Scala: Recursion with future Stack overflow error

Question

Consider below code snippet. Too many take() calls will result in stack overflow error. What is the good strategy to overcome such scenarios?

def take(): Future[Int] = {
    val processResponseF: Future[Boolean] = performSomeAction()
    processResponseF.flatMap(
      processResponse => {
        if(processResponse)
          Future.successful(100)
        else
          take()
      }
    )
  }

def performSomeAction(): Future[Boolean] = {
  //This returns future of boolean
}

Assumption - 1. Method signature should not be changed

Use scalaz or monix Task as they address the very problem you described. — Mateusz Kubuszok, Mar 13 '17 at 10:30
Your code example works on my machine with scala.concurrent.ExecutionContext.Implicits.global, (i.e. stack is fine) — Viktor Klang, Mar 13 '17 at 16:53

score 3 · Accepted Answer · answered Mar 13 '17 at 13:01

3

Too many take() calls will result in stack overflow error.

It won't. When a method that returns a Future recursively calls itself, all that method knows is that it has a future value that will be filled (maybe) later. The actual code is executed on a different stack, as it needs to be done asynchronously from the original call, and may not even happen on the same thread.

answered Mar 13 '17 at 13:01

Michael Zajac

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But how about I change line in else- def take(): Future[Int] = { val processResponseF: Future[Boolean] = performSomeAction() processResponseF.flatMap( processResponse => { if(processResponse) Future.successful(100) else Future.successful(10) + take() //changed line } ) } Now will it need to keep stack of old calls? – user3635344 Mar 14 '17 at 04:25
@user3635344 Then it doesn't compile, because you cannot write `Future(10) + take()`. You can't add futures without mapping. – Michael Zajac Mar 14 '17 at 04:28
Hmm. Right. It will be needed to write in future block. Thank you very much. :) – user3635344 Mar 14 '17 at 04:35

Scala: Recursion with future Stack overflow error

1 Answers1