FreeBSD-5.3/lib/libc/gen/sem.c
/*
* Copyright (C) 2000 Jason Evans <jasone@freebsd.org>.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice(s), this list of conditions and the following disclaimer as
* the first lines of this file unmodified other than the possible
* addition of one or more copyright notices.
* 2. Redistributions in binary form must reproduce the above copyright
* notice(s), this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
* BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
* OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
* EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* $FreeBSD: src/lib/libc/gen/sem.c,v 1.13 2004/02/06 15:15:44 deischen Exp $
*/
/*
* Some notes about this implementation.
*
* This is mostly a simple implementation of POSIX semaphores that
* does not need threading. Any semaphore created is a kernel-based
* semaphore regardless of the pshared attribute. This is necessary
* because libc's stub for pthread_cond_wait() doesn't really wait,
* and it is not worth the effort impose this behavior on libc.
*
* All functions here are designed to be thread-safe so that a
* threads library need not provide wrappers except to make
* sem_wait() and sem_timedwait() cancellation points or to
* provide a faster userland implementation for non-pshared
* semaphores.
*
* Also, this implementation of semaphores cannot really support
* real pshared semaphores. The sem_t is an allocated object
* and can't be seen by other processes when placed in shared
* memory. It should work across forks as long as the semaphore
* is created before any forks.
*
* The function sem_init() should be overridden by a threads
* library if it wants to provide a different userland version
* of semaphores. The functions sem_wait() and sem_timedwait()
* need to be wrapped to provide cancellation points. The function
* sem_post() may need to be wrapped to be signal-safe.
*/
#include "namespace.h"
#include <sys/queue.h>
#include <errno.h>
#include <fcntl.h>
#include <pthread.h>
#include <semaphore.h>
#include <stdarg.h>
#include <stdlib.h>
#include <time.h>
#include <_semaphore.h>
#include "un-namespace.h"
#include "libc_private.h"
static sem_t sem_alloc(unsigned int value, semid_t semid, int system_sem);
static void sem_free(sem_t sem);
static LIST_HEAD(, sem) named_sems = LIST_HEAD_INITIALIZER(&named_sems);
static pthread_mutex_t named_sems_mtx = PTHREAD_MUTEX_INITIALIZER;
__weak_reference(__sem_init, sem_init);
__weak_reference(__sem_destroy, sem_destroy);
__weak_reference(__sem_open, sem_open);
__weak_reference(__sem_close, sem_close);
__weak_reference(__sem_unlink, sem_unlink);
__weak_reference(__sem_wait, sem_wait);
__weak_reference(__sem_trywait, sem_trywait);
__weak_reference(__sem_timedwait, sem_timedwait);
__weak_reference(__sem_post, sem_post);
__weak_reference(__sem_getvalue, sem_getvalue);
static inline int
sem_check_validity(sem_t *sem)
{
if ((sem != NULL) && ((*sem)->magic == SEM_MAGIC))
return (0);
else {
errno = EINVAL;
return (-1);
}
}
static void
sem_free(sem_t sem)
{
_pthread_mutex_destroy(&sem->lock);
_pthread_cond_destroy(&sem->gtzero);
sem->magic = 0;
free(sem);
}
static sem_t
sem_alloc(unsigned int value, semid_t semid, int system_sem)
{
sem_t sem;
if (value > SEM_VALUE_MAX) {
errno = EINVAL;
return (NULL);
}
sem = (sem_t)malloc(sizeof(struct sem));
if (sem == NULL) {
errno = ENOSPC;
return (NULL);
}
sem->count = (u_int32_t)value;
sem->nwaiters = 0;
sem->magic = SEM_MAGIC;
sem->semid = semid;
sem->syssem = system_sem;
sem->lock = PTHREAD_MUTEX_INITIALIZER;
sem->gtzero = PTHREAD_COND_INITIALIZER;
return (sem);
}
int
__sem_init(sem_t *sem, int pshared, unsigned int value)
{
semid_t semid;
/*
* We always have to create the kernel semaphore if the
* threads library isn't present since libc's version of
* pthread_cond_wait() is just a stub that doesn't really
* wait.
*/
if (ksem_init(&semid, value) != 0)
return (-1);
(*sem) = sem_alloc(value, semid, 1);
if ((*sem) == NULL) {
ksem_destroy(semid);
return (-1);
}
return (0);
}
int
__sem_destroy(sem_t *sem)
{
int retval;
if (sem_check_validity(sem) != 0)
return (-1);
_pthread_mutex_lock(&(*sem)->lock);
/*
* If this is a system semaphore let the kernel track it otherwise
* make sure there are no waiters.
