Task


1   package com4j;
2   
3   import java.util.concurrent.Callable  ;
4   
5   /**
6    * Used to execute a chunk of code from {@link ComThread}.
7    *
8    * @author Kohsuke Kawaguchi (kk@kohsuke.org)
9    */
10  abstract class Task<T> implements Callable  <T> {
11      public abstract T call();
12  
13  
14      /**
15       * Executes the task.
16       */
17      public final T execute() {
18          if( ComThread.isComThread() )
19              // if invoked from within ComThread, execute it at once
20              return call();
21          else
22              // otherwise schedule the execution and block
23              return ComThread.get().execute(this);
24      }
25  
26      public final T execute(ComThread t) {
27          if(Thread.currentThread()==t)
28              // if invoked from within ComThread, execute it at once
29              return call();
30          else
31              // otherwise schedule the execution and block
32              return t.execute(this);
33      }
34  
35      /**
36       * Called from {@link ComThread} to run the task.
37       */
38      final synchronized void invoke() {
39          assert next!=null;
40          next = null;
41  
42          result = null;
43          exception = null;
44          try {
45              result = call();
46          } catch( RuntimeException   e ) {
47              exception = e;
48          }
49  
50          // let the calling thread know that we are done.
51          notify();
52      }
53  
54      /**
55       * Managed by {@link ComThread} to form a linked list from
56       * {@link ComThread#taskList}.
57       */
58      Task<?> next;
59  
60      /**
61       * Managed by {@link ComThread} to pass the return value
62       * across threads.
63       */
64      T result;
65  
66      /**
67       * Managed by {@link ComThread} to pass the exception
68       * across threads.
69       */
70      RuntimeException   exception;
71  }
72
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