| /* 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 */ |