interactivespaces.util.concurrency.SequentialEventQueue.java Source code

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Here is the source code for interactivespaces.util.concurrency.SequentialEventQueue.java

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/*
 * 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 interactivespaces.util.concurrency;

import interactivespaces.system.InteractiveSpacesEnvironment;

import org.apache.commons.logging.Log;

import java.util.concurrent.BlockingQueue;
import java.util.concurrent.Future;
import java.util.concurrent.LinkedBlockingQueue;

/**
 * An event queue which will run its event handlers in First in, First Out
 * order.
 *
 * <p>
 * Integrates into Interactive Spaces thread pools.
 *
 * @author Keith M. Hughes
 */
public class SequentialEventQueue {

    /**
     * The list of events to process.
     */
    private BlockingQueue<Runnable> events = new LinkedBlockingQueue<Runnable>();

    /**
     * The queue future, used for shutting the queue down.
     */
    private Future<?> queueFuture;

    /**
     * The space environment to run under.
     */
    private InteractiveSpacesEnvironment spaceEnvironment;

    /**
     * The logger for errors.
     */
    private Log log;

    public SequentialEventQueue(InteractiveSpacesEnvironment spaceEnvironment, Log log) {
        this.spaceEnvironment = spaceEnvironment;
        this.log = log;
    }

    /**
     * Start the event queue running.
     */
    public void startup() {
        queueFuture = spaceEnvironment.getExecutorService().submit(new Runnable() {
            @Override
            public void run() {
                processEvents();
            }
        });
    }

    /**
     * Shut the queue down.
     *
     * <p>
     * Any events which have not processed are not guaranteed to be processed or
     * finished processing.
     */
    public void shutdown() {
        if (queueFuture != null) {
            queueFuture.cancel(true);
            queueFuture = null;

            events.clear();
        }
    }

    /**
     * Add a new event to the queue.
     *
     * @param event
     *          the new event
     */
    public void addEvent(Runnable event) {
        try {
            events.put(event);
        } catch (InterruptedException e) {
            // Don't care
        }
    }

    /**
     * Process events until the event processing thread is interrupted.
     */
    private void processEvents() {
        try {
            while (!Thread.interrupted()) {
                processNextEvent();
            }
        } catch (InterruptedException e) {
            // Don't care
        }
    }

    /**
     * Process the next event.
     *
     * @throws InterruptedException
     */
    private void processNextEvent() throws InterruptedException {
        try {
            Runnable event = events.take();

            event.run();
        } catch (InterruptedException e) {
            throw e;
        } catch (Exception e) {
            log.error("Error during event processing", e);
        }
    }
}