create clock id:

  id->state = OK;


waiting for id:

   lock
   /* once unscheduled, the id cannot be used anymore */
   while (id->state != unscheduled) {
     id->state = busy;
     unlock

     ret = gstpoll (timeout);

     lock
     if (id->state == unscheduled) {
       /* id became unscheduled, read the fd and broadcast */
       read (fd)
       cond_broadcast ()
     }
     else {
       if (ret != 0) {
         /* some other id got unlocked */ 
	 /* mark ourselves as EARLY, we release the lock and we could be
	  * unscheduled ourselves but we don't want the unscheduling thread
	  * to write on the fd */
	 id->state = EARLY;
	 /* wait until it reads the fd and signals us */
         cond_wait ()
       }
       else {
         /* we timed out */
	 id->state = OK | EARLY;
       }
     }
   }
   unlock
   return id->state;


unschedule id:

   lock
   /* when it leaves the poll, it'll detect the unscheduled. */
   id->state = unscheduled;
   /* if it's busy waiting in poll, write to the fd */
   if (id->state == busy) {
     write (fd)
   }
   unlock