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typelevel / cats-effect

The pure asynchronous runtime for Scala
https://typelevel.org/cats-effect/
Apache License 2.0
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PureConc not running finalizers #3430

Open durban opened 1 year ago

durban commented 1 year ago

I might be missing something completely obvious, but PureConc doesn't seem to run finalizers:

    "foo" in {
      val t: PureConc[Int, Int] = for {
        c <- F.ref(0)
        latch <- F.deferred[Unit]
        fib <- F.start((latch.complete(()) *> F.never[Unit]).onCancel(c.update(_ + 1)))
        _ <- latch.get
        _ <- fib.cancel
        v <- c.get
      } yield v

      pure.run(t) mustEqual Outcome.Succeeded(Some(1))
    }

If I put this in PureConcSpec, it fails with:

Succeeded(Some(0)) != Succeeded(Some(1))
djspiewak commented 1 year ago

Well that absolutely looks like a bug…

durban commented 1 year ago

Yeah, something is definitely wrong here; possibly more than one thing.

What I'm (almost) sure is wrong is PureFiber#cancel: https://github.com/typelevel/cats-effect/blob/series/3.x/kernel-testkit/shared/src/main/scala/cats/effect/kernel/testkit/pure.scala#L391. It just writes Outcome.Canceled() into an mvar. So if the fiber will not be scheduled any more (e.g., because it went into a never), who will run the finalizers?

There is also something strange going on with pushing/popping the finalizers, but I'm not sure what (if anything).