/*
* 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 org.h2.message.DbException;
/**
* The base object for all cached objects.
*/
public abstract class CacheObject implements Comparable<CacheObject> {
/**
* The previous element in the LRU linked list. If the previous element is
* the head, then this element is the most recently used object.
*/
public CacheObject cachePrevious;
/**
* The next element in the LRU linked list. If the next element is the head,
* then this element is the least recently used object.
*/
public CacheObject cacheNext;
/**
* The next element in the hash chain.
*/
public CacheObject cacheChained;
private int pos;
private boolean changed;
/**
* Check if the object can be removed from the cache.
* For example pinned objects can not be removed.
*
* @return true if it can be removed
*/
public abstract boolean canRemove();
/**
* Get the estimated used memory.
*
* @return number of words (one word is 4 bytes)
*/
public abstract int getMemory();
public void setPos(int pos) {
if (cachePrevious != null || cacheNext != null || cacheChained != null) {
throw DbException.getInternalError("setPos too late");
}
this.pos = pos;
}
public int getPos() {
return pos;
}
/**
* Check if this cache object has been changed and thus needs to be written
* back to the storage.
*
* @return if it has been changed
*/
public boolean isChanged() {
return changed;
}
public void setChanged(boolean b) {
changed = b;
}
@Override
public int compareTo(CacheObject other) {
return Integer.compare(getPos(), other.getPos());
}
public boolean isStream() {
return false;
}
}