Subj : Re: killing thread
To   : comp.programming.threads
From : Joe Seigh
Date : Wed Aug 10 2005 12:34 pm

Vitale Ferruccio wrote:
> Hi,
> 
> my program runs under *nix and windows, I'm using POSIX threads.
> For clearance, I report two small peace of code:
> 
> void *
> thread_timer(void *parg)
> {       
>     sleep(200);
>     pthread_exit(NULL);
>     return NULL;
> }
> 
> void *
> thread_execute(void *parg)
> {
>     pthread_cancel(thread_id_of_timer_thread);
>     pthread_exit(NULL);
> }
> 
> After thread_execute calls pthread_cancel, I thought that the thread 
> would be
> cancelled: instead thread_timer exists only when 200 seconds are passed.
> I could now rewrite my question: how can I put to sleep a thread and 
> interrupt
> its execution? :-)
> 

Assuming you have a signal handler and you're using the signal to interrupt
a syscall, you may have a race condition.  How do you know the thread in question
is in sleep()?  You don't.  If the signal occurred before the sleep then
what you're seeing is allowable.

Use pthread_cond_signal and pthread_cond_timedwait with a "signaled" flag.

  ts.tv_sec = time() + 200;
  ts.tv_nsec = 0;
  pthread_mutex_lock(&mutex);
  while (!signaled)
    pthread_cond_timedwait(&cvar, &mutex, &ts);
  pthread_mutex_unlock(&mutex);


  pthread_mutex_lock(&mutex);
  signaled = 1;
  pthread_cond_signal(&cvar);
  pthread_mutex_unlock(&mutex);


-- 
Joe Seigh

When you get lemons, you make lemonade.
When you get hardware, you make software.

.