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context: WithCancel should return a cancel function which can accept an error #34764

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fanfuxiaoran opened this issue Oct 8, 2019 · 6 comments
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context: WithCancel should return a cancel function which can accept an error #34764

fanfuxiaoran opened this issue Oct 8, 2019 · 6 comments
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FrozenDueToAge WaitingForInfo Issue is not actionable because of missing required information, which needs to be provided.

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@fanfuxiaoran
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Sometimes, we run multiple go routines in a context, if one go routine fails due to an error, we
want to cancel the context and record the error in it. Such as a task has several workers, each worker works independently, if a worker fails , the task is supposed to fail and report the cause.
I want to cancel the context if a worker fails due to an error, and record the error in the context.
However, the CancelFunc returned by WithCancel can not accept an error. I think a new type of
cancel function is needed which user can pass an error into it and can be returned by WithCancel.
@fanfuxiaoran fanfuxiaoran changed the title Need WithCancel can return a cancel function which can accept an error WithCancel should return a cancel function which can accept an error Oct 8, 2019
@fanfuxiaoran fanfuxiaoran mentioned this issue Oct 8, 2019
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@mvdan
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mvdan commented Oct 8, 2019

WithCancel can't be changed without breaking backwards compatibility. Likewise, we can't change CancelFunc. What exactly are you proposing?

@fanfuxiaoran
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fanfuxiaoran commented Oct 8, 2019 •
edited

WithCancel can't be changed without breaking backwards compatibility. Likewise, we can't change CancelFunc. What exactly are you proposing?

ref: #34761

@dmitshur dmitshur changed the title WithCancel should return a cancel function which can accept an error context: WithCancel should return a cancel function which can accept an error Oct 8, 2019
@bcmills
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bcmills commented Oct 8, 2019

Note that it's fairly trivial to write your own wrapper around context.WithCancel that substitutes a different error: https://play.golang.org/p/X1hpcV2OC7i

@bcmills
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bcmills commented Oct 8, 2019

Such as a task has several workers, each worker works independently, if a worker fails , the task is supposed to fail and report the cause.

That is exactly what an errgroup.Group does. There is typically no need to inject the error back into the controlling Context: the Context is an input to the tasks, but the error is an output.

@fanfuxiaoran
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Such as a task has several workers, each worker works independently, if a worker fails , the task is supposed to fail and report the cause.

That is exactly what an errgroup.Group does. There is typically no need to inject the error back into the controlling Context: the Context is an input to the tasks, but the error is an output.

Great! Thanks for your help.

@ianlancetaylor
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Is there anything else to do for this issue?

@ianlancetaylor ianlancetaylor added the WaitingForInfo Issue is not actionable because of missing required information, which needs to be provided. label Oct 9, 2019
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@ianlancetaylor @mvdan @fanfuxiaoran @bcmills @gopherbot