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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: FreeLogicalRowIdPage.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 logical rowids that were freed. Note
52   *  that the methods have *physical* rowids in their signatures - this is
53   *  because logical and physical rowids are internally the same, only their
54   *  external representation (i.e. in the client API) differs.
55   */
56  class FreeLogicalRowIdPage extends PageHeader {
57      // offsets
58      private static final short O_COUNT = PageHeader.SIZE; // short count
59      static final short O_FREE = (short)(O_COUNT + Magic.SZ_SHORT);
60      static final short ELEMS_PER_PAGE = (short)
61          ((RecordFile.BLOCK_SIZE - O_FREE) / PhysicalRowId.SIZE);
62  
63      // slots we returned.
64      final PhysicalRowId[] slots = new PhysicalRowId[ELEMS_PER_PAGE];
65  
66      /**
67       *  Constructs a data page view from the indicated block.
68       */
69      FreeLogicalRowIdPage(BlockIo block) {
70          super(block);
71      }
72  
73      /**
74       *  Factory method to create or return a data page for the
75       *  indicated block.
76       */
77      static FreeLogicalRowIdPage getFreeLogicalRowIdPageView(BlockIo block) {
78  
79          BlockView view = block.getView();
80          if (view != null && view instanceof FreeLogicalRowIdPage)
81              return (FreeLogicalRowIdPage) view;
82          else
83              return new FreeLogicalRowIdPage(block);
84      }
85  
86      /** Returns the number of free rowids */
87      short getCount() {
88          return block.readShort(O_COUNT);
89      }
90  
91      /** Sets the number of free rowids */
92      private void setCount(short i) {
93          block.writeShort(O_COUNT, i);
94      }
95  
96      /** Frees a slot */
97      void free(int slot) {
98          get(slot).setBlock(0);
99          setCount((short) (getCount() - 1));
100     }
101 
102     /** Allocates a slot */
103     PhysicalRowId alloc(int slot) {
104         setCount((short) (getCount() + 1));
105         get(slot).setBlock(-1);
106         return get(slot);
107     }
108 
109     /** Returns true if a slot is allocated */
110     boolean isAllocated(int slot) {
111         return get(slot).getBlock() > 0;
112     }
113 
114     /** Returns true if a slot is free */
115     boolean isFree(int slot) {
116         return !isAllocated(slot);
117     }
118 
119 
120     /** Returns the value of the indicated slot */
121     PhysicalRowId get(int slot) {
122         if (slots[slot] == null)
123             slots[slot] = new PhysicalRowId(block, slotToOffset(slot));;
124         return slots[slot];
125     }
126 
127     /** Converts slot to offset */
128     private short slotToOffset(int slot) {
129         return (short) (O_FREE +
130                         (slot * PhysicalRowId.SIZE));
131     }
132 
133     /**
134      *  Returns first free slot, -1 if no slots are available
135      */
136     int getFirstFree() {
137         for (int i = 0; i < ELEMS_PER_PAGE; i++) {
138             if (isFree(i))
139                 return i;
140         }
141         return -1;
142     }
143 
144     /**
145      *  Returns first allocated slot, -1 if no slots are available.
146      */
147     int getFirstAllocated() {
148         for (int i = 0; i < ELEMS_PER_PAGE; i++) {
149             if (isAllocated(i))
150                 return i;
151         }
152         return -1;
153     }
154 }