org.directwebremoting.dwrp.JettyContinuationSleeper Maven / Gradle / Ivy

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DWR is easy Ajax for Java. It makes it simple to call Java code directly from Javascript. It gets rid of almost all the boiler plate code between the web browser and your Java code.
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/*
 * Copyright 2005 Joe Walker
 *
 * 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.directwebremoting.dwrp;

import javax.servlet.http.HttpServletRequest;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.directwebremoting.util.Continuation;

/**
 * A Sleeper that works with Jetty Continuations
 * @author Joe Walker [joe at getahead dot ltd dot uk]
 */
public class JettyContinuationSleeper implements Sleeper
{
    /**
     * @param request The request into which we store this as an attribute
     */
    public JettyContinuationSleeper(HttpServletRequest request)
    {
        continuation = new Continuation(request);

        // At this point JettyContinuationSleeper is fully initialized so it is
        // safe to allow other classes to see and use us.
        //noinspection ThisEscapedInObjectConstruction
        request.setAttribute(ATTRIBUTE_JETTY_CONDUIT, this);
    }

    /**
     * Is this a restarted continuation?
     * @param request The request on which a Sleeper might be stored
     * @return true if this request is from a restarted Continuation
     */
    public static boolean isRestart(HttpServletRequest request)
    {
        return request.getAttribute(ATTRIBUTE_JETTY_CONDUIT) != null;
    }

    /**
     * Act on a restarted continuation by executing the onAwakening action
     * @param request The request on which the Sleeper is stored
     */
    public static void restart(HttpServletRequest request)
    {
        JettyContinuationSleeper sleeper = (JettyContinuationSleeper) request.getAttribute(ATTRIBUTE_JETTY_CONDUIT);
        if (sleeper == null)
        {
            throw new IllegalStateException("No JettyContinuationSleeper in HttpServletRequest");
        }

        request.removeAttribute(ATTRIBUTE_JETTY_CONDUIT);
        sleeper.onAwakening.run();
    }

    /* (non-Javadoc)
     * @see org.directwebremoting.dwrp.Sleeper#goToSleep(java.lang.Runnable)
     */
    public void goToSleep(Runnable awakening)
    {
        this.onAwakening = awakening;

        synchronized (wakeUpCalledLock)
        {
            if (wakeUpCalled)
            {
                onAwakening.run();
            }
            else
            {
                try
                {
                    // This throws a RuntimeException that must propagate to the
                    // container. The docs say that a value of 0 should suspend
                    // forever, but that did not to happen in 6.1.1 so we
                    // suspend for BigNum
                    continuation.suspend(Integer.MAX_VALUE);
                }
                catch (Exception ex)
                {
                    Continuation.rethrowIfContinuation(ex);
        
                    log.warn("Exception", ex);
                    proxy = new ThreadWaitSleeper();
                    proxy.goToSleep(onAwakening);
                }
            }
        }
    }

    /* (non-Javadoc)
     * @see org.directwebremoting.dwrp.PollHandler.Sleeper#wakeUp()
     */
    public void wakeUp()
    {
        synchronized (wakeUpCalledLock)
        {
            if (wakeUpCalled)
            {
                return;
            }

            wakeUpCalled = true;

            if (proxy != null)
            {
                proxy.wakeUp();
            }
            else
            {
                synchronized (continuation)
                {
                    if (!resumed)
                    {
                        try
                        {
                            continuation.resume();
                        }
                        catch (Exception ex)
                        {
                            log.error("Broken reflection", ex);
                        }
    
                        resumed = true;
                    }
                }
            }
        }
    }

    /**
     * All operations that involve going to sleep of waking up must hold this
     * lock before they take action.
     */
    private Object wakeUpCalledLock = new Object();

    /**
     * Has wakeUp been called?
     */
    private boolean wakeUpCalled = false;

    /**
     * If continuations fail, we proxy to a Thread Wait version
     */
    private ThreadWaitSleeper proxy = null;

    /**
     * What we do when we are woken up
     */
    private Runnable onAwakening;

    /**
     * The continuation object
     */
    protected final Continuation continuation;

    /**
     * Has the continuation been restarted already?
     */
    protected boolean resumed = false;

    /**
     * We remember the notify conduit so we can reuse it
     */
    public static final String ATTRIBUTE_JETTY_CONDUIT = "org.directwebremoting.dwrp.notifyConduit";

    /**
     * The log stream
     */
    private static final Log log = LogFactory.getLog(JettyContinuationSleeper.class);
}