[New-bugs-announce] [issue40357] asyncio: will shutdown_default_executor work in single step (stop, run_forever) mode?

[Chris Meyer]

New submission from Chris Meyer <cmeyer1969 at gmail.com>:

Is the new asyncio.loop.shutdown_default_executor() suitable for event loops that are run in single-step mode?

event_loop.create_task(event_loop.shutdown_default_executor())
event_loop.stop()
event_loop.run_forever()

I don't see how it will work since shutdown_default_executor() may not be finished during a single 'stopped' run_forever() call. 

Also, what happens to pending executor futures? Previously reported bug #28464.

Here is my currently working code for shutting down the event loop.

# give event loop one chance to finish up
event_loop.stop()
event_loop.run_forever()
# wait for everything to finish, including tasks running in executors
# this assumes that all outstanding tasks finish in a reasonable time (i.e. no infinite loops).
all_tasks_fn = getattr(asyncio, "all_tasks", None)
if not all_tasks_fn:
    all_tasks_fn = asyncio.Task.all_tasks
tasks = all_tasks_fn(loop=event_loop)
if tasks:
    gather_future = asyncio.gather(*tasks, return_exceptions=True)
else:
    # work around fact that gather always uses global event loop in Python 3.8
    gather_future = event_loop.create_future()
    gather_future.set_result([])
event_loop.run_until_complete(gather_future)
# due to a seeming bug in Python libraries, the default executor needs to be shutdown explicitly before the event loop
# see http://bugs.python.org/issue28464 .
_default_executor = getattr(event_loop, "_default_executor", None)
if _default_executor:
    _default_executor.shutdown()
event_loop.close()

----------
messages: 366945
nosy: cmeyer, vstinner
priority: normal
severity: normal
status: open
title: asyncio: will shutdown_default_executor work in single step (stop, run_forever) mode?
versions: Python 3.9

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue40357>
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