[New-bugs-announce] [issue42445] Assertion in run_coroutine_threadsafe

[Jochen Kienzle]

New submission from Jochen Kienzle <Jochen.Kienzle at bosch.io>:

Hello,

in my implementation I want to call mqtt_client.publish_json from a sync method:

-----------------------------
def __on_event(self, ev):
    ...
    asyncio.run_coroutine_threadsafe(self.mqtt_client.publish_json(INGESTION_TOPIC, msg), loop=self.publish_loop)
-----------------------------

where self.broker.publish_json is an async function and publish_loop is a loop which has been started (run_forever) in a separate thread:

---
    self.publish_loop = asyncio.new_event_loop()
    t = threading.Thread(target=self.publish_loop.run_forever)
    t.start()
---

Sometimes (about 1 in 400 calls) I get the following Assertion Error:

-----------------------------
?[94;1m== APP == Exception in callback _ProactorBaseWritePipeTransport._loop_writing(<_OverlappedF...ed result=366>)
?[0m
?[94;1m== APP == handle: <Handle _ProactorBaseWritePipeTransport._loop_writing(<_OverlappedF...ed result=366>)>
[0m
[94;1m== APP == Traceback (most recent call last):
[0m
[94;1m== APP ==   File "C:\Users\sio7fe\AppData\Local\Programs\Python\Python38-32\lib\asyncio\events.py", line 81, in _run
[0m
[94;1m== APP ==     self._context.run(self._callback, *self._args)
[0m
[94;1m== APP ==   File "C:\Users\sio7fe\AppData\Local\Programs\Python\Python38-32\lib\asyncio\proactor_events.py", line 375, in _loop_writing
[0m
[94;1m== APP ==     assert f is self._write_fut
[0m
[94;1m== APP == AssertionError
-----------------------------

Run time behavior:
 - publish_loop will be re-used on each event
 - run_coroutine_threadsafe will be called multiple times without any sleep (its in a for-loop with 1-3 elements)


Since this is a thread safe method and its working multiple times, it seems to be some run-time related issue and I can't figure out the root cause.

----------
components: asyncio
messages: 381674
nosy: JoKi, asvetlov, yselivanov
priority: normal
severity: normal
status: open
title: Assertion in run_coroutine_threadsafe
type: behavior
versions: Python 3.8

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue42445>
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