1 /*
2 * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org>
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.revwalk;
45
46 import java.io.IOException;
47
48 import org.eclipse.jgit.errors.IncorrectObjectTypeException;
49 import org.eclipse.jgit.errors.MissingObjectException;
50
51 abstract class BlockRevQueue extends AbstractRevQueue {
52 protected BlockFreeList free;
53
54 /**
55 * Create an empty revision queue.
56 */
57 protected BlockRevQueue() {
58 free = new BlockFreeList();
59 }
60
61 BlockRevQueue(Generator s) throws MissingObjectException,
62 IncorrectObjectTypeException, IOException {
63 free = new BlockFreeList();
64 outputType = s.outputType();
65 s.shareFreeList(this);
66 for (;;) {
67 final RevCommit c = s.next();
68 if (c == null)
69 break;
70 add(c);
71 }
72 }
73
74 /**
75 * {@inheritDoc}
76 * <p>
77 * Reconfigure this queue to share the same free list as another.
78 * <p>
79 * Multiple revision queues can be connected to the same free list, making
80 * it less expensive for applications to shuttle commits between them. This
81 * method arranges for the receiver to take from / return to the same free
82 * list as the supplied queue.
83 * <p>
84 * Free lists are not thread-safe. Applications must ensure that all queues
85 * sharing the same free list are doing so from only a single thread.
86 */
87 @Override
88 public void shareFreeList(BlockRevQueue q) {
89 free = q.free;
90 }
91
92 static final class BlockFreeList {
93 private Block next;
94
95 Block newBlock() {
96 Block b = next;
97 if (b == null)
98 return new Block();
99 next = b.next;
100 b.clear();
101 return b;
102 }
103
104 void freeBlock(Block b) {
105 b.next = next;
106 next = b;
107 }
108
109 void clear() {
110 next = null;
111 }
112 }
113
114 static final class Block {
115 static final int BLOCK_SIZE = 256;
116
117 /** Next block in our chain of blocks; null if we are the last. */
118 Block next;
119
120 /** Our table of queued commits. */
121 final RevCommit.html#RevCommit">RevCommit[] commits = new RevCommit[BLOCK_SIZE];
122
123 /** Next valid entry in {@link #commits}. */
124 int headIndex;
125
126 /** Next free entry in {@link #commits} for addition at. */
127 int tailIndex;
128
129 boolean isFull() {
130 return tailIndex == BLOCK_SIZE;
131 }
132
133 boolean isEmpty() {
134 return headIndex == tailIndex;
135 }
136
137 boolean canUnpop() {
138 return headIndex > 0;
139 }
140
141 void add(RevCommit c) {
142 commits[tailIndex++] = c;
143 }
144
145 void unpop(RevCommit c) {
146 commits[--headIndex] = c;
147 }
148
149 RevCommit pop() {
150 return commits[headIndex++];
151 }
152
153 RevCommit peek() {
154 return commits[headIndex];
155 }
156
157 void clear() {
158 next = null;
159 headIndex = 0;
160 tailIndex = 0;
161 }
162
163 void resetToMiddle() {
164 headIndex = tailIndex = BLOCK_SIZE / 2;
165 }
166
167 void resetToEnd() {
168 headIndex = tailIndex = BLOCK_SIZE;
169 }
170 }
171 }