } else {
    st->print_cr(" Locks owned:");
    while(cur) {
      cur->print_on(st);
      cur = cur->next();
    }
  }
}

static int ref_use_count  = 0;

bool Thread::owns_locks_but_compiled_lock() const {
  for(Monitor *cur = _owned_locks; cur; cur = cur->next()) {
    if (cur != Compile_lock) return true;
  }
  return false;
}


#endif

#ifndef PRODUCT

// The flag: potential_vm_operation notifies if this particular safepoint state could potential
// invoke the vm-thread (i.e., and oop allocation). In that case, we also have to make sure that
// no threads which allow_vm_block's are held
void Thread::check_for_valid_safepoint_state(bool potential_vm_operation) {
    // Check if current thread is allowed to block at a safepoint
    if (!(_allow_safepoint_count == 0))
      fatal("Possible safepoint reached by thread that does not allow it");
    if (is_Java_thread() && ((JavaThread*)this)->thread_state() != _thread_in_vm) {
      fatal("LEAF method calling lock?");
    }

#ifdef ASSERT
    if (potential_vm_operation && is_Java_thread()
        && !Universe::is_bootstrapping()) {
      // Make sure we do not hold any locks that the VM thread also uses.
      // This could potentially lead to deadlocks
      for(Monitor *cur = _owned_locks; cur; cur = cur->next()) {
        // Threads_lock is special, since the safepoint synchronization will not start before this is
        // acquired. Hence, a JavaThread cannot be holding it at a safepoint. So is VMOperationRequest_lock,
        // since it is used to transfer control between JavaThreads and the VMThread
        // Do not *exclude* any locks unless you are absolutly sure it is correct. Ask someone else first!
        if ( (cur->allow_vm_block() &&
              cur != Threads_lock &&
              cur != Compile_lock &&               // Temporary: should not be necessary when we get spearate compilation
              cur != VMOperationRequest_lock &&
              cur != VMOperationQueue_lock) ||
              cur->rank() == Mutex::special) {
          warning("Thread holding lock at safepoint that vm can block on: %s", cur->name());
        }
      }
    }

    if (GCALotAtAllSafepoints) {
      // We could enter a safepoint here and thus have a gc
      InterfaceSupport::check_gc_alot();
    }
#endif
}
#endif

bool Thread::is_in_stack(address adr) const {
  assert(Thread::current() == this, "is_in_stack can only be called from current thread");
  address end = os::current_stack_pointer();
  if (stack_base() >= adr && adr >= end) return true;

  return false;
}


// We had to move these methods here, because vm threads get into ObjectSynchronizer::enter
// However, there is a note in JavaThread::is_lock_owned() about the VM threads not being
// used for compilation in the future. If that change is made, the need for these methods
// should be revisited, and they should be removed if possible.

bool Thread::is_lock_owned(address adr) const {
  return on_local_stack(adr);
}

bool Thread::set_as_starting_thread() {
 // NOTE: this must be called inside the main thread.
  return os::create_main_thread((JavaThread*)this);
}

static void initialize_class(symbolHandle class_name, TRAPS) {
  klassOop klass = SystemDictionary::resolve_or_fail(class_name, true, CHECK);
  instanceKlass::cast(klass)->initialize(CHECK);
}


// Creates the initial ThreadGroup
static Handle create_initial_thread_group(TRAPS) {
  klassOop k = SystemDictionary::resolve_or_fail(vmSymbolHandles::java_lang_ThreadGroup(), true, CHECK_NH);
  instanceKlassHandle klass (THREAD, k);

  Handle system_instance = klass->allocate_instance_handle(CHECK_NH);
  {
    JavaValue result(T_VOID);
    JavaCalls::call_special(&result,
                            system_instance,
                            klass,
                            vmSymbolHandles::object_initializer_name(),
                            vmSymbolHandles::void_method_signature(),
                            CHECK_NH);
  }
  Universe::set_system_thread_group(system_instance());

  Handle main_instance = klass->allocate_instance_handle(CHECK_NH);
  {
    JavaValue result(T_VOID);
    Handle string = java_lang_String::create_from_str("main", CHECK_NH);
    JavaCalls::call_special(&result,
                            main_instance,
                            klass,
                            vmSymbolHandles::object_initializer_name(),
                            vmSymbolHandles::threadgroup_string_void_signature(),
                            system_instance,
                            string,
                            CHECK_NH);
  }
  return main_instance;
}

// Creates the initial Thread
static oop create_initial_thread(Handle thread_group, JavaThread* thread, TRAPS) {
  klassOop k = SystemDictionary::resolve_or_fail(vmSymbolHandles::java_lang_Thread(), true, CHECK_NULL);
  instanceKlassHandle klass (THREAD, k);
  instanceHandle thread_oop = klass->allocate_instance_handle(CHECK_NULL);

  java_lang_Thread::set_thread(thread_oop(), thread);
  java_lang_Thread::set_priority(thread_oop(), NormPriority);
  thread->set_threadObj(thread_oop());

  Handle string = java_lang_String::create_from_str("main", CHECK_NULL);

  JavaValue result(T_VOID);
  JavaCalls::call_special(&result, thread_oop,
                                   klass,
                                   vmSymbolHandles::object_initializer_name(),
                                   vmSymbolHandles::threadgroup_string_void_signature(),
                                   thread_group,
                                   string,
                                   CHECK_NULL);
  return thread_oop();
}

static void call_initializeSystemClass(TRAPS) {
  klassOop k =  SystemDictionary::resolve_or_fail(vmSymbolHandles::java_lang_System(), true, CHECK);
  instanceKlassHandle klass (THREAD, k);

  JavaValue result(T_VOID);
  JavaCalls::call_static(&result, klass, vmSymbolHandles::initializeSystemClass_name(),
                                         vmSymbolHandles::void_method_signature(), CHECK);
}

#ifdef KERNEL
static void set_jkernel_boot_classloader_hook(TRAPS) {
  klassOop k = SystemDictionary::sun_jkernel_DownloadManager_klass();
  instanceKlassHandle klass (THREAD, k);

  if (k == NULL) {
    // sun.jkernel.DownloadManager may not present in the JDK; just return
    return;
  }

  JavaValue result(T_VOID);
  JavaCalls::call_static(&result, klass, vmSymbolHandles::setBootClassLoaderHook_name(),
                                         vmSymbolHandles::void_method_signature(), CHECK);
}
#endif // KERNEL

static void reset_vm_info_property(TRAPS) {
  // the vm info string
  ResourceMark rm(THREAD);
  const char *vm_info = VM_Version::vm_info_string();

  // java.lang.System class
  klassOop k =  SystemDictionary::resolve_or_fail(vmSymbolHandles::java_lang_System(), true, CHECK);
  instanceKlassHandle klass (THREAD, k);

  // setProperty arguments
  Handle key_str    = java_lang_String::create_from_str("java.vm.info", CHECK);
  Handle value_str  = java_lang_String::create_from_str(vm_info, CHECK);

  // return value
  JavaValue r(T_OBJECT);

  // public static String setProperty(String key, String value);
  JavaCalls::call_static(&r,
                         klass,
                         vmSymbolHandles::setProperty_name(),
                         vmSymbolHandles::string_string_string_signature(),
                         key_str,
                         value_str,
                         CHECK);
}


void JavaThread::allocate_threadObj(Handle thread_group, char* thread_name, bool daemon, TRAPS) {
  assert(thread_group.not_null(), "thread group should be specified");
  assert(threadObj() == NULL, "should only create Java thread object once");

  klassOop k = SystemDictionary::resolve_or_fail(vmSymbolHandles::java_lang_Thread(), true, CHECK);
  instanceKlassHandle klass (THREAD, k);
  instanceHandle thread_oop = klass->allocate_instance_handle(CHECK);

  java_lang_Thread::set_thread(thread_oop(), this);
  java_lang_Thread::set_priority(thread_oop(), NormPriority);
  set_threadObj(thread_oop());

  JavaValue result(T_VOID);
  if (thread_name != NULL) {
    Handle name = java_lang_String::create_from_str(thread_name, CHECK);
    // Thread gets assigned specified name and null target
    JavaCalls::call_special(&result,
                            thread_oop,
                            klass,
                            vmSymbolHandles::object_initializer_name(),
                            vmSymbolHandles::threadgroup_string_void_signature(),
                            thread_group, // Argument 1
                            name,         // Argument 2
                            THREAD);
  } else {
    // Thread gets assigned name "Thread-nnn" and null target
    // (java.lang.Thread doesn't have a constructor taking only a ThreadGroup argument)
    JavaCalls::call_special(&result,
                            thread_oop,
                            klass,
                            vmSymbolHandles::object_initializer_name(),
                            vmSymbolHandles::threadgroup_runnable_void_signature(),
                            thread_group, // Argument 1
                            Handle(),     // Argument 2
                            THREAD);
  }


  if (daemon) {
      java_lang_Thread::set_daemon(thread_oop());
  }

  if (HAS_PENDING_EXCEPTION) {
    return;
  }

  KlassHandle group(this, SystemDictionary::ThreadGroup_klass());
  Handle threadObj(this, this->threadObj());

  JavaCalls::call_special(&result,
                         thread_group,
                         group,
                         vmSymbolHandles::add_method_name(),
                         vmSymbolHandles::thread_void_signature(),
                         threadObj,          // Arg 1
                         THREAD);


}

// NamedThread --  non-JavaThread subclasses with multiple
// uniquely named instances should derive from this.
NamedThread::NamedThread() : Thread() {
  _name = NULL;
  _processed_thread = NULL;
}

NamedThread::~NamedThread() {
  if (_name != NULL) {
    FREE_C_HEAP_ARRAY(char, _name);
    _name = NULL;
  }
}

void NamedThread::set_name(const char* format, ...) {
  guarantee(_name == NULL, "Only get to set name once.");
  _name = NEW_C_HEAP_ARRAY(char, max_name_len);
  guarantee(_name != NULL, "alloc failure");
  va_list ap;
  va_start(ap, format);
  jio_vsnprintf(_name, max_name_len, format, ap);
  va_end(ap);
}

// ======= WatcherThread ========

// The watcher thread exists to simulate timer interrupts.  It should
// be replaced by an abstraction over whatever native support for
// timer interrupts exists on the platform.

WatcherThread* WatcherThread::_watcher_thread   = NULL;
volatile bool  WatcherThread::_should_terminate = false;

WatcherThread::WatcherThread() : Thread() {
  assert(watcher_thread() == NULL, "we can only allocate one WatcherThread");
  if (os::create_thread(this, os::watcher_thread)) {
    _watcher_thread = this;

    // Set the watcher thread to the highest OS priority which should not be
    // used, unless a Java thread with priority java.lang.Thread.MAX_PRIORITY
    // is created. The only normal thread using this priority is the reference
    // handler thread, which runs for very short intervals only.
    // If the VMThread's priority is not lower than the WatcherThread profiling
    // will be inaccurate.
    os::set_priority(this, MaxPriority);
    if (!DisableStartThread) {
      os::start_thread(this);
    }
  }
}

void WatcherThread::run() {
  assert(this == watcher_thread(), "just checking");

  this->record_stack_base_and_size();
  this->initialize_thread_local_storage();
  this->set_active_handles(JNIHandleBlock::allocate_block());
  while(!_should_terminate) {
    assert(watcher_thread() == Thread::current(),  "thread consistency check");
    assert(watcher_thread() == this,  "thread consistency check");

    // Calculate how long it'll be until the next PeriodicTask work
    // should be done, and sleep that amount of time.
    size_t time_to_wait = PeriodicTask::time_to_wait();

    // we expect this to timeout - we only ever get unparked when
    // we should terminate
    {
      OSThreadWaitState osts(this->osthread(), false /* not Object.wait() */);

      jlong prev_time = os::javaTimeNanos();
      for (;;) {
        int res= _SleepEvent->park(time_to_wait);
        if (res == OS_TIMEOUT || _should_terminate)
          break;
        // spurious wakeup of some kind
        jlong now = os::javaTimeNanos();
        time_to_wait -= (now - prev_time) / 1000000;
        if (time_to_wait <= 0)
          break;
        prev_time = now;
      }
    }

    if (is_error_reported()) {
      // A fatal error has happened, the error handler(VMError::report_and_die)
      // should abort JVM after creating an error log file. However in some
      // rare cases, the error handler itself might deadlock. Here we try to
      // kill JVM if the fatal error handler fails to abort in 2 minutes.
      //
      // This code is in WatcherThread because WatcherThread wakes up
      // periodically so the fatal error handler doesn't need to do anything;
      // also because the WatcherThread is less likely to crash than other
      // threads.

      for (;;) {
        if (!ShowMessageBoxOnError
         && (OnError == NULL || OnError[0] == '\0')
         && Arguments::abort_hook() == NULL) {
             os::sleep(this, 2 * 60 * 1000, false);
             fdStream err(defaultStream::output_fd());
             err.print_raw_cr("# [ timer expired, abort... ]");
             // skip atexit/vm_exit/vm_abort hooks
             os::die();
        }

        // Wake up 5 seconds later, the fatal handler may reset OnError or
        // ShowMessageBoxOnError when it is ready to abort.
        os::sleep(this, 5 * 1000, false);
      }
    }

    PeriodicTask::real_time_tick(time_to_wait);

    // If we have no more tasks left due to dynamic disenrollment,
    // shut down the thread since we don't currently support dynamic enrollment
    if (PeriodicTask::num_tasks() == 0) {
      _should_terminate = true;
    }
  }

  // Signal that it is terminated
  {
    MutexLockerEx mu(Terminator_lock, Mutex::_no_safepoint_check_flag);
    _watcher_thread = NULL;
    Terminator_lock->notify();
  }

  // Thread destructor usually does this..
  ThreadLocalStorage::set_thread(NULL);
}

void WatcherThread::start() {
  if (watcher_thread() == NULL) {
    _should_terminate = false;
    // Create the single instance of WatcherThread
    new WatcherThread();
  }
}

void WatcherThread::stop() {
  // it is ok to take late safepoints here, if needed
  MutexLocker mu(Terminator_lock);
  _should_terminate = true;
  OrderAccess::fence();  // ensure WatcherThread sees update in main loop

  Thread* watcher = watcher_thread();
  if (watcher != NULL)
    watcher->_SleepEvent->unpark();

  while(watcher_thread() != NULL) {
    // This wait should make safepoint checks, wait without a timeout,
    // and wait as a suspend-equivalent condition.
    //
    // Note: If the FlatProfiler is running, then this thread is waiting
    // for the WatcherThread to terminate and the WatcherThread, via the
    // FlatProfiler task, is waiting for the external suspend request on
    // this thread to complete. wait_for_ext_suspend_completion() will
    // eventually timeout, but that takes time. Making this wait a
    // suspend-equivalent condition solves that timeout problem.
    //
    Terminator_lock->wait(!Mutex::_no_safepoint_check_flag, 0,
                          Mutex::_as_suspend_equivalent_flag);
  }
}

void WatcherThread::print_on(outputStream* st) const {
  st->print("\"%s\" ", name());
  Thread::print_on(st);
  st->cr();
}

// ======= JavaThread ========

// A JavaThread is a normal Java thread

void JavaThread::initialize() {
  // Initialize fields

  // Set the claimed par_id to -1 (ie not claiming any par_ids)
  set_claimed_par_id(-1);

  set_saved_exception_pc(NULL);
  set_threadObj(NULL);
  _anchor.clear();
  set_entry_point(NULL);
  set_jni_functions(jni_functions());
  set_callee_target(NULL);
  set_vm_result(NULL);
  set_vm_result_2(NULL);
  set_vframe_array_head(NULL);
  set_vframe_array_last(NULL);
  set_deferred_locals(NULL);
  set_deopt_mark(NULL);
  set_deopt_nmethod(NULL);
  clear_must_deopt_id();
  set_monitor_chunks(NULL);
  set_next(NULL);
  set_thread_state(_thread_new);
  _terminated = _not_terminated;
  _privileged_stack_top = NULL;
  _array_for_gc = NULL;
  _suspend_equivalent = false;
  _in_deopt_handler = 0;
  _doing_unsafe_access = false;
  _stack_guard_state = stack_guard_unused;
  _exception_oop = NULL;
  _exception_pc  = 0;
  _exception_handler_pc = 0;
  _exception_stack_size = 0;
  _is_method_handle_return = 0;
  _jvmti_thread_state= NULL;
  _should_post_on_exceptions_flag = JNI_FALSE;
  _jvmti_get_loaded_classes_closure = NULL;
  _interp_only_mode    = 0;
  _special_runtime_exit_condition = _no_async_condition;
  _pending_async_exception = NULL;
  _is_compiling = false;
  _thread_stat = NULL;
  _thread_stat = new ThreadStatistics();
  _blocked_on_compilation = false;
  _jni_active_critical = 0;
  _do_not_unlock_if_synchronized = false;
  _cached_monitor_info = NULL;
  _parker = Parker::Allocate(this) ;

