362 lines
8.3 KiB
C
362 lines
8.3 KiB
C
/*
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* Copyright (C) 2000 Jason Evans <jasone@freebsd.org>.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice(s), this list of conditions and the following disclaimer as
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* the first lines of this file unmodified other than the possible
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* addition of one or more copyright notices.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice(s), this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
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* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
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* BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
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* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
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* OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
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* EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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* $FreeBSD$
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*/
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/*
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* Some notes about this implementation.
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*
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* This is mostly a simple implementation of POSIX semaphores that
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* does not need threading. Any semaphore created is a kernel-based
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* semaphore regardless of the pshared attribute. This is necessary
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* because libc's stub for pthread_cond_wait() doesn't really wait,
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* and it is not worth the effort impose this behavior on libc.
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*
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* All functions here are designed to be thread-safe so that a
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* threads library need not provide wrappers except to make
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* sem_wait() and sem_timedwait() cancellation points or to
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* provide a faster userland implementation for non-pshared
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* semaphores.
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*
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* Also, this implementation of semaphores cannot really support
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* real pshared semaphores. The sem_t is an allocated object
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* and can't be seen by other processes when placed in shared
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* memory. It should work across forks as long as the semaphore
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* is created before any forks.
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*
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* The function sem_init() should be overridden by a threads
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* library if it wants to provide a different userland version
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* of semaphores. The functions sem_wait() and sem_timedwait()
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* need to be wrapped to provide cancellation points. The function
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* sem_post() may need to be wrapped to be signal-safe.
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*/
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#include "namespace.h"
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#include <sys/types.h>
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#include <sys/queue.h>
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#include <errno.h>
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#include <fcntl.h>
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#include <pthread.h>
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#include <semaphore.h>
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#include <stdarg.h>
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#include <stdlib.h>
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#include <time.h>
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#include <_semaphore.h>
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#include "un-namespace.h"
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#include "libc_private.h"
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static sem_t sem_alloc(unsigned int value, semid_t semid, int system_sem);
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static void sem_free(sem_t sem);
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static LIST_HEAD(, sem) named_sems = LIST_HEAD_INITIALIZER(&named_sems);
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static pthread_mutex_t named_sems_mtx = PTHREAD_MUTEX_INITIALIZER;
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__weak_reference(__sem_init, sem_init);
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__weak_reference(__sem_destroy, sem_destroy);
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__weak_reference(__sem_open, sem_open);
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__weak_reference(__sem_close, sem_close);
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__weak_reference(__sem_unlink, sem_unlink);
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__weak_reference(__sem_wait, sem_wait);
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__weak_reference(__sem_trywait, sem_trywait);
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__weak_reference(__sem_timedwait, sem_timedwait);
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__weak_reference(__sem_post, sem_post);
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__weak_reference(__sem_getvalue, sem_getvalue);
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static inline int
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sem_check_validity(sem_t *sem)
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{
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if ((sem != NULL) && ((*sem)->magic == SEM_MAGIC))
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return (0);
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else {
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errno = EINVAL;
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return (-1);
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}
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}
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static void
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sem_free(sem_t sem)
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{
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_pthread_mutex_destroy(&sem->lock);
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_pthread_cond_destroy(&sem->gtzero);
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sem->magic = 0;
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free(sem);
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}
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static sem_t
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sem_alloc(unsigned int value, semid_t semid, int system_sem)
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{
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sem_t sem;
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if (value > SEM_VALUE_MAX) {
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errno = EINVAL;
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return (NULL);
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}
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sem = (sem_t)malloc(sizeof(struct sem));
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if (sem == NULL) {
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errno = ENOSPC;
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return (NULL);
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}
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sem->count = (u_int32_t)value;
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sem->nwaiters = 0;
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sem->magic = SEM_MAGIC;
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sem->semid = semid;
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sem->syssem = system_sem;
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sem->lock = PTHREAD_MUTEX_INITIALIZER;
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sem->gtzero = PTHREAD_COND_INITIALIZER;
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return (sem);
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}
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int
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__sem_init(sem_t *sem, int pshared, unsigned int value)
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{
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semid_t semid;
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/*
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* We always have to create the kernel semaphore if the
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* threads library isn't present since libc's version of
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* pthread_cond_wait() is just a stub that doesn't really
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* wait.
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*/
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if (ksem_init(&semid, value) != 0)
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return (-1);
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(*sem) = sem_alloc(value, semid, 1);
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if ((*sem) == NULL) {
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ksem_destroy(semid);
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return (-1);
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}
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return (0);
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}
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int
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__sem_destroy(sem_t *sem)
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{
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int retval;
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if (sem_check_validity(sem) != 0)
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return (-1);
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_pthread_mutex_lock(&(*sem)->lock);
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/*
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* If this is a system semaphore let the kernel track it otherwise
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* make sure there are no waiters.
