42f10ba5b5
sem.h is included in between # pragma GCC visibility push(hidden) and # pragma GCC visibility pop and includes limits.h there, which since the introduction of sysconf declaration in recent glibcs in there causes trouble. libgomp assumes it is compiled by gcc, so we don't really need to include limits.h there and can use -__INT_MAX__ - 1 instead (which clang and icc support too for years). 2021-07-13 Jakub Jelinek <jakub@redhat.com> Florian Weimer <fweimer@redhat.com> * config/linux/sem.h: Don't include limits.h. (SEM_WAIT): Define to -__INT_MAX__ - 1 instead of INT_MIN. * config/linux/affinity.c: Include limits.h.
96 lines
3.1 KiB
C
96 lines
3.1 KiB
C
/* Copyright (C) 2005-2021 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 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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typedef int gomp_sem_t;
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#define SEM_WAIT (-__INT_MAX__ - 1)
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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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static inline int
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gomp_sem_getcount (gomp_sem_t *sem)
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{
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int count = __atomic_load_n (sem, MEMMODEL_RELAXED);
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if ((count & SEM_WAIT) != 0)
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return -1;
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return count / SEM_INC;
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}
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#endif /* GOMP_SEM_H */
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