Application hangs when separate thread tries to read field of main application

[myazinn]

Compiler version

3.2.2, 3.3.0-RC3

Minimized code

https://scastie.scala-lang.org/YXhWrechQJGiJbcu9DoOkg

object ThreadStartApp extends App {
  def method(arg: Any) = {
    println(s"start $arg")
    while (true) {
      println(s"loop $arg")
      Thread.sleep(1000)
    }
  }

  val arg = "arg"
  val withArg = new Thread(() => {
    println("init arg")
    method(arg)
  })
  withArg.start()

  Thread.sleep(10000)
  withArg.interrupt()
}

Output

init arg
start arg
loop arg

Expectation

Expected output:

init arg
start arg
loop arg
loop arg
loop arg
loop arg
loop arg
loop arg
loop arg
loop arg
loop arg
loop arg

Works fine if I just inline variable
https://scastie.scala-lang.org/eLQ91hqkTtipAz8gVyGYHA
Or make it a local variable
https://scastie.scala-lang.org/MgYjQzRQTUSbHxljDewSdg
Also works fine in Scala 2.13.10
https://scastie.scala-lang.org/SlPxWnelT4uUioUr0l9gDQ

Looks like Thread.sleep(10000) somehow is locking an arg field, since once the main thread is awake, the app manages to start execution of method method but it get interrupted immediately.

[som-snytt]

There is old advice about not starting threads from object initializers.

App is deprecated.

https://docs.scala-lang.org/scala3/reference/changed-features/main-functions.html

Change

//object ThreadStartApp extends App {
@main def test() =

and it works as expected.

[myazinn]

Yeah, usually I don't manually start threads at all. This time I was just doing some experiments in Scala 2 and decided to try them in Scala 3.
Anyway, thanks for the reply. If it's just scala.App specific stuff, then I guess it's not that important. I didn't know if it's applicable to only scala.App or an indication of some other issue.