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Original JDBM Implementation
There is a newer version: 2.0.0-M3
/**
 * JDBM LICENSE v1.00
 *
 * Redistribution and use of this software and associated documentation
 * ("Software"), with or without modification, are permitted provided
 * that the following conditions are met:
 *
 * 1. Redistributions of source code must retain copyright
 *    statements and notices.  Redistributions must also contain a
 *    copy of this document.
 *
 * 2. Redistributions in binary form must reproduce the
 *    above copyright notice, this list of conditions and the
 *    following disclaimer in the documentation and/or other
 *    materials provided with the distribution.
 *
 * 3. The name "JDBM" must not be used to endorse or promote
 *    products derived from this Software without prior written
 *    permission of Cees de Groot.  For written permission,
 *    please contact [email protected].
 *
 * 4. Products derived from this Software may not be called "JDBM"
 *    nor may "JDBM" appear in their names without prior written
 *    permission of Cees de Groot.
 *
 * 5. Due credit should be given to the JDBM Project
 *    (http://jdbm.sourceforge.net/).
 *
 * THIS SOFTWARE IS PROVIDED BY THE JDBM PROJECT AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
 * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
 * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL
 * CEES DE GROOT OR ANY CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * Copyright 2000 (C) Cees de Groot. All Rights Reserved.
 * Contributions are Copyright (C) 2000 by their associated contributors.
 *
 * $Id: FreePhysicalRowIdPageManager.java,v 1.2 2001/11/17 16:14:25 boisvert Exp $
 */
package jdbm.recman;


import java.io.IOException;


/**
 * This class manages free physical rowid pages and provides methods to free 
 * and allocate physical rowids at a high level.
 */
final class FreePhysicalRowIdPageManager
{
    // our record recordFile
    protected RecordFile recordFile;

    // our page manager
    protected PageManager pageManager;

    
    /**
     * Creates a new instance using the indicated record recordFile and page manager.
     */
    FreePhysicalRowIdPageManager( PageManager pageManager ) throws IOException
    {
        this.recordFile = pageManager.getRecordFile();
        this.pageManager = pageManager;
    }


    /**
     * Returns a free physical rowid of the indicated size, or null if nothing 
     * was found.
     */
    Location get( int size ) throws IOException
    {
        // Loop through the free physical rowid list until we find a rowid 
        // that's large enough.
        Location retval = null;
        PageCursor curs = new PageCursor( pageManager, Magic.FREEPHYSIDS_PAGE );

        while ( curs.next() != 0 ) 
        {
            FreePhysicalRowIdPage fp = FreePhysicalRowIdPage
                .getFreePhysicalRowIdPageView( recordFile.get( curs.getCurrent() ) );
            int slot = fp.getFirstLargerThan( size );
            
            if ( slot != -1 ) 
            {
                // got one!
                retval = new Location( fp.get( slot ) );

                fp.free( slot );
                if ( fp.getCount() == 0 ) 
                {
                    // page became empty - free it
                    recordFile.release( curs.getCurrent(), false );
                    pageManager.free( Magic.FREEPHYSIDS_PAGE, curs.getCurrent() );
                } 
                else 
                {
                    recordFile.release( curs.getCurrent(), true );
                }

                return retval;
            } 
            else 
            {
                // no luck, go to next page
                recordFile.release( curs.getCurrent(), false );
            }
        }
        return null;
    }
    

    /**
     * Puts the indicated rowid on the free list.
     */
    void put( Location rowid, int size ) throws IOException 
    {
        FreePhysicalRowId free = null;
        PageCursor curs = new PageCursor( pageManager, Magic.FREEPHYSIDS_PAGE );
        long freePage = 0;
        
        while ( curs.next() != 0 ) 
        {
            freePage = curs.getCurrent();
            BlockIo curBlock = recordFile.get( freePage );
            FreePhysicalRowIdPage fp = FreePhysicalRowIdPage.getFreePhysicalRowIdPageView( curBlock );
            int slot = fp.getFirstFree();
      
            if ( slot != -1 ) 
            {
                free = fp.alloc( slot );
                break;
            }

            recordFile.release( curBlock );
        }
  
        if ( free == null ) 
        {
            // No more space on the free list, add a page.
            freePage = pageManager.allocate( Magic.FREEPHYSIDS_PAGE );
            BlockIo curBlock = recordFile.get( freePage );
            FreePhysicalRowIdPage fp = FreePhysicalRowIdPage.getFreePhysicalRowIdPageView( curBlock );
            free = fp.alloc( 0 );
        }

        free.setBlock( rowid.getBlock() );
        free.setOffset( rowid.getOffset() );
        free.setSize( size );
        recordFile.release( freePage, true );
    }
}