/*

 * Copyright (c) 2019, 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 "runtime/atomic.hpp"

#include "runtime/orderAccess.hpp"

#include "runtime/os.hpp"

#include "utilities/waitBarrier_generic.hpp"

#include "utilities/spinYield.hpp"

void GenericWaitBarrier::arm(int barrier_tag) {

  assert(_barrier_tag == 0, "Already armed");

  assert(_waiters == 0, "We left a thread hanging");

  _barrier_tag = barrier_tag;

  _waiters = 0;

  OrderAccess::fence();

}

int GenericWaitBarrier::wake_if_needed() {

  assert(_barrier_tag == 0, "Not disarmed");

  int w = _waiters;

  if (w == 0) {

    // Load of _barrier_threads in caller must not pass the load of _waiters.

    OrderAccess::loadload();

    return 0;

  }

  assert(w > 0, "Bad counting");

  // We need an exact count which never goes below zero,

  // otherwise the semaphore may be signalled too many times.

  if (Atomic::cmpxchg(w - 1, &_waiters, w) == w) {

    _sem_barrier.signal();

    return w - 1;

  }

  return w;

}

void GenericWaitBarrier::disarm() {

  assert(_barrier_tag != 0, "Not armed");

  _barrier_tag = 0;

  // Loads of _barrier_threads/_waiters must not float above disarm store and

  // disarm store must not sink below.

  OrderAccess::fence();

  int left;

  SpinYield sp;

  do {

    left = GenericWaitBarrier::wake_if_needed();

    if (left == 0 && _barrier_threads > 0) {

      // There is no thread to wake but we still have barrier threads.

      sp.wait();

    }

    // We must loop here until there are no waiters or potential waiters.

  } while (left > 0 || _barrier_threads > 0);

  // API specifies disarm() must provide a trailing fence.

  OrderAccess::fence();

}

void GenericWaitBarrier::wait(int barrier_tag) {

  assert(barrier_tag != 0, "Trying to wait on disarmed value");

  if (barrier_tag != _barrier_tag) {

    // API specifies wait() must provide a trailing fence.

    OrderAccess::fence();

    return;

  }

  if (barrier_tag != 0 && barrier_tag == _barrier_tag) {

    _sem_barrier.wait();

    // We help out with posting, but we need to do so before we decrement the

    // _barrier_threads otherwise we might wake threads up in next wait.

    GenericWaitBarrier::wake_if_needed();

  }

}