CachedPack.java

  1. /*
  2.  * Copyright (C) 2011, Google Inc.
  3.  * and other copyright owners as documented in the project's IP log.
  4.  *
  5.  * This program and the accompanying materials are made available
  6.  * under the terms of the Eclipse Distribution License v1.0 which
  7.  * accompanies this distribution, is reproduced below, and is
  8.  * available at http://www.eclipse.org/org/documents/edl-v10.php
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  13.  * without modification, are permitted provided that the following
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  16.  * - Redistributions of source code must retain the above copyright
  17.  *   notice, this list of conditions and the following disclaimer.
  18.  *
  19.  * - Redistributions in binary form must reproduce the above
  20.  *   copyright notice, this list of conditions and the following
  21.  *   disclaimer in the documentation and/or other materials provided
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  24.  * - Neither the name of the Eclipse Foundation, Inc. nor the
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  26.  *   products derived from this software without specific prior
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  29.  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
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  42.  */

  43. package org.eclipse.jgit.internal.storage.pack;

  44. import java.io.IOException;

  45. /**
  46.  * Describes a pack file
  47.  * {@link org.eclipse.jgit.internal.storage.pack.ObjectReuseAsIs} can append
  48.  * onto a stream.
  49.  */
  50. public abstract class CachedPack {
  51.     /**
  52.      * Get the number of objects in this pack.
  53.      *
  54.      * @return the total object count for the pack.
  55.      * @throws java.io.IOException
  56.      *             if the object count cannot be read.
  57.      */
  58.     public abstract long getObjectCount() throws IOException;

  59.     /**
  60.      * Get the number of delta objects stored in this pack.
  61.      * <p>
  62.      * This is an optional method, not every cached pack storage system knows
  63.      * the precise number of deltas stored within the pack. This number must be
  64.      * smaller than {@link #getObjectCount()} as deltas are not supposed to span
  65.      * across pack files.
  66.      * <p>
  67.      * This method must be fast, if the only way to determine delta counts is to
  68.      * scan the pack file's contents one object at a time, implementors should
  69.      * return 0 and avoid the high cost of the scan.
  70.      *
  71.      * @return the number of deltas; 0 if the number is not known or there are
  72.      *         no deltas.
  73.      * @throws java.io.IOException
  74.      *             if the delta count cannot be read.
  75.      */
  76.     public long getDeltaCount() throws IOException {
  77.         return 0;
  78.     }

  79.     /**
  80.      * Determine if this pack contains the object representation given.
  81.      * <p>
  82.      * PackWriter uses this method during the finding sources phase to prune
  83.      * away any objects from the leading thin-pack that already appear within
  84.      * this pack and should not be sent twice.
  85.      * <p>
  86.      * Implementors are strongly encouraged to rely on looking at {@code rep}
  87.      * only and using its internal state to decide if this object is within this
  88.      * pack. Implementors should ensure a representation from this cached pack
  89.      * is tested as part of
  90.      * {@link org.eclipse.jgit.internal.storage.pack.ObjectReuseAsIs#selectObjectRepresentation(PackWriter, org.eclipse.jgit.lib.ProgressMonitor, Iterable)}
  91.      * , ensuring this method would eventually return true if the object would
  92.      * be included by this cached pack.
  93.      *
  94.      * @param obj
  95.      *            the object being packed. Can be used as an ObjectId.
  96.      * @param rep
  97.      *            representation from the
  98.      *            {@link org.eclipse.jgit.internal.storage.pack.ObjectReuseAsIs}
  99.      *            instance that originally supplied this CachedPack.
  100.      * @return true if this pack contains this object.
  101.      */
  102.     public abstract boolean hasObject(ObjectToPack obj,
  103.             StoredObjectRepresentation rep);
  104. }