ex7.c

Axis 221 camera embedded programing interface

/* ex7
 *
 * Test case that illustrates a timed wait on a condition variable.
 */

#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <pthread.h>
#include <sys/time.h>
#include <unistd.h>

/* Our event variable using a condition variable contruct. */
typedef struct {
    pthread_mutex_t	mutex;
    pthread_cond_t	cond;
    int			flag;
} event_t;


/* Global event to signal main thread the timeout of the child thread. */
event_t main_event;


void *
test_thread (void *ms_param)
{
    int status = 0;
    event_t foo;
    struct timespec time;
    struct timeval  now;
    long ms = (long) ms_param;

    /* initialize cond var */
    pthread_cond_init(&foo.cond, NULL);
    pthread_mutex_init(&foo.mutex, NULL);
    foo.flag = 0;

    /* set the time out value */
    printf("waiting %ld ms ...\n", ms);
    gettimeofday(&now, NULL);
    time.tv_sec  = now.tv_sec + ms/1000 + (now.tv_usec + (ms%1000)*1000)/1000000;
    time.tv_nsec = ((now.tv_usec + (ms%1000)*1000) % 1000000) * 1000;

    /* Just use this to test the time out. The cond var is never signaled. */
    pthread_mutex_lock(&foo.mutex);
    while (foo.flag == 0 && status != ETIMEDOUT) {
	status = pthread_cond_timedwait(&foo.cond, &foo.mutex, &time);
    }
    pthread_mutex_unlock(&foo.mutex);
    
    /* post the main event */
    pthread_mutex_lock(&main_event.mutex);
    main_event.flag = 1;
    pthread_cond_signal(&main_event.cond);
    pthread_mutex_unlock(&main_event.mutex);
    
    /* that's it, bye */
    return (void*) status;
}

int
main (void)
{
  unsigned long count;

  setvbuf (stdout, NULL, _IONBF, 0);

  /* initialize main event cond var */
  pthread_cond_init(&main_event.cond, NULL);
  pthread_mutex_init(&main_event.mutex, NULL);
  main_event.flag = 0;

  for (count = 0; count < 20; ++count)
  {
      pthread_t thread;
      int status;

      /* pass down the milli-second timeout in the void* param */
      status = pthread_create (&thread, NULL, test_thread, (void*) (count*100));
      if (status != 0) {
	  printf ("status = %d, count = %lu: %s\n", status, count,
		  strerror (errno));
	  return 1;
      }
      else {

	  /* wait for the event posted by the child thread */
	  pthread_mutex_lock(&main_event.mutex);
	  while (main_event.flag == 0) {
	      pthread_cond_wait(&main_event.cond, &main_event.mutex);
	  }
	  main_event.flag = 0;
	  pthread_mutex_unlock(&main_event.mutex);

	  printf ("count = %lu\n", count);
      }
      
      usleep (10);
  }

  return 0;
}