run Process#waitFor on virtual thread if available

[onsah]

Run Process.waitFor in virtual thread if possible to solve #3182

I am not sure if this is the correct approach but I wanted to share my progress to get fast feedback.

[armanbilge]

Nice work, thanks for opening the PR, this is the right approach!

[onsah]

@armanbilge I think native test suites crash due to not being able to find getDeclaredMethod https://github.com/typelevel/fs2/actions/runs/13701427909/job/38315972895?pr=3539 How can we solve it?

[armanbilge]

I think native test suites crash due to not being able to find getDeclaredMethod

That's correct, reflection is not supported on Scala Native.

---

How can we solve it?

We should move this code out of jvm-native sources into jvm, since it only works on the JVM.

[onsah]

@armanbilge If I understand correctly, this means we need two ProcessesCompanionPlatform then. Is it correct?

[armanbilge]

this means we need two ProcessesCompanionPlatform then. Is it correct?

Well, that's one possible way ... but I think we should just move all this stuff into a different file, that's already split for the 3 platforms (JVM/JS/Native).

For example, we can add a method to ioplatform:

def evalOnVirtualThreadIfAvailable[F[_], A](fa: F[A]): F[A]

On the JVM, we can move it onto the VT executor if on JDK >= 21. On Native, we can do nothing.

[armanbilge]

Nice work! One last change, we should make sure we test the Virtual Threads in CI using Java 21 (run sbt githubWorkflowGenerate to update the CI workflow):

fs2/build.sbt

Line 18 in 29d6876

ThisBuild / githubWorkflowJavaVersions := Seq(JavaSpec.temurin("17"))

[onsah]

@armanbilge I run Test/dependencyTree on the scalafix project and I see that scalatest version is 3.2.19. I searched for FunSuiteLike in docs but it doesn't exist https://www.scalatest.org/scaladoc/3.2.19/org/index.html?search=FunSuiteLike. There is a similar trait called AnyFunSuiteLike. Should we change to that or drop the dependency version of scalafix?

[armanbilge]

@onsah good investigation! Yes, I think we should switch to AnyFunSuiteLike.

[onsah]

@armanbilge seems like there is a bug in one of the scalafix rules that causes a test to fail. Seems like irrelevant to the changes on this PR. Is it a general issue?

[armanbilge]

@onsah the problem is that now that we added JDK 21 to the CI, the scalafix had not been updated in a while and was not working.

I tried a bit too hard to fix it in your PR (updating versions, fixing the test suite, but now we still needother changes) ... I'm sorry, we should have just resolved in a separate PR 😅

In anycase, it's not a "bug" per se, just some changes we need to make as part of the version update. Feel free to open another PR if you want to give that a try, otherwise I will try to fix it soon.

[armanbilge]

• Scalafix updates #3544

[onsah]

Thank you! I checked the scalafix PR. As soon as it's merged I can rebase this PR.

[armanbilge]

there you go, it's merged :)

[armanbilge]

Nice work, this looks good to me!

[onsah]

Thanks @armanbilge! Who can merge it? I don't see any button to do it myself.

[armanbilge]

@onsah I'll give a little time in case anybody else wants to review, otherwise I will merge in the next day or two :)

Btw, I just realized, we can also use virtual threads for the JDK unix sockets implementation:

fs2/io/jvm/src/main/scala/fs2/io/net/unixsocket/JdkUnixSockets.scala

Line 41 in 1d67ef4

private[unixsocket] class JdkUnixSocketsImpl[F[_]: Files](implicit F: Async[F])

[onsah]

@armanbilge I will check this in the meantime, if it's already merged I can prepare a separate PR.