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Scala example source code file (MessageQueue.scala)

This example Scala source code file (MessageQueue.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

any, b, boolean, boolean, int, mqueue, mqueueelement, mqueueelement, msg, msg, option, outputchannel, outputchannel, string

The Scala MessageQueue.scala source code

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2005-2011, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */


package scala.actors

/**
 * This class is used by our efficient message queue
 * implementation.
 *
 * @author Philipp Haller
 */
@SerialVersionUID(7124278808020037465L)
@deprecated("this class is going to be removed in a future release", "2.7.7")
class MessageQueueElement(msg: Any, session: OutputChannel[Any], next: MessageQueueElement) extends MQueueElement[Any](msg, session, next) with Serializable {
  def this() = this(null, null, null)
  def this(msg: Any, session: OutputChannel[Any]) = this(msg, session, null)
}

private[actors] class MQueueElement[Msg >: Null](val msg: Msg, val session: OutputChannel[Any], var next: MQueueElement[Msg]) {
  def this() = this(null, null, null)
  def this(msg: Msg, session: OutputChannel[Any]) = this(msg, session, null)
}

/**
 * The class <code>MessageQueue provides an efficient
 * implementation of a message queue specialized for this actor
 * library. Classes in this package are supposed to be the only
 * clients of this class.
 *
 * @author Philipp Haller
 */
@SerialVersionUID(2168935872884095767L)
@deprecated("this class is going to be removed in a future release", "2.7.7")
class MessageQueue(label: String) extends MQueue[Any](label) with Serializable

private[actors] class MQueue[Msg >: Null](protected val label: String) {
  protected var first: MQueueElement[Msg] = null
  protected var last: MQueueElement[Msg] = null  // last eq null iff list is empty
  private var _size = 0
  
  def size = _size
  final def isEmpty = last eq null

  protected def changeSize(diff: Int) {
    _size += diff
  }

  def append(msg: Msg, session: OutputChannel[Any]) {
    changeSize(1) // size always increases by 1
    val el = new MQueueElement(msg, session)

    if (isEmpty) first = el
    else last.next = el
    
    last = el
  }

  def append(el: MQueueElement[Msg]) {
    changeSize(1) // size always increases by 1

    if (isEmpty) first = el
    else last.next = el
    
    last = el
  }

  def foreach(f: (Msg, OutputChannel[Any]) => Unit) {
    var curr = first
    while (curr != null) {
      f(curr.msg, curr.session)
      curr = curr.next
    }
  }

  def foreachAppend(target: MQueue[Msg]) {
    var curr = first
    while (curr != null) {
      target.append(curr)
      curr = curr.next
    }
  }

  def foreachDequeue(target: MQueue[Msg]) {
    var curr = first
    while (curr != null) {
      target.append(curr)
      curr = curr.next
    }
    first = null
    last = null
    _size = 0
  }

  def foldLeft[B](z: B)(f: (B, Msg) => B): B = {
    var acc = z
    var curr = first
    while (curr != null) {
      acc = f(acc, curr.msg)
      curr = curr.next
    }
    acc
  }

  /** Returns the n-th message that satisfies the predicate <code>p
   *  without removing it.
   */
  def get(n: Int)(p: Msg => Boolean): Option[Msg] = {
    var pos = 0
    
    def test(msg: Msg): Boolean =
      p(msg) && (pos == n || { pos += 1; false })
      
    var curr = first
    while (curr != null)
      if (test(curr.msg)) return Some(curr.msg) // early return
      else curr = curr.next

    None
  }

  /** Removes the n-th message that satisfies the predicate <code>p.
   */
  def remove(n: Int)(p: (Msg, OutputChannel[Any]) => Boolean): Option[(Msg, OutputChannel[Any])] =
    removeInternal(n)(p) map (x => (x.msg, x.session))
    
  /** Extracts the first message that satisfies the predicate <code>p
   *  or <code>null if p fails for all of them.
   */
  def extractFirst(p: (Msg, OutputChannel[Any]) => Boolean): MQueueElement[Msg] =
    removeInternal(0)(p) orNull

  def extractFirst(pf: PartialFunction[Msg, Any]): MQueueElement[Msg] = {
    if (isEmpty)    // early return
      return null
    
    // special handling if returning the head
    if (pf.isDefinedAt(first.msg)) {
      val res = first
      first = first.next
      if (res eq last)
        last = null
      
      changeSize(-1)
      res
    }
    else {
      var curr = first.next   // init to element #2
      var prev = first
      
      while (curr != null) {
        if (pf.isDefinedAt(curr.msg)) {
          prev.next = curr.next
          if (curr eq last)
            last = prev

          changeSize(-1)
          return curr // early return
        }
        else {
          prev = curr
          curr = curr.next
        }
      }
      // not found
      null
    }
  }

  private def removeInternal(n: Int)(p: (Msg, OutputChannel[Any]) => Boolean): Option[MQueueElement[Msg]] = {
    var pos = 0

    def foundMsg(x: MQueueElement[Msg]) = {        
      changeSize(-1)
      Some(x)
    }
    def test(msg: Msg, session: OutputChannel[Any]): Boolean =
      p(msg, session) && (pos == n || { pos += 1 ; false })

    if (isEmpty)    // early return
      return None
    
    // special handling if returning the head
    if (test(first.msg, first.session)) {
      val res = first
      first = first.next
      if (res eq last)
        last = null
      
      foundMsg(res)
    }
    else {
      var curr = first.next   // init to element #2
      var prev = first
      
      while (curr != null) {
        if (test(curr.msg, curr.session)) {
          prev.next = curr.next
          if (curr eq last)
            last = prev
            
          return foundMsg(curr) // early return
        }
        else {
          prev = curr
          curr = curr.next
        }
      }
      // not found
      None
    }
  }
}

/** Debugging trait.
 */
private[actors] trait MessageQueueTracer extends MQueue[Any]
{
  private val queueNumber = MessageQueueTracer.getQueueNumber

  override def append(msg: Any, session: OutputChannel[Any]) {
    super.append(msg, session)
    printQueue("APPEND %s" format msg)
  }
  override def get(n: Int)(p: Any => Boolean): Option[Any] = {
    val res = super.get(n)(p)
    printQueue("GET %s" format res)
    res
  }
  override def remove(n: Int)(p: (Any, OutputChannel[Any]) => Boolean): Option[(Any, OutputChannel[Any])] = {
    val res = super.remove(n)(p)
    printQueue("REMOVE %s" format res)
    res
  }
  override def extractFirst(p: (Any, OutputChannel[Any]) => Boolean): MQueueElement[Any] = {
    val res = super.extractFirst(p)
    printQueue("EXTRACT_FIRST %s" format res)
    res
  }
  
  private def printQueue(msg: String) = {
    def firstMsg = if (first eq null) "null" else first.msg
    def lastMsg = if (last eq null) "null" else last.msg

    println("[%s size=%d] [%s] first = %s, last = %s".format(this, size, msg, firstMsg, lastMsg))
  }
  override def toString() = "%s:%d".format(label, queueNumber)
}

private[actors] object MessageQueueTracer {
  // for tracing purposes
  private var queueNumberAssigner = 0
  private def getQueueNumber = synchronized {
    queueNumberAssigner += 1
    queueNumberAssigner
  }
}

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