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 }