[Tutor] Threads

[Kent Johnson]

Terry Carroll wrote:
> I just thought of a hybrid solution; have a lock object that's required to 
> be held to reference both the Queue and the Shutdown flag.  Each thread 
> would do something like this:
> 
>  get_lock()
>  if shutdown_flag == 'y':
>     self.shutdown='y'
>     else:
>       request=Queue.get()
>       if request.type = "shutdown"
>           self.shutdown='y'
>           shutdown_flag='y'   # tell the others
>       else:
>          [normal processing]
>  release_lock()
>  if self.shutdown ='y':
>     [shutdown stuff]

I think it can be as simple as this:
while not stopevent.isSet():
     try:
         task = producerQueue.get(True, 0.1)
         # process task
     except Queue.Empty:
         pass

where stopevent is a Queue.Event and producerQueue is a Queue.Queue.

>>What happens if you just leave the consumer threads blocked on the empty 
>>queue? If you will need them again, or if the entire process is 
>>short-lived, this is a simple solution. Just mark the consumers as 
>>daemon threads so the app will exit while they are still alive.
> 
> 
> I won't need them again.  Can the app exit with the threads still blocked?  
> Will Python kill off all the threads then?

If the threads are marked as daemon threads (call 
thread.setDaemon(True)) then Python will exit even if the thread is 
still alive.

Kent