#ifndef PRODUCT
  _jmp_ring_index = 0;
  for (int ji = 0 ; ji < jump_ring_buffer_size ; ji++ ) {
    record_jump(NULL, NULL, NULL, 0);
  }
#endif /* PRODUCT */

  set_thread_profiler(NULL);
  if (FlatProfiler::is_active()) {
    // This is where we would decide to either give each thread it's own profiler
    // or use one global one from FlatProfiler,
    // or up to some count of the number of profiled threads, etc.
    ThreadProfiler* pp = new ThreadProfiler();
    pp->engage();
    set_thread_profiler(pp);
  }

  // Setup safepoint state info for this thread
  ThreadSafepointState::create(this);

  debug_only(_java_call_counter = 0);

  // JVMTI PopFrame support
  _popframe_condition = popframe_inactive;
  _popframe_preserved_args = NULL;
  _popframe_preserved_args_size = 0;

  pd_initialize();
}

#ifndef SERIALGC
SATBMarkQueueSet JavaThread::_satb_mark_queue_set;
DirtyCardQueueSet JavaThread::_dirty_card_queue_set;
#endif // !SERIALGC

JavaThread::JavaThread(bool is_attaching) :
  Thread()
#ifndef SERIALGC
  , _satb_mark_queue(&_satb_mark_queue_set),
  _dirty_card_queue(&_dirty_card_queue_set)
#endif // !SERIALGC
{
  initialize();
  _is_attaching = is_attaching;
  assert(_deferred_card_mark.is_empty(), "Default MemRegion ctor");
}

bool JavaThread::reguard_stack(address cur_sp) {
  if (_stack_guard_state != stack_guard_yellow_disabled) {
    return true; // Stack already guarded or guard pages not needed.
  }

  if (register_stack_overflow()) {
    // For those architectures which have separate register and
    // memory stacks, we must check the register stack to see if
    // it has overflowed.
    return false;
  }

  // Java code never executes within the yellow zone: the latter is only
  // there to provoke an exception during stack banging.  If java code
  // is executing there, either StackShadowPages should be larger, or
  // some exception code in c1, c2 or the interpreter isn't unwinding
  // when it should.
  guarantee(cur_sp > stack_yellow_zone_base(), "not enough space to reguard - increase StackShadowPages");

  enable_stack_yellow_zone();
  return true;
}

bool JavaThread::reguard_stack(void) {
  return reguard_stack(os::current_stack_pointer());
}


void JavaThread::block_if_vm_exited() {
  if (_terminated == _vm_exited) {
    // _vm_exited is set at safepoint, and Threads_lock is never released
    // we will block here forever
    Threads_lock->lock_without_safepoint_check();
    ShouldNotReachHere();
  }
}


// Remove this ifdef when C1 is ported to the compiler interface.
static void compiler_thread_entry(JavaThread* thread, TRAPS);

JavaThread::JavaThread(ThreadFunction entry_point, size_t stack_sz) :
  Thread()
#ifndef SERIALGC
  , _satb_mark_queue(&_satb_mark_queue_set),
  _dirty_card_queue(&_dirty_card_queue_set)
#endif // !SERIALGC
{
  if (TraceThreadEvents) {
    tty->print_cr("creating thread %p", this);
  }
  initialize();
  _is_attaching = false;
  set_entry_point(entry_point);
  // Create the native thread itself.
  // %note runtime_23
  os::ThreadType thr_type = os::java_thread;
  thr_type = entry_point == &compiler_thread_entry ? os::compiler_thread :
                                                     os::java_thread;
  os::create_thread(this, thr_type, stack_sz);

  // The _osthread may be NULL here because we ran out of memory (too many threads active).
  // We need to throw and OutOfMemoryError - however we cannot do this here because the caller
  // may hold a lock and all locks must be unlocked before throwing the exception (throwing
  // the exception consists of creating the exception object & initializing it, initialization
  // will leave the VM via a JavaCall and then all locks must be unlocked).
  //
  // The thread is still suspended when we reach here. Thread must be explicit started
  // by creator! Furthermore, the thread must also explicitly be added to the Threads list
  // by calling Threads:add. The reason why this is not done here, is because the thread
  // object must be fully initialized (take a look at JVM_Start)
}

JavaThread::~JavaThread() {
  if (TraceThreadEvents) {
      tty->print_cr("terminate thread %p", this);
  }

  // JSR166 -- return the parker to the free list
  Parker::Release(_parker);
  _parker = NULL ;

  // Free any remaining  previous UnrollBlock
  vframeArray* old_array = vframe_array_last();

  if (old_array != NULL) {
    Deoptimization::UnrollBlock* old_info = old_array->unroll_block();
    old_array->set_unroll_block(NULL);
    delete old_info;
    delete old_array;
  }

  GrowableArray<jvmtiDeferredLocalVariableSet*>* deferred = deferred_locals();
  if (deferred != NULL) {
    // This can only happen if thread is destroyed before deoptimization occurs.
    assert(deferred->length() != 0, "empty array!");
    do {
      jvmtiDeferredLocalVariableSet* dlv = deferred->at(0);
      deferred->remove_at(0);
      // individual jvmtiDeferredLocalVariableSet are CHeapObj's
      delete dlv;
    } while (deferred->length() != 0);
    delete deferred;
  }

  // All Java related clean up happens in exit
  ThreadSafepointState::destroy(this);
  if (_thread_profiler != NULL) delete _thread_profiler;
  if (_thread_stat != NULL) delete _thread_stat;
}


// The first routine called by a new Java thread
void JavaThread::run() {
  // initialize thread-local alloc buffer related fields
  this->initialize_tlab();

  // used to test validitity of stack trace backs
  this->record_base_of_stack_pointer();

  // Record real stack base and size.
  this->record_stack_base_and_size();

  // Initialize thread local storage; set before calling MutexLocker
  this->initialize_thread_local_storage();

  this->create_stack_guard_pages();

  this->cache_global_variables();

  // Thread is now sufficient initialized to be handled by the safepoint code as being
  // in the VM. Change thread state from _thread_new to _thread_in_vm
  ThreadStateTransition::transition_and_fence(this, _thread_new, _thread_in_vm);

  assert(JavaThread::current() == this, "sanity check");
  assert(!Thread::current()->owns_locks(), "sanity check");

  DTRACE_THREAD_PROBE(start, this);

  // This operation might block. We call that after all safepoint checks for a new thread has
  // been completed.
  this->set_active_handles(JNIHandleBlock::allocate_block());

  if (JvmtiExport::should_post_thread_life()) {
    JvmtiExport::post_thread_start(this);
  }

  // We call another function to do the rest so we are sure that the stack addresses used
  // from there will be lower than the stack base just computed
  thread_main_inner();

  // Note, thread is no longer valid at this point!
}


void JavaThread::thread_main_inner() {
  assert(JavaThread::current() == this, "sanity check");
  assert(this->threadObj() != NULL, "just checking");

  // Execute thread entry point. If this thread is being asked to restart,
  // or has been stopped before starting, do not reexecute entry point.
  // Note: Due to JVM_StopThread we can have pending exceptions already!
  if (!this->has_pending_exception() && !java_lang_Thread::is_stillborn(this->threadObj())) {
    // enter the thread's entry point only if we have no pending exceptions
    HandleMark hm(this);
    this->entry_point()(this, this);
  }

  DTRACE_THREAD_PROBE(stop, this);

  this->exit(false);
  delete this;
}


static void ensure_join(JavaThread* thread) {
  // We do not need to grap the Threads_lock, since we are operating on ourself.
  Handle threadObj(thread, thread->threadObj());
  assert(threadObj.not_null(), "java thread object must exist");
  ObjectLocker lock(threadObj, thread);
  // Ignore pending exception (ThreadDeath), since we are exiting anyway
  thread->clear_pending_exception();
  // It is of profound importance that we set the stillborn bit and reset the thread object,
  // before we do the notify. Since, changing these two variable will make JVM_IsAlive return
  // false. So in case another thread is doing a join on this thread , it will detect that the thread
  // is dead when it gets notified.
  java_lang_Thread::set_stillborn(threadObj());
  // Thread is exiting. So set thread_status field in  java.lang.Thread class to TERMINATED.
  java_lang_Thread::set_thread_status(threadObj(), java_lang_Thread::TERMINATED);
  java_lang_Thread::set_thread(threadObj(), NULL);
  lock.notify_all(thread);
  // Ignore pending exception (ThreadDeath), since we are exiting anyway
  thread->clear_pending_exception();
}


// For any new cleanup additions, please check to see if they need to be applied to
// cleanup_failed_attach_current_thread as well.
void JavaThread::exit(bool destroy_vm, ExitType exit_type) {
  assert(this == JavaThread::current(),  "thread consistency check");
  if (!InitializeJavaLangSystem) return;

  HandleMark hm(this);
  Handle uncaught_exception(this, this->pending_exception());
  this->clear_pending_exception();
  Handle threadObj(this, this->threadObj());
  assert(threadObj.not_null(), "Java thread object should be created");

  if (get_thread_profiler() != NULL) {
    get_thread_profiler()->disengage();
    ResourceMark rm;
    get_thread_profiler()->print(get_thread_name());
  }


  // FIXIT: This code should be moved into else part, when reliable 1.2/1.3 check is in place
  {
    EXCEPTION_MARK;

    CLEAR_PENDING_EXCEPTION;
  }
  // FIXIT: The is_null check is only so it works better on JDK1.2 VM's. This
  // has to be fixed by a runtime query method
  if (!destroy_vm || JDK_Version::is_jdk12x_version()) {
    // JSR-166: change call from from ThreadGroup.uncaughtException to
    // java.lang.Thread.dispatchUncaughtException
    if (uncaught_exception.not_null()) {
      Handle group(this, java_lang_Thread::threadGroup(threadObj()));
      Events::log("uncaught exception INTPTR_FORMAT " " INTPTR_FORMAT " " INTPTR_FORMAT",
        (address)uncaught_exception(), (address)threadObj(), (address)group());
      {
        EXCEPTION_MARK;
        // Check if the method Thread.dispatchUncaughtException() exists. If so
        // call it.  Otherwise we have an older library without the JSR-166 changes,
        // so call ThreadGroup.uncaughtException()
        KlassHandle recvrKlass(THREAD, threadObj->klass());
        CallInfo callinfo;
        KlassHandle thread_klass(THREAD, SystemDictionary::Thread_klass());
        LinkResolver::resolve_virtual_call(callinfo, threadObj, recvrKlass, thread_klass,
                                           vmSymbolHandles::dispatchUncaughtException_name(),
                                           vmSymbolHandles::throwable_void_signature(),
                                           KlassHandle(), false, false, THREAD);
        CLEAR_PENDING_EXCEPTION;
        methodHandle method = callinfo.selected_method();
        if (method.not_null()) {
          JavaValue result(T_VOID);
          JavaCalls::call_virtual(&result,
                                  threadObj, thread_klass,
                                  vmSymbolHandles::dispatchUncaughtException_name(),
                                  vmSymbolHandles::throwable_void_signature(),
                                  uncaught_exception,
                                  THREAD);
        } else {
          KlassHandle thread_group(THREAD, SystemDictionary::ThreadGroup_klass());
          JavaValue result(T_VOID);
          JavaCalls::call_virtual(&result,
                                  group, thread_group,
                                  vmSymbolHandles::uncaughtException_name(),
                                  vmSymbolHandles::thread_throwable_void_signature(),
                                  threadObj,           // Arg 1
                                  uncaught_exception,  // Arg 2
                                  THREAD);
        }
        CLEAR_PENDING_EXCEPTION;
      }
    }

    // Call Thread.exit(). We try 3 times in case we got another Thread.stop during
    // the execution of the method. If that is not enough, then we don't really care. Thread.stop
    // is deprecated anyhow.
    { int count = 3;
      while (java_lang_Thread::threadGroup(threadObj()) != NULL && (count-- > 0)) {
        EXCEPTION_MARK;
        JavaValue result(T_VOID);
        KlassHandle thread_klass(THREAD, SystemDictionary::Thread_klass());
        JavaCalls::call_virtual(&result,
                              threadObj, thread_klass,
                              vmSymbolHandles::exit_method_name(),
                              vmSymbolHandles::void_method_signature(),
                              THREAD);
        CLEAR_PENDING_EXCEPTION;
      }
    }

    // notify JVMTI
    if (JvmtiExport::should_post_thread_life()) {
      JvmtiExport::post_thread_end(this);
    }

    // We have notified the agents that we are exiting, before we go on,
    // we must check for a pending external suspend request and honor it
    // in order to not surprise the thread that made the suspend request.
    while (true) {
      {
        MutexLockerEx ml(SR_lock(), Mutex::_no_safepoint_check_flag);
        if (!is_external_suspend()) {
          set_terminated(_thread_exiting);
          ThreadService::current_thread_exiting(this);
          break;
        }
        // Implied else:
        // Things get a little tricky here. We have a pending external
        // suspend request, but we are holding the SR_lock so we
        // can't just self-suspend. So we temporarily drop the lock
        // and then self-suspend.
      }

      ThreadBlockInVM tbivm(this);
      java_suspend_self();

      // We're done with this suspend request, but we have to loop around
      // and check again. Eventually we will get SR_lock without a pending
      // external suspend request and will be able to mark ourselves as
      // exiting.
    }
    // no more external suspends are allowed at this point
  } else {
    // before_exit() has already posted JVMTI THREAD_END events
  }

  // Notify waiters on thread object. This has to be done after exit() is called
  // on the thread (if the thread is the last thread in a daemon ThreadGroup the
  // group should have the destroyed bit set before waiters are notified).
  ensure_join(this);
  assert(!this->has_pending_exception(), "ensure_join should have cleared");

  // 6282335 JNI DetachCurrentThread spec states that all Java monitors
  // held by this thread must be released.  A detach operation must only
  // get here if there are no Java frames on the stack.  Therefore, any
  // owned monitors at this point MUST be JNI-acquired monitors which are
  // pre-inflated and in the monitor cache.
  //
  // ensure_join() ignores IllegalThreadStateExceptions, and so does this.
  if (exit_type == jni_detach && JNIDetachReleasesMonitors) {
    assert(!this->has_last_Java_frame(), "detaching with Java frames?");
    ObjectSynchronizer::release_monitors_owned_by_thread(this);
    assert(!this->has_pending_exception(), "release_monitors should have cleared");
  }

  // These things needs to be done while we are still a Java Thread. Make sure that thread
  // is in a consistent state, in case GC happens
  assert(_privileged_stack_top == NULL, "must be NULL when we get here");

  if (active_handles() != NULL) {
    JNIHandleBlock* block = active_handles();
    set_active_handles(NULL);
    JNIHandleBlock::release_block(block);
  }

  if (free_handle_block() != NULL) {
    JNIHandleBlock* block = free_handle_block();
    set_free_handle_block(NULL);
    JNIHandleBlock::release_block(block);
  }

  // These have to be removed while this is still a valid thread.
  remove_stack_guard_pages();

  if (UseTLAB) {
    tlab().make_parsable(true);  // retire TLAB
  }

  if (jvmti_thread_state() != NULL) {
    JvmtiExport::cleanup_thread(this);
  }

#ifndef SERIALGC
  // We must flush G1-related buffers before removing a thread from
  // the list of active threads.
  if (UseG1GC) {
    flush_barrier_queues();
  }
#endif

