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Improve consume/produce examples #10

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Oct 17, 2016
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Improve consume/produce examples #10

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bb4bd8d
Use asyncio.gather instead of asyncio.ensure_future
sylvainb Oct 16, 2016
d9dd4ee
Added some comments
sylvainb Oct 16, 2016
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5 changes: 3 additions & 2 deletions examples/producer_consumer.py
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,7 @@ async def consume(queue):

loop = asyncio.get_event_loop()
queue = asyncio.Queue(loop=loop)
asyncio.ensure_future(produce(queue, 10), loop=loop)
loop.run_until_complete(consume(queue))
producer_coro = produce(queue, 10)
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IMO it is deliberate to not wait for the completion of the producer.

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@vxgmichel vxgmichel Oct 17, 2016 •
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Yes, the idea here is to run the producer in a background task while waiting for the consumer to complete. However, I'm not opposed to this change if you think it makes the example more understandable. As an alternative, it is possible to make the producer task more explicit:

loop = asyncio.get_event_loop()
queue = asyncio.Queue(loop=loop)
producer_task = loop.create_task(produce(queue, 10))
loop.run_until_complete(consume(queue))
assert producer_task.done()
loop.close()

In any case, it's probably good to discourage the fire and forget approach for the background task.

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Yesterday, during AsyncIO workshop at PyCON-FR, it was hard for two attendees to understand why we have ensure_future for one coroutine, and not for the other.

I've proposed to change the example as proposed by @sylvainb, it seems more understandable by available beginners.
I've also suggested to propose a pull request for that.

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Then it's fine with me, I'm merging it ;-)

consumer_coro = consume(queue)
loop.run_until_complete(asyncio.gather(producer_coro, consumer_coro))
loop.close()
4 changes: 4 additions & 0 deletions examples/producer_consumer_join.py
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Expand Up @@ -29,9 +29,13 @@ async def consume(queue):

async def run(n):
queue = asyncio.Queue()
# register the consume coroutine
consumer = asyncio.ensure_future(consume(queue))
# launch the producer and wait for completion
await produce(queue, n)
# ensure the consumer consumes all produced items
await queue.join()
# consumer is always awaiting for a new item, cancel it
consumer.cancel()


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