parallel-collections

I want to use parallel arrays for a task, and before I start with the coding, I'd be interested in knowing if this small snipept is threadsafe: import collection.mutable._ var listBuffer = ListBuffer[String]("one","two","three","four","five","six","seven","eight","nine") var jSyncList = java.util.Collections.synchronizedList(new java.util.ArrayList[String]()) listBuffer.par.foreach { e => println("processed :"+e) // using sleep here to simulate a random delay Thread.sleep((scala.math.random * 1000).toLong) jSyncList.add(e) } jSyncList.toArray.foreach(println) Are there better ways of

If I have this: val a = Array(...) and I write a.par.map(e => someFunc(e)) Will the resulting collection be in the same order as the non-parallel collection? Yes, but the function itself is executed without any particular order. List(1,2,3).par foreach print // could print out 213 The parallel collections maintain all of the contracts of their non-parallel equivalents. On collections in which a map operation preserves order, such as List , order will be preserved by the parallel map as well. On collections in which map does not preserve order, such as Set , order will not be preserved in the

Does Scala provide a way to execute parallel map operations as part of the standard language? For example, given: scala> val a = List((1,2), (3,4), (3,6)) a: List[(Int, Int)] = List((1,2), (3,4), (3,6)) I can do: scala> a.map(tup => tup._1 + tup._2) res0: List[Int] = List(3, 7, 9) However, to the best of my knowledge this maps the provided function over the list objects sequentially. Is there a built-in way to have the function applied to each element in a separate thread (or equivalent), and the results then gathered into a resulting list? Akos Krivachy If you add par then you will get a

I've been looking at the new Scala 2.9 parallel collections and am hoping to abandon a whole lot of my crufty amateur versions of similar things. In particular, I'd like to replace the fork join pool which underlies the default implementation with something of my own (for example, something that distributes evaluation of tasks across a network, via actors). My understanding is that this is simply a matter of applying Scala's paradigm of "stackable modifications", but the collections library is intimidating enough that I'm not exactly sure which bits need modifying! Some concrete questions: Is

I tried to make it optional to run a map operation sequentially or in parallel, for example using the following code: val runParallel = true val theList = List(1,2,3,4,5) (if(runParallel) theList.par else theList) map println //Doesn't run in parallel What I noticed is that the 'map' operation does not run in parallel as I'd expected. Although without the conditional, it would: theList.par map println //Runs in parallel as visible in the output The type of the expression (if(runParallel) theList else theList.par) which I expect to be the closest common ancestor of both types of theList and

I take a List[Int] and want to search for a value x where x * 10 > 500 in parallel. So exists should return true if the list contains any value of 51 or greater. def f(x: Int) = { println("calculating for " + x) Thread.sleep(100 - x) println("finished " + x) x * 10 } val res = List.range(1, 100).par.exists(f(_) > 500) Which gives results: calculating for 1 calculating for 25 calculating for 50 calculating for 75 calculating for 13 finished 75 // <-- first valid result found: 75 * 10 > 500 finished 50 calculating for 51 // but it kicks off more expensive calculations finished 25 calculating for