Scala example source code file (Signalling.scala)

This example Scala source code file (Signalling.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Scala source code examples by using tags.

All credit for the original source code belongs to scala-lang.org; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

atomicindexflag, atomicinteger, defaultsignalling, delegatedcontext, delegatedsignalling, idlesignalling, int, signalling, taggeddelegatedcontext, volatileabort

The Signalling.scala Scala example source code

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2003-2013, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */

package scala
package collection
package generic

import java.util.concurrent.atomic.AtomicInteger

/**
 * A message interface serves as a unique interface to the
 * part of the collection capable of receiving messages from
 * a different task.
 *
 * One example of use of this is the `find` method, which can use the
 * signalling interface to inform worker threads that an element has
 * been found and no further search is necessary.
 *
 * @author prokopec
 *
 * @define abortflag
 * Abort flag being true means that a worker can abort and produce whatever result,
 * since its result will not affect the final result of computation. An example
 * of operations using this are `find`, `forall` and `exists` methods.
 *
 * @define indexflag
 * The index flag holds an integer which carries some operation-specific meaning. For
 * instance, `takeWhile` operation sets the index flag to the position of the element
 * where the predicate fails. Other workers may check this index against the indices
 * they are working on and return if this index is smaller than their index. Examples
 * of operations using this are `takeWhile`, `dropWhile`, `span` and `indexOf`.
 */
trait Signalling {
  /**
   * Checks whether an abort signal has been issued.
   *
   * $abortflag
   * @return the state of the abort
   */
  def isAborted: Boolean

  /**
   * Sends an abort signal to other workers.
   *
   * $abortflag
   */
  def abort(): Unit

  /**
   * Returns the value of the index flag.
   *
   * $indexflag
   * @return the value of the index flag
   */
  def indexFlag: Int

  /**
   * Sets the value of the index flag.
   *
   * $indexflag
   * @param f the value to which the index flag is set.
   */
  def setIndexFlag(f: Int)

  /**
   * Sets the value of the index flag if argument is greater than current value.
   * This method does this atomically.
   *
   * $indexflag
   * @param f the value to which the index flag is set
   */
  def setIndexFlagIfGreater(f: Int)

  /**
   * Sets the value of the index flag if argument is lesser than current value.
   * This method does this atomically.
   *
   * $indexflag
   * @param f the value to which the index flag is set
   */
  def setIndexFlagIfLesser(f: Int)

  /**
   * A read only tag specific to the signalling object. It is used to give
   * specific workers information on the part of the collection being operated on.
   */
  def tag: Int
}

/**
 * This signalling implementation returns default values and ignores received signals.
 */
class DefaultSignalling extends Signalling with VolatileAbort {
  def indexFlag = -1
  def setIndexFlag(f: Int) {}
  def setIndexFlagIfGreater(f: Int) {}
  def setIndexFlagIfLesser(f: Int) {}

  def tag = -1
}

/**
 * An object that returns default values and ignores received signals.
 */
object IdleSignalling extends DefaultSignalling

/**
 * A mixin trait that implements abort flag behaviour using volatile variables.
 */
trait VolatileAbort extends Signalling {
  @volatile private var abortflag = false
  override def isAborted = abortflag
  override def abort() = abortflag = true
}

/**
 * A mixin trait that implements index flag behaviour using atomic integers.
 * The `setIndex` operation is wait-free, while conditional set operations `setIndexIfGreater`
 * and `setIndexIfLesser` are lock-free and support only monotonic changes.
 */
trait AtomicIndexFlag extends Signalling {
  private val intflag: AtomicInteger = new AtomicInteger(-1)
  abstract override def indexFlag = intflag.get
  abstract override def setIndexFlag(f: Int) = intflag.set(f)
  abstract override def setIndexFlagIfGreater(f: Int) = {
    var loop = true
    do {
      val old = intflag.get
      if (f <= old) loop = false
      else if (intflag.compareAndSet(old, f)) loop = false
    } while (loop)
  }
  abstract override def setIndexFlagIfLesser(f: Int) = {
    var loop = true
    do {
      val old = intflag.get
      if (f >= old) loop = false
      else if (intflag.compareAndSet(old, f)) loop = false
    } while (loop)
  }
}

/**
 * An implementation of the signalling interface using delegates.
 */
trait DelegatedSignalling extends Signalling {
  /**
   * A delegate that method calls are redirected to.
   */
  var signalDelegate: Signalling

  def isAborted = signalDelegate.isAborted
  def abort() = signalDelegate.abort()

  def indexFlag = signalDelegate.indexFlag
  def setIndexFlag(f: Int) = signalDelegate.setIndexFlag(f)
  def setIndexFlagIfGreater(f: Int) = signalDelegate.setIndexFlagIfGreater(f)
  def setIndexFlagIfLesser(f: Int) = signalDelegate.setIndexFlagIfLesser(f)

  def tag = signalDelegate.tag
}

/**
 * Class implementing delegated signalling.
 */
class DelegatedContext(var signalDelegate: Signalling) extends DelegatedSignalling

/**
 * Class implementing delegated signalling, but having its own distinct `tag`.
 */
class TaggedDelegatedContext(deleg: Signalling, override val tag: Int) extends DelegatedContext(deleg)