Scala - futures does not run

Question

I am trying to run the following future basic code

 future { println("ssss")} onSuccess{ case _ => println("succ")}

However, when I run the main method, nothing to the console is printed and the system exits almost instantly. I am using the implicit ExecutionContext. Any hints?

This code:

  val f = future(Await.ready(Promise().future, d.timeLeft))

   f.onSuccess {
     case _ => println("hee")
   }

also exits immediately....

Answer 1

Futures are executed on a dedicated thread pool. If your main program does not wait for the future, it will exit immediately and the future won't have a chance to execute. What you can do here is to use Await in your main program to block the main thread until the future executes:

def main( args: Array[String] ) {
  val fut = future { println("ssss")}
  fut onSuccess{ case _ => println("succ")}
  Await.result( fut )
}