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.internal.storage.file;
45
46 import java.util.concurrent.atomic.AtomicReferenceArray;
47
48 import org.eclipse.jgit.lib.AnyObjectId;
49 import org.eclipse.jgit.lib.ObjectId;
50
51 /** Remembers objects that are currently unpacked. */
52 class UnpackedObjectCache {
53 private static final int INITIAL_BITS = 5; // size = 32
54
55 private static final int MAX_BITS = 11; // size = 2048
56
57 private volatile Table table;
58
59 UnpackedObjectCache() {
60 table = new Table(INITIAL_BITS);
61 }
62
63 boolean isUnpacked(AnyObjectId objectId) {
64 return table.contains(objectId);
65 }
66
67 void add(AnyObjectId objectId) {
68 Table t = table;
69 if (t.add(objectId)) {
70 // The object either already exists in the table, or was
71 // successfully added. Either way leave the table alone.
72 //
73 } else {
74 // The object won't fit into the table. Implement a crude
75 // cache removal by just dropping the table away, but double
76 // it in size for the next incarnation.
77 //
78 Table n = new Table(Math.min(t.bits + 1, MAX_BITS));
79 n.add(objectId);
80 table = n;
81 }
82 }
83
84 void remove(AnyObjectId objectId) {
85 if (isUnpacked(objectId))
86 clear();
87 }
88
89 void clear() {
90 table = new Table(INITIAL_BITS);
91 }
92
93 private static class Table {
94 private static final int MAX_CHAIN = 8;
95
96 private final AtomicReferenceArray<ObjectId> ids;
97
98 private final int shift;
99
100 final int bits;
101
102 Table(int bits) {
103 this.ids = new AtomicReferenceArray<>(1 << bits);
104 this.shift = 32 - bits;
105 this.bits = bits;
106 }
107
108 boolean contains(AnyObjectId toFind) {
109 int i = index(toFind);
110 for (int n = 0; n < MAX_CHAIN; n++) {
111 ObjectId obj = ids.get(i);
112 if (obj == null)
113 break;
114
115 if (AnyObjectId.equals(obj, toFind))
116 return true;
117
118 if (++i == ids.length())
119 i = 0;
120 }
121 return false;
122 }
123
124 boolean add(AnyObjectId toAdd) {
125 int i = index(toAdd);
126 for (int n = 0; n < MAX_CHAIN;) {
127 ObjectId obj = ids.get(i);
128 if (obj == null) {
129 if (ids.compareAndSet(i, null, toAdd.copy()))
130 return true;
131 else
132 continue;
133 }
134
135 if (AnyObjectId.equals(obj, toAdd))
136 return true;
137
138 if (++i == ids.length())
139 i = 0;
140 n++;
141 }
142 return false;
143 }
144
145 private int index(AnyObjectId id) {
146 return id.hashCode() >>> shift;
147 }
148 }
149 }