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Java > Open Source Codes > gov > nasa > jpf > jvm > DefaultScheduler


1 //
2 // Copyright (C) 2005 United States Government as represented by the
3 // Administrator of the National Aeronautics and Space Administration
4 // (NASA). All Rights Reserved.
5 //
6 // This software is distributed under the NASA Open Source Agreement
7 // (NOSA), version 1.3. The NOSA has been approved by the Open Source
8 // Initiative. See the file NOSA-1.3-JPF at the top of the distribution
9 // directory tree for the complete NOSA document.
10 //
11 // THE SUBJECT SOFTWARE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY OF ANY
12 // KIND, EITHER EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING, BUT NOT
13 // LIMITED TO, ANY WARRANTY THAT THE SUBJECT SOFTWARE WILL CONFORM TO
14 // SPECIFICATIONS, ANY IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR
15 // A PARTICULAR PURPOSE, OR FREEDOM FROM INFRINGEMENT, ANY WARRANTY THAT
16 // THE SUBJECT SOFTWARE WILL BE ERROR FREE, OR ANY WARRANTY THAT
17 // DOCUMENTATION, IF PROVIDED, WILL CONFORM TO THE SUBJECT SOFTWARE.
18 //
19 package gov.nasa.jpf.jvm;
20
21 import gov.nasa.jpf.Config;
22
23
24 /**
25  * a scheduler that simply enumerates all threads, picking the next one (from
26  * it's last choice) that is runnable
27  */
28 public class DefaultScheduler extends Scheduler {
29   private int thread;
30   private int random;
31   private boolean lastRandom;
32
33   public DefaultScheduler (Config config) {
34     initialize();
35   }
36
37   public int getRandom () {
38     return random;
39   }
40
41   public int getThread () {
42     return thread;
43   }
44
45   /**
46    * gets called in every cycle (i.e. we start from thread=0) by
47    * JVM.forward
48    * SystemState.prepareNext
49    */
50   public void initialize () {
51     thread = 0;
52     random = -1;
53     lastRandom = true;
54   }
55
56   /**
57    * sets the thread index to the next runnable thread, called by
58    * JVM.forward
59    * SystemState.nextSuccessor
60    */
61   public ThreadInfo locateThread (SystemState ss) {
62     for (int n = ss.getThreadCount(); thread < n; thread++) {
63       ThreadInfo th = ss.getThreadInfo(thread);
64
65       if (th.isRunnable()) {
66         return th;
67       }
68     }
69
70     return null;
71   }
72
73   /**
74    * this is NOT the next runnable thread index! it just makes sure we get
75    * another thread the next time (if there is a runnable one). Called by
76    * JVM.forward
77    * SystemState.scheduleNext
78    */
79   public void next () {
80     if (lastRandom) {
81       random = -1;
82       thread++;
83     } else {
84       random++;
85     }
86   }
87
88   public int random (int max) {
89     if (random == -1) {
90       random = 0;
91     }
92
93     lastRandom = (random == max - 1);
94
95     return random;
96   }
97 }
98
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