001/**
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.kahadb.page;
018
019import java.io.DataInput;
020import java.io.DataOutput;
021import java.io.IOException;
022import java.util.ArrayList;
023import java.util.Iterator;
024import java.util.List;
025
026import org.apache.kahadb.util.ByteSequence;
027import org.apache.kahadb.util.DataByteArrayInputStream;
028import org.apache.kahadb.util.DataByteArrayOutputStream;
029import org.apache.kahadb.util.Marshaller;
030
031/**
032 * A Page within a file.
033 * 
034 * 
035 */
036public class Page<T> {
037
038    public static final int PAGE_HEADER_SIZE = 21;
039
040    public static final byte PAGE_FREE_TYPE = 0;
041    public static final byte PAGE_PART_TYPE = 1;
042    public static final byte PAGE_END_TYPE = 2;
043
044    long pageId;
045
046    // The following fields are persisted
047    byte type = PAGE_FREE_TYPE;
048    long txId;
049    // A field reserved to hold checksums..  Not in use (yet)
050    int checksum;
051    
052    // Points to the next page in the chunk stream
053    long next;
054    T data;
055
056    public Page() {
057    }
058
059    public Page(long pageId) {
060        this.pageId=pageId;
061    }
062
063    public void copy(Page<T> other) {
064        this.pageId = other.pageId;
065        this.txId = other.txId;
066        this.type = other.type;
067        this.next = other.next;
068        this.data = other.data;
069    }
070
071    Page<T> copy() {
072        Page<T> rc = new Page<T>();
073        rc.copy(this);
074        return rc;
075    }
076
077    void makeFree(long txId) {
078        this.type = Page.PAGE_FREE_TYPE;
079        this.txId = txId;
080        this.data = null;
081        this.next = 0;
082    }
083    
084    public void makePagePart(long next, long txId) {
085        this.type = Page.PAGE_PART_TYPE;
086        this.next = next;
087        this.txId = txId;
088    }
089    
090    public void makePageEnd(long size, long txId) {
091        this.type = Page.PAGE_END_TYPE;
092        this.next = size;
093        this.txId = txId;
094    }
095
096    void write(DataOutput os) throws IOException {
097        os.writeByte(type);
098        os.writeLong(txId);
099        os.writeLong(next);
100        os.writeInt(checksum);
101    }
102
103    void read(DataInput is) throws IOException {
104        type = is.readByte();
105        txId = is.readLong();
106        next = is.readLong();
107        checksum = is.readInt();
108    }
109
110    public long getPageId() {
111        return pageId;
112    }
113
114    public long getTxId() {
115        return txId;
116    }
117
118    public T get() {
119        return data;
120    }
121
122    public void set(T data) {
123        this.data = data;
124    }
125
126    public short getType() {
127        return type;
128    }
129
130    public long getNext() {
131        return next;
132    }
133
134    public String toString() {
135        return "[Page:" + getPageId()+", type: "+type+"]";
136    }
137
138    public int getChecksum() {
139        return checksum;
140    }
141
142    public void setChecksum(int checksum) {
143        this.checksum = checksum;
144    }
145
146
147}