jurt/com/sun/star/lib/uno/protocols/urp/Cache.java

   1 /* -*- Mode: Java; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
   2 /*
   3  * This file is part of the LibreOffice project.
   4  *
   5  * This Source Code Form is subject to the terms of the Mozilla Public
   6  * License, v. 2.0. If a copy of the MPL was not distributed with this
   7  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
   8  *
   9  * This file incorporates work covered by the following license notice:
  10  *
  11  *   Licensed to the Apache Software Foundation (ASF) under one or more
  12  *   contributor license agreements. See the NOTICE file distributed
  13  *   with this work for additional information regarding copyright
  14  *   ownership. The ASF licenses this file to you under the Apache
  15  *   License, Version 2.0 (the "License"); you may not use this file
  16  *   except in compliance with the License. You may obtain a copy of
  17  *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
  18  */
  19
  20 package com.sun.star.lib.uno.protocols.urp;
  21
  22 import java.util.HashMap;
  23
  24 /**
  25  * An LRU cache for arbitrary objects.
  26  *
  27  * <p>This class is not synchronized, as any necessary synchronization will already
  28  * take place in the client.</p>
  29  */
  30 final class Cache {
  31     /**
  32      * Create a cache.
  33      *
  34      * @param size the maximum cache size, must be between 0, inclusive, and
  35      * NOT_CACHED, exclusive.
  36      */
  37     public Cache(int size) {
  38         maxSize = size;
  39     }
  40
  41     public int add(boolean[] found, Object content) {
  42         Entry e = map.get(content);
  43         found[0] = e != null;
  44         if (e == null) {
  45             if (map.size() < maxSize) {
  46                 // There is still room for a new entry at the front:
  47                 e = new Entry(content, map.size(), null, first);
  48                 if (first == null) {
  49                     last = e;
  50                 } else {
  51                     first.prev = e;
  52                 }
  53                 first = e;
  54             } else if (last != null) {
  55                 // Take last entry out and recycle as new front:
  56                 map.remove(last.content);
  57                 e = last;
  58                 e.content = content;
  59                 if (first != last) {
  60                     // Reached only if maxSize > 1:
  61                     last = last.prev;
  62                     last.next = null;
  63                     e.prev = null;
  64                     e.next = first;
  65                     first.prev = e;
  66                     first = e;
  67                 }
  68             } else {
  69                 // Reached iff maxSize == 0:
  70                 return NOT_CACHED;
  71             }
  72             map.put(content, e);
  73         } else if (e != first) {
  74             // Move to front (reached only if maxSize > 1):
  75             e.prev.next = e.next;
  76             if (e.next == null) {
  77                 last = e.prev;
  78             } else {
  79                 e.next.prev = e.prev;
  80             }
  81             e.prev = null;
  82             e.next = first;
  83             first.prev = e;
  84             first = e;
  85         }
  86         return e.index;
  87     }
  88
  89     public static final int NOT_CACHED = 0xFFFF;
  90
  91     private static final class Entry {
  92         public Entry(Object content, int index, Entry prev, Entry next) {
  93             this.content = content;
  94             this.index = index;
  95             this.prev = prev;
  96             this.next = next;
  97         }
  98
  99         public Object content;
 100         public int index;
 101         public Entry prev;
 102         public Entry next;
 103     }
 104
 105     // first/last form a list of 0 to maxSize entries, most recently used first;
 106     // map contains the same entries; each entry has a unique index in the range
 107     // 0 to maxSize - 1
 108     private final int maxSize;
 109     private final HashMap<Object, Entry> map = new HashMap<Object, Entry>(); // from Object to Entry
 110     private Entry first = null;
 111     private Entry last = null;
 112 }
 113
 114 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */