EventDispatcher.java

/*
 * Copyright (C) 2012 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */

package org.ros.concurrent;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.atomic.AtomicBoolean;

/**
 * @author damonkohler@google.com (Damon Kohler)
 *
 * @param <T>
 *          the listener type
 */
public class EventDispatcher<T> extends CancellableLoop {

  private final T listener;
  private final MessageBlockingQueue<SignalRunnable<T>> events;

  private final CountDownLatch fullyShutdownLatch = new CountDownLatch(1);

  private AtomicBoolean isShuttingDown = new AtomicBoolean(false);

  public EventDispatcher(T listener, int queueCapacity) {
    this.listener = listener;
    events = MessageBlockingQueueFactory.newMessageBlockingQueue(queueCapacity, false);
  }

  /**
   * A signal must take place.
   *
   * @param signalRunnable
   *          the runnable that contains the signal
   */
  public void signal(final SignalRunnable<T> signalRunnable) {
    if (isShuttingDown.get()) {
      try {
        fullyShutdownLatch.await();
      } catch (InterruptedException e) {
        // Don't care
      }

      // Just in case something came in while we were waiting.
      // Done this way so always in order it was supposed to happen.
      try {
        events.put(signalRunnable);
      } catch (InterruptedException e) {
        // Don't care.
      }
      flush();
    } else {
      try {
        events.put(signalRunnable);
      } catch (InterruptedException e) {
        // Don't care.
      }
    }
  }

  @Override
  public void loop() throws InterruptedException {
    SignalRunnable<T> signalRunnable = events.take();
    signalRunnable.run(listener);
  }

  @Override
  protected void cleanup() {
    isShuttingDown.set(true);
    flush();
    fullyShutdownLatch.countDown();
  }

  /**
   * Flush all events out of the event dispatcher.
   *
   * <p>
   * This is run after the dispatcher is shut down and empties out any events
   * which have not been written.
   */
  private void flush() {
    SignalRunnable<T> signalRunnable;
    while ((signalRunnable = events.poll()) != null) {
      try {
        signalRunnable.run(listener);
      } catch (Exception e) {
        e.printStackTrace();
      }
    }
  }
}