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 #include <shlib-compat.h>
  25 #include <not-cancel.h>
  26
  27 int __new_sem_init(sem_t *sem, int pshared, unsigned int value)
  28 {
  29   if (value > SEM_VALUE_MAX) {
  30     errno = EINVAL;
  31     return -1;
  32   }
  33   if (pshared) {
  34     errno = ENOSYS;
  35     return -1;
  36   }
  37   __pthread_init_lock(&sem->__sem_lock);
  38   sem->__sem_value = value;
  39   sem->__sem_waiting = NULL;
  40   return 0;
  41 }
  42
  43 /* Function called by pthread_cancel to remove the thread from
  44    waiting inside __new_sem_wait. */
  45
  46 static int new_sem_extricate_func(void *obj, pthread_descr th)
  47 {
  48   volatile pthread_descr self = thread_self();
  49   sem_t *sem = obj;
  50   int did_remove = 0;
  51
  52   __pthread_lock(&sem->__sem_lock, self);
  53   did_remove = remove_from_queue(&sem->__sem_waiting, th);
  54   __pthread_unlock(&sem->__sem_lock);
  55
  56   return did_remove;
  57 }
  58
  59 int __new_sem_wait(sem_t * sem)
  60 {
  61   volatile pthread_descr self = thread_self();
  62   pthread_extricate_if extr;
  63   int already_canceled = 0;
  64   int spurious_wakeup_count;
  65
  66   /* Set up extrication interface */
  67   extr.pu_object = sem;
  68   extr.pu_extricate_func = new_sem_extricate_func;
  69
  70   __pthread_lock(&sem->__sem_lock, self);
  71   if (sem->__sem_value > 0) {
  72     sem->__sem_value--;
  73     __pthread_unlock(&sem->__sem_lock);
  74     return 0;
  75   }
  76   /* Register extrication interface */
  77   THREAD_SETMEM(self, p_sem_avail, 0);
  78   __pthread_set_own_extricate_if(self, &extr);
  79   /* Enqueue only if not already cancelled. */
  80   if (!(THREAD_GETMEM(self, p_canceled)
  81       && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE))
  82     enqueue(&sem->__sem_waiting, self);
  83   else
  84     already_canceled = 1;
  85   __pthread_unlock(&sem->__sem_lock);
  86
  87   if (already_canceled) {
  88     __pthread_set_own_extricate_if(self, 0);
  89     __pthread_do_exit(PTHREAD_CANCELED, CURRENT_STACK_FRAME);
  90   }
  91
  92   /* Wait for sem_post or cancellation, or fall through if already canceled */
  93   spurious_wakeup_count = 0;
  94   while (1)
  95     {
  96       suspend(self);
  97       if (THREAD_GETMEM(self, p_sem_avail) == 0
  98           && (THREAD_GETMEM(self, p_woken_by_cancel) == 0
  99               || THREAD_GETMEM(self, p_cancelstate) != PTHREAD_CANCEL_ENABLE))
 100         {
 101           /* Count resumes that don't belong to us. */
 102           spurious_wakeup_count++;
 103           continue;
 104         }
 105       break;
 106     }
 107   __pthread_set_own_extricate_if(self, 0);
 108
 109   /* Terminate only if the wakeup came from cancellation. */
 110   /* Otherwise ignore cancellation because we got the semaphore. */
 111
 112   if (THREAD_GETMEM(self, p_woken_by_cancel)
 113       && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE) {
 114     THREAD_SETMEM(self, p_woken_by_cancel, 0);
 115     __pthread_do_exit(PTHREAD_CANCELED, CURRENT_STACK_FRAME);
 116   }
 117   /* We got the semaphore */
 118   return 0;
 119 }
 120
 121 int __new_sem_trywait(sem_t * sem)
 122 {
 123   int retval;
 124
 125   __pthread_lock(&sem->__sem_lock, NULL);
 126   if (sem->__sem_value == 0) {
 127     errno = EAGAIN;
 128     retval = -1;
 129   } else {
 130     sem->__sem_value--;
 131     retval = 0;
 132   }
 133   __pthread_unlock(&sem->__sem_lock);
 134   return retval;
 135 }
 136
 137 int __new_sem_post(sem_t * sem)
 138 {
 139   pthread_descr self = thread_self();
 140   pthread_descr th;
 141   struct pthread_request request;
 142
 143   if (THREAD_GETMEM(self, p_in_sighandler) == NULL) {
 144     __pthread_lock(&sem->__sem_lock, self);
 145     if (sem->__sem_waiting == NULL) {
 146       if (sem->__sem_value >= SEM_VALUE_MAX) {
 147         /* Overflow */
 148         errno = ERANGE;
 149         __pthread_unlock(&sem->__sem_lock);
 150         return -1;
 151       }
 152       sem->__sem_value++;
 153       __pthread_unlock(&sem->__sem_lock);
 154     } else {
 155       th = dequeue(&sem->__sem_waiting);
 156       __pthread_unlock(&sem->__sem_lock);
 157       th->p_sem_avail = 1;
 158       WRITE_MEMORY_BARRIER();
 159       restart(th);
 160     }
 161   } else {
 162     /* If we're in signal handler, delegate post operation to
 163        the thread manager. */
 164     if (__pthread_manager_request < 0) {
 165       if (__pthread_initialize_manager() < 0) {
 166         errno = EAGAIN;
 167         return -1;
 168       }
 169     }
 170     request.req_kind = REQ_POST;
 171     request.req_args.post = sem;
 172     TEMP_FAILURE_RETRY(write_not_cancel(__pthread_manager_request,
 173                                         (char *) &request, sizeof(request)));
 174   }
 175   return 0;
 176 }
 177
 178 int __new_sem_getvalue(sem_t * sem, int * sval)
 179 {
 180   *sval = sem->__sem_value;
 181   return 0;
 182 }
 183
 184 int __new_sem_destroy(sem_t * sem)
 185 {
 186   if (sem->__sem_waiting != NULL) {
 187     __set_errno (EBUSY);
 188     return -1;
 189   }
 190   return 0;
 191 }
 192
 193 sem_t *sem_open(const char *name, int oflag, ...)
