Scala actors: long operations io

Question

I have some problems with actors that contain lengthy operations, in my case persistent socket connections. Here are some test codes that work fine if I create less than four server instances, but if I create more instances, I always get only three or sometimes four parallel socket connections, because the others time out. I wonder why this is so and whether there is something clearly wrong with my code.

package test import actors.Actor import actors.Actor._ import java.io.{PrintStream, DataOutputStream, DataInputStream} import java.net.{Socket, InetAddress} import java.text.{SimpleDateFormat} import java.util.{Calendar} case class SInput(input: String) case class SOutput(output: String) case class SClose case class SRepeat import scala.xml._ class Config(xml: Node) { var nick: String = (xml \ "nick").text var realName: String = (xml \ "realName").text var server: String = (xml \ "ip").text var port: Int = (xml \ "port").text.toInt var identPass: String = (xml \ "identPass").text var joinChannels: List[String] = List.fromString((xml \ "join").text.trim, ' ') } object ServerStarter { def main(args: Array[String]): Unit = { var servers = List[Server]() val a = actor { loop { receive { case config: Config => actor { val server = new Server(config) servers = server :: servers server.start } } } } val xml = XML.loadFile("config.xml") (xml \ "server").elements.foreach(config => a ! new Config(config)) } } class Server(config: Config) extends Actor { private var auth = false private val socket = new Socket(InetAddress.getByName(config.server), config.port) private val out = new PrintStream(new DataOutputStream(socket.getOutputStream())) private val in = new DataInputStream(socket.getInputStream()) def act = { val _self = this _self ! SRepeat while (true) { receive { case SRepeat => try { val input = in.readLine if (input != null) { actor {_self ! SInput(input)} } else { actor {_self ! SClose} } } catch { case e: Exception => println(e) actor {_self ! SClose} } case SClose => println(getDate + " closing: " + config.server + " mail: " + mailboxSize) try { socket.close in.close out.close } catch { case e: Exception => println(e) } case SInput(input: String) => println(getDate + " " + config.server + " IN => " + input + " mail: " + mailboxSize) actor {onServerInput(_self, input)} _self ! SRepeat case SOutput(output: String) => println(getDate + " " + config.server + " OUT => " + output + " mail: " + mailboxSize) actor { out.println(output) out.flush() } case x => println("unmatched: " + x + " mail: " + mailboxSize) } } } private def getDate = { new SimpleDateFormat("hh:mm:ss").format(Calendar.getInstance().getTime()); } def onServerInput(a: Actor, input: String) = { if (!auth) { authenticate(a) } else if (input.contains("MOTD")) { identify(a) join(a) } else if (input.contains("PING")) { pong(a, input) } else { } } def authenticate(a: Actor) = { a ! SOutput("NICK " + config.nick) a ! SOutput("USER " + config.nick + " 0 0 : " + config.realName) auth = true } def pong(a: Actor, input: String) = { a ! SOutput("PONG " + input.split(":").last) } def identify(a: Actor) = { if (config.identPass != "") { a ! SOutput("nickserv :identify " + config.nick + " " + config.identPass) } } def join(a: Actor) = { config.joinChannels.foreach(channel => a ! SOutput("JOIN " + channel)) } } 

by the way. I am using scala 2.7.6 final.

Answer 1

There are strange things here. For example:

 actor { val server = new Server(config) servers = server :: servers server.start } 

Or also:

 actor {_self ! SClose} 

The actor method is an actor factory. In the first case, for example, you create an actor that creates another actor (because the server is an actor) and starts it.

Let me repeat: everything between actor { and } is an actor. Inside this actor, you make a new Server , which creates another actor. And this is inside receive , which, of course, is part of the actor. So, inside the actor you are creating an actor who will create the actor.

And in the second example, you create an actor only to send a message to yourself. It doesn't make any sense to me, but I'm not so worried about the actors.