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  1. PO
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    <p>They solve different problems . Actors are good at solving <a href="http://en.wikipedia.org/wiki/Task_parallelism">task parallel problems</a>. While parallel collections are good at solving <a href="http://en.wikipedia.org/wiki/Data_parallelism">data parallel problems</a>. I don't think they are mutually exclusive - you can use parallel collections in actors and parallel collections containing actors.</p> <hr> <p>Edit - quick test: Even something simple like a actor notification loop benefits.</p> <p>In the following code we register a million actors with an actor registry which has to notify them of an event. </p> <p>The non-parallel notification loop ( <code>registry foreach {}</code> ) takes an average of 2.8 seconds on my machine (4 core 2.5 GHz notebook). When the parallel collection loop ( <code>registry.par.foreach {}</code> ) is used it takes 1.2 seconds and uses all four cores.</p> <pre><code>import actors.Actor case class Register(actor: Actor) case class Unregister(actor: Actor) case class Message( contents: String ) object ActorRegistry extends Actor{ var registry: Set[Actor] = Set.empty def act() { loop{ react{ case reg: Register =&gt; register( reg.actor ) case unreg: Unregister =&gt; unregister( unreg.actor ) case message: Message =&gt; fire( message ) } } } def register(reg: Actor) { registry += reg } def unregister(unreg: Actor) { registry -= unreg } def fire(msg: Message){ val starttime = System.currentTimeMillis() registry.par.foreach { client =&gt; client ! msg } //swap registry foreach for single th val endtime = System.currentTimeMillis() println("elapsed: " + (endtime - starttime) + " ms") } } class Client(id: Long) extends Actor{ var lastmsg = "" def act() { loop{ react{ case msg: Message =&gt; got(msg.contents) } } } def got(msg: String) { lastmsg = msg } } object Main extends App { ActorRegistry.start for (i &lt;- 1 to 1000000) { var client = new Client(i) client.start ActorRegistry ! Register( client ) } ActorRegistry ! Message("One") Thread.sleep(6000) ActorRegistry ! Message("Two") Thread.sleep(6000) ActorRegistry ! Message("Three") } </code></pre>
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    1. POParallel collections in Scala 2.9 and Actors
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    1. USJohan Prinsloo
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    1. COThanks for your answer. I can see that one *CAN* use parallel collections within actors, but it doesn't seem like it would be any more advantageous than using a regular collection in this case. The thought of using a parallel collection that contains actors, on the other hand, seems like a useful thing. I like that idea. Thanks for giving me food for thought...
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      1. USBruce Ferguson
    2. COThanks for creating some test code, that's great! I really appreciate it.
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    3. CO@Bruce. Notice there is another opportunity to use parallel collections here - the code above takes about 12 seconds to do the init loop. If we parallelized that it takes about 4 seconds ( (1 to 1000000).par.foreach{ i => ... } ).
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