*/
if ((*sem)->syssem != 0)
retval = ksem_destroy((*sem)->semid);
else if ((*sem)->nwaiters > 0) {
errno = EBUSY;
retval = -1;
}
else {
retval = 0;
(*sem)->magic = 0;
}
_pthread_mutex_unlock(&(*sem)->lock);
if (retval == 0) {
_pthread_mutex_destroy(&(*sem)->lock);
_pthread_cond_destroy(&(*sem)->gtzero);
sem_free(*sem);
}
return (retval);
}
sem_t *
__sem_open(const char *name, int oflag, ...)
{
sem_t *sem;
sem_t s;
semid_t semid;
mode_t mode;
unsigned int value;
mode = 0;
value = 0;
if ((oflag & O_CREAT) != 0) {
va_list ap;
va_start(ap, oflag);
mode = va_arg(ap, int);
value = va_arg(ap, unsigned int);
va_end(ap);
}
/*
* we can be lazy and let the kernel handle the "oflag",
* we'll just merge duplicate IDs into our list.
*/
if (ksem_open(&semid, name, oflag, mode, value) == -1)
return (SEM_FAILED);
/*
* search for a duplicate ID, we must return the same sem_t *
* if we locate one.
*/
_pthread_mutex_lock(&named_sems_mtx);
LIST_FOREACH(s, &named_sems, entry) {
if (s->semid == semid) {
sem = s->backpointer;
_pthread_mutex_unlock(&named_sems_mtx);
return (sem);
}
}
sem = (sem_t *)malloc(sizeof(*sem));
if (sem == NULL)
goto err;
*sem = sem_alloc(value, semid, 1);
if ((*sem) == NULL)
goto err;
LIST_INSERT_HEAD(&named_sems, *sem, entry);
(*sem)->backpointer = sem;
_pthread_mutex_unlock(&named_sems_mtx);
return (sem);
err:
_pthread_mutex_unlock(&named_sems_mtx);
ksem_close(semid);
if (sem != NULL) {
if (*sem != NULL)
sem_free(*sem);
else
errno = ENOSPC;
free(sem);
} else {
errno = ENOSPC;
}
return (SEM_FAILED);
}
int
__sem_close(sem_t *sem)
{
if (sem_check_validity(sem) != 0)
return (-1);
if ((*sem)->syssem == 0) {
errno = EINVAL;
return (-1);
}
_pthread_mutex_lock(&named_sems_mtx);
if (ksem_close((*sem)->semid) != 0) {
_pthread_mutex_unlock(&named_sems_mtx);
return (-1);
}
LIST_REMOVE((*sem), entry);
_pthread_mutex_unlock(&named_sems_mtx);
sem_free(*sem);
*sem = NULL;
free(sem);
return (0);
}
int
__sem_unlink(const char *name)
{
return (ksem_unlink(name));
}
int
__sem_wait(sem_t *sem)
{
if (sem_check_validity(sem) != 0)
return (-1);
return (ksem_wait((*sem)->semid));
}
int
__sem_trywait(sem_t *sem)
{
int retval;
if (sem_check_validity(sem) != 0)
return (-1);
if ((*sem)->syssem != 0)
retval = ksem_trywait((*sem)->semid);
else {
_pthread_mutex_lock(&(*sem)->lock);
if ((*sem)->count > 0) {
(*sem)->count--;
retval = 0;
} else {
errno = EAGAIN;
retval = -1;
}
_pthread_mutex_unlock(&(*sem)->lock);
}
return (retval);
}
int
__sem_timedwait(sem_t * __restrict sem,
struct timespec * __restrict abs_timeout)
{
if (sem_check_validity(sem) != 0)
return (-1);
return (ksem_timedwait((*sem)->semid, abs_timeout));
}
int
__sem_post(sem_t *sem)
{
if (sem_check_validity(sem) != 0)
return (-1);
return (ksem_post((*sem)->semid));
}
int
__sem_getvalue(sem_t * __restrict sem, int * __restrict sval)
{
int retval;
if (sem_check_validity(sem) != 0)
return (-1);
if ((*sem)->syssem != 0)
retval = ksem_getvalue((*sem)->semid, sval);
else {
_pthread_mutex_lock(&(*sem)->lock);
*sval = (int)(*sem)->count;
_pthread_mutex_unlock(&(*sem)->lock);
retval = 0;
}
return (retval);
}