Scala example source code file (SyncChannel.scala)

This example Scala source code file (SyncChannel.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

a, concurrent, list, syncchannel, syncvar

The SyncChannel.scala Scala example source code

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

package scala.concurrent

/** A `SyncChannel` allows one to exchange data synchronously between
 *  a reader and a writer thread. The writer thread is blocked until the
 *  data to be written has been read by a corresponding reader thread.
 *
 *  @author  Philipp Haller
 *  @version 2.0, 04/17/2008
 */
class SyncChannel[A] {

  private var pendingWrites = List[(A, SyncVar[Boolean])]()
  private var pendingReads  = List[SyncVar[A]]()

  def write(data: A) {
    // create write request
    val writeReq = new SyncVar[Boolean]

    this.synchronized {
      // check whether there is a reader waiting
      if (!pendingReads.isEmpty) {
        val readReq  = pendingReads.head
        pendingReads = pendingReads.tail

        // let reader continue
        readReq set data

        // resolve write request
        writeReq set true
      }
      else {
        // enqueue write request
        pendingWrites = pendingWrites ::: List((data, writeReq))
      }
    }

    writeReq.get
  }

  def read: A = {
    // create read request
    val readReq = new SyncVar[A]

    this.synchronized {
      // check whether there is a writer waiting
      if (!pendingWrites.isEmpty) {
        // read data
        val (data, writeReq) = pendingWrites.head
        pendingWrites = pendingWrites.tail

        // let writer continue
        writeReq set true

        // resolve read request
        readReq set data
      }
      else {
        // enqueue read request
        pendingReads = pendingReads ::: List(readReq)
      }
    }

    readReq.get
  }
}