SleepingBarber.scala

package com.github.omnomnom

import java.util.concurrent.Semaphore
import concurrent.Lock

object SleepingBarber extends App {
  val NCustomers = 12
  val NChairs = 5
  val CutTime = 10
  val VisitInterval = 5
  val customers = new Semaphore(1, true);
  val barbers = new Semaphore(1, true);
  val mutex = new Lock();
  var freeChairs = NChairs


  object Barber extends Thread {

    override def run() {
      while (true) {
        println("Barber: I'm waiting for a customer.");
        customers.acquire(); // Wait if # of customers is zero
        // We have at least one customer at this point.
        mutex.acquire(); // protect "freeChairs"
        freeChairs += 1; // a customer moves to the barber chair
        barbers.release(); // the barber is ready to cut hair
        mutex.release();
        // Cut Hair
        println("Barber: I'm ready to cut.");
        Thread.sleep(CutTime);
      }
    }
  }

  class Customer(customerId: Int) extends Thread("Customer " + customerId) {

    override def run() {
      println(getName + ": I need to have my hair cut.");
      mutex.acquire();
      if (freeChairs > 0) {
        println(getName + ": I sit down and wait.");
        freeChairs; // a chair is occupied
        customers.release(); // wake up the barber (if necessary)
        mutex.release(); // "freeChairs" is no longer accessed
        println(getName + ": I'm waiting for my turn...");
        barbers.acquire(); // wait for my turn
        // Hair Cut
        println(getName + ": It's my turn.  \\(^o^)/");
        Thread.sleep(CutTime);
        println(getName + ": Thanks!  Bye. (^o^)/~");
      } else {
        // There is no chairs. Customer must give up.
        println(getName + ": the barber shop is full.  (;_;)");
        mutex.release(); // "freeChairs" is no longer accessed
      }
    }
  }

  Barber.start();


  (1 to NCustomers).foreach(i => {
    Thread.sleep(VisitInterval)
    new Customer(i).start()
  })
}