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/* Copyright (C) 2005-2019 Free Software Foundation, Inc.
Contributed by Richard Henderson <>.
This file is part of the GNU Offloading and Multi Processing Library
Libgomp is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3, or (at your option)
any later version.
Libgomp 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 for
more details.
Under Section 7 of GPL version 3, you are granted additional
permissions described in the GCC Runtime Library Exception, version
3.1, as published by the Free Software Foundation.
You should have received a copy of the GNU General Public License and
a copy of the GCC Runtime Library Exception along with this program;
see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
<>. */
/* This is a Linux specific implementation of a mutex synchronization
mechanism for libgomp. This type is private to the library. This
implementation uses atomic instructions and the futex syscall. */
#include "wait.h"
int gomp_futex_wake = FUTEX_WAKE | FUTEX_PRIVATE_FLAG;
int gomp_futex_wait = FUTEX_WAIT | FUTEX_PRIVATE_FLAG;
gomp_mutex_lock_slow (gomp_mutex_t *mutex, int oldval)
/* First loop spins a while. */
while (oldval == 1)
if (do_spin (mutex, 1))
/* Spin timeout, nothing changed. Set waiting flag. */
oldval = __atomic_exchange_n (mutex, -1, MEMMODEL_ACQUIRE);
if (oldval == 0)
futex_wait (mutex, -1);
/* Something changed. If now unlocked, we're good to go. */
oldval = 0;
if (__atomic_compare_exchange_n (mutex, &oldval, 1, false,
/* Second loop waits until mutex is unlocked. We always exit this
loop with wait flag set, so next unlock will awaken a thread. */
while ((oldval = __atomic_exchange_n (mutex, -1, MEMMODEL_ACQUIRE)))
do_wait (mutex, -1);
gomp_mutex_unlock_slow (gomp_mutex_t *mutex)
futex_wake (mutex, 1);