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⚠ make Start on Source interface cancellable #903

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⚠ make Start on Source interface cancellable #903

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djzager
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@djzager djzager commented Apr 16, 2020

Adding context.Context to the Source interface's Start method makes it
cancellable.

Fixes #879

@k8s-ci-robot k8s-ci-robot added the cncf-cla: yes Indicates the PR's author has signed the CNCF CLA. label Apr 16, 2020
@k8s-ci-robot k8s-ci-robot added the size/M Denotes a PR that changes 30-99 lines, ignoring generated files. label Apr 16, 2020
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djzager commented Apr 16, 2020

/assign @joelanford

@alexeldeib alexeldeib mentioned this pull request Apr 16, 2020
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joelanford
joelanford reviewed Apr 17, 2020
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pkg/internal/controller/controller.go Outdated
for _, watch := range c.watches {
log.Info("Starting EventSource", "controller", c.Name, "source", watch.src)
if err := watch.src.Start(watch.handler, c.Queue, watch.predicates...); err != nil {
if err := watch.src.Start(context.TODO(), watch.handler, c.Queue, watch.predicates...); err != nil {
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Here (and in various other places), we have access to a stop channel but not a context. Rather than using context.TODO(), could we create an equivalent context from the channel?

For example:

func contextWithStopChannel(parent context.Context, stop <-chan struct{}) (context.Context, context.CancelFunc) {
	ctx, cancel := context.WithCancel(parent)

	// If stop is already closed, cancel immediately synchronously.
	// Otherwise start a goroutine that asynchronously cancels when stop is closed.
	select {
	case <-stop:
		cancel()
	default:
		go func() {
			<-stop
			cancel()
		}()
	}
	return ctx, cancel
}

Using something like this, we may be able to make these sources cancellable while not having to fully migrate stop channels to contexts.

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seems reasonable to me

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Here (and in various other places), we have access to a stop channel but not a context.

I don't doubt you, I simply wasn't able to find any inside the current scope of this PR. Should I create an issue to look into this (this being - find other scenarios where we have a stop channel but not a context)?

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I think you're not finding many because you started in a place that used the injection pattern and didn't already accept a context. For the cases where the Start function accepts a context, this might be useful to help use remove the stop channels from children without doing so from the parent right away.

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[APPROVALNOTIFIER] This PR is NOT APPROVED

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joelanford
joelanford reviewed Apr 20, 2020
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pkg/source/source_test.go
package source_test

import (
"context"
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Do we need tests that check whether Start will return an error if the passed context is cancelled?

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done

@k8s-ci-robot k8s-ci-robot added size/L Denotes a PR that changes 100-499 lines, ignoring generated files. and removed size/M Denotes a PR that changes 30-99 lines, ignoring generated files. labels Apr 21, 2020
@djzager
⚠ make Start on Source interface cancellable
adc6740 
Adding context.Context to the Source interface's Start method makes it
cancellable.
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/test pull-controller-runtime-apidiff-master

(just testing)

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@djzager: The following test failed, say /retest to rerun all failed tests:

Test name Commit Details Rerun command
pull-controller-runtime-apidiff-master adc6740 link /test pull-controller-runtime-apidiff-master

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@djzager: PR needs rebase.

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@k8s-ci-robot k8s-ci-robot added the needs-rebase Indicates a PR cannot be merged because it has merge conflicts with HEAD. label May 12, 2020
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/lifecycle stale

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/lifecycle rotten

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This was implemented as part of #1116
/close

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@alvaroaleman: Closed this PR.

In response to this:

This was implemented as part of #1116
/close

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Add context.Context to Source interface's Start method to make cancellable
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