Checking up on a `concurrent.futures.ThreadPoolExecutor`

There is some visibility into the Pool, and the pending workitem queue. To find out what's available, print poolx.__dict__ to see the structure. Read the ThreadPool code, it's pretty good: concurrent.futures.thread

The following creates a pool with one thread. It then creates two jobs: one sleeps for 3 seconds, the other immediately returns. The pool's number of pending work items is then printed.

Following that, we print out items from the work queue. In this case, a thread is already executing the time.sleep(3) function, so that's not in the queue. The function sleep with args [0] and kwargs {} is printed, because that's the next work item for the pool to run.

Kudos to @dano for the nondestructive queue insight, and @abarnert.

source

import concurrent.futures, timepoolx = concurrent.futures.ThreadPoolExecutor(max_workers=1)poolx.submit(time.sleep, 3)poolx.submit(time.sleep, 0)   # very fastprint('pending:', poolx._work_queue.qsize(), 'jobs')print('threads:', len(poolx._threads))print()# TODO: make thread safe; work on copy of queue?print('Estimated Pending Work Queue:')for num,item in enumerate(poolx._work_queue.queue):    print('{}\t{}\t{}\t{}'.format(        num+1, item.fn, item.args, item.kwargs,        ))poolx.shutdown(wait=False)

output

pending: 1 jobsthreads: 1Pending Work Queue:1   <built-in function sleep>   (0,)    {}

Nor very clean and reliable way to find pending futures, but I do it like this:

if 'state=pending' in str(future):    logger.debug('PENDING')elif future.running():    logger.debug('RUNNING')elif future.cancelled():    logger.debug('CANCELLED')elif future.exception():    logger.debug('EXCEPTION')elif future.done():    logger.debug('DONE')