  // Remove from list of active threads list, and notify VM thread if we are the last non-daemon thread
  Threads::remove(this);
}

#ifndef SERIALGC
// Flush G1-related queues.
void JavaThread::flush_barrier_queues() {
  satb_mark_queue().flush();
  dirty_card_queue().flush();
}

void JavaThread::initialize_queues() {
  assert(!SafepointSynchronize::is_at_safepoint(),
         "we should not be at a safepoint");

  ObjPtrQueue& satb_queue = satb_mark_queue();
  SATBMarkQueueSet& satb_queue_set = satb_mark_queue_set();
  // The SATB queue should have been constructed with its active
  // field set to false.
  assert(!satb_queue.is_active(), "SATB queue should not be active");
  assert(satb_queue.is_empty(), "SATB queue should be empty");
  // If we are creating the thread during a marking cycle, we should
  // set the active field of the SATB queue to true.
  if (satb_queue_set.is_active()) {
    satb_queue.set_active(true);
  }

  DirtyCardQueue& dirty_queue = dirty_card_queue();
  // The dirty card queue should have been constructed with its
  // active field set to true.
  assert(dirty_queue.is_active(), "dirty card queue should be active");
}
#endif // !SERIALGC

void JavaThread::cleanup_failed_attach_current_thread() {
  if (get_thread_profiler() != NULL) {
    get_thread_profiler()->disengage();
    ResourceMark rm;
    get_thread_profiler()->print(get_thread_name());
  }

  if (active_handles() != NULL) {
    JNIHandleBlock* block = active_handles();
    set_active_handles(NULL);
    JNIHandleBlock::release_block(block);
  }

  if (free_handle_block() != NULL) {
    JNIHandleBlock* block = free_handle_block();
    set_free_handle_block(NULL);
    JNIHandleBlock::release_block(block);
  }

  // These have to be removed while this is still a valid thread.
  remove_stack_guard_pages();

  if (UseTLAB) {
    tlab().make_parsable(true);  // retire TLAB, if any
  }

#ifndef SERIALGC
  if (UseG1GC) {
    flush_barrier_queues();
  }
#endif

  Threads::remove(this);
  delete this;
}


JavaThread* JavaThread::active() {
  Thread* thread = ThreadLocalStorage::thread();
  assert(thread != NULL, "just checking");
  if (thread->is_Java_thread()) {
    return (JavaThread*) thread;
  } else {
    assert(thread->is_VM_thread(), "this must be a vm thread");
    VM_Operation* op = ((VMThread*) thread)->vm_operation();
    JavaThread *ret=op == NULL ? NULL : (JavaThread *)op->calling_thread();
    assert(ret->is_Java_thread(), "must be a Java thread");
    return ret;
  }
}

bool JavaThread::is_lock_owned(address adr) const {
  if (Thread::is_lock_owned(adr)) return true;

  for (MonitorChunk* chunk = monitor_chunks(); chunk != NULL; chunk = chunk->next()) {
    if (chunk->contains(adr)) return true;
  }

  return false;
}


void JavaThread::add_monitor_chunk(MonitorChunk* chunk) {
  chunk->set_next(monitor_chunks());
  set_monitor_chunks(chunk);
}

void JavaThread::remove_monitor_chunk(MonitorChunk* chunk) {
  guarantee(monitor_chunks() != NULL, "must be non empty");
  if (monitor_chunks() == chunk) {
    set_monitor_chunks(chunk->next());
  } else {
    MonitorChunk* prev = monitor_chunks();
    while (prev->next() != chunk) prev = prev->next();
    prev->set_next(chunk->next());
  }
}

// JVM support.

// Note: this function shouldn't block if it's called in
// _thread_in_native_trans state (such as from
// check_special_condition_for_native_trans()).
void JavaThread::check_and_handle_async_exceptions(bool check_unsafe_error) {

  if (has_last_Java_frame() && has_async_condition()) {
    // If we are at a polling page safepoint (not a poll return)
    // then we must defer async exception because live registers
    // will be clobbered by the exception path. Poll return is
    // ok because the call we a returning from already collides
    // with exception handling registers and so there is no issue.
    // (The exception handling path kills call result registers but
    //  this is ok since the exception kills the result anyway).

    if (is_at_poll_safepoint()) {
      // if the code we are returning to has deoptimized we must defer
      // the exception otherwise live registers get clobbered on the
      // exception path before deoptimization is able to retrieve them.
      //
      RegisterMap map(this, false);
      frame caller_fr = last_frame().sender(&map);
      assert(caller_fr.is_compiled_frame(), "what?");
      if (caller_fr.is_deoptimized_frame()) {
        if (TraceExceptions) {
          ResourceMark rm;
          tty->print_cr("deferred async exception at compiled safepoint");
        }
        return;
      }
    }
  }

  JavaThread::AsyncRequests condition = clear_special_runtime_exit_condition();
  if (condition == _no_async_condition) {
    // Conditions have changed since has_special_runtime_exit_condition()
    // was called:
    // - if we were here only because of an external suspend request,
    //   then that was taken care of above (or cancelled) so we are done
    // - if we were here because of another async request, then it has
    //   been cleared between the has_special_runtime_exit_condition()
    //   and now so again we are done
    return;
  }

  // Check for pending async. exception
  if (_pending_async_exception != NULL) {
    // Only overwrite an already pending exception, if it is not a threadDeath.
    if (!has_pending_exception() || !pending_exception()->is_a(SystemDictionary::ThreadDeath_klass())) {

      // We cannot call Exceptions::_throw(...) here because we cannot block
      set_pending_exception(_pending_async_exception, __FILE__, __LINE__);

      if (TraceExceptions) {
        ResourceMark rm;
        tty->print("Async. exception installed at runtime exit (" INTPTR_FORMAT ")", this);
        if (has_last_Java_frame() ) {
          frame f = last_frame();
          tty->print(" (pc: " INTPTR_FORMAT " sp: " INTPTR_FORMAT " )", f.pc(), f.sp());
        }
        tty->print_cr(" of type: %s", instanceKlass::cast(_pending_async_exception->klass())->external_name());
      }
      _pending_async_exception = NULL;
      clear_has_async_exception();
    }
  }

  if (check_unsafe_error &&
      condition == _async_unsafe_access_error && !has_pending_exception()) {
    condition = _no_async_condition;  // done
    switch (thread_state()) {
    case _thread_in_vm:
      {
        JavaThread* THREAD = this;
        THROW_MSG(vmSymbols::java_lang_InternalError(), "a fault occurred in an unsafe memory access operation");
      }
    case _thread_in_native:
      {
        ThreadInVMfromNative tiv(this);
        JavaThread* THREAD = this;
        THROW_MSG(vmSymbols::java_lang_InternalError(), "a fault occurred in an unsafe memory access operation");
      }
    case _thread_in_Java:
      {
        ThreadInVMfromJava tiv(this);
        JavaThread* THREAD = this;
        THROW_MSG(vmSymbols::java_lang_InternalError(), "a fault occurred in a recent unsafe memory access operation in compiled Java code");
      }
    default:
      ShouldNotReachHere();
    }
  }

  assert(condition == _no_async_condition || has_pending_exception() ||
         (!check_unsafe_error && condition == _async_unsafe_access_error),
         "must have handled the async condition, if no exception");
}

void JavaThread::handle_special_runtime_exit_condition(bool check_asyncs) {
  //
  // Check for pending external suspend. Internal suspend requests do
  // not use handle_special_runtime_exit_condition().
  // If JNIEnv proxies are allowed, don't self-suspend if the target
  // thread is not the current thread. In older versions of jdbx, jdbx
  // threads could call into the VM with another thread's JNIEnv so we
  // can be here operating on behalf of a suspended thread (4432884).
  bool do_self_suspend = is_external_suspend_with_lock();
  if (do_self_suspend && (!AllowJNIEnvProxy || this == JavaThread::current())) {
    //
    // Because thread is external suspended the safepoint code will count
    // thread as at a safepoint. This can be odd because we can be here
    // as _thread_in_Java which would normally transition to _thread_blocked
    // at a safepoint. We would like to mark the thread as _thread_blocked
    // before calling java_suspend_self like all other callers of it but
    // we must then observe proper safepoint protocol. (We can't leave
    // _thread_blocked with a safepoint in progress). However we can be
    // here as _thread_in_native_trans so we can't use a normal transition
    // constructor/destructor pair because they assert on that type of
    // transition. We could do something like:
    //
    // JavaThreadState state = thread_state();
    // set_thread_state(_thread_in_vm);
    // {
    //   ThreadBlockInVM tbivm(this);
    //   java_suspend_self()
    // }
    // set_thread_state(_thread_in_vm_trans);
    // if (safepoint) block;
    // set_thread_state(state);
    //
    // but that is pretty messy. Instead we just go with the way the
    // code has worked before and note that this is the only path to
    // java_suspend_self that doesn't put the thread in _thread_blocked
    // mode.

    frame_anchor()->make_walkable(this);
    java_suspend_self();

    // We might be here for reasons in addition to the self-suspend request
    // so check for other async requests.
  }

  if (check_asyncs) {
    check_and_handle_async_exceptions();
  }
}

void JavaThread::send_thread_stop(oop java_throwable)  {
  assert(Thread::current()->is_VM_thread(), "should be in the vm thread");
  assert(Threads_lock->is_locked(), "Threads_lock should be locked by safepoint code");
  assert(SafepointSynchronize::is_at_safepoint(), "all threads are stopped");

  // Do not throw asynchronous exceptions against the compiler thread
  // (the compiler thread should not be a Java thread -- fix in 1.4.2)
  if (is_Compiler_thread()) return;

  // This is a change from JDK 1.1, but JDK 1.2 will also do it:
  if (java_throwable->is_a(SystemDictionary::ThreadDeath_klass())) {
    java_lang_Thread::set_stillborn(threadObj());
  }

  {
    // Actually throw the Throwable against the target Thread - however
    // only if there is no thread death exception installed already.
    if (_pending_async_exception == NULL || !_pending_async_exception->is_a(SystemDictionary::ThreadDeath_klass())) {
      // If the topmost frame is a runtime stub, then we are calling into
      // OptoRuntime from compiled code. Some runtime stubs (new, monitor_exit..)
      // must deoptimize the caller before continuing, as the compiled  exception handler table
      // may not be valid
      if (has_last_Java_frame()) {
        frame f = last_frame();
        if (f.is_runtime_frame() || f.is_safepoint_blob_frame()) {
          // BiasedLocking needs an updated RegisterMap for the revoke monitors pass
          RegisterMap reg_map(this, UseBiasedLocking);
          frame compiled_frame = f.sender(&reg_map);
          if (compiled_frame.can_be_deoptimized()) {
            Deoptimization::deoptimize(this, compiled_frame, &reg_map);
          }
        }
      }

      // Set async. pending exception in thread.
      set_pending_async_exception(java_throwable);

      if (TraceExceptions) {
       ResourceMark rm;
       tty->print_cr("Pending Async. exception installed of type: %s", instanceKlass::cast(_pending_async_exception->klass())->external_name());
      }
      // for AbortVMOnException flag
      NOT_PRODUCT(Exceptions::debug_check_abort(instanceKlass::cast(_pending_async_exception->klass())->external_name()));
    }
  }


  // Interrupt thread so it will wake up from a potential wait()
  Thread::interrupt(this);
}

// External suspension mechanism.
//
// Tell the VM to suspend a thread when ever it knows that it does not hold on
// to any VM_locks and it is at a transition
// Self-suspension will happen on the transition out of the vm.
// Catch "this" coming in from JNIEnv pointers when the thread has been freed
//
// Guarantees on return:
//   + Target thread will not execute any new bytecode (that's why we need to
//     force a safepoint)
//   + Target thread will not enter any new monitors
//
void JavaThread::java_suspend() {
  { MutexLocker mu(Threads_lock);
    if (!Threads::includes(this) || is_exiting() || this->threadObj() == NULL) {
       return;
    }
  }

  { MutexLockerEx ml(SR_lock(), Mutex::_no_safepoint_check_flag);
    if (!is_external_suspend()) {
      // a racing resume has cancelled us; bail out now
      return;
    }

    // suspend is done
    uint32_t debug_bits = 0;
    // Warning: is_ext_suspend_completed() may temporarily drop the
    // SR_lock to allow the thread to reach a stable thread state if
    // it is currently in a transient thread state.
    if (is_ext_suspend_completed(false /* !called_by_wait */,
                                 SuspendRetryDelay, &debug_bits) ) {
      return;
    }
  }

  VM_ForceSafepoint vm_suspend;
  VMThread::execute(&vm_suspend);
}

// Part II of external suspension.
// A JavaThread self suspends when it detects a pending external suspend
// request. This is usually on transitions. It is also done in places
// where continuing to the next transition would surprise the caller,
// e.g., monitor entry.
//
// Returns the number of times that the thread self-suspended.
//
// Note: DO NOT call java_suspend_self() when you just want to block current
//       thread. java_suspend_self() is the second stage of cooperative
//       suspension for external suspend requests and should only be used
//       to complete an external suspend request.
//
int JavaThread::java_suspend_self() {
  int ret = 0;

  // we are in the process of exiting so don't suspend
  if (is_exiting()) {
     clear_external_suspend();
     return ret;
  }

  assert(_anchor.walkable() ||
    (is_Java_thread() && !((JavaThread*)this)->has_last_Java_frame()),
    "must have walkable stack");

  MutexLockerEx ml(SR_lock(), Mutex::_no_safepoint_check_flag);

  assert(!this->is_ext_suspended(),
    "a thread trying to self-suspend should not already be suspended");

  if (this->is_suspend_equivalent()) {
    // If we are self-suspending as a result of the lifting of a
    // suspend equivalent condition, then the suspend_equivalent
    // flag is not cleared until we set the ext_suspended flag so
    // that wait_for_ext_suspend_completion() returns consistent
    // results.
    this->clear_suspend_equivalent();
  }

  // A racing resume may have cancelled us before we grabbed SR_lock
  // above. Or another external suspend request could be waiting for us
  // by the time we return from SR_lock()->wait(). The thread
  // that requested the suspension may already be trying to walk our
  // stack and if we return now, we can change the stack out from under
  // it. This would be a "bad thing (TM)" and cause the stack walker
  // to crash. We stay self-suspended until there are no more pending
  // external suspend requests.
  while (is_external_suspend()) {
    ret++;
    this->set_ext_suspended();

    // _ext_suspended flag is cleared by java_resume()
    while (is_ext_suspended()) {
      this->SR_lock()->wait(Mutex::_no_safepoint_check_flag);
    }
  }

  return ret;
}

#ifdef ASSERT
// verify the JavaThread has not yet been published in the Threads::list, and
// hence doesn't need protection from concurrent access at this stage
void JavaThread::verify_not_published() {
  if (!Threads_lock->owned_by_self()) {
   MutexLockerEx ml(Threads_lock,  Mutex::_no_safepoint_check_flag);
   assert( !Threads::includes(this),
           "java thread shouldn't have been published yet!");
  }
  else {
   assert( !Threads::includes(this),
           "java thread shouldn't have been published yet!");
  }
}
#endif

// Slow path when the native==>VM/Java barriers detect a safepoint is in
// progress or when _suspend_flags is non-zero.
// Current thread needs to self-suspend if there is a suspend request and/or
// block if a safepoint is in progress.
// Async exception ISN'T checked.
// Note only the ThreadInVMfromNative transition can call this function
// directly and when thread state is _thread_in_native_trans
void JavaThread::check_safepoint_and_suspend_for_native_trans(JavaThread *thread) {
  assert(thread->thread_state() == _thread_in_native_trans, "wrong state");

  JavaThread *curJT = JavaThread::current();
  bool do_self_suspend = thread->is_external_suspend();

  assert(!curJT->has_last_Java_frame() || curJT->frame_anchor()->walkable(), "Unwalkable stack in native->vm transition");

  // If JNIEnv proxies are allowed, don't self-suspend if the target
  // thread is not the current thread. In older versions of jdbx, jdbx
  // threads could call into the VM with another thread's JNIEnv so we
  // can be here operating on behalf of a suspended thread (4432884).
  if (do_self_suspend && (!AllowJNIEnvProxy || curJT == thread)) {
    JavaThreadState state = thread->thread_state();

