001 /**
002 * JDBM LICENSE v1.00
003 *
004 * Redistribution and use of this software and associated documentation
005 * ("Software"), with or without modification, are permitted provided
006 * that the following conditions are met:
007 *
008 * 1. Redistributions of source code must retain copyright
009 * statements and notices. Redistributions must also contain a
010 * copy of this document.
011 *
012 * 2. Redistributions in binary form must reproduce the
013 * above copyright notice, this list of conditions and the
014 * following disclaimer in the documentation and/or other
015 * materials provided with the distribution.
016 *
017 * 3. The name "JDBM" must not be used to endorse or promote
018 * products derived from this Software without prior written
019 * permission of Cees de Groot. For written permission,
020 * please contact cg@cdegroot.com.
021 *
022 * 4. Products derived from this Software may not be called "JDBM"
023 * nor may "JDBM" appear in their names without prior written
024 * permission of Cees de Groot.
025 *
026 * 5. Due credit should be given to the JDBM Project
027 * (http://jdbm.sourceforge.net/).
028 *
029 * THIS SOFTWARE IS PROVIDED BY THE JDBM PROJECT AND CONTRIBUTORS
030 * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
031 * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
032 * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
033 * CEES DE GROOT OR ANY CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
034 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
035 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
036 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
037 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
038 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
039 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
040 * OF THE POSSIBILITY OF SUCH DAMAGE.
041 *
042 * Copyright 2000 (C) Cees de Groot. All Rights Reserved.
043 * Contributions are Copyright (C) 2000 by their associated contributors.
044 *
045 * $Id: PageHeader.java,v 1.2 2003/09/21 15:47:01 boisvert Exp $
046 */
047
048 package jdbm.recman;
049
050 /**
051 * This class represents a page header. It is the common superclass for
052 * all different page views.
053 */
054 public class PageHeader implements BlockView {
055 // offsets
056 private static final short O_MAGIC = 0; // short magic
057 private static final short O_NEXT = Magic.SZ_SHORT; // long next
058 private static final short O_PREV = O_NEXT + Magic.SZ_LONG; // long prev
059 protected static final short SIZE = O_PREV + Magic.SZ_LONG;
060
061 // my block
062 protected BlockIo block;
063
064 /**
065 * Constructs a PageHeader object from a block
066 *
067 * @param block The block that contains the file header
068 * @throws IOException if the block is too short to keep the file
069 * header.
070 */
071 protected PageHeader(BlockIo block) {
072 initialize(block);
073 if (!magicOk())
074 throw new Error("CRITICAL: page header magic for block "
075 + block.getBlockId() + " not OK "
076 + getMagic());
077 }
078
079 /**
080 * Constructs a new PageHeader of the indicated type. Used for newly
081 * created pages.
082 */
083 PageHeader(BlockIo block, short type) {
084 initialize(block);
085 setType(type);
086 }
087
088 /**
089 * Factory method to create or return a page header for the
090 * indicated block.
091 */
092 static PageHeader getView(BlockIo block) {
093 BlockView view = block.getView();
094 if (view != null && view instanceof PageHeader)
095 return (PageHeader) view;
096 else
097 return new PageHeader(block);
098 }
099
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 }