0ad368675b
If the parent context passed to WithCancel or WithTimeout is a known context implementation (one created by this package), we attach the child to the parent by editing data structures directly; otherwise, for unknown parent implementations, we make a goroutine that watches for the parent to finish and propagates the cancellation. A common problem with this scheme, before this CL, is that users who write custom context implementations to manage their value sets cause WithCancel/WithTimeout to start goroutines that would have not been started before. This CL changes the way we map a parent context back to the underlying data structure. Instead of walking up through known context implementations to reach the *cancelCtx, we look up parent.Value(&cancelCtxKey) to return the innermost *cancelCtx, which we use if it matches parent.Done(). This way, a custom context implementation wrapping a *cancelCtx but not changing Done-ness (and not refusing to return wrapped keys) will not require a goroutine anymore in WithCancel/WithTimeout. For #28728. Change-Id: Idba2f435c81b19fe38d0dbf308458ca87c7381e9 Reviewed-on: https://go-review.googlesource.com/c/go/+/196521 Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org> |
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