[9390] - Add tryAcquire to Semaphore #9600

IgorDorokhov · 2025-02-14T20:53:14Z

In this PR I have added tryAcquire and tryAcquireN functions to Semaphore and TSemaphore as per following enhancement request #9390

The functions I added are non-blocking, they check if there are available permits and if yes it decreases the amount of permits and return true. If not, then a false is returned and a fiber is not queued.

Open questions:

If tryAcquire is decreasing the amount of permits, should the algorithm increase amount of permits back once it is done with them?
If we take a look at the Semaphore implementation we will see that functions that can do that (reserve, restore, releaseN) are not part of the Semaphore trait and cannot be called directly by the user to release permits manually.

On the other hand, if use TSemaphore as an example, it has acquireBetween function which does not release permits as well.
Or should something like following be added for tryAcquire?

  def withPermitsBetween[R, E, A](min: Long, max: Long)(zio: Long => ZIO[R, E, A])(implicit
    trace: Trace
  ): ZIO[R, E, A] =
    ZSTM.acquireReleaseWith(acquireBetween(min, max))((actualN: Long) => releaseN(actualN).commit)(zio)

Need a feedback from more experienced engineers.

Links for reference:
Semaphore -

zio/core/shared/src/main/scala/zio/Semaphore.scala

Line 35 in 3f91907

sealed trait Semaphore extends Serializable {

TSemaphore -

zio/core/shared/src/main/scala/zio/stm/TSemaphore.scala

Line 49 in 3f91907

final class TSemaphore private (val permits: TRef[Long]) extends Serializable {

core/shared/src/main/scala/zio/Semaphore.scala

kyri-petrou

Thanks for the contribution, and sorry for taking this long to review this! Looks good to me, just some minor comments

core/shared/src/main/scala/zio/Semaphore.scala

core/shared/src/main/scala/zio/stm/TSemaphore.scala

Co-authored-by: kyri-petrou <[email protected]>

core/shared/src/main/scala/zio/Semaphore.scala

CLAassistant · 2025-03-28T01:58:32Z

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core/shared/src/main/scala/zio/Semaphore.scala

core-tests/shared/src/test/scala/zio/SemaphoreSpec.scala

core/shared/src/main/scala/zio/Semaphore.scala

hearnadam · 2025-04-13T23:34:05Z

@IgorDorokhov is it possible to get this to the finish line? I have no other feedback aside from my last comments.

IgorDorokhov · 2025-04-13T23:38:07Z

Hi, will finish it today-tomorrow. Sorry for the delay. Meant to finish it last week, but unfortunately didn’t have time.

…

On Sun, Apr 13, 2025 at 7:34 PM Adam Hearn ***@***.***> wrote: @IgorDorokhov <https://github.com/IgorDorokhov> is it possible to get this to the finish line? I have no other feedback aside from my last comments. — Reply to this email directly, view it on GitHub <#9600 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AFQSR3SFVREM6PGEUTGGT5D2ZLYAHAVCNFSM6AAAAABXFN575OVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDQMBQGE4DAMZUHE> . You are receiving this because you were mentioned.Message ID: ***@***.***> *hearnadam* left a comment (zio/zio#9600) <#9600 (comment)> @IgorDorokhov <https://github.com/IgorDorokhov> is it possible to get this to the finish line? I have no other feedback aside from my last comments. — Reply to this email directly, view it on GitHub <#9600 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AFQSR3SFVREM6PGEUTGGT5D2ZLYAHAVCNFSM6AAAAABXFN575OVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDQMBQGE4DAMZUHE> . You are receiving this because you were mentioned.Message ID: ***@***.***>

core/shared/src/main/scala/zio/Semaphore.scala

hearnadam · 2025-04-15T00:50:35Z

core/shared/src/main/scala/zio/Semaphore.scala

+          private[zio] val zero = Reservation(ZIO.unit, ZIO.unit)
+        }
+
+        def tryReserve(n: Long)(implicit trace: Trace): UIO[Option[Reservation]] =


I just realized this method doesn't need to return a Reservation since it's only used internally. Sorry for missing this in the previous passes.

