Scala example source code file (semaphore.scala)

This example Scala source code file (semaphore.scala) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Scala tags/keywords

array, chan, sched, sched, sem1, sem2, semaphore, semaphore, signal, signal, unit, unit

The Scala semaphore.scala source code

package examples.pilib

import scala.concurrent.pilib._

/** Solution of exercise session 6 (first question). */
object semaphore {

  class Signal extends Chan[Unit] {
    def send = write(())
    def receive = read
  }

  /** Interface. */
  trait Semaphore {
    def get: Unit
    def release: Unit
  }

  /** First implementation. */
  class Sem1 extends Semaphore {

    private val g = new Signal
    private val r = new Signal

    def get: Unit = g.send
    def release: Unit = r.send

    private def Sched: Unit = choice (
      g * (x => { r.receive; Sched }),
      r * (x => Sched)
    )
    spawn< Sched >
  }

  /** Second implementation. */
  class Sem2 extends Semaphore {

    private val a = new Signal
    private val na = new Signal

    def get { a.receive; spawn< na.send > }
    def release: Unit = choice (
      a * (x => spawn< a.send >),
      na * (x => spawn< a.send >)
    )
    spawn< a.send >
  }

  /** Test program. */
  def main(args: Array[String]) {
    val random = new util.Random()
    val sem = new Sem2
    def mutex(p: => Unit) { sem.get; p; sem.release }

    spawn< {
      Thread.sleep(1 + random.nextInt(100));
      mutex( {
        println("a1");
        Thread.sleep(1 + random.nextInt(100));
        println("a2")
      } )
    } | {
      Thread.sleep(1 + random.nextInt(100));
      mutex( {
        println("b1");
        Thread.sleep(1 + random.nextInt(100));
        println("b2")
      } ) 
    } >;
  }
}