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reardonj
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Fixes a very narrow race condition when trying to `get` in an finalizer in a `Cont`. The implementation in IOFiber: 1. changed the cont state to waiting 2. concurrently, a running callback might check if the state is "waiting" (in `stateLoop`), see that it is, `loop()`, fail to resume, see the finalizing states disagree, and exit. The callback value is lost. 3. back in the fiber thread, it would update `wasFinalizing` on the cont state and wait for a callback that already terminated Now, `wasFinalizing` is set first. This ordering avoids the race.
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As it happens, |
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November 7, 2026 01:59
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Nov 7, 2026
| _ <- fiber.cancel | ||
| } yield () | ||
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| one.parReplicateA_(if (!isJS) 8 else 1).replicateA_(50000) |
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This does take a significant number of tries to fail locally.
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Fixes a very narrow race condition when trying to
getin an finalizer in aCont. The implementation in IOFiber:waiting(instateLoop), see that it is,loop(), fail to resume, see the finalizing states disagree, and exit. The callback value is lost.wasFinalizingon the cont state and wait for a callback that already terminatedNow,
wasFinalizingis set first. This ordering avoids the race.This is probably quite obscure, but I hit this issue while working on #4710 , as I want to
getafter cancellation there.EDIT: fromCompletableFuture actually does use this pattern. Maybe #4469 is related. I also hit this bug on a separate PR trying to update the MacOS build, so I have folded the two together.