Scala: InterruptedException

// 1. Let's start a thread and try to interrupt it:
object Main extends App {
  val thread = new Thread(() => {
    println("Hello")
    Thread.sleep(5000) // wait, join or sleep
    println("Bye")
  })
  thread.setDaemon(true)
  thread.start()

  println("Press ENTER to interrupt")
  StdIn.readLine()
  thread.interrupt()
  println(s"Thread interrupted = ${thread.isInterrupted}")

  println("Press ENTER to finish")
  StdIn.readLine()
  println("End")
}

// Output if (t > 5 sec) => nothing happened:
// Hello
// Press ENTER to interrupt
// Bye

// Thread interrupted = false
// Press ENTER to finish

// End



// Output if (t < 5 sec) => exception:
// Press ENTER to interrupt
// Hello

// Exception in thread "Thread-0" java.lang.InterruptedException: sleep interrupted
//  at java.lang.Thread.sleep(Native Method)
//  at ru.mitrakov.self.sandbox.Main$.$anonfun$thread$1(Main.scala:16)
//  at java.lang.Thread.run(Thread.java:745)
// Thread interrupted = false
// Press ENTER to finish

// End



// 2. Now let's wrap everything with try-catch:
object Main extends App {
  try {
    val thread = new Thread(() => {
      println("Hello")
      Thread.sleep(5000) // wait, join or sleep
      println("Bye")
    })
    thread.setDaemon(true)
    thread.start()

    println("Press ENTER to interrupt")
    StdIn.readLine()
    thread.interrupt()
    println(s"Thread interrupted = ${thread.isInterrupted}")

    println("Press ENTER to finish")
    StdIn.readLine()
    println("End")
  } catch {
    case th: Throwable => println(s"ERROR! $th")
  }
}

// Output if (t < 5 sec): still exception!
// Press ENTER to interrupt
// Hello

// Exception in thread "Thread-0" java.lang.InterruptedException: sleep interrupted
//  at java.lang.Thread.sleep(Native Method)
//  at ru.mitrakov.self.sandbox.Main$.$anonfun$new$1(Main.scala:17)
//  at java.lang.Thread.run(Thread.java:745)
// Thread interrupted = false
// Press ENTER to finish

// End



// 3. What happened? The problem is that we have to wrap only the thread code with try-catch!
object Main extends App {
  val thread = new Thread(() => {
    try {
      println("Hello")
      Thread.sleep(5000) // wait, join or sleep
      println("Bye")
    } catch {
      case th: Throwable => println(s"ERROR! $th")
    }
  })
  thread.setDaemon(true)
  thread.start()

  println("Press ENTER to interrupt")
  StdIn.readLine()
  thread.interrupt()
  println(s"Thread interrupted = ${thread.isInterrupted}")

  println("Press ENTER to finish")
  StdIn.readLine()
  println("End")
}

// Output if (t < 5 sec):
// Press ENTER to interrupt
// Hello

// ERROR! java.lang.InterruptedException: sleep interrupted
// Thread interrupted = false
// Press ENTER to finish

// End



// 4. OK, much better, but we know that we should use NonFatal pattern instead of catching everything:
} catch {
  case NonFatal(e) => println(s"ERROR! $e")
}

// Output if (t < 5 sec): exception!
// Press ENTER to interrupt
// Hello

// Exception in thread "Thread-0" java.lang.InterruptedException: sleep interrupted
//  at java.lang.Thread.sleep(Native Method)
//  at ru.mitrakov.self.sandbox.Main$.$anonfun$thread$1(Main.scala:17)
//  at java.lang.Thread.run(Thread.java:745)
// Thread interrupted = false
// Press ENTER to finish

// End



// 6. The problem is that NonFatal considers InterruptedException as a fatal one; let's fix it:
} catch {
  case NonFatal(e) | ie: InterruptedException => println(s"ERROR! ${e.getMessage}")
}

// Output: compilation error



// 7. It's impossible in Scala. Let's re-write it:
} catch {
  case NonFatal(e) => println(s"ERROR! ${e.getMessage}")
  case e: InterruptedException => println(s"INTERRUPTED! ${e.getMessage}")
}

// Output if (t < 5 sec):
// Hello
// Press ENTER to interrupt

// Thread interrupted = false
// Press ENTER to finish
// INTERRUPTED! sleep interrupted

// End



// 8. Now everything works, except one little thing: why "Thread interrupted = false"?
// All we need to do is to restore interruption flag (see JavaDoc to Thread#interrupt())
case e: InterruptedException => Thread.currentThread().interrupt(); println(s"INTERRUPTED! ${e.getMessage}")

// Output if (t < 5 sec):
// Press ENTER to interrupt
// Hello

// Thread interrupted = true
// Press ENTER to finish
// INTERRUPTED! sleep interrupted

// End



// Summary:
// if you don't work with manual threads interruption and don't use sleep/wait/join manipulations => just skip
// matching InterruptedException (even if something changes in the future, just let it crash)
// if you do work with manual threads interruption and sleep/wait/join are possible => handle it and restore
// interruption flag, so that caller could handle this accordingly.