how to close a stream from a client (Python)

[flazz...@gmail.com]

Hi,

In a Python grpc client & server. Given some unary-stream rpc call:

call = stub.SomeUnaryStream(input_msg)

xs = itertools.islice(call, 2) # take two

call.cancel() # this doesn't seem to signal the server

How can I signal to the server that the call is over, and resources can be freed? The call is cancelled on the client side, but I get no notification until a GeneratorExit is thrown during a subsequent call. I assume the server-side GC is cleaning up and closing the generator. I made a golang client to see if the CloseSend method would signal but the behavior is similar.

Am I missing something here? or is the api incomplete?

-Franco

[Ken Payson]

In order to cancel a call from Python, you need to use the asynchronous API.

It should look something like this:

call_future = stub.SomeUnaryStream.future(input_msg)

call_future.cancel()

Note that if you have a long running server process, you will need to explicitly check if the call has been cancelled from the server.

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[flazz...@gmail.com]

Ken, Thanks for the tip. It didn't work exactly as describe but you pointed me in the right direction for a solution.

UnaryStream calls don't have future, just __call__. butt checking the cancellation state from the server side is what I needed.

I ended up checking context.is_active() in a separate thread on the server. That thread signals the cleanup when ,is_active() returns False.

On Thursday, October 27, 2016 at 1:23:25 PM UTC-5, Ken Payson wrote:

In order to cancel a call from Python, you need to use the asynchronous API.

It should look something like this:

call_future = stub.SomeUnaryStream.future(input_msg)

call_future.cancel()

Note that if you have a long running server process, you will need to explicitly check if the call has been cancelled from the server.

On Thu, Oct 27, 2016 at 10:54 AM, <flazz...@gmail.com> wrote:

Hi,

In a Python grpc client & server. Given some unary-stream rpc call:

call = stub.SomeUnaryStream(input_msg)

xs = itertools.islice(call, 2) # take two

call.cancel() # this doesn't seem to signal the server

How can I signal to the server that the call is over, and resources can be freed? The call is cancelled on the client side, but I get no notification until a GeneratorExit is thrown during a subsequent call. I assume the server-side GC is cleaning up and closing the generator. I made a golang client to see if the CloseSend method would signal but the behavior is similar.

Am I missing something here? or is the api incomplete?

-Franco

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[Nathaniel Manista]

On Thu, Oct 27, 2016 at 12:49 PM, <flazz...@gmail.com> wrote:

I ended up checking context.is_active() in a separate thread on the server. That thread signals the cleanup when ,is_active() returns False.

Polling the is_active method is not intended to be necessary for this case - how about registering a callback with the ServicerContext's add_callback method?

-Nathaniel

[flazz...@gmail.com]

Thanks Nathaniel, exactly what I needed!