Raymond Hettinger wrote:
FWIW, I've been working on a way to simplify the use of queues with daemon consumer threads
Sometimes, I launch one or more consumer threads that wait for a task to enter a queue and then work on the task. A recurring problem is that I sometimes need to know if all of the tasks have been completed so I can exit or do something with the result.
If each thread only does a single task, I can use t.join() to wait until the task is done. However, if the thread stays alive and waits for more Queue entries, then there doesn't seem to be a good way to tell when all the processing is done.
The pattern I use is to use the None object to indicate that no more tasks are coming - just add it to your queue once for every worker thread that exists and have your worker threads exit when they get a task of None. Your setup code to start the threads and add tasks to the queue wouldn't need to change; once all the tasks have been enqueued you'd wait for completion like this: # Tell all the workers to quit for t in worker_threads(): q.put(None) # Wait for all the workers to quit for t in worker_threads(): t.join() do_work_on_results() The worker thread looks like this: while 1: task = q.get() if task is None: break do_work(task) -Dave