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Fix Stream#parJoin for short-circuiting monad transformers #2895

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merged 7 commits into from
May 10, 2022
Merged

Fix Stream#parJoin for short-circuiting monad transformers #2895

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dc4dc3d
fix parJoin stream blocking when lease.cancel raises monad transforme…
yakivy Apr 30, 2022
7073d3d
fix formatting and warnings
yakivy Apr 30, 2022
7e606a0
fix PR comments
yakivy May 3, 2022
1aeebab
move downstream result composition from release to result stream
yakivy May 3, 2022
35e40ea
pass lease.cancel monad transformer errors to the result
yakivy May 3, 2022
da21625
revert "move downstream result composition from release to result str…
yakivy May 3, 2022
311f196
PR comments
SystemFw May 10, 2022
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20 changes: 13 additions & 7 deletions core/shared/src/main/scala/fs2/Stream.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -4049,16 +4049,22 @@ object Stream extends StreamLowPriority {
.compile
.drain
.guaranteeCase(oc =>
lease.cancel
.flatMap(onOutcome(oc, _)) >> available.release >> decrementRunning
lease.cancel.rethrow.guaranteeCase {
case Outcome.Succeeded(fu) =>
onOutcome(oc <* Outcome.succeeded(fu), Either.unit)

case Outcome.Errored(e) =>
onOutcome(oc, Either.left(e))

case _ =>
F.unit
}
)
.handleError(_ => ())
.forceR(available.release >> decrementRunning)
}.void
}
}

val RightUnit = Right(())

def runOuter: F[Unit] =
F.uncancelable { _ =>
outer
Expand All @@ -4071,7 +4077,7 @@ object Stream extends StreamLowPriority {
.interruptWhen(done.map(_.nonEmpty))
.compile
.drain
.guaranteeCase(onOutcome(_, RightUnit) >> decrementRunning)
.guaranteeCase(onOutcome(_, Either.unit) >> decrementRunning)
.handleError(_ => ())
}

Expand Down Expand Up @@ -4107,7 +4113,7 @@ object Stream extends StreamLowPriority {
signalResult(fiber)
}
.flatMap { _ =>
output.stream.flatMap(Stream.chunk(_).covary[F])
output.stream.flatMap(Stream.chunk)
}
}

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24 changes: 24 additions & 0 deletions core/shared/src/test/scala/fs2/StreamParJoinSuite.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -210,6 +210,30 @@ class StreamParJoinSuite extends Fs2Suite {
}
}

test(
"do not block while evaluating a stream in EitherT[IO, Throwable, *] with multiple parJoins"
) {
case object TestException extends Throwable with NoStackTrace
type F[A] = EitherT[IO, Throwable, A]

Stream
.range(1, 64)
.covary[F]
.map(i =>
Stream.eval[F, Unit](
if (i == 7) EitherT.leftT(TestException)
else EitherT.right(IO.unit)
)
)
.parJoin(4)
.map(_ => Stream.eval[F, Unit](EitherT.right(IO.unit)))
.parJoin(4)
.compile
.drain
.value
.assertEquals(Left(TestException))
}

test("do not block while evaluating an EitherT.left outer stream") {
case object TestException extends Throwable with NoStackTrace

Expand Down