ThreadLocal


1   /*
2    * Javolution - Java(TM) Solution for Real-Time and Embedded Systems
3    * Copyright (C) 2005 - Javolution (http://javolution.org/)
4    * All rights reserved.
5    * 
6    * Permission to use, copy, modify, and distribute this software is
7    * freely granted, provided that this notice is preserved.
8    */
9   package j2me.lang;
10  
11  import javolution.util.FastMap;
12  
13  /**
14   * Clean-room implementation of ThreadLocal for J2ME Platform support.
15   */
16  public class ThreadLocal {
17  
18      private static final FastMap THREAD_TO_LOCAL_MAP = new FastMap(256)
19              .setShared(true);
20  
21      public ThreadLocal() {
22      }
23  
24      public Object   get() {
25          FastMap localMap = getLocalMap();
26          Object   value = localMap.get(this);
27          if ((value == null) && !(localMap.containsKey(this))) {
28              value = initialValue();
29              localMap.put(this, value);
30          }
31          return value;
32      }
33  
34      public void set(Object   value) {
35          getLocalMap().put(this, value);
36      }
37  
38      public void remove() {
39          getLocalMap().remove(this);
40      }
41  
42      protected Object   initialValue() {
43          return null;
44      }
45  
46      private FastMap getLocalMap() {
47          FastMap localMap = (FastMap) THREAD_TO_LOCAL_MAP.get(Thread
48                  .currentThread());
49          return (localMap != null) ? localMap : newLocalMap();
50      }
51  
52      private FastMap newLocalMap() {
53          // First, do some cleanup (remove dead threads).
54          for (FastMap.Entry e = THREAD_TO_LOCAL_MAP.head(), end = THREAD_TO_LOCAL_MAP
55                  .tail(); (e = (FastMap.Entry) e.getNext()) != end;) {
56              Thread   thread = (Thread  ) e.getKey();
57              if (!thread.isAlive()) {
58                  THREAD_TO_LOCAL_MAP.remove(thread);
59              }
60          }
61          FastMap localMap = new FastMap();
62          THREAD_TO_LOCAL_MAP.put(Thread.currentThread(), localMap);
63          return localMap;
64      }
65  }
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