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Add internal Promise#succeedUnit method to avoid Exit allocation when possible #9571

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Feb 10, 2025
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Add internal Promise#succeedUnit method to avoid Exit allocation when possible #9571

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50dc42b
Add internal `Promise#succeedUnit` method to avoid `Exit` allocation …
guizmaii Feb 10, 2025
5232c2d
fmt
guizmaii Feb 10, 2025
a086d93
Review: Use `whenZIODiscard` when possible
guizmaii Feb 10, 2025
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2 changes: 1 addition & 1 deletion concurrent/src/main/scala/zio/concurrent/CountdownLatch.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -38,7 +38,7 @@ final class CountdownLatch private (_count: Ref[Int], _waiters: Promise[Nothing,
*/
val countDown: UIO[Unit] = _count.modify {
case 0 => ZIO.unit -> 0
case 1 => _waiters.succeed(()) -> 0
case 1 => _waiters.succeedUnit -> 0
case n => ZIO.unit -> (n - 1)
}.flatten.unit

Expand Down
2 changes: 1 addition & 1 deletion concurrent/src/main/scala/zio/concurrent/CyclicBarrier.scala
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Expand Up @@ -29,7 +29,7 @@ final class CyclicBarrier private (
_lock.get.flatMap(_.fail(()).unit)

private val succeed: UIO[Unit] =
_lock.get.flatMap(_.succeed(()).unit)
_lock.get.flatMap(_.succeedUnit.unit)

/** The number of parties required to trip this barrier. */
def parties: Int = _parties
Expand Down
2 changes: 1 addition & 1 deletion concurrent/src/main/scala/zio/concurrent/ReentrantLock.scala
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Expand Up @@ -130,7 +130,7 @@ final class ReentrantLock private (fairness: Boolean, state: Ref[ReentrantLock.S
ZIO.unit -> State(epoch + 1, None, 0, Map.empty)
else {
val (fiberId, (_, promise)) = if (fairness) holders.minBy(_._2._1) else pickRandom(holders)
promise.succeed(()).unit -> State(epoch + 1, Some(fiberId), 1, holders - fiberId)
promise.succeedUnit.unit -> State(epoch + 1, Some(fiberId), 1, holders - fiberId)
}

private def pickRandom(
Expand Down
8 changes: 3 additions & 5 deletions core/shared/src/main/scala/zio/Hub.scala
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Expand Up @@ -160,10 +160,9 @@ object Hub {
ZIO.fiberIdWith { fiberId =>
shutdownFlag.set(true)
ZIO
.whenZIO(shutdownHook.succeed(())) {
.whenZIODiscard(shutdownHook.succeedUnit) {
scope.close(Exit.interrupt(fiberId)) *> strategy.shutdown
}
.unit
}.uninterruptible
def size(implicit trace: Trace): UIO[Int] =
ZIO.suspendSucceed {
Expand Down Expand Up @@ -229,15 +228,14 @@ object Hub {
ZIO.fiberIdWith { fiberId =>
shutdownFlag.set(true)
ZIO
.whenZIO(shutdownHook.succeed(())) {
ZIO.foreachPar(unsafePollAll(pollers))(_.interruptAs(fiberId)) *>
.whenZIODiscard(shutdownHook.succeedUnit) {
ZIO.foreachParDiscard(unsafePollAll(pollers))(_.interruptAs(fiberId)) *>
ZIO.succeed {
subscribers.remove(subscription -> pollers)
subscription.unsubscribe()
strategy.unsafeOnHubEmptySpace(hub, subscribers)
}
}
.unit
}.uninterruptible
def size(implicit trace: Trace): UIO[Int] =
ZIO.suspendSucceed {
Expand Down
13 changes: 13 additions & 0 deletions core/shared/src/main/scala/zio/Promise.scala
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Expand Up @@ -176,6 +176,15 @@ final class Promise[E, A] private (
def succeed(a: A)(implicit trace: Trace): UIO[Boolean] =
ZIO.succeed(unsafe.succeed(a)(trace, Unsafe.unsafe))

/**
* Internally, you can use this method instead of calling
* `myPromise.succeed(())`
*
* It avoids the `Exit` allocation
*/
private[zio] def succeedUnit(implicit ev0: A =:= Unit, trace: Trace): UIO[Boolean] =
ZIO.succeed(unsafe.succeedUnit(ev0, trace, Unsafe))

private def interruptJoiner(joiner: IO[E, A] => Any)(implicit trace: Trace): UIO[Any] = ZIO.succeed {
var retry = true

