71 lines
2.3 KiB
C
71 lines
2.3 KiB
C
/* Copyright (C) 2005-2020 Free Software Foundation, Inc.
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Contributed by Richard Henderson <rth@redhat.com>.
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This file is part of the GNU Offloading and Multi Processing Library
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(libgomp).
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Libgomp is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3, or (at your option)
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any later version.
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Libgomp is distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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more details.
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Under Section 7 of GPL version 3, you are granted additional
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permissions described in the GCC Runtime Library Exception, version
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3.1, as published by the Free Software Foundation.
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You should have received a copy of the GNU General Public License and
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a copy of the GCC Runtime Library Exception along with this program;
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see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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<http://www.gnu.org/licenses/>. */
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/* This is a Linux specific implementation of a mutex synchronization
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mechanism for libgomp. This type is private to the library. This
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implementation uses atomic instructions and the futex syscall. */
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#include "wait.h"
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int gomp_futex_wake = FUTEX_WAKE | FUTEX_PRIVATE_FLAG;
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int gomp_futex_wait = FUTEX_WAIT | FUTEX_PRIVATE_FLAG;
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void
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gomp_mutex_lock_slow (gomp_mutex_t *mutex, int oldval)
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{
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/* First loop spins a while. */
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while (oldval == 1)
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{
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if (do_spin (mutex, 1))
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{
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/* Spin timeout, nothing changed. Set waiting flag. */
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oldval = __atomic_exchange_n (mutex, -1, MEMMODEL_ACQUIRE);
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if (oldval == 0)
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return;
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futex_wait (mutex, -1);
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break;
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}
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else
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{
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/* Something changed. If now unlocked, we're good to go. */
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oldval = 0;
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if (__atomic_compare_exchange_n (mutex, &oldval, 1, false,
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MEMMODEL_ACQUIRE, MEMMODEL_RELAXED))
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return;
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}
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}
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/* Second loop waits until mutex is unlocked. We always exit this
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loop with wait flag set, so next unlock will awaken a thread. */
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while ((oldval = __atomic_exchange_n (mutex, -1, MEMMODEL_ACQUIRE)))
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do_wait (mutex, -1);
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}
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void
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gomp_mutex_unlock_slow (gomp_mutex_t *mutex)
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{
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futex_wake (mutex, 1);
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}
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