gistfile1.scala

package com.actforex.nst

import java.util.concurrent.{CancellationException, Executors, FutureTask, Callable}
import scala.concurrent.{ExecutionContext, Future}
import ExecutionContext.Implicits.global

trait CancelForFuture {
  def cancel(mayInterruptIfRunning:Boolean):Boolean
}

case class FutureWithCancel[T](future:Future[T], futureTask: FutureTask[_]) extends CancelForFuture {
  def cancel(mayInterruptIfRunning: Boolean): Boolean = futureTask.cancel(mayInterruptIfRunning)
  def map[S](f: T => S)(implicit executor: ExecutionContext) = new FutureWithCancel(future.map(f), futureTask)
  def flatMap[S](f: T => FutureWithCancel[S])(implicit executor: ExecutionContext) = new FutureWithCancel(future.flatMap((t:T) => f(t).future), futureTask)
  def filter(pred: T => Boolean)(implicit executor: ExecutionContext): FutureWithCancel[T] = new FutureWithCancel(future.filter(pred), futureTask)
  def withFilter(p: T => Boolean)(implicit executor: ExecutionContext): FutureWithCancel[T] = new FutureWithCancel(future.withFilter(p), futureTask)
  def foreach[U](f: T => U)(implicit executor: ExecutionContext) = future.foreach(f)
}

object FutureWithCancel {
  def apply[T](body: =>T)(implicit executor: ExecutionContext):FutureWithCancel[T] = {
    val cancelTask = new FutureTask[T](new Callable[T]() {
      def call(): T = {
        body
    }})
    new FutureWithCancel[T](Future[T] { cancelTask.run(); cancelTask.get() }, cancelTask)
  }
}

object Sample {
  def main(args: Array[String]) {

    val f1 = FutureWithCancel[String] {
      println("Started")
      this.synchronized{
        try {
          wait()  // Blocking
        } catch {
          case e: InterruptedException =>
        }
      }
      println("Finished canceled task")
      "Hello" + "World"
    }
    val f2 = f1 map { x ⇒
      x.length
    }
    f2 foreach println
    f2.future.onFailure {
      case e: CancellationException ⇒ println("future was canceled")
    }

    Thread.sleep(100)
    println("try cancel")
    f2.cancel(true)

    Thread.sleep(100)
  }
}