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/* -*- Mode: Java; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/*
* This file is part of the LibreOffice project.
*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*
* This file incorporates work covered by the following license notice:
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed
* with this work for additional information regarding copyright
* ownership. The ASF licenses this file to you under the Apache
* License, Version 2.0 (the "License"); you may not use this file
* except in compliance with the License. You may obtain a copy of
* the License at http://www.apache.org/licenses/LICENSE-2.0 .
*/
package com.sun.star.lib.uno.protocols.urp;
import java.util.HashMap;
/**
* An LRU cache for arbitrary objects.
*
* <p>This class is not synchronized, as any necessary synchronization will already
* take place in the client.</p>
*/
final class Cache {
/**
* Create a cache.
*
* @param size the maximum cache size, must be between 0, inclusive, and
* NOT_CACHED, exclusive.
*/
public Cache(int size) {
maxSize = size;
}
public int add(boolean[] found, Object content) {
Entry e = map.get(content);
found[0] = e != null;
if (e == null) {
if (map.size() < maxSize) {
// There is still room for a new entry at the front:
e = new Entry(content, map.size(), null, first);
if (first == null) {
last = e;
} else {
first.prev = e;
}
first = e;
} else if (last != null) {
// Take last entry out and recycle as new front:
map.remove(last.content);
e = last;
e.content = content;
if (first != last) {
// Reached only if maxSize > 1:
last = last.prev;
last.next = null;
e.prev = null;
e.next = first;
first.prev = e;
first = e;
}
} else {
// Reached iff maxSize == 0:
return NOT_CACHED;
}
map.put(content, e);
} else if (e != first) {
// Move to front (reached only if maxSize > 1):
e.prev.next = e.next;
if (e.next == null) {
last = e.prev;
} else {
e.next.prev = e.prev;
}
e.prev = null;
e.next = first;
first.prev = e;
first = e;
}
return e.index;
}
public static final int NOT_CACHED = 0xFFFF;
private static final class Entry {
public Entry(Object content, int index, Entry prev, Entry next) {
this.content = content;
this.index = index;
this.prev = prev;
this.next = next;
}
public Object content;
public int index;
public Entry prev;
public Entry next;
}
// first/last form a list of 0 to maxSize entries, most recently used first;
// map contains the same entries; each entry has a unique index in the range
// 0 to maxSize - 1
private final int maxSize;
private final HashMap<Object, Entry> map = new HashMap<Object, Entry>(); // from Object to Entry
private Entry first = null;
private Entry last = null;
}
/* vim:set shiftwidth=4 softtabstop=4 expandtab: */
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