jgit/org.eclipse.jgit/src/org/eclipse/jgit/lib/AsyncObjectSizeQueue.java

/*
 * Copyright (C) 2010, Google Inc.
 * and other copyright owners as documented in the project's IP log.
 *
 * This program and the accompanying materials are made available
 * under the terms of the Eclipse Distribution License v1.0 which
 * accompanies this distribution, is reproduced below, and is
 * available at http://www.eclipse.org/org/documents/edl-v10.php
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package org.eclipse.jgit.lib;

import java.io.IOException;

import org.eclipse.jgit.errors.MissingObjectException;

/**
 * Queue to examine object sizes asynchronously.
 *
 * A queue may perform background lookup of object sizes and supply them
 * (possibly out-of-order) to the application.
 *
 * @param <T>
 *            type of identifier supplied to the call that made the queue.
 */
public interface AsyncObjectSizeQueue<T extends ObjectId> extends
		AsyncOperation {

	/**
	 * Position this queue onto the next available result.
	 *
	 * @return true if there is a result available; false if the queue has
	 *         finished its input iteration.
	 * @throws MissingObjectException
	 *             the object does not exist. If the implementation is retaining
	 *             the application's objects {@link #getCurrent()} will be the
	 *             current object that is missing. There may be more results
	 *             still available, so the caller should continue invoking next
	 *             to examine another result.
	 * @throws IOException
	 *             the object store cannot be accessed.
	 */
	public boolean next() throws MissingObjectException, IOException;

	/**
	 * @return the current object, null if the implementation lost track.
	 *         Implementations may for performance reasons discard the caller's
	 *         ObjectId and provider their own through {@link #getObjectId()}.
	 */
	public T getCurrent();

	/** @return the ObjectId of the current object. Never null. */
	public ObjectId getObjectId();

	/** @return the size of the current object. */
	public long getSize();
}