1 /*
2 * Copyright (C) 2016, 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.internal.ketch;
45
46 import org.eclipse.jgit.lib.AnyObjectId;
47 import org.eclipse.jgit.lib.ObjectId;
48
49 /**
50 * An ObjectId for a commit extended with incrementing log index.
51 * <p>
52 * For any two LogIndex instances, {@code A} is an ancestor of {@code C}
53 * reachable through parent edges in the graph if {@code A.index < C.index}.
54 * LogIndex provides a performance optimization for Ketch, the same information
55 * can be obtained from {@link org.eclipse.jgit.revwalk.RevWalk}.
56 * <p>
57 * Index values are only valid within a single
58 * {@link org.eclipse.jgit.internal.ketch.KetchLeader} instance after it has won
59 * an election. By restricting scope to a single leader new leaders do not need
60 * to traverse the entire history to determine the next {@code index} for new
61 * proposals. This differs from Raft, where leader election uses the log index
62 * and the term number to determine which replica holds a sufficiently
63 * up-to-date log. Since Ketch uses Git objects for storage of its replicated
64 * log, it keeps the term number as Raft does but uses standard Git operations
65 * to imply the log index.
66 * <p>
67 * {@link org.eclipse.jgit.internal.ketch.Round#runAsync(AnyObjectId)} bumps the
68 * index as each new round is constructed.
69 */
70 public class LogIndex extends ObjectId {
71 static LogIndex unknown(AnyObjectId id) {
72 return new LogIndex(id, 0);
73 }
74
75 private final long index;
76
77 private LogIndex(AnyObjectId id, long index) {
78 super(id);
79 this.index = index;
80 }
81
82 LogIndex nextIndex(AnyObjectId id) {
83 return new LogIndex(id, index + 1);
84 }
85
86 /**
87 * Get index provided by the current leader instance.
88 *
89 * @return index provided by the current leader instance.
90 */
91 public long getIndex() {
92 return index;
93 }
94
95 /**
96 * Check if this log position committed before another log position.
97 * <p>
98 * Only valid for log positions in memory for the current leader.
99 *
100 * @param c
101 * other (more recent) log position.
102 * @return true if this log position was before {@code c} or equal to c and
103 * therefore any agreement of {@code c} implies agreement on this
104 * log position.
105 */
106 boolean isBefore(LogIndex c) {
107 return index <= c.index;
108 }
109
110 /**
111 * Create string suitable for debug logging containing the log index and
112 * abbreviated ObjectId.
113 *
114 * @return string suitable for debug logging containing the log index and
115 * abbreviated ObjectId.
116 */
117 @SuppressWarnings("boxing")
118 public String describeForLog() {
119 return String.format("%5d/%s", index, abbreviate(6).name()); //$NON-NLS-1$
120 }
121
122 /** {@inheritDoc} */
123 @SuppressWarnings("boxing")
124 @Override
125 public String toString() {
126 return String.format("LogId[%5d/%s]", index, name()); //$NON-NLS-1$
127 }
128 }