mirror of
https://gcc.gnu.org/git/gcc.git
synced 2024-12-26 20:44:53 +08:00
88 lines
2.9 KiB
C
88 lines
2.9 KiB
C
/* Copyright (C) 2005-2014 Free Software Foundation, Inc.
|
|
Contributed by Richard Henderson <rth@redhat.com>.
|
|
|
|
This file is part of the GNU OpenMP Library (libgomp).
|
|
|
|
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
|
|
<http://www.gnu.org/licenses/>. */
|
|
|
|
/* This is a Linux specific implementation of a semaphore synchronization
|
|
mechanism for libgomp. This type is private to the library. This
|
|
counting semaphore implementation uses atomic instructions and the
|
|
futex syscall, and a single 32-bit int to store semaphore state.
|
|
The low 31 bits are the count, the top bit is a flag set when some
|
|
threads may be waiting. */
|
|
|
|
#ifndef GOMP_SEM_H
|
|
#define GOMP_SEM_H 1
|
|
|
|
#include <limits.h> /* For INT_MIN */
|
|
|
|
typedef int gomp_sem_t;
|
|
#define SEM_WAIT INT_MIN
|
|
#define SEM_INC 1
|
|
|
|
extern void gomp_sem_wait_slow (gomp_sem_t *, int);
|
|
extern void gomp_sem_post_slow (gomp_sem_t *);
|
|
|
|
static inline void
|
|
gomp_sem_init (gomp_sem_t *sem, int value)
|
|
{
|
|
*sem = value * SEM_INC;
|
|
}
|
|
|
|
static inline void
|
|
gomp_sem_destroy (gomp_sem_t *sem)
|
|
{
|
|
}
|
|
|
|
static inline void
|
|
gomp_sem_wait (gomp_sem_t *sem)
|
|
{
|
|
int count = *sem;
|
|
|
|
while ((count & ~SEM_WAIT) != 0)
|
|
if (__atomic_compare_exchange_n (sem, &count, count - SEM_INC, true,
|
|
MEMMODEL_ACQUIRE, MEMMODEL_RELAXED))
|
|
return;
|
|
gomp_sem_wait_slow (sem, count);
|
|
}
|
|
|
|
static inline void
|
|
gomp_sem_post (gomp_sem_t *sem)
|
|
{
|
|
int count = *sem;
|
|
|
|
/* Clear SEM_WAIT here so that if there are no more waiting threads
|
|
we transition back to the uncontended state that does not make
|
|
futex syscalls. If there are waiting threads then when one is
|
|
awoken it will set SEM_WAIT again, so other waiting threads are
|
|
woken on a future gomp_sem_post. Furthermore, the awoken thread
|
|
will wake other threads in case gomp_sem_post was called again
|
|
before it had time to set SEM_WAIT. */
|
|
while (!__atomic_compare_exchange_n (sem, &count,
|
|
(count + SEM_INC) & ~SEM_WAIT, true,
|
|
MEMMODEL_RELEASE, MEMMODEL_RELAXED))
|
|
continue;
|
|
|
|
if (__builtin_expect (count & SEM_WAIT, 0))
|
|
gomp_sem_post_slow (sem);
|
|
}
|
|
#endif /* GOMP_SEM_H */
|