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From: dieter.maurer@online.de
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Subject: Re: Using a background thread with asyncio/futures with flask
Date: Fri, 22 Mar 2024 20:28:31 +0100
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dieter.maurer@online.de wrote at 2024-3-22 18:28 +0100:
>Thomas Nyberg wrote at 2024-3-22 11:08 +0100:
>> ... `future` use across thread boundaries ...
>> Here's an example using just the standard library that
>> exhibits the same issue:
> ...
>For use across thread boundaries, you likely will use
>`concurrent.Future` (not `asyncio.Future`).
>You can use `asyncio.futures._chain_futures` to associate
>an `asyncio.Future` with a `concurrent.Future`.
>Then the fate (result or exception set) of one will be reflected in the o=
ther.

You must not set the result/exception for a future in a "foreign" thread
("foreign" here means one not associated with the future's loop).
An aternative to the solution sketched above is to set the result
indirectly via `loop.call_soon_threadsafe`. This way, the
result is set in the futures "native" thread.