smq_read_timestamp.c

#include <unistd.h>    /* for usleep() */
#include <signal.h>    /* for signal() */
#include <shm_arena.h> /* for Shared Memory Arena Library */

static int running = 1;
static smq_t q;

static void catcher(int sig)
{
  printf("catch signal %d\n", sig);

  /* Unblock the current or next smq_rdlock() call. */
  smq_unblock_rdlock(q);
  running = 0;
}

int main(void)
{
  long double offset = 0;

  signal(SIGINT, catcher);

  /* We include the SHM_TIMESTAMP bit flag in smq_get() to make sure
   * the Shared Multi-Queue is time stamped. */
  q = smq_get(NULL, sizeof(int), 24, "q_count", O_CREAT|SHM_TIMESTAMP);
  if(!q)
    {
      printf("smq_get() failed\n");
      return 1;
    }

  while(running)
    {
      int num;

      /* block until there is at least 1 in the queue */
      num = smq_rdlock(q, 1);

      while(num > 0)
    {
      int *ptr;
      long double *t;
      ptr = smq_read(q);
      t = smq_timestamp(q, ptr);
      if(offset == 0) offset = *t;
      printf("(%Lf)%d ", *t - offset, *ptr);
      fflush(stdout);
      num--;
    }

      smq_unlock(q);
    }

  /* Because smq_unblock_rdlock() spawns a thread to release the
   * blocking smq_rdlock() and that thread must make mutex calls, we
   * need to call smq_delete(q) to wait for thread to finish, to avoid
   * deadlocking the multi-queue.  smq_delete(q) only cleans up the
   * local process data and not the shared memory data. */
  smq_delete(q);

  return 0;
}