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Scala example source code file (Publisher.scala)

This example Scala source code file (Publisher.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

a, a, anyref, boolean, boolean, int, iterable, none, none, reaction, ref, ref, reference, singlerefcollection

The Scala Publisher.scala source code

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2007-2011, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */



package scala.swing

import scala.collection._
import scala.collection.mutable.{Buffer, HashSet, Set}
import event.Event

/** <p>
 *    Notifies registered reactions when an event is published. Publishers are 
 *    also reactors and listen to themselves per default as a convenience.
 *  </p>
 *  <p>
 *    In order to reduce memory leaks, reactions are weakly referenced by default, 
 *    unless they implement <code>Reactions.StronglyReferenced. That way, 
 *    the lifetime of reactions are more easily bound to the registering object, 
 *    which are reactors in common client code and hold strong references to their 
 *    reactions. As a result, reactors can be garbage collected even though they 
 *    still have reactions registered at some publisher, but not vice versa
 *    since reactors (strongly) reference publishers they are interested in.
 *  </p>
 */
trait Publisher extends Reactor {
  import Reactions._
  
  protected val listeners = new RefSet[Reaction] {
    import scala.ref._
    val underlying = new HashSet[Reference[Reaction]]
    protected def Ref(a: Reaction) = a match {
      case a: StronglyReferenced => new StrongReference[Reaction](a) with super.Ref[Reaction]
      case _ => new WeakReference[Reaction](a, referenceQueue) with super.Ref[Reaction]
    }
  }

  private[swing] def subscribe(listener: Reaction) { listeners += listener }
  private[swing] def unsubscribe(listener: Reaction) { listeners -= listener }
  
  /**
   * Notify all registered reactions.
   */
  def publish(e: Event) { for (l <- listeners) l(e) }
  
  listenTo(this)
}

/**
 * A publisher that subscribes itself to an underlying event source not before the first 
 * reaction is installed. Can unsubscribe itself when the last reaction is uninstalled.
 */
private[swing] trait LazyPublisher extends Publisher {
  import Reactions._
  
  protected def onFirstSubscribe()
  protected def onLastUnsubscribe()
  
  override def subscribe(listener: Reaction) { 
    if(listeners.size == 1) onFirstSubscribe() 
    super.subscribe(listener) 
  }
  override def unsubscribe(listener: Reaction) { 
    super.unsubscribe(listener) 
    if(listeners.size == 1) onLastUnsubscribe()
  }
}



import scala.ref._

private[swing] trait SingleRefCollection[+A <: AnyRef] extends Iterable[A] { self =>

  trait Ref[+A <: AnyRef] extends Reference[A] {
    override def hashCode() = get match {
      case Some(x)  => x.##
      case _        => 0
    }
    override def equals(that: Any) = that match {
      case that: ReferenceWrapper[_] => 
        val v1 = this.get
        val v2 = that.get
        v1 == v2
      case _ => false
    }
  }

  //type Ref <: Reference[A] // TODO: could use higher kinded types, but currently crashes
  protected[this] def Ref(a: A): Ref[A]
  protected[this] val referenceQueue = new ReferenceQueue[A]
  
  protected val underlying: Iterable[Reference[A]]
      
  def purgeReferences() { 
    var ref = referenceQueue.poll
    while (ref != None) { 
      removeReference(ref.get.asInstanceOf[Reference[A]])
      ref = referenceQueue.poll
    }
  }
  
  protected[this] def removeReference(ref: Reference[A])
  
  def iterator = new Iterator[A] {
    private val elems = self.underlying.iterator
    private var hd: A = _
    private var ahead: Boolean = false
    private def skip(): Unit =
      while (!ahead && elems.hasNext) {
        // make sure we have a reference to the next element, 
        // otherwise it might be garbage collected
        val next = elems.next.get
        ahead = next != None 
        if (ahead) hd = next.get
      }
    def hasNext: Boolean = { skip; ahead }
    def next(): A =
      if (hasNext) { ahead = false; hd }
      else throw new NoSuchElementException("next on empty iterator")
  }
}

private[swing] class StrongReference[+T <: AnyRef](value: T) extends Reference[T] {
    private[this] var ref: Option[T] = Some(value)
    def isValid: Boolean = ref != None
    def apply(): T = ref.get
    def get : Option[T] = ref
    override def toString = get.map(_.toString).getOrElse("<deleted>")
    def clear() { ref = None }
    def enqueue(): Boolean = false
    def isEnqueued(): Boolean = false
  }
  
abstract class RefBuffer[A <: AnyRef] extends Buffer[A] with SingleRefCollection[A] { self =>
  protected val underlying: Buffer[Reference[A]]

  def +=(el: A): this.type = { purgeReferences(); underlying += Ref(el); this }
  def +=:(el: A) = { purgeReferences(); Ref(el) +=: underlying; this }
  def remove(el: A) { underlying -= Ref(el); purgeReferences(); }
  def remove(n: Int) = { val el = apply(n); remove(el); el }
  def insertAll(n: Int, iter: Iterable[A]) {
    purgeReferences()
    underlying.insertAll(n, iter.view.map(Ref(_)))
  }
  def update(n: Int, el: A) { purgeReferences(); underlying(n) = Ref(el) }
  def apply(n: Int) = { 
    purgeReferences()
    var el = underlying(n).get
    while (el == None) {
      purgeReferences(); el = underlying(n).get
    }
    el.get
  }
  
  def length = { purgeReferences(); underlying.length }
  def clear() { underlying.clear(); purgeReferences() }

  protected[this] def removeReference(ref: Reference[A]) { underlying -= ref }
}
 
private[swing] abstract class RefSet[A <: AnyRef] extends Set[A] with SingleRefCollection[A] { self =>
  protected val underlying: Set[Reference[A]]
  
  def -=(el: A): this.type = { underlying -= Ref(el); purgeReferences(); this }
  def +=(el: A): this.type = { purgeReferences(); underlying += Ref(el); this }
  def contains(el: A): Boolean = { purgeReferences(); underlying.contains(Ref(el)) }
  override def size = { purgeReferences(); underlying.size }
  
  protected[this] def removeReference(ref: Reference[A]) { underlying -= ref }
}

Other Scala examples (source code examples)

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