Scala Chat Application, separate threads for local IO and socket IO - multithreading

Question

I'm writing a chat application in Scala, the problem is with the clients, the client reads from StdIn (which blocks) before sending the data to the echo server, so if multiple clients are connected then they don't receive data from the server until reading from StdIn has completed. I'm thinking that local IO, i.e reading from StdIn and reading/writing to the socket should be on separate threads but I can't think of a way to do this, below is the Client singleton code:
import java.net._
import scala.io._
import java.io._
import java.security._
object Client {
var msgAcc = ""
def main(args: Array[String]): Unit = {
val conn = new ClientConnection(InetAddress.getByName(args(0)), args(1).toInt)
val server = conn.connect()
println("Enter a username")
val user = new User(StdIn.readLine())
println("Welcome to the chat " + user.username)
sys.addShutdownHook(this.shutdown(conn, server))
while (true) {
val txMsg = StdIn.readLine()//should be on a separate thread?
if (txMsg != null) {
conn.sendMsg(server, user, txMsg)
val rxMsg = conn.getMsg(server)
val parser = new JsonParser(rxMsg)
val formattedMsg = parser.formatMsg(parser.toJson())
println(formattedMsg)
msgAcc = msgAcc + formattedMsg + "\n"
}
}
}
def shutdown(conn: ClientConnection, server: Socket): Unit = {
conn.close(server)
val fileWriter = new BufferedWriter(new FileWriter(new File("history.txt"), true))
fileWriter.write(msgAcc)
fileWriter.close()
println("Leaving chat, thanks for using")
}
}
below is the ClientConnection class used in conjunction with the Client singleton:
import javax.net.ssl.SSLSocket
import javax.net.ssl.SSLSocketFactory
import javax.net.SocketFactory
import java.net.Socket
import java.net.InetAddress
import java.net.InetSocketAddress
import java.security._
import java.io._
import scala.io._
import java.util.GregorianCalendar
import java.util.Calendar
import java.util.Date
import com.sun.net.ssl.internal.ssl.Provider
import scala.util.parsing.json._
class ClientConnection(host: InetAddress, port: Int) {
def connect(): Socket = {
Security.addProvider(new Provider())
val sslFactory = SSLSocketFactory.getDefault()
val sslSocket = sslFactory.createSocket(host, port).asInstanceOf[SSLSocket]
sslSocket
}
def getMsg(server: Socket): String = new BufferedSource(server.getInputStream()).getLines().next()
def sendMsg(server: Socket, user: User, msg: String): Unit = {
val out = new PrintStream(server.getOutputStream())
out.println(this.toMinifiedJson(user.username, msg))
out.flush()
}
private def toMinifiedJson(user: String, msg: String): String = {
s"""{"time":"${this.getTime()}","username":"$user","msg":"$msg"}"""
}
private def getTime(): String = {
val cal = Calendar.getInstance()
cal.setTime(new Date())
"(" + cal.get(Calendar.HOUR_OF_DAY) + ":" + cal.get(Calendar.MINUTE) + ":" + cal.get(Calendar.SECOND) + ")"
}
def close(server: Socket): Unit = server.close()
}

Answer 1

You can add concurrency by using Scala Akka Actors. As of this writing the current Scala version is 2.11.8. See Actor documentation here:
http://docs.scala-lang.org/overviews/core/actors.html
This chat example is old but demonstrates a technique to handle in the neighborhood of a million simultaneous clients using Actors:
http://doc.akka.io/docs/akka/1.3.1/scala/tutorial-chat-server.html
Finally you can also Google the Twitter Finagle project which uses Scala and provides servers with concurrency. A lot of work to learn it I think...