linuxthreads/semaphore.c

   1 /* Linuxthreads - a simple clone()-based implementation of Posix        */
   2 /* threads for Linux.                                                   */
   3 /* Copyright (C) 1996 Xavier Leroy (Xavier.Leroy@inria.fr)              */
   4 /*                                                                      */
   5 /* This program is free software; you can redistribute it and/or        */
   6 /* modify it under the terms of the GNU Library General Public License  */
   7 /* as published by the Free Software Foundation; either version 2       */
   8 /* of the License, or (at your option) any later version.               */
   9 /*                                                                      */
  10 /* This program is distributed in the hope that it will be useful,      */
  11 /* but WITHOUT ANY WARRANTY; without even the implied warranty of       */
  12 /* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the        */
  13 /* GNU Library General Public License for more details.                 */
  14
  15 /* Semaphores a la POSIX 1003.1b */
  16
  17 #include <errno.h>
  18 #include "pthread.h"
  19 #include "semaphore.h"
  20 #include "internals.h"
  21 #include "spinlock.h"
  22 #include "restart.h"
  23 #include "queue.h"
  24
  25 int sem_init(sem_t *sem, int pshared, unsigned int value)
  26 {
  27   if (value > SEM_VALUE_MAX) {
  28     errno = EINVAL;
  29     return -1;
  30   }
  31   if (pshared) {
  32     errno = ENOSYS;
  33     return -1;
  34   }
  35   __pthread_init_lock((struct _pthread_fastlock *) &sem->sem_lock);
  36   sem->sem_value = value;
  37   sem->sem_waiting = NULL;
  38   return 0;
  39 }
  40
  41 int sem_wait(sem_t * sem)
  42 {
  43   volatile pthread_descr self = thread_self();
  44
  45   __pthread_lock((struct _pthread_fastlock *) &sem->sem_lock, self);
  46   if (sem->sem_value > 0) {
  47     sem->sem_value--;
  48     __pthread_unlock((struct _pthread_fastlock *) &sem->sem_lock);
  49     return 0;
  50   }
  51   enqueue(&sem->sem_waiting, self);
  52   /* Wait for sem_post or cancellation */
  53   __pthread_unlock((struct _pthread_fastlock *) &sem->sem_lock);
  54   suspend_with_cancellation(self);
  55   /* This is a cancellation point */
  56   if (THREAD_GETMEM(self, p_canceled)
  57       && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE) {
  58     /* Remove ourselves from the waiting list if we're still on it */
  59     __pthread_lock((struct _pthread_fastlock *) &sem->sem_lock, self);
  60     remove_from_queue(&sem->sem_waiting, self);
  61     __pthread_unlock((struct _pthread_fastlock *) &sem->sem_lock);
  62     pthread_exit(PTHREAD_CANCELED);
  63   }
  64   /* We got the semaphore */
  65   return 0;
  66 }
  67
  68 int sem_trywait(sem_t * sem)
  69 {
  70   int retval;
  71
  72   __pthread_lock((struct _pthread_fastlock *) &sem->sem_lock, NULL);
  73   if (sem->sem_value == 0) {
  74     errno = EAGAIN;
  75     retval = -1;
  76   } else {
  77     sem->sem_value--;
  78     retval = 0;
  79   }
  80   __pthread_unlock((struct _pthread_fastlock *) &sem->sem_lock);
  81   return retval;
  82 }
  83
  84 int sem_post(sem_t * sem)
  85 {
  86   pthread_descr self = thread_self();
  87   pthread_descr th;
  88   struct pthread_request request;
  89
  90   if (THREAD_GETMEM(self, p_in_sighandler) == NULL) {
  91     __pthread_lock((struct _pthread_fastlock *) &sem->sem_lock, self);
  92     if (sem->sem_waiting == NULL) {
  93       if (sem->sem_value >= SEM_VALUE_MAX) {
  94         /* Overflow */
  95         errno = ERANGE;
  96         __pthread_unlock((struct _pthread_fastlock *) &sem->sem_lock);
  97         return -1;
  98       }
  99       sem->sem_value++;
 100       __pthread_unlock((struct _pthread_fastlock *) &sem->sem_lock);
 101     } else {
 102       th = dequeue(&sem->sem_waiting);
 103       __pthread_unlock((struct _pthread_fastlock *) &sem->sem_lock);
 104       restart(th);
 105     }
 106   } else {
 107     /* If we're in signal handler, delegate post operation to
 108        the thread manager. */
 109     if (__pthread_manager_request < 0) {
 110       if (__pthread_initialize_manager() < 0) {
 111         errno = EAGAIN;
 112         return -1;
 113       }
 114     }
 115     request.req_kind = REQ_POST;
 116     request.req_args.post = sem;
 117     __libc_write(__pthread_manager_request,
 118                  (char *) &request, sizeof(request));
 119   }
 120   return 0;
 121 }
 122
 123 int sem_getvalue(sem_t * sem, int * sval)
 124 {
 125   *sval = sem->sem_value;
 126   return 0;
 127 }
 128
 129 int sem_destroy(sem_t * sem)
 130 {
 131   if (sem->sem_waiting != NULL) {
 132     errno = EBUSY;
 133     return -1;
 134   }
 135   return 0;
 136 }