//========================================================================
   //Copyright 2011-2012 Mort Bay Consulting Pty. Ltd.
   //------------------------------------------------------------------------
   //All rights reserved. This program and the accompanying materials
   //are made available under the terms of the Eclipse Public License v1.0
   //and Apache License v2.0 which accompanies this distribution.
   //The Eclipse Public License is available at
   //http://www.eclipse.org/legal/epl-v10.html
   //The Apache License v2.0 is available at
  //http://www.opensource.org/licenses/apache2.0.php
  //You may elect to redistribute this code under either of these licenses.
  //========================================================================
  
  package org.eclipse.jetty.spdy;
  
  import java.util.concurrent.CancellationException;
  import java.util.concurrent.CountDownLatch;
  import java.util.concurrent.ExecutionException;
  import java.util.concurrent.Future;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.TimeoutException;
  
  import org.eclipse.jetty.spdy.api.Handler;
  
  /**
   * <p>A {@link Promise} is a {@link Future} that allows a result or a failure to be set,
   * so that the {@link Future} will be {@link #isDone() done}.</p>
   *
   * @param <T> the type of the result object
   */
  public class Promise<T> implements Handler<T>, Future<T>
  {
      private final CountDownLatch latch = new CountDownLatch(1);
      private boolean cancelled;
      private Throwable failure;
      private T promise;
  
      @Override
      public void completed(T result)
      {
          this.promise = result;
          latch.countDown();
      }
  
      @Override
      public void failed(T context, Throwable x)
      {
          this.failure = x;
          latch.countDown();
      }
  
      @Override
      public boolean cancel(boolean mayInterruptIfRunning)
      {
          cancelled = true;
          latch.countDown();
          return true;
      }
  
      @Override
      public boolean isCancelled()
      {
          return cancelled;
      }
  
      @Override
      public boolean isDone()
      {
          return cancelled || latch.getCount() == 0;
      }
  
      @Override
      public T get() throws InterruptedException, ExecutionException
      {
          latch.await();
          return result();
      }
  
      @Override
      public T get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException
      {
          boolean elapsed = !latch.await(timeout, unit);
          if (elapsed)
              throw new TimeoutException();
          return result();
      }
  
      private T result() throws ExecutionException
      {
          if (isCancelled())
              throw new CancellationException();
          Throwable failure = this.failure;
          if (failure != null)
              throw new ExecutionException(failure);
          return promise;
      }
  }