c_cpp/pthreadtest/04conditionexample.c

   1 /*
   2  * cond.c
   3  *
   4  * Demonstrate a simple condition variable wait.
   5  *
   6  * to compile me for Linux, type:  gcc -o conditionexample conditionexample.c -lpthread
   7  */
   8 #include <pthread.h>
   9 #include <stdio.h>
  10 #include <stdlib.h>
  11
  12 typedef struct {
  13     pthread_mutex_t     mutex;  /* Protects access to value */
  14     pthread_cond_t      cond;   /* Signals change to value */
  15     int                 value;  /* Access protected by mutex */
  16 } cond_struct_t;
  17
  18 cond_struct_t data = {
  19     PTHREAD_MUTEX_INITIALIZER, PTHREAD_COND_INITIALIZER, 0};
  20
  21
  22 /*
  23  * Thread start routine. It will set the main thread's predicate
  24  * and signal the condition variable.
  25  */
  26 void * wait_thread (int *hibernation)
  27 {
  28     int status;
  29
  30     sleep (*hibernation);
  31
  32     /****** ENTER THE MONITOR HERE *******/
  33     status = pthread_mutex_lock (&data.mutex);
  34     if (status != 0) {fprintf(stderr,"Lock error!\n"); exit(-1);}
  35
  36     data.value = 1;             /* Set predicate */
  37
  38     status = pthread_cond_signal (&data.cond);
  39     if (status != 0) {fprintf(stderr,"Signal error!\n"); exit(-1);}
  40
  41     status = pthread_mutex_unlock (&data.mutex);
  42     if (status != 0) {fprintf(stderr,"Unlock error!\n"); exit(-1);}
  43     /******* EXIT the MONITOR ************/
  44
  45     return NULL;
  46 }
  47
  48 int main (int argc, char *argv[])
  49 {
  50     int status;
  51     pthread_t wait_thread_id;
  52     struct timespec timeout;
  53     int hibernation = 1;
  54
  55     /*
  56      * If an argument is specified, interpret it as the number
  57      * of seconds for wait_thread to sleep before signaling the
  58      * condition variable.  You can play with this to see the
  59      * condition wait below time out or wake normally.
  60      */
  61     //thr_setconcurrency(2);
  62     if (argc > 1)
  63         hibernation = atoi (argv[1]);
  64
  65     /*
  66      * Create wait_thread.
  67      */
  68     status =
  69        pthread_create (&wait_thread_id, NULL, (void *) wait_thread, &hibernation);
  70     if (status != 0) {fprintf(stderr,"Create error!\n"); exit(-1);}
  71
  72     /*
  73      * Wait on the condition variable until signaled by
  74      * the wait_thread.
  75      */
  76
  77     /***** ENTER the MONITOR HERE **********/
  78     status = pthread_mutex_lock (&data.mutex);
  79     if (status != 0) {fprintf(stderr,"Lock error!\n"); exit(-1);}
  80
  81     while (data.value == 0) {
  82         status = pthread_cond_wait(&data.cond, &data.mutex);
  83         }
  84     if (status != 0) {fprintf(stderr,"Wait error!\n"); exit(-1);}
  85
  86     status = pthread_mutex_unlock (&data.mutex);
  87     if (status != 0) {fprintf(stderr,"Unlock error!\n"); exit(-1);}
  88     /******* EXIT the MONITOR **************/
  89
  90     printf("Condition was signalled, data.value=%d\n",data.value);
  91     return 0;
  92 }