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*/
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if ((*sem)->syssem != 0)
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retval = ksem_destroy((*sem)->semid);
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else if ((*sem)->nwaiters > 0) {
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errno = EBUSY;
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retval = -1;
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}
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else {
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retval = 0;
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(*sem)->magic = 0;
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}
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_pthread_mutex_unlock(&(*sem)->lock);
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if (retval == 0) {
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_pthread_mutex_destroy(&(*sem)->lock);
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_pthread_cond_destroy(&(*sem)->gtzero);
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sem_free(*sem);
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}
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return (retval);
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}
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sem_t *
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__sem_open(const char *name, int oflag, ...)
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{
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sem_t *sem;
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sem_t s;
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semid_t semid;
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mode_t mode;
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unsigned int value;
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mode = 0;
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value = 0;
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if ((oflag & O_CREAT) != 0) {
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va_list ap;
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va_start(ap, oflag);
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mode = va_arg(ap, int);
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value = va_arg(ap, unsigned int);
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va_end(ap);
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}
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/*
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* we can be lazy and let the kernel handle the "oflag",
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* we'll just merge duplicate IDs into our list.
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*/
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if (ksem_open(&semid, name, oflag, mode, value) == -1)
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return (SEM_FAILED);
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/*
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* search for a duplicate ID, we must return the same sem_t *
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* if we locate one.
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*/
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_pthread_mutex_lock(&named_sems_mtx);
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LIST_FOREACH(s, &named_sems, entry) {
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if (s->semid == semid) {
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sem = s->backpointer;
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_pthread_mutex_unlock(&named_sems_mtx);
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return (sem);
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}
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}
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sem = (sem_t *)malloc(sizeof(*sem));
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if (sem == NULL)
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goto err;
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*sem = sem_alloc(value, semid, 1);
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if ((*sem) == NULL)
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goto err;
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LIST_INSERT_HEAD(&named_sems, *sem, entry);
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(*sem)->backpointer = sem;
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_pthread_mutex_unlock(&named_sems_mtx);
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return (sem);
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err:
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_pthread_mutex_unlock(&named_sems_mtx);
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ksem_close(semid);
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if (sem != NULL) {
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if (*sem != NULL)
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sem_free(*sem);
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else
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errno = ENOSPC;
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free(sem);
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} else {
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errno = ENOSPC;
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}
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return (SEM_FAILED);
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}
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int
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__sem_close(sem_t *sem)
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{
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if (sem_check_validity(sem) != 0)
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return (-1);
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if ((*sem)->syssem == 0) {
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errno = EINVAL;
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return (-1);
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}
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_pthread_mutex_lock(&named_sems_mtx);
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if (ksem_close((*sem)->semid) != 0) {
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_pthread_mutex_unlock(&named_sems_mtx);
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return (-1);
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}
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LIST_REMOVE((*sem), entry);
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_pthread_mutex_unlock(&named_sems_mtx);
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sem_free(*sem);
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*sem = NULL;
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free(sem);
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return (0);
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}
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int
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__sem_unlink(const char *name)
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{
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return (ksem_unlink(name));
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}
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int
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__sem_wait(sem_t *sem)
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{
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if (sem_check_validity(sem) != 0)
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return (-1);
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return (ksem_wait((*sem)->semid));
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}
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int
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__sem_trywait(sem_t *sem)
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{
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int retval;
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if (sem_check_validity(sem) != 0)
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return (-1);
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if ((*sem)->syssem != 0)
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retval = ksem_trywait((*sem)->semid);
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else {
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_pthread_mutex_lock(&(*sem)->lock);
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if ((*sem)->count > 0) {
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(*sem)->count--;
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retval = 0;
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} else {
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errno = EAGAIN;
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retval = -1;
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}
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_pthread_mutex_unlock(&(*sem)->lock);
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}
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return (retval);
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}
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int
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__sem_timedwait(sem_t * __restrict sem,
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const struct timespec * __restrict abs_timeout)
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{
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if (sem_check_validity(sem) != 0)
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return (-1);
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return (ksem_timedwait((*sem)->semid, abs_timeout));
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}
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int
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__sem_post(sem_t *sem)
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{
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if (sem_check_validity(sem) != 0)
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return (-1);
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return (ksem_post((*sem)->semid));
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}
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int
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__sem_getvalue(sem_t * __restrict sem, int * __restrict sval)
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{
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int retval;
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if (sem_check_validity(sem) != 0)
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return (-1);
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if ((*sem)->syssem != 0)
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retval = ksem_getvalue((*sem)->semid, sval);
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else {
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_pthread_mutex_lock(&(*sem)->lock);
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*sval = (int)(*sem)->count;
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_pthread_mutex_unlock(&(*sem)->lock);
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retval = 0;
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}
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return (retval);
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}
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