ExportTable


1   package hudson.remoting;
2   
3   import java.util.HashMap  ;
4   import java.util.Map  ;
5   
6   /**
7    * Manages unique ID for exported objects, and allows look-up from IDs.
8    *
9    * @author Kohsuke Kawaguchi
10   */
11  final class ExportTable<T> {
12      private final Map  <Integer  ,T> table = new HashMap  <Integer  ,T>();
13      private final Map  <T,Integer  > reverse = new HashMap  <T,Integer  >();
14  
15      /**
16       * Unique ID generator.
17       */
18      private int iota = 1;
19  
20      /**
21       * Exports the given object.
22       *
23       * <p>
24       * Until the object is {@link #unexport(Object) unexported}, it will
25       * not be subject to GC.
26       *
27       * @return
28       *      The assigned 'object ID'. If the object is already exported,
29       *      it will return the ID already assigned to it.
30       */
31      // TODO: the 'intern' semantics requires reference counting for proper unexport op.
32      public synchronized int export(T t) {
33          if(t==null)    return 0;   // bootstrap classloader
34  
35          Integer   id = reverse.get(t);
36          if(id==null) {
37              id = iota++;
38              table.put(id,t);
39              reverse.put(t,id);
40          }
41  
42          return id;
43      }
44  
45      public synchronized T get(int id) {
46          return table.get(id);
47      }
48  
49      /**
50       * Removes the exported object from the table.
51       */
52      public synchronized void unexport(T t) {
53          if(t==null)     return;
54          Integer   id = reverse.remove(t);
55          if(id==null)    return; // presumably already unexported
56          table.remove(id);
57      }
58  }
59
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