--- Ga�l Le Mignot <[EMAIL PROTECTED]> wrote:
>
> Hello,
>
> While trying to compile abiword, and so gnome-vfs, on GNU/Hurd, I've
> seen that it uses POSIX semaphore, that we don't implement yet.>
> So, I've done an implementation of POSIX semaphores using a pthread_mutex
> and a pthread_cond. I didn't test it yet, but it compiles, and I'm pretty
> confident in it (but I'm sure of the correct behavior of the destroy
> function if some threads are locked on the semaphore).
Thanks for this work, did you compile it with -Wall?
>
> Anyway, here it is. I think it should be merged in libpthreads as soon
> as someone reviewed it.
>
> > /* Copyright (C) 2000,02 Free Software Foundation, Inc.
> This file is part of the GNU C Library.
> Written by Ga�l Le Mignot <[EMAIL PROTECTED]>
>
> The GNU C Library 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.
>
> 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
> Library General Public License for more details.
>
> You should have received a copy of the GNU Library General Public
> License along with the GNU C Library; see the file COPYING.LIB. If not,
> write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
> Boston, MA 02111-1307, USA. */
>
> /*
> * POSIX Threads Extension: Semaphores <semaphore.c>
> */
>
> #include <semaphore.h>
> #include <stdlib.h>
>
> /* Initialize the semaphore and set the initial value - as in LinuxThreads
> pshared must be zero right now. */
> int
> sem_init (sem_t *sem, int pshared, unsigned int value)
> {
> if (pshared)
> return -1;
If you wanted to be consistant with LinuxThreads this should be
if (pshared)
{
errno = ENOSYS;
return -1;
}
However, I think it would be better to actually implement this feature.
>
> sem = malloc (sizeof (*sem));
> if (sem == NULL)
> return -1;
>
> sem->count = value;
> pthread_cond_init (&sem->lock, NULL);
> pthread_mutex_init (&sem->count_lock, NULL);
> return 0;
> }
>
>
> /* Destroys the semaphore */
> int
> sem_destroy (sem_t *sem)
> {
> pthread_mutex_destroy (&sem->count_lock);
> pthread_cond_destroy (&sem->lock);
> free (sem);
> return 0;
> }
>
> /* Wait until the count is > 0, and then decrease it */
> int
> sem_wait (sem_t *sem)
> {
> pthread_mutex_lock (&sem->count_lock);
> while (1)
> {
> if (sem->count)
> {
> sem->count--;
> pthread_mutex_unlock (&sem->count_lock);
> return 0;
> }
> pthread_cond_wait (&sem->lock, &sem->count_lock);
> }
> pthread_mutex_unlock (&sem->count_lock);
Why is there an unlock here? while (1) is an infinite loop so this line
should not be reached. Although,
while (!(sem->count))
pthread_cond_wait (&sem->lock, &sem->count_lock);
sem->count--;
pthread_mutex_unlock (&sem->count_lock);
return 0;
would be shorter. The real question is, are either of these implementations
cancellable? As far as I can tell both are because pthread_cond_wait is
cancellable.
> }
>
> /* Non-blocking variant of sem_wait. Returns -1 if count == 0. */
> int
> sem_trywait (sem_t *sem)
> {
> int res = -1;
>
> pthread_mutex_lock (&sem->count_lock);
> if (sem->count)
> {
> res = 0;
> sem->count--;
> }
> pthread_mutex_unlock (&sem->count_lock);
>
> return res;
> }
>
> /* Increments the count */
> int
> sem_post (sem_t *sem)
> {
> pthread_mutex_lock (&sem->count_lock);
To be paranoid, this should also contain
if (sem->count == SEM_VALUE_MAX)
{
pthread_mutex_unlock (&sem->count_lock);
return -1;
}
> sem->count++;
> pthread_cond_signal (&sem->lock);
> pthread_mutex_unlock (&sem->count_lock);
> return 0;
> }
>
> /* Return the value of the semaphore */
> int
> sem_getvalue (sem_t *sem, int *sval)
> {
> pthread_mutex_lock (&sem->count_lock);
> *sval = sem->count;
> pthread_mutex_unlock (&sem->count_lock);
> return 0;
> }
>
> > /* Copyright (C) 2000,02 Free Software Foundation, Inc.
> This file is part of the GNU C Library.
> Written by Ga�l Le Mignot <[EMAIL PROTECTED]>
>
> The GNU C Library 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.
>
> 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
> Library General Public License for more details.
>
> You should have received a copy of the GNU Library General Public
> License along with the GNU C Library; see the file COPYING.LIB. If not,
> write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
> Boston, MA 02111-1307, USA. */
>
> /*
> * POSIX Threads Extension: Semaphores <semaphore.h>
> */
>
> #ifndef _SEMAPHORE_H
> #define _SEMAPHORE_H 1
>
> #include <pthread.h>
>
> __BEGIN_DECLS
>
> struct __sem_t
> {
> unsigned int count;
> pthread_mutex_t count_lock;
> pthread_cond_t lock;
> };
Somewhere in here
#define SEM_VALUE_MAX UINT_MAX
should probably occur.
>
> typedef struct __sem_t sem_t;
>
> /* Initialize the semaphore and set the initial value - as in LinuxThreads
> pshared must be zero right now. */
How about for a comment:
/* Initialize the semaphore and set the initial value. PSHARED must be set
to 0 processes sharing semaphores is not implemented yet. */
> extern int sem_init (sem_t *sem, int pshared, unsigned int value);
>
> /* Destroys the semaphore */
> extern int sem_destroy (sem_t *sem);
>
> /* Wait until the count is > 0, and then decrease it */
> extern int sem_wait (sem_t *sem);
>
> /* Non-blocking variant of sem_wait. Returns -1 if count == 0. */
> extern int sem_trywait (sem_t *sem);
>
> /* Increments the count */
> extern int sem_post (sem_t *sem);
>
> /* Return the value of the semaphore */
> extern int sem_getvalue (sem_t *sem, int *sval);
>
> __END_DECLS
>
> #endif /* pthread.h */
> >
>
> --
> Gael Le Mignot "Kilobug" - [EMAIL PROTECTED] - http://kilobug.free.fr
> GSM : 06.71.47.18.22 (in France) ICQ UIN : 7299959
> Fingerprint : 1F2C 9804 7505 79DF 95E6 7323 B66B F67B 7103 C5DA
>
> Member of HurdFr: http://hurdfr.org - The GNU Hurd: http://hurd.gnu.org
>
=====
James Morrison
University of Waterloo
Computer Science - Digital Hardware
2A co-op
http://hurd.dyndns.org
Anyone referring to this as 'Open Source' shall be eaten by a GNU
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