CopyOnWriteMap


1   package hudson.util;
2   
3   import java.util.Collection  ;
4   import java.util.Collections  ;
5   import java.util.Comparator  ;
6   import java.util.HashMap  ;
7   import java.util.Map  ;
8   import java.util.Set  ;
9   import java.util.TreeMap  ;
10  
11  /**
12   * {@link Map} that has copy-on-write semantics.
13   *
14   * <p>
15   * This class is suitable where highly concurrent access is needed, yet
16   * the write operation is relatively uncommon.
17   *
18   * @author Kohsuke Kawaguchi
19   */
20  public abstract class CopyOnWriteMap<K,V> implements Map  <K,V> {
21      protected volatile Map  <K,V> core;
22      /**
23       * Read-only view of {@link #core}.
24       */
25      private volatile Map  <K,V> view;
26  
27      protected CopyOnWriteMap(Map  <K, V> core) {
28          update(core);
29      }
30  
31      protected CopyOnWriteMap() {
32          update(Collections.<K,V>emptyMap());
33      }
34  
35      private void update(Map  <K, V> m) {
36          core = m;
37          view = Collections.unmodifiableMap(core);
38      }
39  
40      public int size() {
41          return core.size();
42      }
43  
44      public boolean isEmpty() {
45          return core.isEmpty();
46      }
47  
48      public boolean containsKey(Object   key) {
49          return core.containsKey(key);
50      }
51  
52      public boolean containsValue(Object   value) {
53          return core.containsValue(value);
54      }
55  
56      public V get(Object   key) {
57          return core.get(key);
58      }
59  
60      public synchronized V put(K key, V value) {
61          Map  <K,V> m = copy();
62          V r = m.put(key,value);
63          update(m);
64  
65          return r;
66      }
67  
68      public synchronized V remove(Object   key) {
69          Map  <K,V> m = copy();
70          V r = m.remove(key);
71          update(m);
72  
73          return r;
74      }
75  
76      public synchronized void putAll(Map  <? extends K, ? extends V> t) {
77          Map  <K,V> m = copy();
78          m.putAll(t);
79          update(m);
80      }
81  
82      protected abstract Map  <K,V> copy();
83  
84      public synchronized void clear() {
85          update(Collections.<K,V>emptyMap());
86      }
87  
88      /**
89       * This method will return a read-only {@link Set}.
90       */
91      public Set  <K> keySet() {
92          return view.keySet();
93      }
94  
95      /**
96       * This method will return a read-only {@link Collection}.
97       */
98      public Collection  <V> values() {
99          return view.values();
100     }
101 
102     /**
103      * This method will return a read-only {@link Set}.
104      */
105     public Set  <Entry<K,V>> entrySet() {
106         return view.entrySet();
107     }
108 
109     /**
110      * {@link CopyOnWriteMap} backed by {@link HashMap}.
111      */
112     public static final class Hash<K,V> extends CopyOnWriteMap<K,V> {
113         public Hash(Map  <K, V> core) {
114             super(new HashMap  <K,V>(core));
115         }
116 
117         public Hash() {
118         }
119 
120         protected Map  <K,V> copy() {
121             return new HashMap  <K,V>(core);
122         }
123     }
124 
125     /**
126      * {@link CopyOnWriteMap} backed by {@link TreeMap}.
127      */
128     public static final class Tree<K,V> extends CopyOnWriteMap<K,V> {
129         private final Comparator  <K> comparator;
130 
131         public Tree(Map  <K,V> core, Comparator  <K> comparator) {
132             this(comparator);
133             putAll(core);
134         }
135 
136         public Tree(Comparator  <K> comparator) {
137             this.comparator = comparator;
138         }
139 
140         public Tree() {
141             this(null);
142         }
143 
144         protected Map  <K,V> copy() {
145             TreeMap  <K, V> m = new TreeMap  <K, V>(comparator);
146             m.putAll(core);
147             return m;
148         }
149     }
150 }
151
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