Expand Down Expand Up @@ -205,6 +214,7 @@ final class Promise[E, A] private (
def poll(implicit unsafe: Unsafe): Option[IO[E, A]]
def refailCause(e: Cause[E])(implicit trace: Trace, unsafe: Unsafe): Boolean
def succeed(a: A)(implicit trace: Trace, unsafe: Unsafe): Boolean
def succeedUnit(implicit ev0: A =:= Unit, trace: Trace, unsafe: Unsafe): Boolean
}

private[zio] val unsafe: UnsafeAPI =
Expand Down Expand Up @@ -280,6 +290,9 @@ final class Promise[E, A] private (

def succeed(a: A)(implicit trace: Trace, unsafe: Unsafe): Boolean =
completeWith(Exit.succeed(a))

override def succeedUnit(implicit ev0: A =:= Unit, trace: Trace, unsafe: Unsafe): Boolean =
completeWith(Exit.unit.asInstanceOf[IO[E, A]])
}

}
Expand Down
4 changes: 2 additions & 2 deletions core/shared/src/main/scala/zio/Semaphore.scala
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Expand Up @@ -155,9 +155,9 @@ object Semaphore {
case None => acc -> Right(n)
case Some(((promise, permits), queue)) =>
if (n > permits)
loop(n - permits, Left(queue), acc *> promise.succeed(()))
loop(n - permits, Left(queue), acc *> promise.succeedUnit)
else if (n == permits)
(acc *> promise.succeed(())) -> Left(queue)
(acc *> promise.succeedUnit) -> Left(queue)
else
acc -> Left((promise -> (permits - n)) +: queue)
}
Expand Down
22 changes: 11 additions & 11 deletions streams/shared/src/main/scala/zio/stream/ZChannel.scala
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Expand Up @@ -689,11 +689,11 @@ sealed trait ZChannel[-Env, -InErr, -InElem, -InDone, +OutErr, +OutElem, +OutDon

permits
.withPermit(
latch.succeed(()) *>
latch.succeedUnit *>
f(outElem)
.catchAllCause(cause =>
failureRef.update(_ && cause).unless(cause.isInterruptedOnly) *>
errorSignal.succeed(()) *>
errorSignal.succeedUnit *>
ZChannel.failLeftUnit
)
)
Expand Down Expand Up @@ -770,11 +770,11 @@ sealed trait ZChannel[-Env, -InErr, -InElem, -InDone, +OutErr, +OutElem, +OutDon
for {
_ <- permits
.withPermit(
latch.succeed(()) *> f(outElem)
latch.succeedUnit *> f(outElem)
.foldCauseZIO(
cause =>
failure.update(_ && cause).unless(cause.isInterruptedOnly) *>
errorSignal.succeed(()) *>
errorSignal.succeedUnit *>
outgoing.offer(ZChannel.failLeftUnit),
elem => outgoing.offer(Exit.succeed(elem))
)
Expand Down Expand Up @@ -1248,8 +1248,8 @@ sealed trait ZChannel[-Env, -InErr, -InElem, -InDone, +OutErr, +OutElem, +OutDon
fiber <- restore(run(channelPromise, scopePromise, child)).forkDaemon
_ <- parent.addFinalizer {
channelPromise.isDone.flatMap { isDone =>
if (isDone) scopePromise.succeed(()) *> fiber.await *> fiber.inheritAll
else scopePromise.succeed(()) *> fiber.interrupt *> fiber.inheritAll
if (isDone) scopePromise.succeedUnit *> fiber.await *> fiber.inheritAll
else scopePromise.succeedUnit *> fiber.interrupt *> fiber.inheritAll
}
}
done <- restore(channelPromise.await)
Expand Down Expand Up @@ -1986,9 +1986,9 @@ object ZChannel {
}
}
case Left(l: Left[OutErr, OutDone]) =>
outgoing.offer(Result.Error(l.value)) *> errorSignal.succeed(()).unit
outgoing.offer(Result.Error(l.value)) *> errorSignal.succeedUnit.unit
case Right(cause) =>
outgoing.offer(Result.Fatal(cause)) *> errorSignal.succeed(()).unit
outgoing.offer(Result.Fatal(cause)) *> errorSignal.succeedUnit.unit
}
)