    // We mark this thread_blocked state as a suspend-equivalent so
    // that a caller to is_ext_suspend_completed() won't be confused.
    // The suspend-equivalent state is cleared by java_suspend_self().
    thread->set_suspend_equivalent();

    // If the safepoint code sees the _thread_in_native_trans state, it will
    // wait until the thread changes to other thread state. There is no
    // guarantee on how soon we can obtain the SR_lock and complete the
    // self-suspend request. It would be a bad idea to let safepoint wait for
    // too long. Temporarily change the state to _thread_blocked to
    // let the VM thread know that this thread is ready for GC. The problem
    // of changing thread state is that safepoint could happen just after
    // java_suspend_self() returns after being resumed, and VM thread will
    // see the _thread_blocked state. We must check for safepoint
    // after restoring the state and make sure we won't leave while a safepoint
    // is in progress.
    thread->set_thread_state(_thread_blocked);
    thread->java_suspend_self();
    thread->set_thread_state(state);
    // Make sure new state is seen by VM thread
    if (os::is_MP()) {
      if (UseMembar) {
        // Force a fence between the write above and read below
        OrderAccess::fence();
      } else {
        // Must use this rather than serialization page in particular on Windows
        InterfaceSupport::serialize_memory(thread);
      }
    }
  }

  if (SafepointSynchronize::do_call_back()) {
    // If we are safepointing, then block the caller which may not be
    // the same as the target thread (see above).
    SafepointSynchronize::block(curJT);
  }

  if (thread->is_deopt_suspend()) {
    thread->clear_deopt_suspend();
    RegisterMap map(thread, false);
    frame f = thread->last_frame();
    while ( f.id() != thread->must_deopt_id() && ! f.is_first_frame()) {
      f = f.sender(&map);
    }
    if (f.id() == thread->must_deopt_id()) {
      thread->clear_must_deopt_id();
      f.deoptimize(thread);
    } else {
      fatal("missed deoptimization!");
    }
  }
}

// Slow path when the native==>VM/Java barriers detect a safepoint is in
// progress or when _suspend_flags is non-zero.
// Current thread needs to self-suspend if there is a suspend request and/or
// block if a safepoint is in progress.
// Also check for pending async exception (not including unsafe access error).
// Note only the native==>VM/Java barriers can call this function and when
// thread state is _thread_in_native_trans.
void JavaThread::check_special_condition_for_native_trans(JavaThread *thread) {
  check_safepoint_and_suspend_for_native_trans(thread);

  if (thread->has_async_exception()) {
    // We are in _thread_in_native_trans state, don't handle unsafe
    // access error since that may block.
    thread->check_and_handle_async_exceptions(false);
  }
}

// We need to guarantee the Threads_lock here, since resumes are not
// allowed during safepoint synchronization
// Can only resume from an external suspension
void JavaThread::java_resume() {
  assert_locked_or_safepoint(Threads_lock);

  // Sanity check: thread is gone, has started exiting or the thread
  // was not externally suspended.
  if (!Threads::includes(this) || is_exiting() || !is_external_suspend()) {
    return;
  }

  MutexLockerEx ml(SR_lock(), Mutex::_no_safepoint_check_flag);

  clear_external_suspend();

  if (is_ext_suspended()) {
    clear_ext_suspended();
    SR_lock()->notify_all();
  }
}

void JavaThread::create_stack_guard_pages() {
  if (! os::uses_stack_guard_pages() || _stack_guard_state != stack_guard_unused) return;
  address low_addr = stack_base() - stack_size();
  size_t len = (StackYellowPages + StackRedPages) * os::vm_page_size();

  int allocate = os::allocate_stack_guard_pages();
  // warning("Guarding at " PTR_FORMAT " for len " SIZE_FORMAT "\n", low_addr, len);

  if (allocate && !os::create_stack_guard_pages((char *) low_addr, len)) {
    warning("Attempt to allocate stack guard pages failed.");
    return;
  }

  if (os::guard_memory((char *) low_addr, len)) {
    _stack_guard_state = stack_guard_enabled;
  } else {
    warning("Attempt to protect stack guard pages failed.");
    if (os::uncommit_memory((char *) low_addr, len)) {
      warning("Attempt to deallocate stack guard pages failed.");
    }
  }
}

void JavaThread::remove_stack_guard_pages() {
  if (_stack_guard_state == stack_guard_unused) return;
  address low_addr = stack_base() - stack_size();
  size_t len = (StackYellowPages + StackRedPages) * os::vm_page_size();

  if (os::allocate_stack_guard_pages()) {
    if (os::remove_stack_guard_pages((char *) low_addr, len)) {
      _stack_guard_state = stack_guard_unused;
    } else {
      warning("Attempt to deallocate stack guard pages failed.");
    }
  } else {
    if (_stack_guard_state == stack_guard_unused) return;
    if (os::unguard_memory((char *) low_addr, len)) {
      _stack_guard_state = stack_guard_unused;
    } else {
        warning("Attempt to unprotect stack guard pages failed.");
    }
  }
}

void JavaThread::enable_stack_yellow_zone() {
  assert(_stack_guard_state != stack_guard_unused, "must be using guard pages.");
  assert(_stack_guard_state != stack_guard_enabled, "already enabled");

  // The base notation is from the stacks point of view, growing downward.
  // We need to adjust it to work correctly with guard_memory()
  address base = stack_yellow_zone_base() - stack_yellow_zone_size();

  guarantee(base < stack_base(),"Error calculating stack yellow zone");
  guarantee(base < os::current_stack_pointer(),"Error calculating stack yellow zone");

  if (os::guard_memory((char *) base, stack_yellow_zone_size())) {
    _stack_guard_state = stack_guard_enabled;
  } else {
    warning("Attempt to guard stack yellow zone failed.");
  }
  enable_register_stack_guard();
}

void JavaThread::disable_stack_yellow_zone() {
  assert(_stack_guard_state != stack_guard_unused, "must be using guard pages.");
  assert(_stack_guard_state != stack_guard_yellow_disabled, "already disabled");

  // Simply return if called for a thread that does not use guard pages.
  if (_stack_guard_state == stack_guard_unused) return;

  // The base notation is from the stacks point of view, growing downward.
  // We need to adjust it to work correctly with guard_memory()
  address base = stack_yellow_zone_base() - stack_yellow_zone_size();

  if (os::unguard_memory((char *)base, stack_yellow_zone_size())) {
    _stack_guard_state = stack_guard_yellow_disabled;
  } else {
    warning("Attempt to unguard stack yellow zone failed.");
  }
  disable_register_stack_guard();
}

void JavaThread::enable_stack_red_zone() {
  // The base notation is from the stacks point of view, growing downward.
  // We need to adjust it to work correctly with guard_memory()
  assert(_stack_guard_state != stack_guard_unused, "must be using guard pages.");
  address base = stack_red_zone_base() - stack_red_zone_size();

  guarantee(base < stack_base(),"Error calculating stack red zone");
  guarantee(base < os::current_stack_pointer(),"Error calculating stack red zone");

  if(!os::guard_memory((char *) base, stack_red_zone_size())) {
    warning("Attempt to guard stack red zone failed.");
  }
}

void JavaThread::disable_stack_red_zone() {
  // The base notation is from the stacks point of view, growing downward.
  // We need to adjust it to work correctly with guard_memory()
  assert(_stack_guard_state != stack_guard_unused, "must be using guard pages.");
  address base = stack_red_zone_base() - stack_red_zone_size();
  if (!os::unguard_memory((char *)base, stack_red_zone_size())) {
    warning("Attempt to unguard stack red zone failed.");
  }
}

void JavaThread::frames_do(void f(frame*, const RegisterMap* map)) {
  // ignore is there is no stack
  if (!has_last_Java_frame()) return;
  // traverse the stack frames. Starts from top frame.
  for(StackFrameStream fst(this); !fst.is_done(); fst.next()) {
    frame* fr = fst.current();
    f(fr, fst.register_map());
  }
}


#ifndef PRODUCT
// Deoptimization
// Function for testing deoptimization
void JavaThread::deoptimize() {
  // BiasedLocking needs an updated RegisterMap for the revoke monitors pass
  StackFrameStream fst(this, UseBiasedLocking);
  bool deopt = false;           // Dump stack only if a deopt actually happens.
  bool only_at = strlen(DeoptimizeOnlyAt) > 0;
  // Iterate over all frames in the thread and deoptimize
  for(; !fst.is_done(); fst.next()) {
    if(fst.current()->can_be_deoptimized()) {

      if (only_at) {
        // Deoptimize only at particular bcis.  DeoptimizeOnlyAt
        // consists of comma or carriage return separated numbers so
        // search for the current bci in that string.
        address pc = fst.current()->pc();
        nmethod* nm =  (nmethod*) fst.current()->cb();
        ScopeDesc* sd = nm->scope_desc_at( pc);
        char buffer[8];
        jio_snprintf(buffer, sizeof(buffer), "%d", sd->bci());
        size_t len = strlen(buffer);
        const char * found = strstr(DeoptimizeOnlyAt, buffer);
        while (found != NULL) {
          if ((found[len] == ',' || found[len] == '\n' || found[len] == '\0') &&
              (found == DeoptimizeOnlyAt || found[-1] == ',' || found[-1] == '\n')) {
            // Check that the bci found is bracketed by terminators.
            break;
          }
          found = strstr(found + 1, buffer);
        }
        if (!found) {
          continue;
        }
      }

      if (DebugDeoptimization && !deopt) {
        deopt = true; // One-time only print before deopt
        tty->print_cr("[BEFORE Deoptimization]");
        trace_frames();
        trace_stack();
      }
      Deoptimization::deoptimize(this, *fst.current(), fst.register_map());
    }
  }

  if (DebugDeoptimization && deopt) {
    tty->print_cr("[AFTER Deoptimization]");
    trace_frames();
  }
}


// Make zombies
void JavaThread::make_zombies() {
  for(StackFrameStream fst(this); !fst.is_done(); fst.next()) {
    if (fst.current()->can_be_deoptimized()) {
      // it is a Java nmethod
      nmethod* nm = CodeCache::find_nmethod(fst.current()->pc());
      nm->make_not_entrant();
    }
  }
}
#endif // PRODUCT


void JavaThread::deoptimized_wrt_marked_nmethods() {
  if (!has_last_Java_frame()) return;
  // BiasedLocking needs an updated RegisterMap for the revoke monitors pass
  StackFrameStream fst(this, UseBiasedLocking);
  for(; !fst.is_done(); fst.next()) {
    if (fst.current()->should_be_deoptimized()) {
      Deoptimization::deoptimize(this, *fst.current(), fst.register_map());
    }
  }
}


// GC support
static void frame_gc_epilogue(frame* f, const RegisterMap* map) { f->gc_epilogue(); }

void JavaThread::gc_epilogue() {
  frames_do(frame_gc_epilogue);
}


static void frame_gc_prologue(frame* f, const RegisterMap* map) { f->gc_prologue(); }

void JavaThread::gc_prologue() {
  frames_do(frame_gc_prologue);
}

// If the caller is a NamedThread, then remember, in the current scope,
// the given JavaThread in its _processed_thread field.
class RememberProcessedThread: public StackObj {
  NamedThread* _cur_thr;
public:
  RememberProcessedThread(JavaThread* jthr) {
    Thread* thread = Thread::current();
    if (thread->is_Named_thread()) {
      _cur_thr = (NamedThread *)thread;
      _cur_thr->set_processed_thread(jthr);
    } else {
      _cur_thr = NULL;
    }
  }

  ~RememberProcessedThread() {
    if (_cur_thr) {
      _cur_thr->set_processed_thread(NULL);
    }
  }
};

void JavaThread::oops_do(OopClosure* f, CodeBlobClosure* cf) {
  // Verify that the deferred card marks have been flushed.
  assert(deferred_card_mark().is_empty(), "Should be empty during GC");

  // The ThreadProfiler oops_do is done from FlatProfiler::oops_do
  // since there may be more than one thread using each ThreadProfiler.

  // Traverse the GCHandles
  Thread::oops_do(f, cf);

  assert( (!has_last_Java_frame() && java_call_counter() == 0) ||
          (has_last_Java_frame() && java_call_counter() > 0), "wrong java_sp info!");

  if (has_last_Java_frame()) {
    // Record JavaThread to GC thread
    RememberProcessedThread rpt(this);

    // Traverse the privileged stack
    if (_privileged_stack_top != NULL) {
      _privileged_stack_top->oops_do(f);
    }

    // traverse the registered growable array
    if (_array_for_gc != NULL) {
      for (int index = 0; index < _array_for_gc->length(); index++) {
        f->do_oop(_array_for_gc->adr_at(index));
      }
    }

    // Traverse the monitor chunks
    for (MonitorChunk* chunk = monitor_chunks(); chunk != NULL; chunk = chunk->next()) {
      chunk->oops_do(f);
    }

    // Traverse the execution stack
    for(StackFrameStream fst(this); !fst.is_done(); fst.next()) {
      fst.current()->oops_do(f, cf, fst.register_map());
    }
  }

  // callee_target is never live across a gc point so NULL it here should
  // it still contain a methdOop.

  set_callee_target(NULL);

  assert(vframe_array_head() == NULL, "deopt in progress at a safepoint!");
  // If we have deferred set_locals there might be oops waiting to be
  // written
  GrowableArray<jvmtiDeferredLocalVariableSet*>* list = deferred_locals();
  if (list != NULL) {
    for (int i = 0; i < list->length(); i++) {
      list->at(i)->oops_do(f);
    }
  }

  // Traverse instance variables at the end since the GC may be moving things
  // around using this function
  f->do_oop((oop*) &_threadObj);
  f->do_oop((oop*) &_vm_result);
  f->do_oop((oop*) &_vm_result_2);
  f->do_oop((oop*) &_exception_oop);
  f->do_oop((oop*) &_pending_async_exception);

  if (jvmti_thread_state() != NULL) {
    jvmti_thread_state()->oops_do(f);
  }
}

void JavaThread::nmethods_do(CodeBlobClosure* cf) {
  Thread::nmethods_do(cf);  // (super method is a no-op)

  assert( (!has_last_Java_frame() && java_call_counter() == 0) ||
          (has_last_Java_frame() && java_call_counter() > 0), "wrong java_sp info!");

  if (has_last_Java_frame()) {
    // Traverse the execution stack
    for(StackFrameStream fst(this); !fst.is_done(); fst.next()) {
      fst.current()->nmethods_do(cf);
    }
  }
}

// Printing
const char* _get_thread_state_name(JavaThreadState _thread_state) {
  switch (_thread_state) {
  case _thread_uninitialized:     return "_thread_uninitialized";
  case _thread_new:               return "_thread_new";
  case _thread_new_trans:         return "_thread_new_trans";
  case _thread_in_native:         return "_thread_in_native";
  case _thread_in_native_trans:   return "_thread_in_native_trans";
  case _thread_in_vm:             return "_thread_in_vm";
  case _thread_in_vm_trans:       return "_thread_in_vm_trans";
  case _thread_in_Java:           return "_thread_in_Java";
  case _thread_in_Java_trans:     return "_thread_in_Java_trans";
  case _thread_blocked:           return "_thread_blocked";
  case _thread_blocked_trans:     return "_thread_blocked_trans";
  default:                        return "unknown thread state";
  }
}

#ifndef PRODUCT
void JavaThread::print_thread_state_on(outputStream *st) const {
  st->print_cr("   JavaThread state: %s", _get_thread_state_name(_thread_state));
};
void JavaThread::print_thread_state() const {
  print_thread_state_on(tty);
};
#endif // PRODUCT

// Called by Threads::print() for VM_PrintThreads operation
void JavaThread::print_on(outputStream *st) const {
  st->print("\"%s\" ", get_thread_name());
  oop thread_oop = threadObj();
  if (thread_oop != NULL && java_lang_Thread::is_daemon(thread_oop))  st->print("daemon ");
  Thread::print_on(st);
  // print guess for valid stack memory region (assume 4K pages); helps lock debugging
  st->print_cr("[" INTPTR_FORMAT "]", (intptr_t)last_Java_sp() & ~right_n_bits(12));
  if (thread_oop != NULL && JDK_Version::is_gte_jdk15x_version()) {
    st->print_cr("   java.lang.Thread.State: %s", java_lang_Thread::thread_status_name(thread_oop));
  }
#ifndef PRODUCT
  print_thread_state_on(st);
  _safepoint_state->print_on(st);
#endif // PRODUCT
}

