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Scala example source code file (WorkScheduler.scala)

This example Scala source code file (WorkScheduler.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, action, action, emptyaction, none, none, option, option, queue, seq, throwable, unit, workscheduler

The Scala WorkScheduler.scala source code

package scala.tools.nsc
package util

import scala.collection.mutable.Queue

class WorkScheduler {

  type Action = () => Unit

  private var todo = new Queue[Action]
  private var throwables = new Queue[Throwable]
  private var interruptReqs = new Queue[InterruptReq]

  /** Called from server: block until one of todo list, throwables or interruptReqs is nonempty */
  def waitForMoreWork() = synchronized {
    while (todo.isEmpty && throwables.isEmpty && interruptReqs.isEmpty) { wait() } 
  }

  /** called from Server: test whether one of todo list, throwables, or InterruptReqs is nonempty */
  def moreWork: Boolean = synchronized {
    todo.nonEmpty || throwables.nonEmpty || interruptReqs.nonEmpty
  }
  
  /** Called from server: get first action in todo list, and pop it off */
  def nextWorkItem(): Option[Action] = synchronized {
    if (todo.isEmpty) None else Some(todo.dequeue()) 
  }

  def dequeueAll[T](f: Action => Option[T]): Seq[T] = synchronized {
    todo.dequeueAll(a => f(a).isDefined).map(a => f(a).get)
  }

  /** Called from server: return optional exception posted by client
   *  Reset to no exception.
   */
  def pollThrowable(): Option[Throwable] = synchronized {
    if (throwables.isEmpty) 
      None
    else {
      val result = Some(throwables.dequeue())
      if (!throwables.isEmpty)
        postWorkItem { () => }
      result
    }
  }

  def pollInterrupt(): Option[InterruptReq] = synchronized {
    if (interruptReqs.isEmpty) None else Some(interruptReqs.dequeue())
  }

  /** Called from client: have interrupt executed by server and return result */
  def doQuickly[A](op: () => A): A = {
    val ir = new InterruptReq {
      type R = A
      val todo = op
    }
    synchronized {
      interruptReqs enqueue ir
      notify()
    }
    ir.getResult()
  }

  /** Called from client: have action executed by server */
  def postWorkItem(action: Action) = synchronized {
    todo enqueue action
    notify()
  }
  
  /** Called from client: cancel all queued actions */
  def cancelQueued() = synchronized {
    todo.clear()
  }

  /** Called from client:
   *  Require an exception to be thrown on next poll.
   */
  def raise(exc: Throwable) = synchronized {
    throwables enqueue exc
    postWorkItem { new EmptyAction }
  }
}

class EmptyAction extends (() => Unit) {
  def apply() {}
}

Other Scala examples (source code examples)

Here is a short list of links related to this Scala WorkScheduler.scala source code file:

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