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[/] [openrisc/] [trunk/] [gnu-dev/] [or1k-gcc/] [libgomp/] [config/] [linux/] [sem.h] - Blame information for rev 735

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1 735 jeremybenn
/* Copyright (C) 2005, 2009, 2011 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 OpenMP Library (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 semaphore synchronization
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   mechanism for libgomp.  This type is private to the library.  This
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   counting semaphore implementation uses atomic instructions and the
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   futex syscall, and a single 32-bit int to store semaphore state.
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   The low 31 bits are the count, the top bit is a flag set when some
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   threads may be waiting.  */
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#ifndef GOMP_SEM_H
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#define GOMP_SEM_H 1
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#include <limits.h> /* For INT_MIN */
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typedef int gomp_sem_t;
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#define SEM_WAIT INT_MIN
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#define SEM_INC 1
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extern void gomp_sem_wait_slow (gomp_sem_t *, int);
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extern void gomp_sem_post_slow (gomp_sem_t *);
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static inline void
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gomp_sem_init (gomp_sem_t *sem, int value)
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{
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  *sem = value * SEM_INC;
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}
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static inline void
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gomp_sem_destroy (gomp_sem_t *sem)
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{
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}
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static inline void
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gomp_sem_wait (gomp_sem_t *sem)
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{
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  int count = *sem;
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  while ((count & ~SEM_WAIT) != 0)
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    if (__atomic_compare_exchange_n (sem, &count, count - SEM_INC, true,
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                                     MEMMODEL_ACQUIRE, MEMMODEL_RELAXED))
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      return;
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  gomp_sem_wait_slow (sem, count);
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}
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static inline void
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gomp_sem_post (gomp_sem_t *sem)
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{
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  int count = *sem;
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  /* Clear SEM_WAIT here so that if there are no more waiting threads
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     we transition back to the uncontended state that does not make
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     futex syscalls.  If there are waiting threads then when one is
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     awoken it will set SEM_WAIT again, so other waiting threads are
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     woken on a future gomp_sem_post.  Furthermore, the awoken thread
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     will wake other threads in case gomp_sem_post was called again
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     before it had time to set SEM_WAIT.  */
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  while (!__atomic_compare_exchange_n (sem, &count,
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                                       (count + SEM_INC) & ~SEM_WAIT, true,
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                                       MEMMODEL_RELEASE, MEMMODEL_RELAXED))
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    continue;
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  if (__builtin_expect (count & SEM_WAIT, 0))
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    gomp_sem_post_slow (sem);
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}
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#endif /* GOMP_SEM_H */

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