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//
//  ========================================================================
//  Copyright (c) 1995-2014 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 java.util.concurrent.atomic.AtomicBoolean;

/**
 * A callback to be used by driver code that needs to know whether the callback has been
 * succeeded or failed (that is, completed) just after the asynchronous operation or not,
 * typically because further processing depends on the callback being completed.
 * The driver code competes with the asynchronous operation to complete the callback.
 * 

* If the callback is already completed, the driver code continues the processing, * otherwise it suspends it. If it is suspended, the callback will be completed some time * later, and {@link #resume()} or {@link #abort(Throwable)} will be called to allow the * application to resume the processing. *

* Typical usage: *

 * CompletableCallback callback = new CompletableCallback()
 * {
 *     @Override
 *     public void resume()
 *     {
 *         // continue processing
 *     }
 *
 *     @Override
 *     public void abort(Throwable failure)
 *     {
 *         // abort processing
 *     }
 * }
 * asyncOperation(callback);
 * boolean completed = callback.tryComplete();
 * if (completed)
 *     // suspend processing, async operation not done yet
 * else
 *     // continue processing, async operation already done
 * 
*/ public abstract class CompletableCallback implements Callback { private final AtomicBoolean completed = new AtomicBoolean(); @Override public void succeeded() { if (!tryComplete()) resume(); } @Override public void failed(Throwable x) { if (!tryComplete()) abort(x); } /** * Callback method invoked when this callback is succeeded * after a first call to {@link #tryComplete()}. */ public abstract void resume(); /** * Callback method invoked when this callback is failed * after a first call to {@link #tryComplete()}. */ public abstract void abort(Throwable failure); /** * Tries to complete this callback; driver code should call * this method once after the asynchronous operation * to detect whether the asynchronous operation has already * completed or not. * * @return whether the attempt to complete was successful. */ public boolean tryComplete() { return completed.compareAndSet(false, true); } }




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