IteratingNestedCallback.java

//
//  ========================================================================
//  Copyright (c) 1995-2017 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.util;

import org.eclipse.jetty.util.thread.Invocable.InvocationType;

/* ------------------------------------------------------------ */
/** Iterating Nested Callback.
 * <p>This specialized callback is used when breaking up an
 * asynchronous task into smaller asynchronous tasks.  A typical pattern
 * is that a successful callback is used to schedule the next sub task, but 
 * if that task completes quickly and uses the calling thread to callback
 * the success notification, this can result in a growing stack depth.
 * </p>
 * <p>To avoid this issue, this callback uses an AtomicBoolean to note 
 * if the success callback has been called during the processing of a 
 * sub task, and if so then the processing iterates rather than recurses.
 * </p>
 * <p>This callback is passed to the asynchronous handling of each sub
 * task and a call the {@link #succeeded()} on this call back represents
 * completion of the subtask.  Only once all the subtasks are completed is 
 * the {@link Callback#succeeded()} method called on the {@link Callback} instance
 * passed the the {@link #IteratingNestedCallback(Callback)} constructor.</p>
 *  
 */
public abstract class IteratingNestedCallback extends IteratingCallback
{
    final Callback _callback;
    
    public IteratingNestedCallback(Callback callback)
    {
        _callback=callback;
    }

    @Override
    public InvocationType getInvocationType()
    { 
        return _callback.getInvocationType();
    }
    
    @Override
    protected void onCompleteSuccess()
    {
        _callback.succeeded();
    }
    
    @Override
    protected void onCompleteFailure(Throwable x)
    {
        _callback.failed(x);
    }

    @Override
    public String toString()
    {
        return String.format("%s@%x",getClass().getSimpleName(),hashCode());
    }
}