Scala parallelization method

Question

Having a look at the forall method implementation, how could this method be parallel?

  def forall(p: A => Boolean): Boolean = {
    var result = true
    breakable {
      for (x <- this)
        if (!p(x)) { result = false; break }
    }
    result
  }

As I understand for better parallelization, avoid using var's and prefer val's. How is this now supposed to work if I use forall?

Beryllium · Accepted Answer · 2014-08-05 16:00:15Z

2

You are looking at a non-parallel version of forall.

A parallel version looks like this (provided by a parallel collection, in this case ParIterableLike):

def forall(pred: T => Boolean): Boolean = {
  tasksupport.executeAndWaitResult
    (new Forall(pred, splitter assign new DefaultSignalling with VolatileAbort))
}

To get a parallel collection, insert a .par, for example:

List.range(1, 10).par.forall(n => n % 2 == 0)

If you use an IDE like IntelliJ, just "zoom" into that forall, and you'll see the code above. Otherwise here is the source of ParIterableLike (thanks @Kigyo for sharing the URL).

edited Aug 5, 2014 at 16:00

answered Aug 5, 2014 at 15:52

Beryllium

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4 Comments

joesan Over a year ago

Where did you get this from? Can you post the path to the API?

Kigyo Over a year ago

It's here: github.com/scala/scala/blob/2.12.x/src/library/scala/collection/… ParIterableLike also defines several other parallel methods

Beryllium Over a year ago

Just "zoom" in, otherwise look for ParIterableLike.scala

Beryllium Over a year ago

@Kigyou Thanks for your comment - I have added it to the answer.

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