Can it just return Option[UIO[Unit]]?

tryReserve follows the same pattern as reserve. reserve is used only internally as well.
I would keep current implementation as it is aligns with the reserve and it is easy to use in ZIO.acquireReleaseWith(tryReserve(n))

zio/core/shared/src/main/scala/zio/Semaphore.scala

Lines 152 to 167 in c64488f

def reserve(n: Long)(implicit trace: Trace): UIO[Reservation] =

if (n < 0)

ZIO.die(new IllegalArgumentException(s"Unexpected negative `$n` permits requested."))

else if (n == 0L)

ZIO.succeed(Reservation.zero)

else

Promise.make[Nothing, Unit].flatMap { promise =>

ref.modify {

case Right(permits) if permits >= n =>

Reservation(ZIO.unit, releaseN(n)) -> Right(permits - n)

case Right(permits) =>

Reservation(promise.await, restore(promise, n)) -> Left(ScalaQueue(promise -> (n - permits)))

case Left(queue) =>

Reservation(promise.await, restore(promise, n)) -> Left(queue.enqueue(promise -> n))

}

}

IgorDorokhov · 2025-04-26T17:38:40Z

Closing this PR due to commits which were made from the default account which is not CLA signed.
Instead of rebasing I decided to open a new PR #9825
@hearnadam

IgorDorokhov added 3 commits February 14, 2025 11:19

9390 add tryAcquire and tryAcquireN to TSemaphore

696f3b5

run scalafmt

9942122

add tryAcquire to Semaphore

cae94b3

IgorDorokhov mentioned this pull request Feb 14, 2025

Consider adding a tryAcquire to Semaphore #9390

Closed

hearnadam reviewed Feb 14, 2025

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core/shared/src/main/scala/zio/Semaphore.scala Outdated Show resolved Hide resolved

IgorDorokhov added 4 commits February 17, 2025 15:20

refactor implemetation

ddcf2d1

Merge branch 'series/2.x' into 9390-tryAcquire

6196ea6

make update to tryReserve

3aae3b5

Merge branch 'series/2.x' into 9390-tryAcquire

11217c8

IgorDorokhov commented Feb 27, 2025

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IgorDorokhov requested a review from hearnadam February 28, 2025 02:33

kyri-petrou reviewed Mar 13, 2025

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Avoid None match

3d1c5a7

Co-authored-by: kyri-petrou <[email protected]>

hearnadam reviewed Mar 17, 2025

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hearnadam and others added 2 commits March 17, 2025 16:50

Merge branch 'series/2.x' into 9390-tryAcquire

9ddfc6d

address comments

a97d877

Merge branch 'series/2.x' into 9390-tryAcquire

45decbb

IgorDorokhov requested review from hearnadam and kyri-petrou March 28, 2025 02:06

revert back to Exit.none

d1ef09b

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refactor

5a8de0e

IgorDorokhov force-pushed the 9390-tryAcquire branch from 44aaa6e to 5a8de0e Compare April 1, 2025 00:11

Merge branch 'series/2.x' into 9390-tryAcquire

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Igor Dorokhov added 2 commits April 14, 2025 20:35

address comments

ae5fce9

Merge remote-tracking branch 'origin/series/2.x' into 9390-tryAcquire

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IgorDorokhov requested a review from hearnadam April 15, 2025 00:43

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Igor Dorokhov and others added 3 commits April 14, 2025 20:56

fmt

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address comments

74a8287

Merge branch 'series/2.x' into 9390-tryAcquire

dbf1dba

IgorDorokhov requested a review from hearnadam April 23, 2025 21:06

Merge branch 'series/2.x' into 9390-tryAcquire

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hearnadam approved these changes Apr 26, 2025

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Merge branch 'series/2.x' into 9390-tryAcquire

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IgorDorokhov closed this Apr 26, 2025

IgorDorokhov mentioned this pull request Apr 26, 2025

[9390] - add tryAcquire to Semaphore #9825

Merged

	def reserve(n: Long)(implicit trace: Trace): UIO[Reservation] =
	if (n < 0)
	ZIO.die(new IllegalArgumentException(s"Unexpected negative `$n` permits requested."))
	else if (n == 0L)
	ZIO.succeed(Reservation.zero)
	else
	Promise.make[Nothing, Unit].flatMap { promise =>
	ref.modify {
	case Right(permits) if permits >= n =>
	Reservation(ZIO.unit, releaseN(n)) -> Right(permits - n)
	case Right(permits) =>
	Reservation(promise.await, restore(promise, n)) -> Left(ScalaQueue(promise -> (n - permits)))
	case Left(queue) =>
	Reservation(promise.await, restore(promise, n)) -> Left(queue.enqueue(promise -> n))
	}
	}

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[9390] - Add tryAcquire to Semaphore #9600

[9390] - Add tryAcquire to Semaphore #9600

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IgorDorokhov commented Feb 14, 2025 •

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