001: /**
002: * JDBM LICENSE v1.00
003: *
004: * Redistribution and use of this software and associated documentation
005: * ("Software"), with or without modification, are permitted provided
006: * that the following conditions are met:
007: *
008: * 1. Redistributions of source code must retain copyright
009: * statements and notices. Redistributions must also contain a
010: * copy of this document.
011: *
012: * 2. Redistributions in binary form must reproduce the
013: * above copyright notice, this list of conditions and the
014: * following disclaimer in the documentation and/or other
015: * materials provided with the distribution.
016: *
017: * 3. The name "JDBM" must not be used to endorse or promote
018: * products derived from this Software without prior written
019: * permission of Cees de Groot. For written permission,
020: * please contact cg@cdegroot.com.
021: *
022: * 4. Products derived from this Software may not be called "JDBM"
023: * nor may "JDBM" appear in their names without prior written
024: * permission of Cees de Groot.
025: *
026: * 5. Due credit should be given to the JDBM Project
027: * (http://jdbm.sourceforge.net/).
028: *
029: * THIS SOFTWARE IS PROVIDED BY THE JDBM PROJECT AND CONTRIBUTORS
030: * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
031: * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
032: * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
033: * CEES DE GROOT OR ANY CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
034: * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
035: * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
036: * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
037: * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
038: * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
039: * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
040: * OF THE POSSIBILITY OF SUCH DAMAGE.
041: *
042: * Copyright 2000 (C) Cees de Groot. All Rights Reserved.
043: * Contributions are Copyright (C) 2000 by their associated contributors.
044: *
045: * $Id: FreePhysicalRowIdPage.java,v 1.1 2000/05/06 00:00:31 boisvert Exp $
046: */package jdbm.recman;
047:
048: /**
049: * Class describing a page that holds physical rowids that were freed.
050: */
051: final class FreePhysicalRowIdPage extends PageHeader {
052: // offsets
053: private static final short O_COUNT = PageHeader.SIZE; // short count
054: static final short O_FREE = O_COUNT + Magic.SZ_SHORT;
055: static final short ELEMS_PER_PAGE = (RecordFile.BLOCK_SIZE - O_FREE)
056: / FreePhysicalRowId.SIZE;
057:
058: // slots we returned.
059: FreePhysicalRowId[] slots = new FreePhysicalRowId[ELEMS_PER_PAGE];
060:
061: /**
062: * Constructs a data page view from the indicated block.
063: */
064: FreePhysicalRowIdPage(BlockIo block) {
065: super (block);
066: }
067:
068: /**
069: * Factory method to create or return a data page for the
070: * indicated block.
071: */
072: static FreePhysicalRowIdPage getFreePhysicalRowIdPageView(
073: BlockIo block) {
074: BlockView view = block.getView();
075: if (view != null && view instanceof FreePhysicalRowIdPage)
076: return (FreePhysicalRowIdPage) view;
077: else
078: return new FreePhysicalRowIdPage(block);
079: }
080:
081: /** Returns the number of free rowids */
082: short getCount() {
083: return block.readShort(O_COUNT);
084: }
085:
086: /** Sets the number of free rowids */
087: private void setCount(short i) {
088: block.writeShort(O_COUNT, i);
089: }
090:
091: /** Frees a slot */
092: void free(int slot) {
093: get(slot).setSize(0);
094: setCount((short) (getCount() - 1));
095: }
096:
097: /** Allocates a slot */
098: FreePhysicalRowId alloc(int slot) {
099: setCount((short) (getCount() + 1));
100: return get(slot);
101: }
102:
103: /** Returns true if a slot is allocated */
104: boolean isAllocated(int slot) {
105: return get(slot).getSize() != 0;
106: }
107:
108: /** Returns true if a slot is free */
109: boolean isFree(int slot) {
110: return !isAllocated(slot);
111: }
112:
113: /** Returns the value of the indicated slot */
114: FreePhysicalRowId get(int slot) {
115: if (slots[slot] == null)
116: slots[slot] = new FreePhysicalRowId(block,
117: slotToOffset(slot));
118: ;
119: return slots[slot];
120: }
121:
122: /** Converts slot to offset */
123: short slotToOffset(int slot) {
124: return (short) (O_FREE + (slot * FreePhysicalRowId.SIZE));
125: }
126:
127: /**
128: * Returns first free slot, -1 if no slots are available
129: */
130: int getFirstFree() {
131: for (int i = 0; i < ELEMS_PER_PAGE; i++) {
132: if (isFree(i))
133: return i;
134: }
135: return -1;
136: }
137:
138: /**
139: * Returns first slot with available size >= indicated size,
140: * or -1 if no slots are available.
141: **/
142: int getFirstLargerThan(int size) {
143: for (int i = 0; i < ELEMS_PER_PAGE; i++) {
144: if (isAllocated(i) && get(i).getSize() >= size)
145: return i;
146: }
147: return -1;
148: }
149: }
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