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 }