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Improve CancellationException #3039

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merged 3 commits into from
Aug 13, 2024

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idelpivnitskiy
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@idelpivnitskiy idelpivnitskiy commented Aug 9, 2024

Motivation:

  1. H2ClientParentConnectionContext.StacklessCancellationException was reused by SpliceFlatStreamToMetaSingle, which created a false impression in logs that this exception is related to HTTP/2.
  2. We should capture the Subscriber's stack-trace for CancellationException in BeforeFinallyHttpOperator instead of a netty stack-trace, it will help to debug paths that subscribe to the payload post cancel.

Modifications:

  1. Make H2ClientParentConnectionContext.StacklessCancellationException a top-level class.
  2. Wrap CancellationException with Publisher.defer(...) in BeforeFinallyHttpOperator.
  3. Add an exception message in DefaultBlockingIterableProcessor.

Result:

Easier for users to reason about received CancellationException.

Motivation:

1. `H2ClientParentConnectionContext.StacklessCancellationException` was
reused by `SpliceFlatStreamToMetaSingle`, which created a false
impression in logs that this exception is related to HTTP/2.
2. There is not much value in a stacktrace for `CancellationException`
in `BeforeFinallyHttpOperator`.

Modifications:

1. Make `H2ClientParentConnectionContext.StacklessCancellationException`
a top level class.
2. Create a `StacklessCancellationException` in http-utils module for
`BeforeFinallyHttpOperator`.
3. Add exception message in `DefaultBlockingIterableProcessor`.

Result:

Easier for users to reason about received `CancellationException`.

import java.util.concurrent.CancellationException;

final class StacklessCancellationException extends CancellationException {
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I was not sure if it's worth making it public in a module like concurrent-internal and created a copy for now. Can move if someone prefers.

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Feels a bit confusing to have the same exception in two different places, especially since http-netty depends on utils?

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Actually, I changed my mind. It's worth capturing the full stack-trace if we capture the Subscriber's stack-trace instead of the netty transport stack-trace. Updated PR

@idelpivnitskiy idelpivnitskiy merged commit 2f2bf85 into apple:main Aug 13, 2024
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@idelpivnitskiy idelpivnitskiy deleted the CancellationException branch August 13, 2024 18:03
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4 participants