/*

 * 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/precompiled.hpp"

#include "runtime/orderAccess.hpp"

#include "runtime/os.hpp"

#include "waitBarrier_linux.hpp"

#include <sys/syscall.h>

#include <linux/futex.h>

#define check_with_errno(check_type, cond, msg)                             \

  do {                                                                      \

    int err = errno;                                                        \

    check_type(cond, "%s: error='%s' (errno=%s)", msg, os::strerror(err),   \

               os::errno_name(err));                                        \

} while (false)

#define guarantee_with_errno(cond, msg) check_with_errno(guarantee, cond, msg)

static int futex(volatile int *addr, int futex_op, int op_arg) {

  return syscall(SYS_futex, addr, futex_op, op_arg, NULL, NULL, 0);

}

void LinuxWaitBarrier::arm(int barrier_tag) {

  assert(_futex_barrier == 0, "Should not be already armed: "

         "_futex_barrier=%d", _futex_barrier);

  _futex_barrier = barrier_tag;

  OrderAccess::fence();

}

void LinuxWaitBarrier::disarm() {

  assert(_futex_barrier != 0, "Should be armed/non-zero.");

  _futex_barrier = 0;

  int s = futex(&_futex_barrier,

                FUTEX_WAKE_PRIVATE,

                INT_MAX /* wake a max of this many threads */);

  guarantee_with_errno(s > -1, "futex FUTEX_WAKE failed");

}

void LinuxWaitBarrier::wait(int barrier_tag) {

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

  if (barrier_tag == 0 ||

      barrier_tag != _futex_barrier) {

    OrderAccess::fence();

    return;

  }

  do {

    int s = futex(&_futex_barrier,

                  FUTEX_WAIT_PRIVATE,

                  barrier_tag /* should be this tag */);

    guarantee_with_errno((s == 0) ||

                         (s == -1 && errno == EAGAIN) ||

                         (s == -1 && errno == EINTR),

                         "futex FUTEX_WAIT failed");

    // Return value 0: woken up, but re-check in case of spurious wakeup.

    // Error EINTR: woken by signal, so re-check and re-wait if necessary.

    // Error EAGAIN: we are already disarmed and so will pass the check.

  } while (barrier_tag == _futex_barrier);

}