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client-go events: support context.Background() as context

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If, for whatever reason, the context was context.Background(), the additional
goroutine was started and then got stuck forever because
context.Background().Done() is a nil channel. Found when indirectly
instantiating a broadcaster with such a context:

    found unexpected goroutines:
    [Goroutine 9106 in state chan receive (nil chan), with k8s.io/kubernetes/vendor/k8s.io/client-go/tools/record.NewBroadcaster.func1 on top of the stack:
	goroutine 9106 [chan receive (nil chan)]:
	k8s.io/kubernetes/vendor/k8s.io/client-go/tools/record.NewBroadcaster.func1()
		/home/prow/go/src/k8s.io/kubernetes/_output/local/go/src/k8s.io/kubernetes/vendor/k8s.io/client-go/tools/record/event.go:206 +0x2c
	created by k8s.io/kubernetes/vendor/k8s.io/client-go/tools/record.NewBroadcaster in goroutine 8957
		/home/prow/go/src/k8s.io/kubernetes/_output/local/go/src/k8s.io/kubernetes/vendor/k8s.io/client-go/tools/record/event.go:205 +0x1a5

This can be fixed by checking for a nil channel.

Another problem also gets addressed: if Shutdown was called without canceling
the context, the goroutine also didn't stop. Now it waits for the cancelation
context and thus terminates in both cases.
This commit is contained in:
Patrick Ohly 2023-12-01 18:35:28 +01:00
parent 55f2bc1043
commit eed6e29a5b
1 changed files with 16 additions and 3 deletions
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19
staging/src/k8s.io/client-go/tools/record/event.go
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@ -198,16 +198,29 @@ func NewBroadcaster(opts ...BroadcasterOption) EventBroadcaster {
ctx := c.Context
if ctx == nil {
ctx = context.Background()
} else {
}
// The are two scenarios where it makes no sense to wait for context cancelation:
// - The context was nil.
// - The context was context.Background() to begin with.
//
// Both cases get checked here.
haveCtxCancelation := ctx.Done() == nil
eventBroadcaster.cancelationCtx, eventBroadcaster.cancel = context.WithCancel(ctx)
if haveCtxCancelation {
// Calling Shutdown is not required when a context was provided:
// when the context is canceled, this goroutine will shut down
// the broadcaster.
//
// If Shutdown is called first, then this goroutine will
// also stop.
go func() {
<-ctx.Done()
<-eventBroadcaster.cancelationCtx.Done()
eventBroadcaster.Broadcaster.Shutdown()
}()
}
eventBroadcaster.cancelationCtx, eventBroadcaster.cancel = context.WithCancel(ctx)
return eventBroadcaster
}