1 /**
2 * JDBM LICENSE v1.00
3 *
4 * Redistribution and use of this software and associated documentation
5 * ("Software"), with or without modification, are permitted provided
6 * that the following conditions are met:
7 *
8 * 1. Redistributions of source code must retain copyright
9 * statements and notices. Redistributions must also contain a
10 * copy of this document.
11 *
12 * 2. Redistributions in binary form must reproduce the
13 * above copyright notice, this list of conditions and the
14 * following disclaimer in the documentation and/or other
15 * materials provided with the distribution.
16 *
17 * 3. The name "JDBM" must not be used to endorse or promote
18 * products derived from this Software without prior written
19 * permission of Cees de Groot. For written permission,
20 * please contact cg@cdegroot.com.
21 *
22 * 4. Products derived from this Software may not be called "JDBM"
23 * nor may "JDBM" appear in their names without prior written
24 * permission of Cees de Groot.
25 *
26 * 5. Due credit should be given to the JDBM Project
27 * (http://jdbm.sourceforge.net/).
28 *
29 * THIS SOFTWARE IS PROVIDED BY THE JDBM PROJECT AND CONTRIBUTORS
30 * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
31 * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
32 * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
33 * CEES DE GROOT OR ANY CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
34 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
35 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
36 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
37 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
38 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
39 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
40 * OF THE POSSIBILITY OF SUCH DAMAGE.
41 *
42 * Copyright 2000 (C) Cees de Groot. All Rights Reserved.
43 * Contributions are Copyright (C) 2000 by their associated contributors.
44 *
45 * $Id: PageHeader.java,v 1.2 2003/09/21 15:47:01 boisvert Exp $
46 */
47
48 package jdbm.recman;
49
50 /**
51 * This class represents a page header. It is the common superclass for
52 * all different page views.
53 */
54 public class PageHeader implements BlockView {
55 // offsets
56 private static final short O_MAGIC = 0; // short magic
57 private static final short O_NEXT = Magic.SZ_SHORT; // long next
58 private static final short O_PREV = O_NEXT + Magic.SZ_LONG; // long prev
59 protected static final short SIZE = O_PREV + Magic.SZ_LONG;
60
61 // my block
62 protected BlockIo block;
63
64 /**
65 * Constructs a PageHeader object from a block
66 *
67 * @param block The block that contains the file header
68 * @throws IOException if the block is too short to keep the file
69 * header.
70 */
71 protected PageHeader(BlockIo block) {
72 initialize(block);
73 if (!magicOk())
74 throw new Error("CRITICAL: page header magic for block "
75 + block.getBlockId() + " not OK "
76 + getMagic());
77 }
78
79 /**
80 * Constructs a new PageHeader of the indicated type. Used for newly
81 * created pages.
82 */
83 PageHeader(BlockIo block, short type) {
84 initialize(block);
85 setType(type);
86 }
87
88 /**
89 * Factory method to create or return a page header for the
90 * indicated block.
91 */
92 static PageHeader getView(BlockIo block) {
93 BlockView view = block.getView();
94 if (view != null && view instanceof PageHeader)
95 return (PageHeader) view;
96 else
97 return new PageHeader(block);
98 }
99
100 private void initialize(BlockIo block) {
101 this.block = block;
102 block.setView(this);
103 }
104
105 /**
106 * Returns true if the magic corresponds with the fileHeader magic.
107 */
108 private boolean magicOk() {
109 int magic = getMagic();
110 return magic >= Magic.BLOCK
111 && magic <= (Magic.BLOCK + Magic.FREEPHYSIDS_PAGE);
112 }
113
114 /**
115 * For paranoia mode
116 */
117 protected void paranoiaMagicOk() {
118 if (!magicOk())
119 throw new Error("CRITICAL: page header magic not OK "
120 + getMagic());
121 }
122
123 /** Returns the magic code */
124 short getMagic() {
125 return block.readShort(O_MAGIC);
126 }
127
128 /** Returns the next block. */
129 long getNext() {
130 paranoiaMagicOk();
131 return block.readLong(O_NEXT);
132 }
133
134 /** Sets the next block. */
135 void setNext(long next) {
136 paranoiaMagicOk();
137 block.writeLong(O_NEXT, next);
138 }
139
140 /** Returns the previous block. */
141 long getPrev() {
142 paranoiaMagicOk();
143 return block.readLong(O_PREV);
144 }
145
146 /** Sets the previous block. */
147 void setPrev(long prev) {
148 paranoiaMagicOk();
149 block.writeLong(O_PREV, prev);
150 }
151
152 /** Sets the type of the page header */
153 void setType(short type) {
154 block.writeShort(O_MAGIC, (short) (Magic.BLOCK + type));
155 }
156 }