Quadcap Embeddable Database

com/quadcap/sql/file/Page.java

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package com.quadcap.sql.file;

/* Copyright 1999 - 2003 Quadcap Software.  All rights reserved.
 *
 * This software is distributed under the Quadcap Free Software License.
 * This software may be used or modified for any purpose, personal or
 * commercial.  Open Source redistributions are permitted.  Commercial
 * redistribution of larger works derived from, or works which bundle
 * this software requires a "Commercial Redistribution License"; see
 * http://www.quadcap.com/purchase.
 *
 * Redistributions qualify as "Open Source" under  one of the following terms:
 *   
 *    Redistributions are made at no charge beyond the reasonable cost of
 *    materials and delivery.
 *
 *    Redistributions are accompanied by a copy of the Source Code or by an
 *    irrevocable offer to provide a copy of the Source Code for up to three
 *    years at the cost of materials and delivery.  Such redistributions
 *    must allow further use, modification, and redistribution of the Source
 *    Code under substantially the same terms as this license.
 *
 * Redistributions of source code must retain the copyright notices as they
 * appear in each source code file, these license terms, and the
 * disclaimer/limitation of liability set forth as paragraph 6 below.
 *
 * Redistributions in binary form must reproduce this Copyright Notice,
 * these license terms, and the disclaimer/limitation of liability set
 * forth as paragraph 6 below, in the documentation and/or other materials
 * provided with the distribution.
 *
 * The Software is provided on an "AS IS" basis.  No warranty is
 * provided that the Software is free of defects, or fit for a
 * particular purpose.  
 *
 * Limitation of Liability. Quadcap Software shall not be liable
 * for any damages suffered by the Licensee or any third party resulting
 * from use of the Software.
 */

/**
 * This interface models a page of data in a block file, either a main page
 * (aka a Block) or a sub-page.
 *
 * @author Stan Bailes
 */
public interface Page {
    /**
     * Return this page's block number
     */
    public long getPageNum();

    /**
     * An artifact of the Cacheable interface implemented by the Block
     * class, we need to keep track of which objects are actually being
     * used so unused objects can be flushed from the cache to make room
     * for new objects.  At some point, we can get rid of this in favor
     * of weak references.
     */
    public void decrRefCount();

    /**
     * Read a range of bytes from the page.
     *
     * @param pos the offset in the page of the first byte to read
     * @param pbuf the buffer into which the bytes are placed.
     * @param offset the offset in <code>pbuf</code> where the first byte
     *                  is placed.
     * @param len the number of bytes to read
     */
    public int read(int pos, byte[] pbuf, int offset, int len);

    /**
     * Write a range of bytes to the page.
     *
     * @param pos the offset in the page of the first byte to write
     * @param pbuf the buffer from which the bytes are obtained
     * @param offset the offset in <code>pbuf</code> of the first byte
     *                  to write
     * @param len the number of bytes to write
     */
    public int write(int pos, byte[] pbuf, int offset, int len);

    /**
     * Read an integer (4-byte) value from the page.
     *
     * @param pos the offset in the page of the integer.
     */
    public int readInt(int pos);

    /**
     * Write an integer (4-byte) value to the page.
     *
     * @param pos the offset in the page of the integer.
     * @param val the integer value to write.
     */
    public void writeInt(int pos, int val);

    /**
     * Read an long (8-byte) value from the page.
     *
     * @param pos the offset in the page of the long.
     */
    public long readLong(int pos);

    /**
     * Write an long (8-byte) value to the page.
     *
     * @param pos the offset in the page of the long.
     * @param val the long value to write.
     */
    public void writeLong(int pos, long val);

    /**
     * Move the contents of the other page to this page, and zero out
     * the other page.
     */
    public void takeData(Page p);

    /**
     * Zero this page
     */
    public void clear();
    
}