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   return retval;
  81 }
  82
  83 int sem_post(sem_t * sem)
  84 {
  85   pthread_descr self = thread_self();
  86   pthread_descr th;
  87   struct pthread_request request;
  88
  89   if (THREAD_GETMEM(self, p_in_sighandler) == NULL) {
  90     __pthread_lock((struct _pthread_fastlock *) &sem->sem_lock, self);
  91     if (sem->sem_waiting == NULL) {
  92       if (sem->sem_value >= SEM_VALUE_MAX) {
  93         /* Overflow */
  94         errno = ERANGE;
  95         __pthread_unlock((struct _pthread_fastlock *) &sem->sem_lock);
  96         return -1;
  97       }
  98       sem->sem_value++;
  99       __pthread_unlock((struct _pthread_fastlock *) &sem->sem_lock);
 100     } else {
 101       th = dequeue(&sem->sem_waiting);
 102       __pthread_unlock((struct _pthread_fastlock *) &sem->sem_lock);
 103       restart(th);
 104     }
 105   } else {
 106     /* If we're in signal handler, delegate post operation to
 107        the thread manager. */
 108     if (__pthread_manager_request < 0) {
 109       if (__pthread_initialize_manager() < 0) {
 110         errno = EAGAIN;
 111         return -1;
 112       }
 113     }
 114     request.req_kind = REQ_POST;
 115     request.req_args.post = sem;
 116     __libc_write(__pthread_manager_request,
 117                  (char *) &request, sizeof(request));
 118   }
 119   return 0;
 120 }
 121
 122 int sem_getvalue(sem_t * sem, int * sval)
 123 {
 124   *sval = sem->sem_value;
 125   return 0;
 126 }
 127
 128 int sem_destroy(sem_t * sem)
 129 {
 130   if (sem->sem_waiting != NULL) {
 131     errno = EBUSY;
 132     return -1;
 133   }
 134   return 0;
 135 }