Source Code Cross Referenced for LRUCache.java in  » Scripting » Pnuts » org » pnuts » util » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Scripting » Pnuts » org.pnuts.util 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /*
002:         * LRUCache.java
003:         *
004:         * Copyright (c) 1997-2005 Sun Microsystems, Inc. All Rights Reserved.
005:         *
006:         * See the file "LICENSE.txt" for information on usage and redistribution
007:         * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
008:         */
009:        package org.pnuts.util;
010:
011:        import java.util.*;
012:
013:        /**
014:         * An implementation of LRU cache
015:         */
016:        public class LRUCache implements  Cache {
017:
018:            private Cell[] cells;
019:
020:            private int size;
021:
022:            private Cell head;
023:
024:            private Cell tail;
025:
026:            private int count = 0;
027:
028:            static class Cell implements  Map.Entry {
029:                Cell next;
030:                Cell prev;
031:                Cell chain;
032:                Object key;
033:                Object value;
034:                int index;
035:
036:                Cell(int index, Cell prev, Cell chain, Object key, Object value) {
037:                    this .index = index;
038:                    this .prev = prev;
039:                    this .chain = chain;
040:                    this .key = key;
041:                    this .value = value;
042:                }
043:
044:                public Object getKey() {
045:                    return key;
046:                }
047:
048:                public Object getValue() {
049:                    return value;
050:                }
051:
052:                public Object setValue(Object value) {
053:                    Object old = this .value;
054:                    this .value = value;
055:                    return old;
056:                }
057:
058:                public int hashCode() {
059:                    return key.hashCode() + value.hashCode();
060:                }
061:
062:                public boolean equals(Object obj) {
063:                    if (obj instanceof  Cell) {
064:                        Cell c = (Cell) obj;
065:                        return (key == null && c.key == null || key
066:                                .equals(c.key))
067:                                && (value == null && c.value == null || value
068:                                        .equals(c.value));
069:                    } else {
070:                        return false;
071:                    }
072:                }
073:
074:                public String toString() {
075:                    return key + "=" + value;
076:                }
077:            }
078:
079:            protected LRUCache() {
080:            }
081:
082:            /**
083:             * @param size
084:             *            cache size
085:             */
086:            public LRUCache(int size) {
087:                cells = new Cell[size];
088:                this .size = size;
089:            }
090:
091:            void update(Cell b) {
092:                if (b != tail) {
093:                    if (b.prev != null) {
094:                        b.prev.next = b.next;
095:                    }
096:                    if (b.next != null) {
097:                        b.next.prev = b.prev;
098:                    }
099:                    tail.next = b;
100:                    b.prev = tail;
101:                    tail = b;
102:                }
103:                if (b == head) {
104:                    head = b.next;
105:                }
106:                b.next = null;
107:            }
108:
109:            private Cell findCell(Object key) {
110:                int index = (key.hashCode() & 0x7FFFFFFF) % size;
111:                Cell b = cells[index];
112:                while (b != null) {
113:                    if (b.key.equals(key)) {
114:                        update(b);
115:                        return b;
116:                    }
117:                    b = b.chain;
118:                }
119:                return null;
120:            }
121:
122:            /**
123:             * If key is in the cache it returns value, otherwise null.
124:             */
125:            public Object get(Object key) {
126:                Cell cell = findCell(key);
127:                if (cell != null) {
128:                    return cell.value;
129:                } else {
130:                    return null;
131:                }
132:            }
133:
134:            /**
135:             * Register key and its value into the cache.
