Add try-except for process.send_signal so it can work on Windows.

[jamesroseman]

The current subprocess_server uses process.send_signal to terminate the process. On Windows, this will raise a ValueError, as .terminate() should be used instead.

Please add a meaningful description for your change here

This would close #21069

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[shunping]

LGTM! Thanks.

[github-actions]

R: @tvalentyn for final approval

[tvalentyn]

Thanks!
Curious, in which scenario are you using Beam + Windows?

[jamesroseman]

Thanks! Curious, in which scenario are you using Beam + Windows?

Doing some prototyping at work where we're stuck on Windows machines (even though we deploy on Linux boxes). We also aren't allowed access to Docker on dev boxes which is another hurdle for using Beam...

[victorrgez]

We use it for debugging code in Local with DirectRunner before uploading changes to Dataflow. Because of this issue we had some problems and could not use in Local some Java cross-language transforms

Thanks! Curious, in which scenario are you using Beam + Windows?

[the-xentropy]

I think this patch regressed at some point. The stop code now is a raw SIGINT with no try-except block.