Permalink
Cannot retrieve contributors at this time
Name already in use
A tag already exists with the provided branch name. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Are you sure you want to create this branch?
glibc/nptl/sem_post.c
Go to fileThis commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
103 lines (89 sloc)
3.24 KB
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
/* sem_post -- post to a POSIX semaphore. Generic futex-using version. | |
Copyright (C) 2003-2016 Free Software Foundation, Inc. | |
This file is part of the GNU C Library. | |
Contributed by Jakub Jelinek <jakub@redhat.com>, 2003. | |
The GNU C Library is free software; you can redistribute it and/or | |
modify it under the terms of the GNU Lesser General Public | |
License as published by the Free Software Foundation; either | |
version 2.1 of the License, or (at your option) any later version. | |
The GNU C Library 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 | |
Lesser General Public License for more details. | |
You should have received a copy of the GNU Lesser General Public | |
License along with the GNU C Library; if not, see | |
<http://www.gnu.org/licenses/>. */ | |
#include <atomic.h> | |
#include <errno.h> | |
#include <sysdep.h> | |
#include <lowlevellock.h> /* lll_futex* used by the old code. */ | |
#include <futex-internal.h> | |
#include <internaltypes.h> | |
#include <semaphore.h> | |
#include <shlib-compat.h> | |
/* See sem_wait for an explanation of the algorithm. */ | |
int | |
__new_sem_post (sem_t *sem) | |
{ | |
struct new_sem *isem = (struct new_sem *) sem; | |
int private = isem->private; | |
#if __HAVE_64B_ATOMICS | |
/* Add a token to the semaphore. We use release MO to make sure that a | |
thread acquiring this token synchronizes with us and other threads that | |
added tokens before (the release sequence includes atomic RMW operations | |
by other threads). */ | |
/* TODO Use atomic_fetch_add to make it scale better than a CAS loop? */ | |
uint64_t d = atomic_load_relaxed (&isem->data); | |
do | |
{ | |
if ((d & SEM_VALUE_MASK) == SEM_VALUE_MAX) | |
{ | |
__set_errno (EOVERFLOW); | |
return -1; | |
} | |
} | |
while (!atomic_compare_exchange_weak_release (&isem->data, &d, d + 1)); | |
/* If there is any potentially blocked waiter, wake one of them. */ | |
if ((d >> SEM_NWAITERS_SHIFT) > 0) | |
futex_wake (((unsigned int *) &isem->data) + SEM_VALUE_OFFSET, 1, private); | |
#else | |
/* Add a token to the semaphore. Similar to 64b version. */ | |
unsigned int v = atomic_load_relaxed (&isem->value); | |
do | |
{ | |
if ((v >> SEM_VALUE_SHIFT) == SEM_VALUE_MAX) | |
{ | |
__set_errno (EOVERFLOW); | |
return -1; | |
} | |
} | |
while (!atomic_compare_exchange_weak_release | |
(&isem->value, &v, v + (1 << SEM_VALUE_SHIFT))); | |
/* If there is any potentially blocked waiter, wake one of them. */ | |
if ((v & SEM_NWAITERS_MASK) != 0) | |
futex_wake (&isem->value, 1, private); | |
#endif | |
return 0; | |
} | |
versioned_symbol (libpthread, __new_sem_post, sem_post, GLIBC_2_1); | |
#if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1) | |
int | |
attribute_compat_text_section | |
__old_sem_post (sem_t *sem) | |
{ | |
int *futex = (int *) sem; | |
/* We must need to synchronize with consumers of this token, so the atomic | |
increment must have release MO semantics. */ | |
atomic_write_barrier (); | |
(void) atomic_increment_val (futex); | |
/* We always have to assume it is a shared semaphore. */ | |
int err = lll_futex_wake (futex, 1, LLL_SHARED); | |
if (__builtin_expect (err, 0) < 0) | |
{ | |
__set_errno (-err); | |
return -1; | |
} | |
return 0; | |
} | |
compat_symbol (libpthread, __old_sem_post, sem_post, GLIBC_2_0); | |
#endif |