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/* Linuxthreads - a simple clone()-based implementation of Posix */
/* threads for Linux. */
/* Copyright (C) 1996 Xavier Leroy (Xavier.Leroy@inria.fr) */
/* */
/* This program is free software; you can redistribute it and/or */
/* modify it under the terms of the GNU Library General Public License */
/* as published by the Free Software Foundation; either version 2 */
/* of the License, or (at your option) any later version. */
/* */
/* This program 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 Library General Public License for more details. */
/* Semaphores a la POSIX 1003.1b */
#include <errno.h>
#include "pthread.h"
#include "semaphore.h"
#include "internals.h"
#include "spinlock.h"
#include "restart.h"
#include "queue.h"
int sem_init(sem_t *sem, int pshared, unsigned int value)
{
if (value > SEM_VALUE_MAX) {
errno = EINVAL;
return -1;
}
if (pshared) {
errno = ENOSYS;
return -1;
}
__pthread_init_lock((struct _pthread_fastlock *) &sem->sem_lock);
sem->sem_value = value;
sem->sem_waiting = NULL;
return 0;
}
int sem_wait(sem_t * sem)
{
volatile pthread_descr self = thread_self();
__pthread_lock((struct _pthread_fastlock *) &sem->sem_lock, self);
if (sem->sem_value > 0) {
sem->sem_value--;
__pthread_unlock((struct _pthread_fastlock *) &sem->sem_lock);
return 0;
}
enqueue(&sem->sem_waiting, self);
/* Wait for sem_post or cancellation */
__pthread_unlock((struct _pthread_fastlock *) &sem->sem_lock);
suspend_with_cancellation(self);
/* This is a cancellation point */
if (THREAD_GETMEM(self, p_canceled)
&& THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE) {
/* Remove ourselves from the waiting list if we're still on it */
__pthread_lock((struct _pthread_fastlock *) &sem->sem_lock, self);
remove_from_queue(&sem->sem_waiting, self);
__pthread_unlock((struct _pthread_fastlock *) &sem->sem_lock);
pthread_exit(PTHREAD_CANCELED);
}
/* We got the semaphore */
return 0;
}
int sem_trywait(sem_t * sem)
{
int retval;
__pthread_lock((struct _pthread_fastlock *) &sem->sem_lock, NULL);
if (sem->sem_value == 0) {
errno = EAGAIN;
retval = -1;
} else {
sem->sem_value--;
retval = 0;
}
return retval;
}
int sem_post(sem_t * sem)
{
pthread_descr self = thread_self();
pthread_descr th;
struct pthread_request request;
if (THREAD_GETMEM(self, p_in_sighandler) == NULL) {
__pthread_lock((struct _pthread_fastlock *) &sem->sem_lock, self);
if (sem->sem_waiting == NULL) {
if (sem->sem_value >= SEM_VALUE_MAX) {
/* Overflow */
errno = ERANGE;
__pthread_unlock((struct _pthread_fastlock *) &sem->sem_lock);
return -1;
}
sem->sem_value++;
__pthread_unlock((struct _pthread_fastlock *) &sem->sem_lock);
} else {
th = dequeue(&sem->sem_waiting);
__pthread_unlock((struct _pthread_fastlock *) &sem->sem_lock);
restart(th);
}
} else {
/* If we're in signal handler, delegate post operation to
the thread manager. */
if (__pthread_manager_request < 0) {
if (__pthread_initialize_manager() < 0) {
errno = EAGAIN;
return -1;
}
}
request.req_kind = REQ_POST;
request.req_args.post = sem;
__libc_write(__pthread_manager_request,
(char *) &request, sizeof(request));
}
return 0;
}
int sem_getvalue(sem_t * sem, int * sval)
{
*sval = sem->sem_value;
return 0;
}
int sem_destroy(sem_t * sem)
{
if (sem->sem_waiting != NULL) {
errno = EBUSY;
return -1;
}
return 0;
}
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