// Called by fatal error handler. The difference between this and
// JavaThread::print() is that we can't grab lock or allocate memory.
void JavaThread::print_on_error(outputStream* st, char *buf, int buflen) const {
  st->print("JavaThread \"%s\"",  get_thread_name_string(buf, buflen));
  oop thread_obj = threadObj();
  if (thread_obj != NULL) {
     if (java_lang_Thread::is_daemon(thread_obj)) st->print(" daemon");
  }
  st->print(" [");
  st->print("%s", _get_thread_state_name(_thread_state));
  if (osthread()) {
    st->print(", id=%d", osthread()->thread_id());
  }
  st->print(", stack(" PTR_FORMAT "," PTR_FORMAT ")",
            _stack_base - _stack_size, _stack_base);
  st->print("]");
  return;
}

// Verification

static void frame_verify(frame* f, const RegisterMap *map) { f->verify(map); }

void JavaThread::verify() {
  // Verify oops in the thread.
  oops_do(&VerifyOopClosure::verify_oop, NULL);

  // Verify the stack frames.
  frames_do(frame_verify);
}

// CR 6300358 (sub-CR 2137150)
// Most callers of this method assume that it can't return NULL but a
// thread may not have a name whilst it is in the process of attaching to
// the VM - see CR 6412693, and there are places where a JavaThread can be
// seen prior to having it's threadObj set (eg JNI attaching threads and
// if vm exit occurs during initialization). These cases can all be accounted
// for such that this method never returns NULL.
const char* JavaThread::get_thread_name() const {
#ifdef ASSERT
  // early safepoints can hit while current thread does not yet have TLS
  if (!SafepointSynchronize::is_at_safepoint()) {
    Thread *cur = Thread::current();
    if (!(cur->is_Java_thread() && cur == this)) {
      // Current JavaThreads are allowed to get their own name without
      // the Threads_lock.
      assert_locked_or_safepoint(Threads_lock);
    }
  }
#endif // ASSERT
    return get_thread_name_string();
}

// Returns a non-NULL representation of this thread's name, or a suitable
// descriptive string if there is no set name
const char* JavaThread::get_thread_name_string(char* buf, int buflen) const {
  const char* name_str;
  oop thread_obj = threadObj();
  if (thread_obj != NULL) {
    typeArrayOop name = java_lang_Thread::name(thread_obj);
    if (name != NULL) {
      if (buf == NULL) {
        name_str = UNICODE::as_utf8((jchar*) name->base(T_CHAR), name->length());
      }
      else {
        name_str = UNICODE::as_utf8((jchar*) name->base(T_CHAR), name->length(), buf, buflen);
      }
    }
    else if (is_attaching()) { // workaround for 6412693 - see 6404306
      name_str = "<no-name - thread is attaching>";
    }
    else {
      name_str = Thread::name();
    }
  }
  else {
    name_str = Thread::name();
  }
  assert(name_str != NULL, "unexpected NULL thread name");
  return name_str;
}


const char* JavaThread::get_threadgroup_name() const {
  debug_only(if (JavaThread::current() != this) assert_locked_or_safepoint(Threads_lock);)
  oop thread_obj = threadObj();
  if (thread_obj != NULL) {
    oop thread_group = java_lang_Thread::threadGroup(thread_obj);
    if (thread_group != NULL) {
      typeArrayOop name = java_lang_ThreadGroup::name(thread_group);
      // ThreadGroup.name can be null
      if (name != NULL) {
        const char* str = UNICODE::as_utf8((jchar*) name->base(T_CHAR), name->length());
        return str;
      }
    }
  }
  return NULL;
}

const char* JavaThread::get_parent_name() const {
  debug_only(if (JavaThread::current() != this) assert_locked_or_safepoint(Threads_lock);)
  oop thread_obj = threadObj();
  if (thread_obj != NULL) {
    oop thread_group = java_lang_Thread::threadGroup(thread_obj);
    if (thread_group != NULL) {
      oop parent = java_lang_ThreadGroup::parent(thread_group);
      if (parent != NULL) {
        typeArrayOop name = java_lang_ThreadGroup::name(parent);
        // ThreadGroup.name can be null
        if (name != NULL) {
          const char* str = UNICODE::as_utf8((jchar*) name->base(T_CHAR), name->length());
          return str;
        }
      }
    }
  }
  return NULL;
}

ThreadPriority JavaThread::java_priority() const {
  oop thr_oop = threadObj();
  if (thr_oop == NULL) return NormPriority; // Bootstrapping
  ThreadPriority priority = java_lang_Thread::priority(thr_oop);
  assert(MinPriority <= priority && priority <= MaxPriority, "sanity check");
  return priority;
}

void JavaThread::prepare(jobject jni_thread, ThreadPriority prio) {

  assert(Threads_lock->owner() == Thread::current(), "must have threads lock");
  // Link Java Thread object <-> C++ Thread

  // Get the C++ thread object (an oop) from the JNI handle (a jthread)
  // and put it into a new Handle.  The Handle "thread_oop" can then
  // be used to pass the C++ thread object to other methods.

  // Set the Java level thread object (jthread) field of the
  // new thread (a JavaThread *) to C++ thread object using the
  // "thread_oop" handle.

  // Set the thread field (a JavaThread *) of the
  // oop representing the java_lang_Thread to the new thread (a JavaThread *).

  Handle thread_oop(Thread::current(),
                    JNIHandles::resolve_non_null(jni_thread));
  assert(instanceKlass::cast(thread_oop->klass())->is_linked(),
    "must be initialized");
  set_threadObj(thread_oop());
  java_lang_Thread::set_thread(thread_oop(), this);

  if (prio == NoPriority) {
    prio = java_lang_Thread::priority(thread_oop());
    assert(prio != NoPriority, "A valid priority should be present");
  }

  // Push the Java priority down to the native thread; needs Threads_lock
  Thread::set_priority(this, prio);

  // Add the new thread to the Threads list and set it in motion.
  // We must have threads lock in order to call Threads::add.
  // It is crucial that we do not block before the thread is
  // added to the Threads list for if a GC happens, then the java_thread oop
  // will not be visited by GC.
  Threads::add(this);
}

oop JavaThread::current_park_blocker() {
  // Support for JSR-166 locks
  oop thread_oop = threadObj();
  if (thread_oop != NULL &&
      JDK_Version::current().supports_thread_park_blocker()) {
    return java_lang_Thread::park_blocker(thread_oop);
  }
  return NULL;
}


void JavaThread::print_stack_on(outputStream* st) {
  if (!has_last_Java_frame()) return;
  ResourceMark rm;
  HandleMark   hm;

  RegisterMap reg_map(this);
  vframe* start_vf = last_java_vframe(&reg_map);
  int count = 0;
  for (vframe* f = start_vf; f; f = f->sender() ) {
    if (f->is_java_frame()) {
      javaVFrame* jvf = javaVFrame::cast(f);
      java_lang_Throwable::print_stack_element(st, jvf->method(), jvf->bci());

      // Print out lock information
      if (JavaMonitorsInStackTrace) {
        jvf->print_lock_info_on(st, count);
      }
    } else {
      // Ignore non-Java frames
    }

    // Bail-out case for too deep stacks
    count++;
    if (MaxJavaStackTraceDepth == count) return;
  }
}


// JVMTI PopFrame support
void JavaThread::popframe_preserve_args(ByteSize size_in_bytes, void* start) {
  assert(_popframe_preserved_args == NULL, "should not wipe out old PopFrame preserved arguments");
  if (in_bytes(size_in_bytes) != 0) {
    _popframe_preserved_args = NEW_C_HEAP_ARRAY(char, in_bytes(size_in_bytes));
    _popframe_preserved_args_size = in_bytes(size_in_bytes);
    Copy::conjoint_jbytes(start, _popframe_preserved_args, _popframe_preserved_args_size);
  }
}

void* JavaThread::popframe_preserved_args() {
  return _popframe_preserved_args;
}

ByteSize JavaThread::popframe_preserved_args_size() {
  return in_ByteSize(_popframe_preserved_args_size);
}

WordSize JavaThread::popframe_preserved_args_size_in_words() {
  int sz = in_bytes(popframe_preserved_args_size());
  assert(sz % wordSize == 0, "argument size must be multiple of wordSize");
  return in_WordSize(sz / wordSize);
}

void JavaThread::popframe_free_preserved_args() {
  assert(_popframe_preserved_args != NULL, "should not free PopFrame preserved arguments twice");
  FREE_C_HEAP_ARRAY(char, (char*) _popframe_preserved_args);
  _popframe_preserved_args = NULL;
  _popframe_preserved_args_size = 0;
}

#ifndef PRODUCT

void JavaThread::trace_frames() {
  tty->print_cr("[Describe stack]");
  int frame_no = 1;
  for(StackFrameStream fst(this); !fst.is_done(); fst.next()) {
    tty->print("  %d. ", frame_no++);
    fst.current()->print_value_on(tty,this);
    tty->cr();
  }
}


void JavaThread::trace_stack_from(vframe* start_vf) {
  ResourceMark rm;
  int vframe_no = 1;
  for (vframe* f = start_vf; f; f = f->sender() ) {
    if (f->is_java_frame()) {
      javaVFrame::cast(f)->print_activation(vframe_no++);
    } else {
      f->print();
    }
    if (vframe_no > StackPrintLimit) {
      tty->print_cr("...<more frames>...");
      return;
    }
  }
}


void JavaThread::trace_stack() {
  if (!has_last_Java_frame()) return;
  ResourceMark rm;
  HandleMark   hm;
  RegisterMap reg_map(this);
  trace_stack_from(last_java_vframe(&reg_map));
}


#endif // PRODUCT


javaVFrame* JavaThread::last_java_vframe(RegisterMap *reg_map) {
  assert(reg_map != NULL, "a map must be given");
  frame f = last_frame();
  for (vframe* vf = vframe::new_vframe(&f, reg_map, this); vf; vf = vf->sender() ) {
    if (vf->is_java_frame()) return javaVFrame::cast(vf);
  }
  return NULL;
}


klassOop JavaThread::security_get_caller_class(int depth) {
  vframeStream vfst(this);
  vfst.security_get_caller_frame(depth);
  if (!vfst.at_end()) {
    return vfst.method()->method_holder();
  }
  return NULL;
}

static void compiler_thread_entry(JavaThread* thread, TRAPS) {
  assert(thread->is_Compiler_thread(), "must be compiler thread");
  CompileBroker::compiler_thread_loop();
}

// Create a CompilerThread
CompilerThread::CompilerThread(CompileQueue* queue, CompilerCounters* counters)
: JavaThread(&compiler_thread_entry) {
  _env   = NULL;
  _log   = NULL;
  _task  = NULL;
  _queue = queue;
  _counters = counters;
  _buffer_blob = NULL;

#ifndef PRODUCT
  _ideal_graph_printer = NULL;
#endif
}


// ======= Threads ========

// The Threads class links together all active threads, and provides
// operations over all threads.  It is protected by its own Mutex
// lock, which is also used in other contexts to protect thread
// operations from having the thread being operated on from exiting
// and going away unexpectedly (e.g., safepoint synchronization)

JavaThread* Threads::_thread_list = NULL;
int         Threads::_number_of_threads = 0;
int         Threads::_number_of_non_daemon_threads = 0;
int         Threads::_return_code = 0;
size_t      JavaThread::_stack_size_at_create = 0;

// All JavaThreads
#define ALL_JAVA_THREADS(X) for (JavaThread* X = _thread_list; X; X = X->next())

void os_stream();

// All JavaThreads + all non-JavaThreads (i.e., every thread in the system)
void Threads::threads_do(ThreadClosure* tc) {
  assert_locked_or_safepoint(Threads_lock);
  // ALL_JAVA_THREADS iterates through all JavaThreads
  ALL_JAVA_THREADS(p) {
    tc->do_thread(p);
  }
  // Someday we could have a table or list of all non-JavaThreads.
  // For now, just manually iterate through them.
  tc->do_thread(VMThread::vm_thread());
  Universe::heap()->gc_threads_do(tc);
  WatcherThread *wt = WatcherThread::watcher_thread();
  // Strictly speaking, the following NULL check isn't sufficient to make sure
  // the data for WatcherThread is still valid upon being examined. However,
  // considering that WatchThread terminates when the VM is on the way to
  // exit at safepoint, the chance of the above is extremely small. The right
  // way to prevent termination of WatcherThread would be to acquire
  // Terminator_lock, but we can't do that without violating the lock rank
  // checking in some cases.
  if (wt != NULL)
    tc->do_thread(wt);

  // If CompilerThreads ever become non-JavaThreads, add them here
}

jint Threads::create_vm(JavaVMInitArgs* args, bool* canTryAgain) {

  extern void JDK_Version_init();

  // Check version
  if (!is_supported_jni_version(args->version)) return JNI_EVERSION;

  // Initialize the output stream module
  ostream_init();

  // Process java launcher properties.
  Arguments::process_sun_java_launcher_properties(args);

  // Initialize the os module before using TLS
  os::init();

  // Initialize system properties.
  Arguments::init_system_properties();

  // So that JDK version can be used as a discrimintor when parsing arguments
  JDK_Version_init();

  // Update/Initialize System properties after JDK version number is known
  Arguments::init_version_specific_system_properties();

  // Parse arguments
  jint parse_result = Arguments::parse(args);
  if (parse_result != JNI_OK) return parse_result;

  if (PauseAtStartup) {
    os::pause();
  }

  HS_DTRACE_PROBE(hotspot, vm__init__begin);

  // Record VM creation timing statistics
  TraceVmCreationTime create_vm_timer;
  create_vm_timer.start();

  // Timing (must come after argument parsing)
  TraceTime timer("Create VM", TraceStartupTime);

  // Initialize the os module after parsing the args
  jint os_init_2_result = os::init_2();
  if (os_init_2_result != JNI_OK) return os_init_2_result;

  // Initialize output stream logging
  ostream_init_log();

  // Convert -Xrun to -agentlib: if there is no JVM_OnLoad
  // Must be before create_vm_init_agents()
  if (Arguments::init_libraries_at_startup()) {
    convert_vm_init_libraries_to_agents();
  }

  // Launch -agentlib/-agentpath and converted -Xrun agents
  if (Arguments::init_agents_at_startup()) {
    create_vm_init_agents();
  }

  // Initialize Threads state
  _thread_list = NULL;
  _number_of_threads = 0;
  _number_of_non_daemon_threads = 0;

  // Initialize TLS
  ThreadLocalStorage::init();

  // Initialize global data structures and create system classes in heap
  vm_init_globals();

  // Attach the main thread to this os thread
  JavaThread* main_thread = new JavaThread();
  main_thread->set_thread_state(_thread_in_vm);
  // must do this before set_active_handles and initialize_thread_local_storage
  // Note: on solaris initialize_thread_local_storage() will (indirectly)
  // change the stack size recorded here to one based on the java thread
  // stacksize. This adjusted size is what is used to figure the placement
  // of the guard pages.
  main_thread->record_stack_base_and_size();
  main_thread->initialize_thread_local_storage();

  main_thread->set_active_handles(JNIHandleBlock::allocate_block());

  if (!main_thread->set_as_starting_thread()) {
    vm_shutdown_during_initialization(
      "Failed necessary internal allocation. Out of swap space");
    delete main_thread;
    *canTryAgain = false; // don't let caller call JNI_CreateJavaVM again
    return JNI_ENOMEM;
  }

  // Enable guard page *after* os::create_main_thread(), otherwise it would
  // crash Linux VM, see notes in os_linux.cpp.
  main_thread->create_stack_guard_pages();

  // Initialize Java-Level synchronization subsystem
  ObjectMonitor::Initialize() ;

