Fix memory leak in Supervisor internal state
#4500
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+178
−129
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durban
commented
Oct 8, 2025
| apply[F](false) | ||
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| private sealed abstract class State[F[_]] { | ||
| private[std] sealed abstract class State[F[_]] { |
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Most of the changes in Supervisor are just to make it testable (its internal state inspectable).
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| case None => (fa, fin) => F.start(fa.guarantee(fin)) | ||
| case None => { (fa, fin) => | ||
| F.start(fa).flatMap { fib => F.start(fib.join.guarantee(fin)).as(fib) } |
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This is the actual fix.
(I believe the other case is already correct, because cancel joins the underlying fiber.)
djspiewak
approved these changes
Dec 28, 2025
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djspiewak
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Wow
It's really unfortunate how racy this is but the fix does look good to me. Excellent job.
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Should fix issue #4490.
Reproducing that issue with the repro in the description there:
With this PR:
This issue also adds an (ugly) unittest, which inspects the internal state of the
Supervisor. We could remove that, if we're satisfied with the fix, but I think it's useful to have it.(Draft, because the test is racy, so I'm waiting for any possible CI failures.)