UncaughtExceptionHandler not triggered on Linux

[Craig Street]

Here is the code that I am using

object Main {
    def main(args: Array[String]): Unit = {
      Thread.setDefaultUncaughtExceptionHandler(new AppUncaughtExceptionHandler)
      throw new RuntimeException("bang!")

}

class AppUncaughtExceptionHandler extends Thread.UncaughtExceptionHandler {
  def uncaughtException(thread: Thread, cause: Throwable): Unit =
  {
    println("uncaught")
  }
}


When compiling an executing on windows, the handler is triggered, however when I build this code on Linux the exception is thrown

setting handler
java.lang.RuntimeException: bang!
        at stuff.Main$.main(Main.scala:36)
        at stuff.Main.main(Main.scala)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:606)
        at scala.reflect.internal.util.ScalaClassLoader$$anonfun$run$1.apply(ScalaClassLoader.scala:70)
        at scala.reflect.internal.util.ScalaClassLoader$class.asContext(ScalaClassLoader.scala:31)
        at scala.reflect.internal.util.ScalaClassLoader$URLClassLoader.asContext(ScalaClassLoader.scala:101)
        at scala.reflect.internal.util.ScalaClassLoader$class.run(ScalaClassLoader.scala:70)
        at scala.reflect.internal.util.ScalaClassLoader$URLClassLoader.run(ScalaClassLoader.scala:101)
        at scala.tools.nsc.CommonRunner$class.run(ObjectRunner.scala:22)
        at scala.tools.nsc.ObjectRunner$.run(ObjectRunner.scala:39)
        at scala.tools.nsc.CommonRunner$class.runAndCatch(ObjectRunner.scala:29)
        at scala.tools.nsc.ObjectRunner$.runAndCatch(ObjectRunner.scala:39)
        at scala.tools.nsc.MainGenericRunner.runTarget$1(MainGenericRunner.scala:65)
        at scala.tools.nsc.MainGenericRunner.run$1(MainGenericRunner.scala:87)
        at scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala:98)
        at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:103)
        at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)

The build processes are different (Windows I'm compiling using Intellij), Linux is build under Gradle. Still, i have looked at the byte code on each and see nothing untoward.

Any pointers as to what might be happening here please?

Thanks

[Viktor Klang]

I wouldn't be surprised if [main]'s UEH is set prior to calling main(), and therefor not delegating to the global default. Could you verify?

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[Craig Street]

Thanks for the response. 

println(Option(Thread.getDefaultUncaughtExceptionHandler).getOrElse("None"))
println(Option(Thread.currentThread().getUncaughtExceptionHandler).getOrElse("None").toString)

Thread.setDefaultUncaughtExceptionHandler(new AppUncaughtExceptionHandler)
Thread.currentThread().setUncaughtExceptionHandler(new AppUncaughtExceptionHandler)

println(Option(Thread.getDefaultUncaughtExceptionHandler).getOrElse("None"))
println(Option(Thread.currentThread().getUncaughtExceptionHandler).getOrElse("None").toString)

throw new RuntimeException("bang!")

results in

None

java.lang.ThreadGroup[name=main,maxpri=10]

stuff.AppUncaughtExceptionHandler@59c86ddb

stuff.AppUncaughtExceptionHandler@130d19a9

java.lang.RuntimeException: bang!

        at stuff.Main$.main(Main.scala:41)

        at stuff.Main.main(Main.scala)

Almost as if the handler is being ignored.

[Viktor Klang]

How are you running the program? perhaps the main() is invoked by another main() which wraps it in a try-catch?

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[som-snytt]

This is why I don't apply for a job at google. I thought I understood the basics of Thread API.

For the record, it's really annoying to look up API under java.lang. How many hours have I spent re-reading java.lang.String?

Anyway, on Ubuntu it works if you kick off a thread. I don't know what's special about the "main" thread. I would have expected simple hierarchical handling, for current thread, thread group and default.

package uncaught

object Main {
  def main(args: Array[String]): Unit = {

    new Thread(new Runnable {
      def run(): Unit = test()
    }).start();
    Thread sleep 1000L
  }
  def test(): Unit = {
    Console println Thread.currentThread.getThreadGroup
    Console println Thread.currentThread.getUncaughtExceptionHandler
    //Thread.setDefaultUncaughtExceptionHandler(new AppUncaughtExceptionHandler)
    Thread.currentThread.setUncaughtExceptionHandler(new AppUncaughtExceptionHandler)

    throw new RuntimeException("bang!")
  }

  class AppUncaughtExceptionHandler extends Thread.UncaughtExceptionHandler {
    def uncaughtException(thread: Thread, cause: Throwable): Unit = {
      println("uncaught")
    }
  }
}

i.e.,

apm@mara:~/tmp$ scalac uncaught.scala && scala uncaught.Main
java.lang.ThreadGroup[name=main,maxpri=10]
java.lang.ThreadGroup[name=main,maxpri=10]
uncaught