136:             */
137:            public Object put(Object key, Object value) {
138:                int index = (key.hashCode() & 0x7FFFFFFF) % size;
139:
140:                Cell b = cells[index];
141:                Cell n = null;
142:                Object old = null;
143:                while (b != null) {
144:                    if (b.key.equals(key)) {
145:                        old = b.value;
146:                        b.value = value;
147:                        update(b);
148:                        return old;
149:                    }
150:                    b = b.chain;
151:                }
152:                if (head != null) {
153:                    if (count >= size) {
154:                        Cell second = head.next;
155:                        n = head;
156:                        expired(n.value);
157:                        n.prev = tail;
158:                        tail.next = n;
159:                        n.next = null;
160:                        n.key = key;
161:                        n.value = value;
162:                        if (n.index == index) {
163:                            if (n != cells[index]) {
164:                                for (Cell x = cells[index];; x = x.chain) {
165:                                    if (x.chain == null) {
166:                                        throw new RuntimeException(
167:                                                "[BUG] Reused cell must be found in the chain of index="
168:                                                        + index);
169:                                    } else if (x.chain == n) {
170:                                        x.chain = n.chain;
171:                                        break;
172:                                    }
173:                                }
174:                                n.chain = cells[index];
175:                                cells[index] = n;
176:                            }
177:                        } else {
178:                            Cell t = cells[n.index];
179:                            if (t == n) {
180:                                cells[n.index] = n.chain;
181:                            } else {
182:                                while (t != null && t.chain != null) {
183:                                    if (t.chain == n) {
184:                                        t.chain = n.chain;
185:                                        break;
186:                                    }
187:                                    t = t.chain;
188:                                }
189:                            }
190:                            n.chain = cells[index];
191:                            cells[index] = n;
192:                        }
193:                        n.index = index;
194:                        head = second;
195:                        if (head == null) {
196:                            head = n;
197:                        }
198:                        tail = n;
199:                    } else {
200:                        count++;
201:                        n = new Cell(index, tail, cells[index], key, value);
202:                        cells[index] = n;
203:                        tail.next = n;
204:                        tail = n;
205:                    }
206:                } else {
207:                    count++;
208:                    n = new Cell(index, null, cells[index], key, value);
209:                    n.prev = n;
210:                    n.next = n;
211:                    cells[index] = n;
212:                    head = n;
213:                    tail = n;
214:                }
215:                return old;
216:            }
217:
218:            /**
219:             * Called when an object is expired from the cache
220:             *
221:             * @param old an expired object
222:             */
223:            public void expired(Object old) {
224:                // skip
225:            }
226:
227:            /**
228:             * Initializes the cache
229:             */
230:            public void reset() {
231:                head = tail = null;
232:                cells = new Cell[size];
233:                count = 0;
234:            }
235:
236:            /**
237:             * Returns the number of items in the cache
238:             */
239:            public int size() {
240:                return count;
241:            }
242:
243:            public Set keySet() {
244:                Set keys = new HashSet();
245:                for (Iterator it = new Itr(0); it.hasNext();) {
246:                    keys.add(it.next());
247:                }
248:                return keys;
249:            }
250:
251:            public Set entrySet() {
252:                Set entries = new HashSet();
253:                for (Iterator it = new Itr(2); it.hasNext();) {
254:                    entries.add(it.next());
255:                }
256:                return entries;
257:            }
258:
259:            public Collection values() {
260:                ArrayList v = new ArrayList();
261:                for (Iterator it = new Itr(1); it.hasNext();) {
262:                    v.add(it.next());
263:                }
264:                return v;
265:            }
266:
267:            class Itr implements  Iterator {
268:                Cell ref = head;
269:                int kind;
270:
271:                Itr(int kind) {
272:                    this .kind = kind;
273:                }
274:
275:                public boolean hasNext() {
276:                    return ref != null;
277:                }
278:
279:                public Object next() {
280:                    switch (kind) {
281:                    case 0:
282:                        Object key = ref.key;
283:                        ref = ref.next;
284:                        return key;
285:                    case 1:
286:                        Object value = ref.value;
287:                        ref = ref.next;
288:                        return value;
289:                    case 2:
290:                        Object entry = ref;
291:                        ref = ref.next;
292:                        return entry;
293:                    default:
294:                        throw new RuntimeException();
295:                    }
296:                }
297:
298:                public void remove() {
299:                    throw new UnsupportedOperationException();
300:                }
301:            }
302:        }
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