mirror of https://go.googlesource.com/go
dfe781e1eb
This change fixes problems with thread-locked goroutines using newcoro/coroswitch/etc. Currently, the coro paths do not consider thread-locked goroutines at all and can quickly result in broken scheduler state or lost/leaked goroutines. One possible fix to these issues is to fall back on goroutine+channel semantics, but that turns out to be fairly complicated to implement and results in significant performance cliffs. More complex thread-lock state donation tricks also result in some fairly complicated state tracking that doesn't seem worth it given the use-cases of iter.Pull (and even then, there will be performance cliffs). This change implements a much simpler, but more restrictive semantics. In particular, thread-lock state is tied to the coro at the first call to newcoro (i.e. iter.Pull). From then on, the invariant is that if the coro has any thread-lock state *or* a goroutine calling into coroswitch has any thread-lock state, that the full gamut of thread-lock state must remain the same as it was when newcoro was called (the full gamut meaning internal and external lock counts as well as the identity of the thread that was locked to). This semantics allows the common cases to be always fast, but comes with a non-orthogonality caveat. Specifically, when iter.Pull is used in conjunction with thread-locked goroutines, complex cases (passing next between goroutines or passing yield between goroutines) are likely to fail. Simple cases, where any number of iter.Pull iterators are used in a straightforward way (nested, in series, etc.) from the same goroutine, will work and will be guaranteed to be fast regardless of thread-lock state. This is a compromise for the near-term and we may consider lifting the restrictions imposed by this CL in the future. Fixes #65889. Fixes #65946. Change-Id: I3fb5791e36a61f5ded50226a229a79d28739b24e Reviewed-on: https://go-review.googlesource.com/c/go/+/583675 LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: David Chase <drchase@google.com> Reviewed-by: Austin Clements <austin@google.com> |
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