linuxthreads/condvar.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 /* and Pavel Krauz (krauz@fsid.cvut.cz).                                */
   5 /*                                                                      */
   6 /* This program is free software; you can redistribute it and/or        */
   7 /* modify it under the terms of the GNU Library General Public License  */
   8 /* as published by the Free Software Foundation; either version 2       */
   9 /* of the License, or (at your option) any later version.               */
  10 /*                                                                      */
  11 /* This program is distributed in the hope that it will be useful,      */
  12 /* but WITHOUT ANY WARRANTY; without even the implied warranty of       */
  13 /* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the        */
  14 /* GNU Library General Public License for more details.                 */
  15
  16 /* Condition variables */
  17
  18 #include <errno.h>
  19 #include <sched.h>
  20 #include <stddef.h>
  21 #include <sys/time.h>
  22 #include "pthread.h"
  23 #include "internals.h"
  24 #include "spinlock.h"
  25 #include "queue.h"
  26 #include "restart.h"
  27
  28 int pthread_cond_init(pthread_cond_t *cond,
  29                       const pthread_condattr_t *cond_attr)
  30 {
  31   __pthread_init_lock(&cond->__c_lock);
  32   cond->__c_waiting = NULL;
  33   return 0;
  34 }
  35
  36 int pthread_cond_destroy(pthread_cond_t *cond)
  37 {
  38   if (cond->__c_waiting != NULL) return EBUSY;
  39   return 0;
  40 }
  41
  42 int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex)
  43 {
  44   volatile pthread_descr self = thread_self();
  45
  46   __pthread_lock(&cond->__c_lock, self);
  47   enqueue(&cond->__c_waiting, self);
  48   __pthread_unlock(&cond->__c_lock);
  49   pthread_mutex_unlock(mutex);
  50   suspend_with_cancellation(self);
  51   pthread_mutex_lock(mutex);
  52   /* This is a cancellation point */
  53   if (THREAD_GETMEM(self, p_canceled)
  54       && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE) {
  55     /* Remove ourselves from the waiting queue if we're still on it */
  56     __pthread_lock(&cond->__c_lock, self);
  57     remove_from_queue(&cond->__c_waiting, self);
  58     __pthread_unlock(&cond->__c_lock);
  59     pthread_exit(PTHREAD_CANCELED);
  60   }
  61   return 0;
  62 }
  63
  64 static inline int
  65 pthread_cond_timedwait_relative(pthread_cond_t *cond,
  66                                 pthread_mutex_t *mutex,
  67                                 const struct timespec * reltime)
  68 {
  69   volatile pthread_descr self = thread_self();
  70   sigset_t unblock, initial_mask;
  71   int retsleep;
  72   sigjmp_buf jmpbuf;
  73
  74   /* Wait on the condition */
  75   __pthread_lock(&cond->__c_lock, self);
  76   enqueue(&cond->__c_waiting, self);
  77   __pthread_unlock(&cond->__c_lock);
  78   pthread_mutex_unlock(mutex);
  79   /* Set up a longjmp handler for the restart and cancel signals */
  80   if (sigsetjmp(jmpbuf, 1) == 0) {
  81     THREAD_SETMEM(self, p_signal_jmp, &jmpbuf);
  82     THREAD_SETMEM(self, p_cancel_jmp, &jmpbuf);
  83     THREAD_SETMEM(self, p_signal, 0);
  84     /* Check for cancellation */
  85     if (THREAD_GETMEM(self, p_canceled)
  86         && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE) {
  87       retsleep = -1;
  88     } else {
  89       /* Unblock the restart signal */
  90       sigemptyset(&unblock);
  91       sigaddset(&unblock, __pthread_sig_restart);
  92       sigprocmask(SIG_UNBLOCK, &unblock, &initial_mask);
  93       /* Sleep for the required duration */
  94       retsleep = __libc_nanosleep(reltime, NULL);
  95       /* Block the restart signal again */
  96       sigprocmask(SIG_SETMASK, &initial_mask, NULL);
  97     }
  98   } else {
  99     retsleep = -1;
 100   }
 101   THREAD_SETMEM(self, p_signal_jmp, NULL);
 102   THREAD_SETMEM(self, p_cancel_jmp, NULL);
 103   /* Here, either the condition was signaled (self->p_signal != 0)
 104                    or we got canceled (self->p_canceled != 0)
 105                    or the timeout occurred (retsleep == 0)
 106                    or another interrupt occurred (retsleep == -1) */
 107   /* This is a cancellation point */
 108   if (THREAD_GETMEM(self, p_canceled)
 109       && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE) {
 110     __pthread_lock(&cond->__c_lock, self);
 111     remove_from_queue(&cond->__c_waiting, self);
 112     __pthread_unlock(&cond->__c_lock);
 113     pthread_mutex_lock(mutex);
 114     pthread_exit(PTHREAD_CANCELED);
 115   }
 116   /* If not signaled: also remove ourselves and return an error code */
 117   if (THREAD_GETMEM(self, p_signal) == 0) {
 118     __pthread_lock(&cond->__c_lock, self);
 119     remove_from_queue(&cond->__c_waiting, self);
 120     __pthread_unlock(&cond->__c_lock);
 121     pthread_mutex_lock(mutex);
 122     return retsleep == 0 ? ETIMEDOUT : EINTR;
 123   }
 124   /* Otherwise, return normally */
 125   pthread_mutex_lock(mutex);
 126   return 0;
 127 }
 128
 129 int pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex,
 130                            const struct timespec * abstime)
 131 {
 132   struct timeval now;
 133   struct timespec reltime;
 134   /* Compute a time offset relative to now */
 135   __gettimeofday(&now, NULL);
 136   reltime.tv_sec = abstime->tv_sec - now.tv_sec;
 137   reltime.tv_nsec = abstime->tv_nsec - now.tv_usec * 1000;
 138   if (reltime.tv_nsec < 0) {
 139     reltime.tv_nsec += 1000000000;
 140     reltime.tv_sec -= 1;
 141   }
 142   if (reltime.tv_sec < 0) return ETIMEDOUT;
 143   return pthread_cond_timedwait_relative(cond, mutex, &reltime);
 144 }
 145
 146 int pthread_cond_signal(pthread_cond_t *cond)
 147 {
 148   pthread_descr th;
 149
 150   __pthread_lock(&cond->__c_lock, NULL);
 151   th = dequeue(&cond->__c_waiting);
 152   __pthread_unlock(&cond->__c_lock);
 153   if (th != NULL) restart(th);
 154   return 0;
 155 }
 156
 157 int pthread_cond_broadcast(pthread_cond_t *cond)
 158 {
 159   pthread_descr tosignal, th;
 160
 161   __pthread_lock(&cond->__c_lock, NULL);
 162   /* Copy the current state of the waiting queue and empty it */
 163   tosignal = cond->__c_waiting;
 164   cond->__c_waiting = NULL;
 165   __pthread_unlock(&cond->__c_lock);
 166   /* Now signal each process in the queue */
 167   while ((th = dequeue(&tosignal)) != NULL) restart(th);
 168   return 0;
 169 }
 170
 171 int pthread_condattr_init(pthread_condattr_t *attr)
 172 {
 173   return 0;
 174 }
 175
 176 int pthread_condattr_destroy(pthread_condattr_t *attr)
 177 {
 178   return 0;
 179 }