CODEWITHSUNDEEP
pythonmultithreadingpython-3.x
WoJ
WoJ

Reputation: 29987

How to get results from threads as they complete?

The following code starts a few threads and prints the result after they are all done:

import threading

results = [None] * 5
threads = [None] * 5

def worker(i):
    results[i] = i

for i in range(5):
    threads[i] = threading.Thread(target=worker, args=(i,))
    threads[i].start()

# here I would like to use the results of the threads which are finished
# while others still run

for i in range(5):
    threads[i].join()

# here I have the results but only when all threads are done
print(results)

As mentioned in the code, I would like to use the results of the threads which are finished while others are still running. What is the correct way to do that?

Should I simply start a new thread which would have a while True: loop and continuously check for a new entry in results or is there a buil-in mechanism for such operations (as part of the threading.Thread call which would point to a callback when the thread is done)?

Upvotes: 1

Views: 127

Answers (1)

John Zwinck
John Zwinck

Reputation: 249153

Since you're using Python 3, concurrent.futures is a better fit than threading:

import concurrent.futures

results = [None] * 5

def worker(i):
    results[i] = i

with concurrent.futures.ThreadPoolExecutor(5) as pool:
    futmap = {pool.submit(worker, i): i for i in range(len(results))}
    for fut in concurrent.futures.as_completed(futmap):
        print("doing more stuff with", futmap[fut])

Upvotes: 1

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