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From: Zachary Ware <zachary.ware+pylist@gmail.com>
Newsgroups: comp.lang.python
Subject: Re: Adding run_in_executor task to already existing loop.
Date: Fri, 25 Mar 2016 16:00:16 -0500
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On Fri, Mar 25, 2016 at 3:24 PM, Ray Cote
<rgacote@appropriatesolutions.com> wrote:
> Hello:
>
> I=E2=80=99m trying to perform an synchronous task while using asyncio.
> I understand the solution is to use run_in_executor.
> I=E2=80=99m not clear on how to add this into an already running event lo=
op.
>
> I=E2=80=99ve found lots of examples showing how to set up a loop and run =
this, but
> I=E2=80=99m blocked in regards to doing this when the loop is already est=
ablished.
>
>
> Example code:
>
> def blocking_func(param1):
>     # call the blocking call here.
>     return results
>
> async def process_request():
>     loop =3D asyncio.get_event_loop()
>     block =3D loop.run_in_executor(None, blocking_func, =E2=80=9Chello=E2=
=80=9D)
>     results =3D await loop.run_until_complete(asyncio.gather(*[block, ])
>
> The above code says =E2=80=9Cloop already running.=E2=80=9D because we=E2=
=80=99re already in an
> async ask that has been awaited. What is the proper method of adding in
> this new synchronous task?

I'm assuming you're doing `await process_request()` elsewhere, which
is what's producing your error: you're trying to start the loop within
a coroutine running on that loop.  loop.run_in_executor() returns a
Future just like any other coroutine, so process_request just needs
this:

   async def process_request():
       loop =3D asyncio.get_event_loop()
       results =3D await loop.run_in_executor(None, blocking_func, 'hello')

--=20
Zach