ubuntu：sem_timedwait没有醒来（C）

#include <stdio.h>
#include <time.h>
#include <string.h>
#include <errno.h>
#include <semaphore.h>

sem_t trigger_sem1, trigger_sem2, trigger_sem3;

// The main thread process.  Called three times with a different num arg - 1, 2 or 3.
void *thread(void *arg)
{
  int num = (int) arg;
  sem_t *wait, *trigger;
  int val, retval;
  struct timespec ts;
  struct timeval tv;

  switch (num)
    {
      case 1:
        wait = &trigger_sem1;
        trigger = &trigger_sem2;
        break;
      case 2:
        wait = &trigger_sem2;
        trigger = &trigger_sem3;
        break;
      case 3:
        wait = &trigger_sem3;
        trigger = &trigger_sem1;
        break;
    }

  while (1)
    {
      // The first thread delays by 40ms to time the whole loop.  
      // This is an external sync in the real app.
      if (num == 1)   
        usleep(40000);

      // print sem value before we wait.  If this is 1, sem_timedwait() will
      // return immediately, otherwise it will block until sem_post() is called on this sem. 
      sem_getvalue(wait, &val);
      printf("sem%d wait sync sem%d. val before %dn", num, num, val);

          // get current time and add half a second for timeout.
      gettimeofday(&tv, NULL);
      ts.tv_sec = tv.tv_sec;
      ts.tv_nsec = (tv.tv_usec + 500000);    // add half a second
      if (ts.tv_nsec > 1000000)
        {
          ts.tv_sec++;
          ts.tv_nsec -= 1000000;
        }
      ts.tv_nsec *= 1000;    /* convert to nanosecs */

      retval = sem_timedwait(wait, &ts);
      if (retval == -1)
        {
          // timed out.  Print value of sem now.  This should be 0, otherwise sem_timedwait
          // would have woken before timeout (unless the sem_post happened between the 
          // timeout and this call to sem_getvalue).
          sem_getvalue(wait, &val);
          printf("!!!!!!    sem%d sem_timedwait failed: %s, val now %dn", 
            num, strerror(errno), val);
        }
      else
        printf("sem%d wakeup.n", num);

        // get value of semaphore to trigger.  If it's 1, don't post as it has already been 
        // triggered and sem_timedwait on this sem *should* not block.
      sem_getvalue(trigger, &val);
      if (val <= 0)
        {
          printf("sem%d send sync sem%d. val before %dn", num, (num == 3 ? 1 : num+1), val);
          sem_post(trigger);
        }
      else
        printf("!! sem%d not sending sync, val %dn", num, val);
    }
}



int main(int argc, char *argv[])
{
  pthread_t t1, t2, t3;

   // create semaphores.  val of sem1 is 1 to trigger straight away and start the whole ball rolling.
  if (sem_init(&trigger_sem1, 0, 1) == -1)
    perror("Error creating trigger_listman semaphore");
  if (sem_init(&trigger_sem2, 0, 0) == -1)
    perror("Error creating trigger_comms semaphore");
  if (sem_init(&trigger_sem3, 0, 0) == -1)
    perror("Error creating trigger_vws semaphore");

  pthread_create(&t1, NULL, thread, (void *) 1);
  pthread_create(&t2, NULL, thread, (void *) 2);
  pthread_create(&t3, NULL, thread, (void *) 3);

  pthread_join(t1, NULL);
  pthread_join(t2, NULL);
  pthread_join(t3, NULL);
}

[...]
sem1 wait sync sem1. val before 1
sem1 wakeup.
sem1 send sync sem2. val before 0
sem2 wakeup.
sem2 send sync sem3. val before 0
sem2 wait sync sem2. val before 0
sem3 wakeup.
sem3 send sync sem1. val before 0
sem3 wait sync sem3. val before 0
sem1 wait sync sem1. val before 1
sem1 wakeup.
sem1 send sync sem2. val before 0
[...]

01  sem3 wait sync sem3. val before 0
02  sem1 wakeup.
03  sem1 send sync sem2. val before 0
04  sem2 wakeup.
05  sem2 send sync sem3. val before 0
06  sem2 wait sync sem2. val before 0
07  sem1 wait sync sem1. val before 0
08  !!!!!!    sem3 sem_timedwait failed: Connection timed out, val now 1
09  sem3 send sync sem1. val before 0
10  sem3 wait sync sem3. val before 1
11  sem3 wakeup.
12  !! sem3 not sending sync, val 1
13  sem3 wait sync sem3. val before 0
14  sem1 wakeup.
[...]