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 class BlockObjQueue {
47 private BlockFreeList free;
48
49 private Block head;
50
51 private Block tail;
52
53 /** Create an empty queue. */
54 BlockObjQueue() {
55 free = new BlockFreeList();
56 }
57
58 void add(RevObject c) {
59 Block b = tail;
60 if (b == null) {
61 b = free.newBlock();
62 b.add(c);
63 head = b;
64 tail = b;
65 return;
66 } else if (b.isFull()) {
67 b = free.newBlock();
68 tail.next = b;
69 tail = b;
70 }
71 b.add(c);
72 }
73
74 RevObject next() {
75 final Block b = head;
76 if (b == null)
77 return null;
78
79 final RevObject c = b.pop();
80 if (b.isEmpty()) {
81 head = b.next;
82 if (head == null)
83 tail = null;
84 free.freeBlock(b);
85 }
86 return c;
87 }
88
89 static final class BlockFreeList {
90 private Block next;
91
92 Block newBlock() {
93 Block b = next;
94 if (b == null)
95 return new Block();
96 next = b.next;
97 b.clear();
98 return b;
99 }
100
101 void freeBlock(Block b) {
102 b.next = next;
103 next = b;
104 }
105 }
106
107 static final class Block {
108 private static final int BLOCK_SIZE = 256;
109
110 /** Next block in our chain of blocks; null if we are the last. */
111 Block next;
112
113 /** Our table of queued objects. */
114 final RevObject[] objects = new RevObject[BLOCK_SIZE];
115
116 /** Next valid entry in {@link #objects}. */
117 int headIndex;
118
119 /** Next free entry in {@link #objects} for addition at. */
120 int tailIndex;
121
122 boolean isFull() {
123 return tailIndex == BLOCK_SIZE;
124 }
125
126 boolean isEmpty() {
127 return headIndex == tailIndex;
128 }
129
130 void add(RevObject c) {
131 objects[tailIndex++] = c;
132 }
133
134 RevObject pop() {
135 return objects[headIndex++];
136 }
137
138 void clear() {
139 next = null;
140 headIndex = 0;
141 tailIndex = 0;
142 }
143 }
144 }