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//  Copyright (c) 1995-2019 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
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//      The Apache License v2.0 is available at
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//  You may elect to redistribute this code under either of these licenses.
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package org.eclipse.jetty.util;

import java.util.concurrent.atomic.AtomicInteger;

A callback wrapper that succeeds the wrapped callback when the count is
reached, or on first failure.
This callback is particularly useful when an async operation is split
into multiple parts, for example when an original byte buffer that needs
to be written, along with a callback, is split into multiple byte buffers,
since it allows the original callback to be wrapped and notified only when
the last part has been processed.
Example:
public void process(EndPoint endPoint, ByteBuffer buffer, Callback callback)
{
    ByteBuffer[] buffers = split(buffer);
    CountCallback countCallback = new CountCallback(callback, buffers.length);
    endPoint.write(countCallback, buffers);
}

/**
 * <p>A callback wrapper that succeeds the wrapped callback when the count is
 * reached, or on first failure.</p>
 * <p>This callback is particularly useful when an async operation is split
 * into multiple parts, for example when an original byte buffer that needs
 * to be written, along with a callback, is split into multiple byte buffers,
 * since it allows the original callback to be wrapped and notified only when
 * the last part has been processed.</p>
 * <p>Example:</p>
 * <pre>
 * public void process(EndPoint endPoint, ByteBuffer buffer, Callback callback)
 * {
 *     ByteBuffer[] buffers = split(buffer);
 *     CountCallback countCallback = new CountCallback(callback, buffers.length);
 *     endPoint.write(countCallback, buffers);
 * }
 * </pre>
 */
public class CountingCallback extends Callback.Nested
{
    private final AtomicInteger count;

    public CountingCallback(Callback callback, int count)
    {
        super(callback);
        if (count < 1)
            throw new IllegalArgumentException();
        this.count = new AtomicInteger(count);
    }

    @Override
    public void succeeded()
    {
        // Forward success on the last success.
        while (true)
        {
            int current = count.get();

            // Already completed ?
            if (current == 0)
                return;

            if (count.compareAndSet(current, current - 1))
            {
                if (current == 1)
                    super.succeeded();
                return;
            }
        }
    }

    @Override
    public void failed(Throwable failure)
    {
        // Forward failure on the first failure.
        while (true)
        {
            int current = count.get();

            // Already completed ?
            if (current == 0)
                return;

            if (count.compareAndSet(current, 0))
            {
                super.failed(failure);
                return;
            }
        }
    }

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