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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: FreePhysicalRowIdPage.java,v 1.1 2000/05/06 00:00:31 boisvert Exp $
46   */
47  
48  package jdbm.recman;
49  
50  /**
51   *  Class describing a page that holds physical rowids that were freed.
52   */
53  final class FreePhysicalRowIdPage extends PageHeader {
54      // offsets
55      private static final short O_COUNT = PageHeader.SIZE; // short count
56      static final short O_FREE = O_COUNT + Magic.SZ_SHORT;
57      static final short ELEMS_PER_PAGE = 
58    (RecordFile.BLOCK_SIZE - O_FREE) / FreePhysicalRowId.SIZE;
59      
60      // slots we returned.
61      FreePhysicalRowId[] slots = new FreePhysicalRowId[ELEMS_PER_PAGE];
62  
63      /**
64       *  Constructs a data page view from the indicated block.
65       */
66      FreePhysicalRowIdPage(BlockIo block) {
67    super(block);
68      }
69  
70      /**
71       *  Factory method to create or return a data page for the
72       *  indicated block.
73       */
74      static FreePhysicalRowIdPage getFreePhysicalRowIdPageView(BlockIo block) {
75    BlockView view = block.getView();
76    if (view != null && view instanceof FreePhysicalRowIdPage)
77        return (FreePhysicalRowIdPage) view;
78    else
79        return new FreePhysicalRowIdPage(block);
80      }
81  
82      /** Returns the number of free rowids */
83      short getCount() {
84    return block.readShort(O_COUNT);
85      }
86  
87      /** Sets the number of free rowids */
88      private void setCount(short i) {
89    block.writeShort(O_COUNT, i);
90      }
91  
92      /** Frees a slot */
93      void free(int slot) {
94    get(slot).setSize(0);
95    setCount((short) (getCount() - 1));
96      }
97  
98      /** Allocates a slot */
99      FreePhysicalRowId alloc(int slot) {
100   setCount((short) (getCount() + 1));
101   return get(slot);
102     }
103 
104     /** Returns true if a slot is allocated */
105     boolean isAllocated(int slot) {
106   return get(slot).getSize() != 0;
107     }
108 
109     /** Returns true if a slot is free */
110     boolean isFree(int slot) {
111   return !isAllocated(slot);
112     }
113     
114     
115     /** Returns the value of the indicated slot */
116     FreePhysicalRowId get(int slot) {
117   if (slots[slot] == null) 
118       slots[slot] = new FreePhysicalRowId(block, slotToOffset(slot));;
119   return slots[slot];
120     }
121 
122     /** Converts slot to offset */
123     short slotToOffset(int slot) {
124   return (short) (O_FREE +
125       (slot * FreePhysicalRowId.SIZE));
126     }
127     
128     /** 
129      *  Returns first free slot, -1 if no slots are available
130      */
131     int getFirstFree() {
132   for (int i = 0; i < ELEMS_PER_PAGE; i++) {
133       if (isFree(i))
134     return i;
135   }
136   return -1;
137     }
138 
139     /** 
140      *  Returns first slot with available size >= indicated size,  
141      *  or -1 if no slots are available.
142      **/
143     int getFirstLargerThan(int size) {
144   for (int i = 0; i < ELEMS_PER_PAGE; i++) {
145       if (isAllocated(i) && get(i).getSize() >= size)
146     return i;
147   }
148   return -1;
149     }
150 }