  // Initialize global modules
  jint status = init_globals();
  if (status != JNI_OK) {
    delete main_thread;
    *canTryAgain = false; // don't let caller call JNI_CreateJavaVM again
    return status;
  }

  // Should be done after the heap is fully created
  main_thread->cache_global_variables();

  HandleMark hm;

  { MutexLocker mu(Threads_lock);
    Threads::add(main_thread);
  }

  // Any JVMTI raw monitors entered in onload will transition into
  // real raw monitor. VM is setup enough here for raw monitor enter.
  JvmtiExport::transition_pending_onload_raw_monitors();

  if (VerifyBeforeGC &&
      Universe::heap()->total_collections() >= VerifyGCStartAt) {
    Universe::heap()->prepare_for_verify();
    Universe::verify();   // make sure we're starting with a clean slate
  }

  // Create the VMThread
  { TraceTime timer("Start VMThread", TraceStartupTime);
    VMThread::create();
    Thread* vmthread = VMThread::vm_thread();

    if (!os::create_thread(vmthread, os::vm_thread))
      vm_exit_during_initialization("Cannot create VM thread. Out of system resources.");

    // Wait for the VM thread to become ready, and VMThread::run to initialize
    // Monitors can have spurious returns, must always check another state flag
    {
      MutexLocker ml(Notify_lock);
      os::start_thread(vmthread);
      while (vmthread->active_handles() == NULL) {
        Notify_lock->wait();
      }
    }
  }

  assert (Universe::is_fully_initialized(), "not initialized");
  EXCEPTION_MARK;

  // At this point, the Universe is initialized, but we have not executed
  // any byte code.  Now is a good time (the only time) to dump out the
  // internal state of the JVM for sharing.

  if (DumpSharedSpaces) {
    Universe::heap()->preload_and_dump(CHECK_0);
    ShouldNotReachHere();
  }

  // Always call even when there are not JVMTI environments yet, since environments
  // may be attached late and JVMTI must track phases of VM execution
  JvmtiExport::enter_start_phase();

  // Notify JVMTI agents that VM has started (JNI is up) - nop if no agents.
  JvmtiExport::post_vm_start();

  {
    TraceTime timer("Initialize java.lang classes", TraceStartupTime);

    if (EagerXrunInit && Arguments::init_libraries_at_startup()) {
      create_vm_init_libraries();
    }

    if (InitializeJavaLangString) {
      initialize_class(vmSymbolHandles::java_lang_String(), CHECK_0);
    } else {
      warning("java.lang.String not initialized");
    }

    if (AggressiveOpts) {
      {
        // Forcibly initialize java/util/HashMap and mutate the private
        // static final "frontCacheEnabled" field before we start creating instances
#ifdef ASSERT
        klassOop tmp_k = SystemDictionary::find(vmSymbolHandles::java_util_HashMap(), Handle(), Handle(), CHECK_0);
        assert(tmp_k == NULL, "java/util/HashMap should not be loaded yet");
#endif
        klassOop k_o = SystemDictionary::resolve_or_null(vmSymbolHandles::java_util_HashMap(), Handle(), Handle(), CHECK_0);
        KlassHandle k = KlassHandle(THREAD, k_o);
        guarantee(k.not_null(), "Must find java/util/HashMap");
        instanceKlassHandle ik = instanceKlassHandle(THREAD, k());
        ik->initialize(CHECK_0);
        fieldDescriptor fd;
        // Possible we might not find this field; if so, don't break
        if (ik->find_local_field(vmSymbols::frontCacheEnabled_name(), vmSymbols::bool_signature(), &fd)) {
          k()->bool_field_put(fd.offset(), true);
        }
      }

      if (UseStringCache) {
        // Forcibly initialize java/lang/StringValue and mutate the private
        // static final "stringCacheEnabled" field before we start creating instances
        klassOop k_o = SystemDictionary::resolve_or_null(vmSymbolHandles::java_lang_StringValue(), Handle(), Handle(), CHECK_0);
        // Possible that StringValue isn't present: if so, silently don't break
        if (k_o != NULL) {
          KlassHandle k = KlassHandle(THREAD, k_o);
          instanceKlassHandle ik = instanceKlassHandle(THREAD, k());
          ik->initialize(CHECK_0);
          fieldDescriptor fd;
          // Possible we might not find this field: if so, silently don't break
          if (ik->find_local_field(vmSymbols::stringCacheEnabled_name(), vmSymbols::bool_signature(), &fd)) {
            k()->bool_field_put(fd.offset(), true);
          }
        }
      }
    }

    // Initialize java_lang.System (needed before creating the thread)
    if (InitializeJavaLangSystem) {
      initialize_class(vmSymbolHandles::java_lang_System(), CHECK_0);
      initialize_class(vmSymbolHandles::java_lang_ThreadGroup(), CHECK_0);
      Handle thread_group = create_initial_thread_group(CHECK_0);
      Universe::set_main_thread_group(thread_group());
      initialize_class(vmSymbolHandles::java_lang_Thread(), CHECK_0);
      oop thread_object = create_initial_thread(thread_group, main_thread, CHECK_0);
      main_thread->set_threadObj(thread_object);
      // Set thread status to running since main thread has
      // been started and running.
      java_lang_Thread::set_thread_status(thread_object,
                                          java_lang_Thread::RUNNABLE);

      // The VM preresolve methods to these classes. Make sure that get initialized
      initialize_class(vmSymbolHandles::java_lang_reflect_Method(), CHECK_0);
      initialize_class(vmSymbolHandles::java_lang_ref_Finalizer(),  CHECK_0);
      // The VM creates & returns objects of this class. Make sure it's initialized.
      initialize_class(vmSymbolHandles::java_lang_Class(), CHECK_0);
      call_initializeSystemClass(CHECK_0);
    } else {
      warning("java.lang.System not initialized");
    }

    // an instance of OutOfMemory exception has been allocated earlier
    if (InitializeJavaLangExceptionsErrors) {
      initialize_class(vmSymbolHandles::java_lang_OutOfMemoryError(), CHECK_0);
      initialize_class(vmSymbolHandles::java_lang_NullPointerException(), CHECK_0);
      initialize_class(vmSymbolHandles::java_lang_ClassCastException(), CHECK_0);
      initialize_class(vmSymbolHandles::java_lang_ArrayStoreException(), CHECK_0);
      initialize_class(vmSymbolHandles::java_lang_ArithmeticException(), CHECK_0);
      initialize_class(vmSymbolHandles::java_lang_StackOverflowError(), CHECK_0);
      initialize_class(vmSymbolHandles::java_lang_IllegalMonitorStateException(), CHECK_0);
    } else {
      warning("java.lang.OutOfMemoryError has not been initialized");
      warning("java.lang.NullPointerException has not been initialized");
      warning("java.lang.ClassCastException has not been initialized");
      warning("java.lang.ArrayStoreException has not been initialized");
      warning("java.lang.ArithmeticException has not been initialized");
      warning("java.lang.StackOverflowError has not been initialized");
    }

    if (EnableInvokeDynamic) {
      // JSR 292: An intialized java.dyn.InvokeDynamic is required in
      // the compiler.
      initialize_class(vmSymbolHandles::java_dyn_InvokeDynamic(), CHECK_0);
    }
  }

  // See        : bugid 4211085.
  // Background : the static initializer of java.lang.Compiler tries to read
  //              property"java.compiler" and read & write property "java.vm.info".
  //              When a security manager is installed through the command line
  //              option "-Djava.security.manager", the above properties are not
  //              readable and the static initializer for java.lang.Compiler fails
  //              resulting in a NoClassDefFoundError.  This can happen in any
  //              user code which calls methods in java.lang.Compiler.
  // Hack :       the hack is to pre-load and initialize this class, so that only
  //              system domains are on the stack when the properties are read.
  //              Currently even the AWT code has calls to methods in java.lang.Compiler.
  //              On the classic VM, java.lang.Compiler is loaded very early to load the JIT.
  // Future Fix : the best fix is to grant everyone permissions to read "java.compiler" and
  //              read and write"java.vm.info" in the default policy file. See bugid 4211383
  //              Once that is done, we should remove this hack.
  initialize_class(vmSymbolHandles::java_lang_Compiler(), CHECK_0);

  // More hackery - the static initializer of java.lang.Compiler adds the string "nojit" to
  // the java.vm.info property if no jit gets loaded through java.lang.Compiler (the hotspot
  // compiler does not get loaded through java.lang.Compiler).  "java -version" with the
  // hotspot vm says "nojit" all the time which is confusing.  So, we reset it here.
  // This should also be taken out as soon as 4211383 gets fixed.
  reset_vm_info_property(CHECK_0);

  quicken_jni_functions();

  // Set flag that basic initialization has completed. Used by exceptions and various
  // debug stuff, that does not work until all basic classes have been initialized.
  set_init_completed();

  HS_DTRACE_PROBE(hotspot, vm__init__end);

  // record VM initialization completion time
  Management::record_vm_init_completed();

  // Compute system loader. Note that this has to occur after set_init_completed, since
  // valid exceptions may be thrown in the process.
  // Note that we do not use CHECK_0 here since we are inside an EXCEPTION_MARK and
  // set_init_completed has just been called, causing exceptions not to be shortcut
  // anymore. We call vm_exit_during_initialization directly instead.
  SystemDictionary::compute_java_system_loader(THREAD);
  if (HAS_PENDING_EXCEPTION) {
    vm_exit_during_initialization(Handle(THREAD, PENDING_EXCEPTION));
  }

#ifdef KERNEL
  if (JDK_Version::is_gte_jdk17x_version()) {
    set_jkernel_boot_classloader_hook(THREAD);
  }
#endif // KERNEL

#ifndef SERIALGC
  // Support for ConcurrentMarkSweep. This should be cleaned up
  // and better encapsulated. The ugly nested if test would go away
  // once things are properly refactored. XXX YSR
  if (UseConcMarkSweepGC || UseG1GC) {
    if (UseConcMarkSweepGC) {
      ConcurrentMarkSweepThread::makeSurrogateLockerThread(THREAD);
    } else {
      ConcurrentMarkThread::makeSurrogateLockerThread(THREAD);
    }
    if (HAS_PENDING_EXCEPTION) {
      vm_exit_during_initialization(Handle(THREAD, PENDING_EXCEPTION));
    }
  }
#endif // SERIALGC

  // Always call even when there are not JVMTI environments yet, since environments
  // may be attached late and JVMTI must track phases of VM execution
  JvmtiExport::enter_live_phase();

  // Signal Dispatcher needs to be started before VMInit event is posted
  os::signal_init();

  // Start Attach Listener if +StartAttachListener or it can't be started lazily
  if (!DisableAttachMechanism) {
    if (StartAttachListener || AttachListener::init_at_startup()) {
      AttachListener::init();
    }
  }

  // Launch -Xrun agents
  // Must be done in the JVMTI live phase so that for backward compatibility the JDWP
  // back-end can launch with -Xdebug -Xrunjdwp.
  if (!EagerXrunInit && Arguments::init_libraries_at_startup()) {
    create_vm_init_libraries();
  }

  // Notify JVMTI agents that VM initialization is complete - nop if no agents.
  JvmtiExport::post_vm_initialized();

  Chunk::start_chunk_pool_cleaner_task();

  // initialize compiler(s)
  CompileBroker::compilation_init();

  Management::initialize(THREAD);
  if (HAS_PENDING_EXCEPTION) {
    // management agent fails to start possibly due to
    // configuration problem and is responsible for printing
    // stack trace if appropriate. Simply exit VM.
    vm_exit(1);
  }

  if (Arguments::has_profile())       FlatProfiler::engage(main_thread, true);
  if (Arguments::has_alloc_profile()) AllocationProfiler::engage();
  if (MemProfiling)                   MemProfiler::engage();
  StatSampler::engage();
  if (CheckJNICalls)                  JniPeriodicChecker::engage();

  BiasedLocking::init();


  // Start up the WatcherThread if there are any periodic tasks
  // NOTE:  All PeriodicTasks should be registered by now. If they
  //   aren't, late joiners might appear to start slowly (we might
  //   take a while to process their first tick).
  if (PeriodicTask::num_tasks() > 0) {
    WatcherThread::start();
  }

  // Give os specific code one last chance to start
  os::init_3();

  create_vm_timer.end();
  return JNI_OK;
}

// type for the Agent_OnLoad and JVM_OnLoad entry points
extern "C" {
  typedef jint (JNICALL *OnLoadEntry_t)(JavaVM *, char *, void *);
}
// Find a command line agent library and return its entry point for
//         -agentlib:  -agentpath:   -Xrun
// num_symbol_entries must be passed-in since only the caller knows the number of symbols in the array.
static OnLoadEntry_t lookup_on_load(AgentLibrary* agent, const char *on_load_symbols[], size_t num_symbol_entries) {
  OnLoadEntry_t on_load_entry = NULL;
  void *library = agent->os_lib();  // check if we have looked it up before

  if (library == NULL) {
    char buffer[JVM_MAXPATHLEN];
    char ebuf[1024];
    const char *name = agent->name();
    const char *msg = "Could not find agent library ";

    if (agent->is_absolute_path()) {
      library = os::dll_load(name, ebuf, sizeof ebuf);
      if (library == NULL) {
        const char *sub_msg = " in absolute path, with error: ";
        size_t len = strlen(msg) + strlen(name) + strlen(sub_msg) + strlen(ebuf) + 1;
        char *buf = NEW_C_HEAP_ARRAY(char, len);
        jio_snprintf(buf, len, "%s%s%s%s", msg, name, sub_msg, ebuf);
        // If we can't find the agent, exit.
        vm_exit_during_initialization(buf, NULL);
        FREE_C_HEAP_ARRAY(char, buf);
      }
    } else {
      // Try to load the agent from the standard dll directory
      os::dll_build_name(buffer, sizeof(buffer), Arguments::get_dll_dir(), name);
      library = os::dll_load(buffer, ebuf, sizeof ebuf);
#ifdef KERNEL
      // Download instrument dll
      if (library == NULL && strcmp(name, "instrument") == 0) {
        char *props = Arguments::get_kernel_properties();
        char *home  = Arguments::get_java_home();
        const char *fmt   = "%s/bin/java %s -Dkernel.background.download=false"
                      " sun.jkernel.DownloadManager -download client_jvm";
        size_t length = strlen(props) + strlen(home) + strlen(fmt) + 1;
        char *cmd = NEW_C_HEAP_ARRAY(char, length);
        jio_snprintf(cmd, length, fmt, home, props);
        int status = os::fork_and_exec(cmd);
        FreeHeap(props);
        if (status == -1) {
          warning(cmd);
          vm_exit_during_initialization("fork_and_exec failed: %s",
                                         strerror(errno));
        }
        FREE_C_HEAP_ARRAY(char, cmd);
        // when this comes back the instrument.dll should be where it belongs.
        library = os::dll_load(buffer, ebuf, sizeof ebuf);
      }
#endif // KERNEL
      if (library == NULL) { // Try the local directory
        char ns[1] = {0};
        os::dll_build_name(buffer, sizeof(buffer), ns, name);
        library = os::dll_load(buffer, ebuf, sizeof ebuf);
        if (library == NULL) {
          const char *sub_msg = " on the library path, with error: ";
          size_t len = strlen(msg) + strlen(name) + strlen(sub_msg) + strlen(ebuf) + 1;
          char *buf = NEW_C_HEAP_ARRAY(char, len);
          jio_snprintf(buf, len, "%s%s%s%s", msg, name, sub_msg, ebuf);
          // If we can't find the agent, exit.
          vm_exit_during_initialization(buf, NULL);
          FREE_C_HEAP_ARRAY(char, buf);
        }
      }
    }
    agent->set_os_lib(library);
  }

  // Find the OnLoad function.
  for (size_t symbol_index = 0; symbol_index < num_symbol_entries; symbol_index++) {
    on_load_entry = CAST_TO_FN_PTR(OnLoadEntry_t, os::dll_lookup(library, on_load_symbols[symbol_index]));
    if (on_load_entry != NULL) break;
  }
  return on_load_entry;
}

