InterruptableTask


1   package snow.concurrent;
2   
3   import java.util.concurrent.*;
4   import java.util.*;
5   
6   /** wraps a runnable into an interruptable task.
7     I.e. creates a thread that can be interrupted.
8        should only be interrupted when not stopping itself correctely with the Interrupter
9   */
10  public abstract class InterruptableTask <T> implements Callable<T>, Runnable  
11  {
12    Thread   thread;
13    final public Interrupter interrupter = new Interrupter();  // correct way to stop the thread
14    Future future;  // set at submit
15    private boolean isExecuting = false;
16  
17  
18    public InterruptableTask()
19    {
20  
21    } // Constructor
22  
23    public boolean isExecuting() { return isExecuting; }
24  
25    public final T call() throws Exception  
26    {
27       if(this.interrupter.shouldStopEvaluation())
28       {
29         // never evaluates !
30         return null;
31       }
32  
33       isExecuting = true;
34       thread = new Thread  (this);
35       // wait until completion
36       try
37       {
38         thread.start();
39         thread.join();
40       }
41       catch(Exception   e)
42       {
43         kill();
44         throw e;
45       }
46       finally
47       {
48         isExecuting = false;
49       }
50       return null;
51    }
52  
53    /** use only if request stop has not succeded.
54       This kills the thread.
55       BE CAREFUL: if the therad calls EventQueue.invokeAndWait, and catch Exception without throwing them
56        the thread continues !!
57    */
58    public void kill()
59    {
60       if(thread!=null && thread.isAlive())
61       {
62         thread.interrupt();  // throws an exception that may be catched => not 100% stops
63       }
64  
65       // thread.stop()  // stops 100% but not safe ! deprecated !!
66    }
67  
68    public void requestStop()
69    {
70       if(interrupter.shouldStopEvaluation())
71       {
72         // already cool stopped but still called => kill
73         kill();
74       }
75       else
76       {
77         // first attempt : cool stop
78         interrupter.stopEvaluation();
79       }
80    }
81  
82  
83  } // InterruptableTask
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