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package de.lmu.ifi.dbs.elki.persistent;
/*
This file is part of ELKI:
Environment for Developing KDD-Applications Supported by Index-Structures
Copyright (C) 2015
Ludwig-Maximilians-Universität München
Lehr- und Forschungseinheit für Datenbanksysteme
ELKI Development Team
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Affero General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU Affero General Public License for more details.
You should have received a copy of the GNU Affero General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
import java.util.Stack;
import de.lmu.ifi.dbs.elki.logging.statistics.LongStatistic;
/**
* Abstract class implementing general methods of a PageFile. A PageFile stores
* objects that implement the <code>Page</code> interface.
*
* @author Elke Achtert
*
* @param <P> Page type
*/
public abstract class AbstractStoringPageFile<P extends Page> extends AbstractPageFile<P> {
/**
* A stack holding the empty page ids.
*/
protected Stack<Integer> emptyPages;
/**
* The last page ID.
*/
protected int nextPageID;
/**
* The size of a page in Bytes.
*/
protected int pageSize;
/**
* Creates a new PageFile.
*/
protected AbstractStoringPageFile(int pageSize) {
this.emptyPages = new Stack<>();
this.nextPageID = 0;
this.pageSize = pageSize;
}
/**
* Sets the id of the given page.
*
* @param page the page to set the id
*/
@Override
public int setPageID(P page) {
int pageID = page.getPageID();
if(pageID == -1) {
pageID = getNextEmptyPageID();
if(pageID == -1) {
pageID = nextPageID++;
}
page.setPageID(pageID);
}
return pageID;
}
/**
* Deletes the node with the specified id from this file.
*
* @param pageID the id of the node to be deleted
*/
@Override
public void deletePage(int pageID) {
// put id to empty nodes
emptyPages.push(pageID);
}
/**
* Returns the next empty page id.
*
* @return the next empty page id
*/
private int getNextEmptyPageID() {
if(!emptyPages.empty()) {
return emptyPages.pop();
}
else {
return -1;
}
}
/**
* Returns the next page id.
*
* @return the next page id
*/
@Override
public int getNextPageID() {
return nextPageID;
}
/**
* Sets the next page id.
*
* @param nextPageID the next page id to be set
*/
@Override
public void setNextPageID(int nextPageID) {
this.nextPageID = nextPageID;
}
/**
* Get the page size of this page file.
*
* @return page size
*/
@Override
public int getPageSize() {
return pageSize;
}
/**
* Initialize the page file with the given header - return "true" if the file
* already existed.
*
* @param header Header
* @return true when the file already existed.
*/
@Override
public boolean initialize(PageHeader header) {
this.pageSize = header.getPageSize();
return false;
}
@Override
public void logStatistics() {
super.logStatistics();
if (getLogger().isStatistics()) {
getLogger().statistics(new LongStatistic(this.getClass().getName() + ".numpages", nextPageID - emptyPages.size()));
}
}
}
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