[issue41660] multiprocessing.Manager objects lose connection info

[Tim Peters]

Tim Peters <tim at python.org> added the comment:

Weird. If I insert these between the two process starts:

    import time
    time.sleep(2)

then the producer produces the expected output:

at start: 666
at producer start: 666

and the program blows up instead when it gets to

    print("in consumer:", self.val.value)

Same thing if, instead of a sleep, I put

    producerprocess.join()

before starting the consumer.

If I change the tail end to:

    producerprocess.start()
    import time
    time.sleep(2)
    print(state_value)
    consumerprocess = MyConsumer(state_value, state_ready)
    consumerprocess.start()

then I see

    at start: 666
    at producer start: 666
    Value('i', 42)

before it blows up in the consumer.  So `state_value` appears to survive intact, and mutated as intended, across the producer's life - but gets corrupted somehow when it's _also_ passed to the consumer.

Weirder ;-) , if I replace the tail with the ever-more elaborate:

    producerprocess = MyProducer(state_value, state_ready)
    producerprocess.start()
    import time
    time.sleep(2)
    producerprocess.join()
    print(state_value)

    state_value.value = 13
    producerprocess = MyProducer(state_value, state_ready)
    producerprocess.start()
    time.sleep(2)
    producerprocess.join()
    print(state_value)

    consumerprocess = MyConsumer(state_value, state_ready)
    consumerprocess.start()

then I see

    at start: 666
    at producer start: 666
    Value('i', 42)
    at producer start: 13
    Value('i', 42)

before it blows up in the consumer - so it survived two full producer lifetimes!  So ... generalize ... change the tail to:


    for i in range(10):
        state_value.value = i
        producerprocess = MyProducer(state_value, state_ready)
        producerprocess.start()
        producerprocess.join()
        print(state_value)

    consumerprocess = MyConsumer(state_value, state_ready)
    consumerprocess.start()

and I see everything working fine before it blows up in the consumer:

    at start: 666
    at producer start: 0
    Value('i', 42)
    at producer start: 1
    Value('i', 42)
    at producer start: 2
    Value('i', 42)
    at producer start: 3
    Value('i', 42)
    at producer start: 4
    Value('i', 42)
    at producer start: 5
    Value('i', 42)
    at producer start: 6
    Value('i', 42)
    at producer start: 7
    Value('i', 42)
    at producer start: 8
    Value('i', 42)
    at producer start: 9
    Value('i', 42)

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue41660>
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