1 /*
2 * Copyright (C) 2010, 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
9 *
10 * All rights reserved.
11 *
12 * Redistribution and use in source and binary forms, with or
13 * without modification, are permitted provided that the following
14 * conditions are met:
15 *
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
22 * with the distribution.
23 *
24 * - Neither the name of the Eclipse Foundation, Inc. nor the
25 * names of its contributors may be used to endorse or promote
26 * products derived from this software without specific prior
27 * written permission.
28 *
29 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
30 * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
31 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
32 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
33 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
34 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
35 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
36 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
37 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
38 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
39 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
40 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
41 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
42 */
43
44 package org.eclipse.jgit.lib;
45
46 import java.io.IOException;
47
48 import org.eclipse.jgit.errors.MissingObjectException;
49
50 /**
51 * Queue to open objects asynchronously.
52 *
53 * A queue may perform background decompression of objects and supply them
54 * (possibly out-of-order) to the application.
55 *
56 * @param <T>
57 * type of identifier supplied to the call that made the queue.
58 */
59 public interface AsyncObjectLoaderQueue<T extends ObjectId> extends
60 AsyncOperation {
61
62 /**
63 * Position this queue onto the next available result.
64 *
65 * Even if this method returns true, {@link #open()} may still throw
66 * {@link MissingObjectException} if the underlying object database was
67 * concurrently modified and the current object is no longer available.
68 *
69 * @return true if there is a result available; false if the queue has
70 * finished its input iteration.
71 * @throws MissingObjectException
72 * the object does not exist. If the implementation is retaining
73 * the application's objects {@link #getCurrent()} will be the
74 * current object that is missing. There may be more results
75 * still available, so the caller should continue invoking next
76 * to examine another result.
77 * @throws IOException
78 * the object store cannot be accessed.
79 */
80 public boolean next() throws MissingObjectException, IOException;
81
82 /**
83 * @return the current object, null if the implementation lost track.
84 * Implementations may for performance reasons discard the caller's
85 * ObjectId and provider their own through {@link #getObjectId()}.
86 */
87 public T getCurrent();
88
89 /** @return the ObjectId of the current object. Never null. */
90 public ObjectId getObjectId();
91
92 /**
93 * Obtain a loader to read the object.
94 *
95 * This method can only be invoked once per result
96 *
97 * Due to race conditions with a concurrent modification of the underlying
98 * object database, an object may be unavailable when this method is
99 * invoked, even though next returned successfully.
100 *
101 * @return the ObjectLoader to read this object. Never null.
102 * @throws MissingObjectException
103 * the object does not exist. If the implementation is retaining
104 * the application's objects {@link #getCurrent()} will be the
105 * current object that is missing. There may be more results
106 * still available, so the caller should continue invoking next
107 * to examine another result.
108 * @throws IOException
109 * the object store cannot be accessed.
110 */
111 public ObjectLoader open() throws IOException;
112 }