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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 IteratingCallback.succeeded() on this call back represents completion of the subtask. Only once all the subtasks are completed is the Callback.succeeded() method called on the Callback instance passed the the IteratingNestedCallback(Callback) constructor.
/**
 * 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());
    }
}