Async Runnable Listeners

[cbornet]

Checked

• I searched existing ideas and did not find a similar one
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• I've clearly described the feature request and motivation for it

Feature request

Add async support to Runnable.with_listeners method.
Currently it's only possible to attach Callables and not Coroutines.

Motivation

The current behavior is problematic when running in asyncio and the callback uses I/O as it will block the event loop.
For instance RunnableWithMessageHistory is configured with runnable.with_listeners(on_end=self._exit_history) and _exit_history will in turn get messages from BaseChatMessageHistory in a synchronous way.

Proposal (If applicable)

No response

[tgram-3D]

I ran into the same thing and found an interim workaround. You have to make async versions of BaseTracer, RootListenersTracer, and RunnableWithMessageHistory, but most of it’s just adding async await statements. I got it to work with a custom async MongoDB ChatMessageHistory class and haven’t had any issues…yet. See link below.

#19237

[cbornet]

Yes. The idea would be to have all this built in LangChain and not have to rewrite everything async.