Expand All @@ -2005,7 +2005,7 @@ object ZChannel {
}

permits
.withPermit(latch.succeed(()) *> raceIOs)
.withPermit(latch.succeedUnit *> raceIOs)
.interruptible
.forkIn(childScope) *> latch.await
}
Expand All @@ -2017,7 +2017,7 @@ object ZChannel {

for {
size <- cancelers.size
_ <- ZIO.when(size >= n0)(cancelers.take.flatMap(_.succeed(())))
_ <- ZIO.when(size >= n0)(cancelers.take.flatMap(_.succeedUnit))
_ <- cancelers.offer(canceler)
raceIOs =
ZIO.scopedWith { scope =>
Expand All @@ -2026,7 +2026,7 @@ object ZChannel {
.flatMap(evaluatePull(_).race(canceler.await.interruptible))
}
_ <- permits
.withPermit(latch.succeed(()) *> raceIOs)
.withPermit(latch.succeedUnit *> raceIOs)
.interruptible
.forkIn(childScope)
_ <- latch.await
Expand Down
12 changes: 6 additions & 6 deletions streams/shared/src/main/scala/zio/stream/ZStream.scala
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Expand Up @@ -534,7 +534,7 @@ final class ZStream[-R, +E, +A] private (val channel: ZChannel[R, Any, Any, Any,
): ZChannel[R1, Any, Any, Any, E1, Chunk[A1], Unit] = {
lazy val process: ZChannel[Any, Any, Any, Any, E1, Chunk[A1], Unit] =
ZChannel.fromZIO(queue.take).flatMap { case (take, promise) =>
ZChannel.fromZIO(promise.succeed(())) *>
ZChannel.fromZIO(promise.succeedUnit) *>
take.fold(
ZChannel.unit,
error => ZChannel.refailCause(error),
Expand All @@ -549,7 +549,7 @@ final class ZStream[-R, +E, +A] private (val channel: ZChannel[R, Any, Any, Any,
for {
queue <- scoped
start <- Promise.make[Nothing, Unit]
_ <- start.succeed(())
_ <- start.succeedUnit
ref <- Ref.make(start)
_ <- (channel >>> producer(queue, ref)).runScoped.forkScoped
} yield consumer(queue)
Expand Down Expand Up @@ -3320,7 +3320,7 @@ final class ZStream[-R, +E, +A] private (val channel: ZChannel[R, Any, Any, Any,
.pipeTo(loop)
.ensuring(queue.offer(Take.end).forkDaemon *> queue.awaitShutdown) *> ZChannel.unit
)
.merge(ZStream.execute((promise.succeed(()) *> right.run(sink)).ensuring(queue.shutdown)), HaltStrategy.Both)
.merge(ZStream.execute((promise.succeedUnit *> right.run(sink)).ensuring(queue.shutdown)), HaltStrategy.Both)
}

/**
Expand Down Expand Up @@ -5656,22 +5656,22 @@ object ZStream extends ZStreamPlatformSpecificConstructors {
Promise.make[Nothing, Unit].flatMap { p =>
ref.modify {
case s @ Handoff.State.Full(_, notifyProducer) => (notifyProducer.await *> offer(a), s)
case Handoff.State.Empty(notifyConsumer) => (notifyConsumer.succeed(()) *> p.await, Handoff.State.Full(a, p))
case Handoff.State.Empty(notifyConsumer) => (notifyConsumer.succeedUnit *> p.await, Handoff.State.Full(a, p))
}.flatten
}

def take(implicit trace: Trace): UIO[A] =
Promise.make[Nothing, Unit].flatMap { p =>
ref.modify {
case Handoff.State.Full(a, notifyProducer) => (notifyProducer.succeed(()).as(a), Handoff.State.Empty(p))
case Handoff.State.Full(a, notifyProducer) => (notifyProducer.succeedUnit.as(a), Handoff.State.Empty(p))
case s @ Handoff.State.Empty(notifyConsumer) => (notifyConsumer.await *> take, s)
}.flatten
}

def poll(implicit trace: Trace): UIO[Option[A]] =
Promise.make[Nothing, Unit].flatMap { p =>
ref.modify {
case Handoff.State.Full(a, notifyProducer) => (notifyProducer.succeed(()).as(Some(a)), Handoff.State.Empty(p))
case Handoff.State.Full(a, notifyProducer) => (notifyProducer.succeedUnit.as(Some(a)), Handoff.State.Empty(p))
case s @ Handoff.State.Empty(_) => (ZIO.succeed(None), s)
}.flatten
}
Expand Down
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