 194 {
 195   __set_errno (ENOSYS);
 196   return SEM_FAILED;
 197 }
 198
 199 int sem_close(sem_t *sem)
 200 {
 201   __set_errno (ENOSYS);
 202   return -1;
 203 }
 204
 205 int sem_unlink(const char *name)
 206 {
 207   __set_errno (ENOSYS);
 208   return -1;
 209 }
 210
 211 int sem_timedwait(sem_t *sem, const struct timespec *abstime)
 212 {
 213   pthread_descr self = thread_self();
 214   pthread_extricate_if extr;
 215   int already_canceled = 0;
 216   int spurious_wakeup_count;
 217
 218   __pthread_lock(&sem->__sem_lock, self);
 219   if (sem->__sem_value > 0) {
 220     --sem->__sem_value;
 221     __pthread_unlock(&sem->__sem_lock);
 222     return 0;
 223   }
 224
 225   if (abstime->tv_nsec < 0 || abstime->tv_nsec >= 1000000000) {
 226     /* The standard requires that if the function would block and the
 227        time value is illegal, the function returns with an error.  */
 228     __pthread_unlock(&sem->__sem_lock);
 229     __set_errno (EINVAL);
 230     return -1;
 231   }
 232
 233   /* Set up extrication interface */
 234   extr.pu_object = sem;
 235   extr.pu_extricate_func = new_sem_extricate_func;
 236
 237   /* Register extrication interface */
 238   THREAD_SETMEM(self, p_sem_avail, 0);
 239   __pthread_set_own_extricate_if(self, &extr);
 240   /* Enqueue only if not already cancelled. */
 241   if (!(THREAD_GETMEM(self, p_canceled)
 242       && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE))
 243     enqueue(&sem->__sem_waiting, self);
 244   else
 245     already_canceled = 1;
 246   __pthread_unlock(&sem->__sem_lock);
 247
 248   if (already_canceled) {
 249     __pthread_set_own_extricate_if(self, 0);
 250     __pthread_do_exit(PTHREAD_CANCELED, CURRENT_STACK_FRAME);
 251   }
 252
 253   spurious_wakeup_count = 0;
 254   while (1)
 255     {
 256       if (timedsuspend(self, abstime) == 0) {
 257         int was_on_queue;
 258
 259         /* __pthread_lock will queue back any spurious restarts that
 260            may happen to it. */
 261
 262         __pthread_lock(&sem->__sem_lock, self);
 263         was_on_queue = remove_from_queue(&sem->__sem_waiting, self);
 264         __pthread_unlock(&sem->__sem_lock);
 265
 266         if (was_on_queue) {
 267           __pthread_set_own_extricate_if(self, 0);
 268           __set_errno (ETIMEDOUT);
 269           return -1;
 270         }
 271
 272         /* Eat the outstanding restart() from the signaller */
 273         suspend(self);
 274       }
 275
 276       if (THREAD_GETMEM(self, p_sem_avail) == 0
 277           && (THREAD_GETMEM(self, p_woken_by_cancel) == 0
 278               || THREAD_GETMEM(self, p_cancelstate) != PTHREAD_CANCEL_ENABLE))
 279         {
 280           /* Count resumes that don't belong to us. */
 281           spurious_wakeup_count++;
 282           continue;
 283         }
 284       break;
 285     }
 286
 287  __pthread_set_own_extricate_if(self, 0);
 288
 289   /* Terminate only if the wakeup came from cancellation. */
 290   /* Otherwise ignore cancellation because we got the semaphore. */
 291
 292   if (THREAD_GETMEM(self, p_woken_by_cancel)
 293       && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE) {
 294     THREAD_SETMEM(self, p_woken_by_cancel, 0);
 295     __pthread_do_exit(PTHREAD_CANCELED, CURRENT_STACK_FRAME);
 296   }
 297   /* We got the semaphore */
 298   return 0;
 299 }
 300
 301
 302 versioned_symbol (libpthread, __new_sem_init, sem_init, GLIBC_2_1);
 303 versioned_symbol (libpthread, __new_sem_wait, sem_wait, GLIBC_2_1);
 304 versioned_symbol (libpthread, __new_sem_trywait, sem_trywait, GLIBC_2_1);
 305 versioned_symbol (libpthread, __new_sem_post, sem_post, GLIBC_2_1);
 306 versioned_symbol (libpthread, __new_sem_getvalue, sem_getvalue, GLIBC_2_1);
 307 versioned_symbol (libpthread, __new_sem_destroy, sem_destroy, GLIBC_2_1);