// Find the JVM_OnLoad entry point
static OnLoadEntry_t lookup_jvm_on_load(AgentLibrary* agent) {
  const char *on_load_symbols[] = JVM_ONLOAD_SYMBOLS;
  return lookup_on_load(agent, on_load_symbols, sizeof(on_load_symbols) / sizeof(char*));
}

// Find the Agent_OnLoad entry point
static OnLoadEntry_t lookup_agent_on_load(AgentLibrary* agent) {
  const char *on_load_symbols[] = AGENT_ONLOAD_SYMBOLS;
  return lookup_on_load(agent, on_load_symbols, sizeof(on_load_symbols) / sizeof(char*));
}

// For backwards compatibility with -Xrun
// Convert libraries with no JVM_OnLoad, but which have Agent_OnLoad to be
// treated like -agentpath:
// Must be called before agent libraries are created
void Threads::convert_vm_init_libraries_to_agents() {
  AgentLibrary* agent;
  AgentLibrary* next;

  for (agent = Arguments::libraries(); agent != NULL; agent = next) {
    next = agent->next();  // cache the next agent now as this agent may get moved off this list
    OnLoadEntry_t on_load_entry = lookup_jvm_on_load(agent);

    // If there is an JVM_OnLoad function it will get called later,
    // otherwise see if there is an Agent_OnLoad
    if (on_load_entry == NULL) {
      on_load_entry = lookup_agent_on_load(agent);
      if (on_load_entry != NULL) {
        // switch it to the agent list -- so that Agent_OnLoad will be called,
        // JVM_OnLoad won't be attempted and Agent_OnUnload will
        Arguments::convert_library_to_agent(agent);
      } else {
        vm_exit_during_initialization("Could not find JVM_OnLoad or Agent_OnLoad function in the library", agent->name());
      }
    }
  }
}

// Create agents for -agentlib:  -agentpath:  and converted -Xrun
// Invokes Agent_OnLoad
// Called very early -- before JavaThreads exist
void Threads::create_vm_init_agents() {
  extern struct JavaVM_ main_vm;
  AgentLibrary* agent;

  JvmtiExport::enter_onload_phase();
  for (agent = Arguments::agents(); agent != NULL; agent = agent->next()) {
    OnLoadEntry_t  on_load_entry = lookup_agent_on_load(agent);

    if (on_load_entry != NULL) {
      // Invoke the Agent_OnLoad function
      jint err = (*on_load_entry)(&main_vm, agent->options(), NULL);
      if (err != JNI_OK) {
        vm_exit_during_initialization("agent library failed to init", agent->name());
      }
    } else {
      vm_exit_during_initialization("Could not find Agent_OnLoad function in the agent library", agent->name());
    }
  }
  JvmtiExport::enter_primordial_phase();
}

extern "C" {
  typedef void (JNICALL *Agent_OnUnload_t)(JavaVM *);
}

void Threads::shutdown_vm_agents() {
  // Send any Agent_OnUnload notifications
  const char *on_unload_symbols[] = AGENT_ONUNLOAD_SYMBOLS;
  extern struct JavaVM_ main_vm;
  for (AgentLibrary* agent = Arguments::agents(); agent != NULL; agent = agent->next()) {

    // Find the Agent_OnUnload function.
    for (uint symbol_index = 0; symbol_index < ARRAY_SIZE(on_unload_symbols); symbol_index++) {
      Agent_OnUnload_t unload_entry = CAST_TO_FN_PTR(Agent_OnUnload_t,
               os::dll_lookup(agent->os_lib(), on_unload_symbols[symbol_index]));

      // Invoke the Agent_OnUnload function
      if (unload_entry != NULL) {
        JavaThread* thread = JavaThread::current();
        ThreadToNativeFromVM ttn(thread);
        HandleMark hm(thread);
        (*unload_entry)(&main_vm);
        break;
      }
    }
  }
}

// Called for after the VM is initialized for -Xrun libraries which have not been converted to agent libraries
// Invokes JVM_OnLoad
void Threads::create_vm_init_libraries() {
  extern struct JavaVM_ main_vm;
  AgentLibrary* agent;

  for (agent = Arguments::libraries(); agent != NULL; agent = agent->next()) {
    OnLoadEntry_t on_load_entry = lookup_jvm_on_load(agent);

    if (on_load_entry != NULL) {
      // Invoke the JVM_OnLoad function
      JavaThread* thread = JavaThread::current();
      ThreadToNativeFromVM ttn(thread);
      HandleMark hm(thread);
      jint err = (*on_load_entry)(&main_vm, agent->options(), NULL);
      if (err != JNI_OK) {
        vm_exit_during_initialization("-Xrun library failed to init", agent->name());
      }
    } else {
      vm_exit_during_initialization("Could not find JVM_OnLoad function in -Xrun library", agent->name());
    }
  }
}

// Last thread running calls java.lang.Shutdown.shutdown()
void JavaThread::invoke_shutdown_hooks() {
  HandleMark hm(this);

  // We could get here with a pending exception, if so clear it now.
  if (this->has_pending_exception()) {
    this->clear_pending_exception();
  }

  EXCEPTION_MARK;
  klassOop k =
    SystemDictionary::resolve_or_null(vmSymbolHandles::java_lang_Shutdown(),
                                      THREAD);
  if (k != NULL) {
    // SystemDictionary::resolve_or_null will return null if there was
    // an exception.  If we cannot load the Shutdown class, just don't
    // call Shutdown.shutdown() at all.  This will mean the shutdown hooks
    // and finalizers (if runFinalizersOnExit is set) won't be run.
    // Note that if a shutdown hook was registered or runFinalizersOnExit
    // was called, the Shutdown class would have already been loaded
    // (Runtime.addShutdownHook and runFinalizersOnExit will load it).
    instanceKlassHandle shutdown_klass (THREAD, k);
    JavaValue result(T_VOID);
    JavaCalls::call_static(&result,
                           shutdown_klass,
                           vmSymbolHandles::shutdown_method_name(),
                           vmSymbolHandles::void_method_signature(),
                           THREAD);
  }
  CLEAR_PENDING_EXCEPTION;
}

// Threads::destroy_vm() is normally called from jni_DestroyJavaVM() when
// the program falls off the end of main(). Another VM exit path is through
// vm_exit() when the program calls System.exit() to return a value or when
// there is a serious error in VM. The two shutdown paths are not exactly
// the same, but they share Shutdown.shutdown() at Java level and before_exit()
// and VM_Exit op at VM level.
//
// Shutdown sequence:
//   + Wait until we are the last non-daemon thread to execute
//     <-- every thing is still working at this moment -->
//   + Call java.lang.Shutdown.shutdown(), which will invoke Java level
//        shutdown hooks, run finalizers if finalization-on-exit
//   + Call before_exit(), prepare for VM exit
//      > run VM level shutdown hooks (they are registered through JVM_OnExit(),
//        currently the only user of this mechanism is File.deleteOnExit())
//      > stop flat profiler, StatSampler, watcher thread, CMS threads,
//        post thread end and vm death events to JVMTI,
//        stop signal thread
//   + Call JavaThread::exit(), it will:
//      > release JNI handle blocks, remove stack guard pages
//      > remove this thread from Threads list
//     <-- no more Java code from this thread after this point -->
//   + Stop VM thread, it will bring the remaining VM to a safepoint and stop
//     the compiler threads at safepoint
//     <-- do not use anything that could get blocked by Safepoint -->
//   + Disable tracing at JNI/JVM barriers
//   + Set _vm_exited flag for threads that are still running native code
//   + Delete this thread
//   + Call exit_globals()
//      > deletes tty
//      > deletes PerfMemory resources
//   + Return to caller

bool Threads::destroy_vm() {
  JavaThread* thread = JavaThread::current();

  // Wait until we are the last non-daemon thread to execute
  { MutexLocker nu(Threads_lock);
    while (Threads::number_of_non_daemon_threads() > 1 )
      // This wait should make safepoint checks, wait without a timeout,
      // and wait as a suspend-equivalent condition.
      //
      // Note: If the FlatProfiler is running and this thread is waiting
      // for another non-daemon thread to finish, then the FlatProfiler
      // is waiting for the external suspend request on this thread to
      // complete. wait_for_ext_suspend_completion() will eventually
      // timeout, but that takes time. Making this wait a suspend-
      // equivalent condition solves that timeout problem.
      //
      Threads_lock->wait(!Mutex::_no_safepoint_check_flag, 0,
                         Mutex::_as_suspend_equivalent_flag);
  }

  // Hang forever on exit if we are reporting an error.
  if (ShowMessageBoxOnError && is_error_reported()) {
    os::infinite_sleep();
  }

  if (JDK_Version::is_jdk12x_version()) {
    // We are the last thread running, so check if finalizers should be run.
    // For 1.3 or later this is done in thread->invoke_shutdown_hooks()
    HandleMark rm(thread);
    Universe::run_finalizers_on_exit();
  } else {
    // run Java level shutdown hooks
    thread->invoke_shutdown_hooks();
  }

  before_exit(thread);

  thread->exit(true);

  // Stop VM thread.
  {
    // 4945125 The vm thread comes to a safepoint during exit.
    // GC vm_operations can get caught at the safepoint, and the
    // heap is unparseable if they are caught. Grab the Heap_lock
    // to prevent this. The GC vm_operations will not be able to
    // queue until after the vm thread is dead.
    MutexLocker ml(Heap_lock);

    VMThread::wait_for_vm_thread_exit();
    assert(SafepointSynchronize::is_at_safepoint(), "VM thread should exit at Safepoint");
    VMThread::destroy();
  }

  // clean up ideal graph printers
#if defined(COMPILER2) && !defined(PRODUCT)
  IdealGraphPrinter::clean_up();
#endif

  // Now, all Java threads are gone except daemon threads. Daemon threads
  // running Java code or in VM are stopped by the Safepoint. However,
  // daemon threads executing native code are still running.  But they
  // will be stopped at native=>Java/VM barriers. Note that we can't
  // simply kill or suspend them, as it is inherently deadlock-prone.

#ifndef PRODUCT
  // disable function tracing at JNI/JVM barriers
  TraceJNICalls = false;
  TraceJVMCalls = false;
  TraceRuntimeCalls = false;
#endif

  VM_Exit::set_vm_exited();

  notify_vm_shutdown();

  delete thread;

  // exit_globals() will delete tty
  exit_globals();

  return true;
}


jboolean Threads::is_supported_jni_version_including_1_1(jint version) {
  if (version == JNI_VERSION_1_1) return JNI_TRUE;
  return is_supported_jni_version(version);
}


jboolean Threads::is_supported_jni_version(jint version) {
  if (version == JNI_VERSION_1_2) return JNI_TRUE;
  if (version == JNI_VERSION_1_4) return JNI_TRUE;
  if (version == JNI_VERSION_1_6) return JNI_TRUE;
  return JNI_FALSE;
}


void Threads::add(JavaThread* p, bool force_daemon) {
  // The threads lock must be owned at this point
  assert_locked_or_safepoint(Threads_lock);

  // See the comment for this method in thread.hpp for its purpose and
  // why it is called here.
  p->initialize_queues();
  p->set_next(_thread_list);
  _thread_list = p;
  _number_of_threads++;
  oop threadObj = p->threadObj();
  bool daemon = true;
  // Bootstrapping problem: threadObj can be null for initial
  // JavaThread (or for threads attached via JNI)
  if ((!force_daemon) && (threadObj == NULL || !java_lang_Thread::is_daemon(threadObj))) {
    _number_of_non_daemon_threads++;
    daemon = false;
  }

  ThreadService::add_thread(p, daemon);

  // Possible GC point.
  Events::log("Thread added: " INTPTR_FORMAT, p);
}

void Threads::remove(JavaThread* p) {
  // Extra scope needed for Thread_lock, so we can check
  // that we do not remove thread without safepoint code notice
  { MutexLocker ml(Threads_lock);

    assert(includes(p), "p must be present");

    JavaThread* current = _thread_list;
    JavaThread* prev    = NULL;

    while (current != p) {
      prev    = current;
      current = current->next();
    }

    if (prev) {
      prev->set_next(current->next());
    } else {
      _thread_list = p->next();
    }
    _number_of_threads--;
    oop threadObj = p->threadObj();
    bool daemon = true;
    if (threadObj == NULL || !java_lang_Thread::is_daemon(threadObj)) {
      _number_of_non_daemon_threads--;
      daemon = false;

      // Only one thread left, do a notify on the Threads_lock so a thread waiting
      // on destroy_vm will wake up.
      if (number_of_non_daemon_threads() == 1)
        Threads_lock->notify_all();
    }
    ThreadService::remove_thread(p, daemon);

    // Make sure that safepoint code disregard this thread. This is needed since
    // the thread might mess around with locks after this point. This can cause it
    // to do callbacks into the safepoint code. However, the safepoint code is not aware
    // of this thread since it is removed from the queue.
    p->set_terminated_value();
  } // unlock Threads_lock

  // Since Events::log uses a lock, we grab it outside the Threads_lock
  Events::log("Thread exited: " INTPTR_FORMAT, p);
}

// Threads_lock must be held when this is called (or must be called during a safepoint)
bool Threads::includes(JavaThread* p) {
  assert(Threads_lock->is_locked(), "sanity check");
  ALL_JAVA_THREADS(q) {
    if (q == p ) {
      return true;
    }
  }
  return false;
}

// Operations on the Threads list for GC.  These are not explicitly locked,
// but the garbage collector must provide a safe context for them to run.
// In particular, these things should never be called when the Threads_lock
// is held by some other thread. (Note: the Safepoint abstraction also
// uses the Threads_lock to gurantee this property. It also makes sure that
// all threads gets blocked when exiting or starting).

void Threads::oops_do(OopClosure* f, CodeBlobClosure* cf) {
  ALL_JAVA_THREADS(p) {
    p->oops_do(f, cf);
  }
  VMThread::vm_thread()->oops_do(f, cf);
}

void Threads::possibly_parallel_oops_do(OopClosure* f, CodeBlobClosure* cf) {
  // Introduce a mechanism allowing parallel threads to claim threads as
  // root groups.  Overhead should be small enough to use all the time,
  // even in sequential code.
  SharedHeap* sh = SharedHeap::heap();
  bool is_par = (sh->n_par_threads() > 0);
  int cp = SharedHeap::heap()->strong_roots_parity();
  ALL_JAVA_THREADS(p) {
    if (p->claim_oops_do(is_par, cp)) {
      p->oops_do(f, cf);
    }
  }
  VMThread* vmt = VMThread::vm_thread();
  if (vmt->claim_oops_do(is_par, cp))
    vmt->oops_do(f, cf);
}

#ifndef SERIALGC
// Used by ParallelScavenge
void Threads::create_thread_roots_tasks(GCTaskQueue* q) {
  ALL_JAVA_THREADS(p) {
    q->enqueue(new ThreadRootsTask(p));
  }
  q->enqueue(new ThreadRootsTask(VMThread::vm_thread()));
}

// Used by Parallel Old
void Threads::create_thread_roots_marking_tasks(GCTaskQueue* q) {
  ALL_JAVA_THREADS(p) {
    q->enqueue(new ThreadRootsMarkingTask(p));
  }
  q->enqueue(new ThreadRootsMarkingTask(VMThread::vm_thread()));
}
#endif // SERIALGC

void Threads::nmethods_do(CodeBlobClosure* cf) {
  ALL_JAVA_THREADS(p) {
    p->nmethods_do(cf);
  }
  VMThread::vm_thread()->nmethods_do(cf);
}

void Threads::gc_epilogue() {
  ALL_JAVA_THREADS(p) {
    p->gc_epilogue();
  }
}

void Threads::gc_prologue() {
  ALL_JAVA_THREADS(p) {
    p->gc_prologue();
  }
}

void Threads::deoptimized_wrt_marked_nmethods() {
  ALL_JAVA_THREADS(p) {
    p->deoptimized_wrt_marked_nmethods();
  }
}


