File D:\maven-qcr-plugin-testsunitaires\qcr4java\jenkins-master\target\site\qc\core\src\main\java\hudson\util\Memoizer.java.html

1 /*
2 * The MIT License
3 *
4 * Copyright (c) 2004-2009, Sun Microsystems, Inc.
5 *
6 * Permission is hereby granted, free of charge, to any person obtaining a copy
7 * of this software and associated documentation files (the "Software"), to deal
8 * in the Software without restriction, including without limitation the rights
9 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
10 * copies of the Software, and to permit persons to whom the Software is
11 * furnished to do so, subject to the following conditions:
12 *
13 * The above copyright notice and this permission notice shall be included in
14 * all copies or substantial portions of the Software.
15 *
16 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
17 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
19 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
20 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
21 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
22 * THE SOFTWARE.
23 */
24 package hudson.util;
25
26 import java.util.concurrent.ConcurrentHashMap;
27
28 /**
29 * Implements memoization semantics.
30 *
31 * <p>
32 * Conceptually a function from K -> V that computes values lazily and remembers the results.
33 * Often used to implement a data store per key.
34 *
35 * @author Kohsuke Kawaguchi
36 * @since 1.281
37 */
38 public abstract class Memoizer<K,V> {
39 private final ConcurrentHashMap<K,V> store = new ConcurrentHashMap<K,V>();
40
41 public V get(K key) {
42 V v = store.get(key);
43 if(v!=null) return v;
44
45 // TODO: if we want to, we can avoid locking altogether by putting a sentinel value
46 // that represents "the value is being computed". FingerprintMap does this.
47 synchronized (this) {
48 v = store.get(key);
49 if(v!=null) return v;
50
51 v = compute(key);
52 store.put(key,v);
53 return v;
54 }
55 }
56
57 /**
58 * Creates a new instance.
59 */
60 public abstract V compute(K key);
61
62 /**
63 * Clears all the computed values.
64 */
65 public void clear() {
66 store.clear();
67 }
68
69 /**
70 * Provides a snapshot view of all {@code V}s.
71 */
72 public Iterable<V> values() {
73 return store.values();
74 }
75 }
76