asyncio (original) (raw)

This repository was archived by the owner on Nov 23, 2017. It is now read-only.

Description

I've been attempting to update to python 3.5 today, but it has been causing some of our unit tests to fail with an assert error.

I've reproduced in the repl with this code:

import asyncio

@asyncio.coroutine
def consumer(queue, num_expected):
    for _ in range(num_expected):
        yield from queue.get()

@asyncio.coroutine
def producer(queue, num_items):
    for i in range(num_items):
        yield from queue.put(i)


queue_size = 1
producer_num_items = 5
q = asyncio.Queue(queue_size)

results = asyncio.get_event_loop().run_until_complete(
    asyncio.gather(producer(q, producer_num_items),
                   consumer(q, producer_num_items)),
)

This code causes AssertionError: queue non-empty, why are getters waiting? to be thrown. Strangely, if I increase queue_size to 3 or 4, this causes the code to hang. 5 seems to be the magic queue_size that makes problems go away.