// Get count Java threads that are waiting to enter the specified monitor.
GrowableArray<JavaThread*>* Threads::get_pending_threads(int count,
  address monitor, bool doLock) {
  assert(doLock || SafepointSynchronize::is_at_safepoint(),
    "must grab Threads_lock or be at safepoint");
  GrowableArray<JavaThread*>* result = new GrowableArray<JavaThread*>(count);

  int i = 0;
  {
    MutexLockerEx ml(doLock ? Threads_lock : NULL);
    ALL_JAVA_THREADS(p) {
      if (p->is_Compiler_thread()) continue;

      address pending = (address)p->current_pending_monitor();
      if (pending == monitor) {             // found a match
        if (i < count) result->append(p);   // save the first count matches
        i++;
      }
    }
  }
  return result;
}


JavaThread *Threads::owning_thread_from_monitor_owner(address owner, bool doLock) {
  assert(doLock ||
         Threads_lock->owned_by_self() ||
         SafepointSynchronize::is_at_safepoint(),
         "must grab Threads_lock or be at safepoint");

  // NULL owner means not locked so we can skip the search
  if (owner == NULL) return NULL;

  {
    MutexLockerEx ml(doLock ? Threads_lock : NULL);
    ALL_JAVA_THREADS(p) {
      // first, see if owner is the address of a Java thread
      if (owner == (address)p) return p;
    }
  }
  assert(UseHeavyMonitors == false, "Did not find owning Java thread with UseHeavyMonitors enabled");
  if (UseHeavyMonitors) return NULL;

  //
  // If we didn't find a matching Java thread and we didn't force use of
  // heavyweight monitors, then the owner is the stack address of the
  // Lock Word in the owning Java thread's stack.
  //
  JavaThread* the_owner = NULL;
  {
    MutexLockerEx ml(doLock ? Threads_lock : NULL);
    ALL_JAVA_THREADS(q) {
      if (q->is_lock_owned(owner)) {
        the_owner = q;
        break;
      }
    }
  }
  assert(the_owner != NULL, "Did not find owning Java thread for lock word address");
  return the_owner;
}

// Threads::print_on() is called at safepoint by VM_PrintThreads operation.
void Threads::print_on(outputStream* st, bool print_stacks, bool internal_format, bool print_concurrent_locks) {
  char buf[32];
  st->print_cr(os::local_time_string(buf, sizeof(buf)));

  st->print_cr("Full thread dump %s (%s %s):",
                Abstract_VM_Version::vm_name(),
                Abstract_VM_Version::vm_release(),
                Abstract_VM_Version::vm_info_string()
               );
  st->cr();

#ifndef SERIALGC
  // Dump concurrent locks
  ConcurrentLocksDump concurrent_locks;
  if (print_concurrent_locks) {
    concurrent_locks.dump_at_safepoint();
  }
#endif // SERIALGC

  ALL_JAVA_THREADS(p) {
    ResourceMark rm;
    p->print_on(st);
    if (print_stacks) {
      if (internal_format) {
        p->trace_stack();
      } else {
        p->print_stack_on(st);
      }
    }
    st->cr();
#ifndef SERIALGC
    if (print_concurrent_locks) {
      concurrent_locks.print_locks_on(p, st);
    }
#endif // SERIALGC
  }

  VMThread::vm_thread()->print_on(st);
  st->cr();
  Universe::heap()->print_gc_threads_on(st);
  WatcherThread* wt = WatcherThread::watcher_thread();
  if (wt != NULL) wt->print_on(st);
  st->cr();
  CompileBroker::print_compiler_threads_on(st);
  st->flush();
}

// Threads::print_on_error() is called by fatal error handler. It's possible
// that VM is not at safepoint and/or current thread is inside signal handler.
// Don't print stack trace, as the stack may not be walkable. Don't allocate
// memory (even in resource area), it might deadlock the error handler.
void Threads::print_on_error(outputStream* st, Thread* current, char* buf, int buflen) {
  bool found_current = false;
  st->print_cr("Java Threads: ( => current thread )");
  ALL_JAVA_THREADS(thread) {
    bool is_current = (current == thread);
    found_current = found_current || is_current;

    st->print("%s", is_current ? "=>" : "  ");

    st->print(PTR_FORMAT, thread);
    st->print(" ");
    thread->print_on_error(st, buf, buflen);
    st->cr();
  }
  st->cr();

  st->print_cr("Other Threads:");
  if (VMThread::vm_thread()) {
    bool is_current = (current == VMThread::vm_thread());
    found_current = found_current || is_current;
    st->print("%s", current == VMThread::vm_thread() ? "=>" : "  ");

    st->print(PTR_FORMAT, VMThread::vm_thread());
    st->print(" ");
    VMThread::vm_thread()->print_on_error(st, buf, buflen);
    st->cr();
  }
  WatcherThread* wt = WatcherThread::watcher_thread();
  if (wt != NULL) {
    bool is_current = (current == wt);
    found_current = found_current || is_current;
    st->print("%s", is_current ? "=>" : "  ");

    st->print(PTR_FORMAT, wt);
    st->print(" ");
    wt->print_on_error(st, buf, buflen);
    st->cr();
  }
  if (!found_current) {
    st->cr();
    st->print("=>" PTR_FORMAT " (exited) ", current);
    current->print_on_error(st, buf, buflen);
    st->cr();
  }
}

// Internal SpinLock and Mutex
// Based on ParkEvent

// Ad-hoc mutual exclusion primitives: SpinLock and Mux
//
// We employ SpinLocks _only for low-contention, fixed-length
// short-duration critical sections where we're concerned
// about native mutex_t or HotSpot Mutex:: latency.
// The mux construct provides a spin-then-block mutual exclusion
// mechanism.
//
// Testing has shown that contention on the ListLock guarding gFreeList
// is common.  If we implement ListLock as a simple SpinLock it's common
// for the JVM to devolve to yielding with little progress.  This is true
// despite the fact that the critical sections protected by ListLock are
// extremely short.
//
// TODO-FIXME: ListLock should be of type SpinLock.
// We should make this a 1st-class type, integrated into the lock
// hierarchy as leaf-locks.  Critically, the SpinLock structure
// should have sufficient padding to avoid false-sharing and excessive
// cache-coherency traffic.


typedef volatile int SpinLockT ;

void Thread::SpinAcquire (volatile int * adr, const char * LockName) {
  if (Atomic::cmpxchg (1, adr, 0) == 0) {
     return ;   // normal fast-path return
  }

  // Slow-path : We've encountered contention -- Spin/Yield/Block strategy.
  TEVENT (SpinAcquire - ctx) ;
  int ctr = 0 ;
  int Yields = 0 ;
  for (;;) {
     while (*adr != 0) {
        ++ctr ;
        if ((ctr & 0xFFF) == 0 || !os::is_MP()) {
           if (Yields > 5) {
             // Consider using a simple NakedSleep() instead.
             // Then SpinAcquire could be called by non-JVM threads
             Thread::current()->_ParkEvent->park(1) ;
           } else {
             os::NakedYield() ;
             ++Yields ;
           }
        } else {
           SpinPause() ;
        }
     }
     if (Atomic::cmpxchg (1, adr, 0) == 0) return ;
  }
}

void Thread::SpinRelease (volatile int * adr) {
  assert (*adr != 0, "invariant") ;
  OrderAccess::fence() ;      // guarantee at least release consistency.
  // Roach-motel semantics.
  // It's safe if subsequent LDs and STs float "up" into the critical section,
  // but prior LDs and STs within the critical section can't be allowed
  // to reorder or float past the ST that releases the lock.
  *adr = 0 ;
}

// muxAcquire and muxRelease:
//
// *  muxAcquire and muxRelease support a single-word lock-word construct.
//    The LSB of the word is set IFF the lock is held.
//    The remainder of the word points to the head of a singly-linked list
//    of threads blocked on the lock.
//
// *  The current implementation of muxAcquire-muxRelease uses its own
//    dedicated Thread._MuxEvent instance.  If we're interested in
//    minimizing the peak number of extant ParkEvent instances then
//    we could eliminate _MuxEvent and "borrow" _ParkEvent as long
//    as certain invariants were satisfied.  Specifically, care would need
//    to be taken with regards to consuming unpark() "permits".
//    A safe rule of thumb is that a thread would never call muxAcquire()
//    if it's enqueued (cxq, EntryList, WaitList, etc) and will subsequently
//    park().  Otherwise the _ParkEvent park() operation in muxAcquire() could
//    consume an unpark() permit intended for monitorenter, for instance.
//    One way around this would be to widen the restricted-range semaphore
//    implemented in park().  Another alternative would be to provide
//    multiple instances of the PlatformEvent() for each thread.  One
//    instance would be dedicated to muxAcquire-muxRelease, for instance.
//
// *  Usage:
//    -- Only as leaf locks
//    -- for short-term locking only as muxAcquire does not perform
//       thread state transitions.
//
// Alternatives:
// *  We could implement muxAcquire and muxRelease with MCS or CLH locks
//    but with parking or spin-then-park instead of pure spinning.
// *  Use Taura-Oyama-Yonenzawa locks.
// *  It's possible to construct a 1-0 lock if we encode the lockword as
//    (List,LockByte).  Acquire will CAS the full lockword while Release
//    will STB 0 into the LockByte.  The 1-0 scheme admits stranding, so
//    acquiring threads use timers (ParkTimed) to detect and recover from
//    the stranding window.  Thread/Node structures must be aligned on 256-byte
//    boundaries by using placement-new.
// *  Augment MCS with advisory back-link fields maintained with CAS().
//    Pictorially:  LockWord -> T1 <-> T2 <-> T3 <-> ... <-> Tn <-> Owner.
//    The validity of the backlinks must be ratified before we trust the value.
//    If the backlinks are invalid the exiting thread must back-track through the
//    the forward links, which are always trustworthy.
// *  Add a successor indication.  The LockWord is currently encoded as
//    (List, LOCKBIT:1).  We could also add a SUCCBIT or an explicit _succ variable
//    to provide the usual futile-wakeup optimization.
//    See RTStt for details.
// *  Consider schedctl.sc_nopreempt to cover the critical section.
//


typedef volatile intptr_t MutexT ;      // Mux Lock-word
enum MuxBits { LOCKBIT = 1 } ;

void Thread::muxAcquire (volatile intptr_t * Lock, const char * LockName) {
  intptr_t w = Atomic::cmpxchg_ptr (LOCKBIT, Lock, 0) ;
  if (w == 0) return ;
  if ((w & LOCKBIT) == 0 && Atomic::cmpxchg_ptr (w|LOCKBIT, Lock, w) == w) {
     return ;
  }

  TEVENT (muxAcquire - Contention) ;
  ParkEvent * const Self = Thread::current()->_MuxEvent ;
  assert ((intptr_t(Self) & LOCKBIT) == 0, "invariant") ;
  for (;;) {
     int its = (os::is_MP() ? 100 : 0) + 1 ;

     // Optional spin phase: spin-then-park strategy
     while (--its >= 0) {
       w = *Lock ;
       if ((w & LOCKBIT) == 0 && Atomic::cmpxchg_ptr (w|LOCKBIT, Lock, w) == w) {
          return ;
       }
     }

     Self->reset() ;
     Self->OnList = intptr_t(Lock) ;
     // The following fence() isn't _strictly necessary as the subsequent
     // CAS() both serializes execution and ratifies the fetched *Lock value.
     OrderAccess::fence();
     for (;;) {
        w = *Lock ;
        if ((w & LOCKBIT) == 0) {
            if (Atomic::cmpxchg_ptr (w|LOCKBIT, Lock, w) == w) {
                Self->OnList = 0 ;   // hygiene - allows stronger asserts
                return ;
            }
            continue ;      // Interference -- *Lock changed -- Just retry
        }
        assert (w & LOCKBIT, "invariant") ;
        Self->ListNext = (ParkEvent *) (w & ~LOCKBIT );
        if (Atomic::cmpxchg_ptr (intptr_t(Self)|LOCKBIT, Lock, w) == w) break ;
     }

     while (Self->OnList != 0) {
        Self->park() ;
     }
  }
}

void Thread::muxAcquireW (volatile intptr_t * Lock, ParkEvent * ev) {
  intptr_t w = Atomic::cmpxchg_ptr (LOCKBIT, Lock, 0) ;
  if (w == 0) return ;
  if ((w & LOCKBIT) == 0 && Atomic::cmpxchg_ptr (w|LOCKBIT, Lock, w) == w) {
    return ;
  }

  TEVENT (muxAcquire - Contention) ;
  ParkEvent * ReleaseAfter = NULL ;
  if (ev == NULL) {
    ev = ReleaseAfter = ParkEvent::Allocate (NULL) ;
  }
  assert ((intptr_t(ev) & LOCKBIT) == 0, "invariant") ;
  for (;;) {
    guarantee (ev->OnList == 0, "invariant") ;
    int its = (os::is_MP() ? 100 : 0) + 1 ;

    // Optional spin phase: spin-then-park strategy
    while (--its >= 0) {
      w = *Lock ;
      if ((w & LOCKBIT) == 0 && Atomic::cmpxchg_ptr (w|LOCKBIT, Lock, w) == w) {
        if (ReleaseAfter != NULL) {
          ParkEvent::Release (ReleaseAfter) ;
        }
        return ;
      }
    }

    ev->reset() ;
    ev->OnList = intptr_t(Lock) ;
    // The following fence() isn't _strictly necessary as the subsequent
    // CAS() both serializes execution and ratifies the fetched *Lock value.
    OrderAccess::fence();
    for (;;) {
      w = *Lock ;
      if ((w & LOCKBIT) == 0) {
        if (Atomic::cmpxchg_ptr (w|LOCKBIT, Lock, w) == w) {
          ev->OnList = 0 ;
          // We call ::Release while holding the outer lock, thus
          // artificially lengthening the critical section.
          // Consider deferring the ::Release() until the subsequent unlock(),
          // after we've dropped the outer lock.
          if (ReleaseAfter != NULL) {
            ParkEvent::Release (ReleaseAfter) ;
          }
          return ;
        }
        continue ;      // Interference -- *Lock changed -- Just retry
      }
      assert (w & LOCKBIT, "invariant") ;
      ev->ListNext = (ParkEvent *) (w & ~LOCKBIT );
      if (Atomic::cmpxchg_ptr (intptr_t(ev)|LOCKBIT, Lock, w) == w) break ;
    }

    while (ev->OnList != 0) {
      ev->park() ;
    }
  }
}

// Release() must extract a successor from the list and then wake that thread.
// It can "pop" the front of the list or use a detach-modify-reattach (DMR) scheme
// similar to that used by ParkEvent::Allocate() and ::Release().  DMR-based
// Release() would :
// (A) CAS() or swap() null to *Lock, releasing the lock and detaching the list.
// (B) Extract a successor from the private list "in-hand"
// (C) attempt to CAS() the residual back into *Lock over null.
//     If there were any newly arrived threads and the CAS() would fail.
//     In that case Release() would detach the RATs, re-merge the list in-hand
//     with the RATs and repeat as needed.  Alternately, Release() might
//     detach and extract a successor, but then pass the residual list to the wakee.
//     The wakee would be responsible for reattaching and remerging before it
//     competed for the lock.
//
// Both "pop" and DMR are immune from ABA corruption -- there can be
// multiple concurrent pushers, but only one popper or detacher.
// This implementation pops from the head of the list.  This is unfair,
// but tends to provide excellent throughput as hot threads remain hot.
// (We wake recently run threads first).

void Thread::muxRelease (volatile intptr_t * Lock)  {
  for (;;) {
    const intptr_t w = Atomic::cmpxchg_ptr (0, Lock, LOCKBIT) ;
    assert (w & LOCKBIT, "invariant") ;
    if (w == LOCKBIT) return ;
    ParkEvent * List = (ParkEvent *) (w & ~LOCKBIT) ;
    assert (List != NULL, "invariant") ;
    assert (List->OnList == intptr_t(Lock), "invariant") ;
    ParkEvent * nxt = List->ListNext ;

    // The following CAS() releases the lock and pops the head element.
    if (Atomic::cmpxchg_ptr (intptr_t(nxt), Lock, w) != w) {
      continue ;
    }
    List->OnList = 0 ;
    OrderAccess::fence() ;
    List->unpark () ;
    return ;
  }
}


void Threads::verify() {
  ALL_JAVA_THREADS(p) {
    p->verify();
  }
  VMThread* thread = VMThread::vm_thread();
  if (thread != NULL) thread->verify();
}