New submission from Dmitry Malinovsky: When there is a huge amount of `writer.write` calls followed by `await writer.drain()` on a non-paused channel, and there are no other coroutine switches, `await writer.drain()` immediately returns without a switch. This is because `asyncio.stream.FlowControlMixin._drain_helper` do not `yield` or `yield from` on a non-paused stream.
Use-case: AMQP basic.publish method, for which the broker (rabbitmq) do not send any replies back. Trying to publish 4k messages results in the following warnings (PYTHONASYNCIODEBUG env variable is set): `Executing <Handle <TaskWakeupMethWrapper object at 0x1106fde28>(<Future finis...events.py:275>) created at /Users/malinoff/Projects/ideas/amqproto/amqproto/channel.py:85> took 2.371 seconds` 2.371 seconds is the time spent on 4k `basic_publish` calls. You can find the test itself on github: https://github.com/malinoff/amqproto/blob/master/tests/stress/test_4k_msgs.py#L11-L12 An easy fix would be to replace return (https://github.com/python/cpython/blob/master/Lib/asyncio/streams.py#L206) with yield (and but the code below under the else clause; I'm willing to prepare a pull request), but maybe I'm missing something and such behavior is intentional? ---------- components: asyncio messages: 299610 nosy: Dmitry Malinovsky, yselivanov priority: normal severity: normal status: open title: asyncio.stream.FlowControlMixin._drain_helper may lead to a blocking behavior versions: Python 3.5, Python 3.6, Python 3.7 _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue31096> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
