| /** |
| * JDBM LICENSE v1.00 |
| * |
| * Redistribution and use of this software and associated documentation |
| * ("Software"), with or without modification, are permitted provided |
| * that the following conditions are met: |
| * |
| * 1. Redistributions of source code must retain copyright |
| * statements and notices. Redistributions must also contain a |
| * copy of this document. |
| * |
| * 2. Redistributions in binary form must reproduce the |
| * above copyright notice, this list of conditions and the |
| * following disclaimer in the documentation and/or other |
| * materials provided with the distribution. |
| * |
| * 3. The name "JDBM" must not be used to endorse or promote |
| * products derived from this Software without prior written |
| * permission of Cees de Groot. For written permission, |
| * please contact cg@cdegroot.com. |
| * |
| * 4. Products derived from this Software may not be called "JDBM" |
| * nor may "JDBM" appear in their names without prior written |
| * permission of Cees de Groot. |
| * |
| * 5. Due credit should be given to the JDBM Project |
| * (http://jdbm.sourceforge.net/). |
| * |
| * THIS SOFTWARE IS PROVIDED BY THE JDBM PROJECT AND CONTRIBUTORS |
| * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT |
| * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND |
| * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL |
| * CEES DE GROOT OR ANY CONTRIBUTORS BE LIABLE FOR ANY DIRECT, |
| * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES |
| * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR |
| * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) |
| * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, |
| * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) |
| * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED |
| * OF THE POSSIBILITY OF SUCH DAMAGE. |
| * |
| * Copyright 2000 (C) Cees de Groot. All Rights Reserved. |
| * Contributions are Copyright (C) 2000 by their associated contributors. |
| * |
| * $Id: FreeLogicalRowIdPage.java,v 1.1 2000/05/06 00:00:31 boisvert Exp $ |
| */ |
| |
| package jdbm.recman; |
| |
| /** |
| * Class describing a page that holds logical rowids that were freed. Note |
| * that the methods have *physical* rowids in their signatures - this is |
| * because logical and physical rowids are internally the same, only their |
| * external representation (i.e. in the client API) differs. |
| */ |
| class FreeLogicalRowIdPage extends PageHeader { |
| // offsets |
| private static final short O_COUNT = PageHeader.SIZE; // short count |
| static final short O_FREE = (short)(O_COUNT + Magic.SZ_SHORT); |
| static final short ELEMS_PER_PAGE = (short) |
| ((RecordFile.BLOCK_SIZE - O_FREE) / PhysicalRowId.SIZE); |
| |
| // slots we returned. |
| final PhysicalRowId[] slots = new PhysicalRowId[ELEMS_PER_PAGE]; |
| |
| /** |
| * Constructs a data page view from the indicated block. |
| */ |
| FreeLogicalRowIdPage(BlockIo block) { |
| super(block); |
| } |
| |
| /** |
| * Factory method to create or return a data page for the |
| * indicated block. |
| */ |
| static FreeLogicalRowIdPage getFreeLogicalRowIdPageView(BlockIo block) { |
| |
| BlockView view = block.getView(); |
| if (view != null && view instanceof FreeLogicalRowIdPage) |
| return (FreeLogicalRowIdPage) view; |
| else |
| return new FreeLogicalRowIdPage(block); |
| } |
| |
| /** Returns the number of free rowids */ |
| short getCount() { |
| return block.readShort(O_COUNT); |
| } |
| |
| /** Sets the number of free rowids */ |
| private void setCount(short i) { |
| block.writeShort(O_COUNT, i); |
| } |
| |
| /** Frees a slot */ |
| void free(int slot) { |
| get(slot).setBlock(0); |
| setCount((short) (getCount() - 1)); |
| } |
| |
| /** Allocates a slot */ |
| PhysicalRowId alloc(int slot) { |
| setCount((short) (getCount() + 1)); |
| get(slot).setBlock(-1); |
| return get(slot); |
| } |
| |
| /** Returns true if a slot is allocated */ |
| boolean isAllocated(int slot) { |
| return get(slot).getBlock() > 0; |
| } |
| |
| /** Returns true if a slot is free */ |
| boolean isFree(int slot) { |
| return !isAllocated(slot); |
| } |
| |
| |
| /** Returns the value of the indicated slot */ |
| PhysicalRowId get(int slot) { |
| if (slots[slot] == null) |
| slots[slot] = new PhysicalRowId(block, slotToOffset(slot));; |
| return slots[slot]; |
| } |
| |
| /** Converts slot to offset */ |
| private short slotToOffset(int slot) { |
| return (short) (O_FREE + |
| (slot * PhysicalRowId.SIZE)); |
| } |
| |
| /** |
| * Returns first free slot, -1 if no slots are available |
| */ |
| int getFirstFree() { |
| for (int i = 0; i < ELEMS_PER_PAGE; i++) { |
| if (isFree(i)) |
| return i; |
| } |
| return -1; |
| } |
| |
| /** |
| * Returns first allocated slot, -1 if no slots are available. |
| */ |
| int getFirstAllocated() { |
| for (int i = 0; i < ELEMS_PER_PAGE; i++) { |
| if (isAllocated(i)) |
| return i; |
| } |
| return -1; |
| } |
| } |