/*
* Copyright 2004-2023 H2 Group. Multiple-Licensed under the MPL 2.0,
* and the EPL 1.0 (https://h2database.com/html/license.html).
* Initial Developer: H2 Group
*/
package org.h2.util;
import java.util.HashMap;
import java.util.Iterator;
import org.h2.api.ErrorCode;
import org.h2.message.DbException;
/**
* A simple hash table with an optimization for the last recently used object.
*/
public class SmallMap {
private final HashMap<Integer, Object> map = new HashMap<>();
private Object cache;
private int cacheId;
private int lastId;
private final int maxElements;
/**
* Create a map with the given maximum number of entries.
*
* @param maxElements the maximum number of entries
*/
public SmallMap(int maxElements) {
this.maxElements = maxElements;
}
/**
* Add an object to the map. If the size of the map is larger than twice the
* maximum size, objects with a low id are removed.
*
* @param id the object id
* @param o the object
* @return the id
*/
public int addObject(int id, Object o) {
if (map.size() > maxElements * 2) {
Iterator<Integer> it = map.keySet().iterator();
while (it.hasNext()) {
Integer k = it.next();
if (k + maxElements < lastId) {
it.remove();
}
}
}
if (id > lastId) {
lastId = id;
}
map.put(id, o);
cacheId = id;
cache = o;
return id;
}
/**
* Remove an object from the map.
*
* @param id the id of the object to remove
*/
public void freeObject(int id) {
if (cacheId == id) {
cacheId = -1;
cache = null;
}
map.remove(id);
}
/**
* Get an object from the map if it is stored.
*
* @param id the id of the object
* @param ifAvailable only return it if available, otherwise return null
* @return the object or null
* @throws DbException if isAvailable is false and the object has not been
* found
*/
public Object getObject(int id, boolean ifAvailable) {
if (id == cacheId) {
return cache;
}
Object obj = map.get(id);
if (obj == null && !ifAvailable) {
throw DbException.get(ErrorCode.OBJECT_CLOSED);
}
return obj;
}
}