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);
  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 (self->p_canceled && self->p_cancelstate == PTHREAD_CANCEL_ENABLE) {
  54     /* Remove ourselves from the waiting queue if we're still on it */
  55     __pthread_lock(&cond->c_lock);
  56     remove_from_queue(&cond->c_waiting, self);
  57     __pthread_unlock(&cond->c_lock);
  58     pthread_exit(PTHREAD_CANCELED);
  59   }
  60   return 0;
  61 }
  62
  63 static inline int
  64 pthread_cond_timedwait_relative(pthread_cond_t *cond,
  65                                 pthread_mutex_t *mutex,
  66                                 const struct timespec * reltime)
  67 {
  68   volatile pthread_descr self = thread_self();
  69   sigset_t unblock, initial_mask;
  70   int retsleep;
  71   sigjmp_buf jmpbuf;
  72
  73   /* Wait on the condition */
  74   __pthread_lock(&cond->c_lock);
  75   enqueue(&cond->c_waiting, self);
  76   __pthread_unlock(&cond->c_lock);
  77   pthread_mutex_unlock(mutex);
  78   /* Set up a longjmp handler for the restart and cancel signals */
  79   if (sigsetjmp(jmpbuf, 1) == 0) {
  80     self->p_signal_jmp = &jmpbuf;
  81     self->p_cancel_jmp = &jmpbuf;
  82     self->p_signal = 0;
  83     /* Check for cancellation */
  84     if (self->p_canceled && self->p_cancelstate == PTHREAD_CANCEL_ENABLE) {
  85       retsleep = -1;
  86     } else {
  87       /* Unblock the restart signal */
  88       sigemptyset(&unblock);
  89       sigaddset(&unblock, PTHREAD_SIG_RESTART);
  90       sigprocmask(SIG_UNBLOCK, &unblock, &initial_mask);
  91       /* Sleep for the required duration */
  92       retsleep = __libc_nanosleep(reltime, NULL);
  93       /* Block the restart signal again */
  94       sigprocmask(SIG_SETMASK, &initial_mask, NULL);
  95     }
  96   } else {
  97     retsleep = -1;
  98   }
  99   self->p_signal_jmp = NULL;
 100   self->p_cancel_jmp = NULL;
 101   /* Here, either the condition was signaled (self->p_signal != 0)
 102                    or we got canceled (self->p_canceled != 0)
 103                    or the timeout occurred (retsleep == 0)
 104                    or another interrupt occurred (retsleep == -1) */
 105   /* This is a cancellation point */
 106   if (self->p_canceled && self->p_cancelstate == PTHREAD_CANCEL_ENABLE) {
 107     __pthread_lock(&cond->c_lock);
 108     remove_from_queue(&cond->c_waiting, self);
 109     __pthread_unlock(&cond->c_lock);
 110     pthread_mutex_lock(mutex);
 111     pthread_exit(PTHREAD_CANCELED);
 112   }
 113   /* If not signaled: also remove ourselves and return an error code */
 114   if (self->p_signal == 0) {
 115     __pthread_lock(&cond->c_lock);
 116     remove_from_queue(&cond->c_waiting, self);
 117     __pthread_unlock(&cond->c_lock);
 118     pthread_mutex_lock(mutex);
 119     return retsleep == 0 ? ETIMEDOUT : EINTR;
 120   }
 121   /* Otherwise, return normally */
 122   pthread_mutex_lock(mutex);
 123   return 0;
 124 }
 125
 126 int pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex,
 127                            const struct timespec * abstime)
 128 {
 129   struct timeval now;
 130   struct timespec reltime;
 131   /* Compute a time offset relative to now */
 132   __gettimeofday(&now, NULL);
 133   reltime.tv_sec = abstime->tv_sec - now.tv_sec;
 134   reltime.tv_nsec = abstime->tv_nsec - now.tv_usec * 1000;
 135   if (reltime.tv_nsec < 0) {
 136     reltime.tv_nsec += 1000000000;
 137     reltime.tv_sec -= 1;
 138   }
 139   if (reltime.tv_sec < 0) return ETIMEDOUT;
 140   return pthread_cond_timedwait_relative(cond, mutex, &reltime);
 141 }
 142
 143 int pthread_cond_signal(pthread_cond_t *cond)
 144 {
 145   pthread_descr th;
 146
 147   __pthread_lock(&cond->c_lock);
 148   th = dequeue(&cond->c_waiting);
 149   __pthread_unlock(&cond->c_lock);
 150   if (th != NULL) restart(th);
 151   return 0;
 152 }
 153
 154 int pthread_cond_broadcast(pthread_cond_t *cond)
 155 {
 156   pthread_descr tosignal, th;
 157
 158   __pthread_lock(&cond->c_lock);
 159   /* Copy the current state of the waiting queue and empty it */
 160   tosignal = cond->c_waiting;
 161   cond->c_waiting = NULL;
 162   __pthread_unlock(&cond->c_lock);
 163   /* Now signal each process in the queue */
 164   while ((th = dequeue(&tosignal)) != NULL) restart(th);
 165   return 0;
 166 }
 167
 168 int pthread_condattr_init(pthread_condattr_t *attr)
 169 {
 170   return 0;
 171 }
 172
 173 int pthread_condattr_destroy(pthread_condattr_t *attr)
 174 {
 175   return 0;
 176 }