How to stop listening on a stream in python gRPC client

Question

I am listening in a python thread on a gRPC stream that never ends:

responses = some_grpc_stub.FunctionThatReturnsStream()
for response in responses:
  on_event(response)

I want to do this for a while, and then stop listening, so that on_event isn't called again, possibly before the stream is done.

How do I do that? Is there a correct way to just kill the thread in which this loop is running? Or is there some way to have responses end prematurely so iteration ends and the thread can run to completion?

I had been using asyncio but I'm willing to use whatever accomplishes this goal. — Diogenes Creosote
– Diogenes Creosote, Commented May 12, 2022 at 0:13

Lidi Zheng · Accepted Answer · 2022-05-20 18:31:10Z

5

maybe you can consider using cancel()[1]? The streaming call returns an object that is both a Future and an iterator, you can invoke responses.cancel() to cancel it. In practice, this needs to happen in another thread, because the consumption of the iterator blocks.

If you are using AsyncIO API, the invoking a streaming call returns an object that implemented asyncio.Task, and supports cancel [2]. You can still use responses.cancel() to stop a stream.

[1] https://grpc.github.io/grpc/python/grpc.html#grpc.RpcContext.cancel

[2] https://docs.python.org/3/library/asyncio-task.html#asyncio.Task.cancel

answered May 20, 2022 at 18:31

Lidi Zheng

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2 Comments

Diogenes Creosote Over a year ago

Yep, works! It might be nice to make that a bit clearer in the examples that involve iterating over a stream. If you don't object, lmk, and I might make a PR adding it.

Lidi Zheng Over a year ago

Improvements are always welcomed! Feel free to @ me in the PR.

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