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Utility classes for Jetty

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//
// ========================================================================
// Copyright (c) 1995-2021 Mort Bay Consulting Pty Ltd and others.
//
// This program and the accompanying materials are made available under the
// terms of the Eclipse Public License v. 2.0 which is available at
// https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
// which is available at https://www.apache.org/licenses/LICENSE-2.0.
//
// SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
// ========================================================================
//

package org.eclipse.jetty.util;

/**
 * Iterating Nested Callback.
 * 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.
 * 
 * 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.
 * 
 * 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.
 */
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());
    }
}