/*

 * Copyright (c) 2014, 2017, 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 "gc/shared/suspendibleThreadSet.hpp"

#include "runtime/mutexLocker.hpp"

#include "runtime/semaphore.hpp"

#include "runtime/thread.inline.hpp"

uint   SuspendibleThreadSet::_nthreads          = 0;

uint   SuspendibleThreadSet::_nthreads_stopped  = 0;

bool   SuspendibleThreadSet::_suspend_all       = false;

double SuspendibleThreadSet::_suspend_all_start = 0.0;

static Semaphore* _synchronize_wakeup = NULL;

void SuspendibleThreadSet_init() {

  assert(_synchronize_wakeup == NULL, "STS already initialized");

  _synchronize_wakeup = new Semaphore();

}

bool SuspendibleThreadSet::is_synchronized() {

  assert_lock_strong(STS_lock);

  assert(_nthreads_stopped <= _nthreads, "invariant");

  return _nthreads_stopped == _nthreads;

}

void SuspendibleThreadSet::join() {

  assert(!Thread::current()->is_suspendible_thread(), "Thread already joined");

  MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);

  while (_suspend_all) {

    ml.wait(Mutex::_no_safepoint_check_flag);

  }

  _nthreads++;

  DEBUG_ONLY(Thread::current()->set_suspendible_thread();)

}

void SuspendibleThreadSet::leave() {

  assert(Thread::current()->is_suspendible_thread(), "Thread not joined");

  MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);

  assert(_nthreads > 0, "Invalid");

  DEBUG_ONLY(Thread::current()->clear_suspendible_thread();)

  _nthreads--;

  if (_suspend_all && is_synchronized()) {

    // This leave completes a request, so inform the requestor.

    _synchronize_wakeup->signal();

  }

}

void SuspendibleThreadSet::yield() {

  assert(Thread::current()->is_suspendible_thread(), "Must have joined");

  MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);

  if (_suspend_all) {

    _nthreads_stopped++;

    if (is_synchronized()) {

      if (ConcGCYieldTimeout > 0) {

        double now = os::elapsedTime();

        guarantee((now - _suspend_all_start) * 1000.0 < (double)ConcGCYieldTimeout, "Long delay");

      }

      // This yield completes the request, so inform the requestor.

      _synchronize_wakeup->signal();

    }

    while (_suspend_all) {

      ml.wait(Mutex::_no_safepoint_check_flag);

    }

    assert(_nthreads_stopped > 0, "Invalid");

    _nthreads_stopped--;

  }

}

void SuspendibleThreadSet::synchronize() {

  assert(Thread::current()->is_VM_thread(), "Must be the VM thread");

  if (ConcGCYieldTimeout > 0) {

    _suspend_all_start = os::elapsedTime();

  }

  {

    MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);

    assert(!_suspend_all, "Only one at a time");

    _suspend_all = true;

    if (is_synchronized()) {

      return;

    }

  } // Release lock before semaphore wait.

  // Semaphore initial count is zero.  To reach here, there must be at

  // least one not yielded thread in the set, e.g. is_synchronized()

  // was false before the lock was released.  A thread in the set will

  // signal the semaphore iff it is the last to yield or leave while

  // there is an active suspend request.  So there will be exactly one

  // signal, which will increment the semaphore count to one, which

  // will then be consumed by this wait, returning it to zero.  No

  // thread can exit yield or enter the set until desynchronize is

  // called, so there are no further opportunities for the semaphore

  // being signaled until we get back here again for some later

  // synchronize call.  Hence, there is no need to re-check for

  // is_synchronized after the wait; it will always be true there.

  _synchronize_wakeup->wait();

#ifdef ASSERT

  MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);

  assert(_suspend_all, "STS not synchronizing");

  assert(is_synchronized(), "STS not synchronized");

#endif

}

void SuspendibleThreadSet::desynchronize() {

  assert(Thread::current()->is_VM_thread(), "Must be the VM thread");

  MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag);

  assert(_suspend_all, "STS not synchronizing");

  assert(is_synchronized(), "STS not synchronized");

  _suspend_all = false;

  ml.notify_all();

}