examples/ConcurrentCount.java

   1 import java.util.concurrent.atomic.AtomicBoolean;
   2
   3 public class ConcurrentCount {
   4         static final int COUNT = 30000;
   5         volatile static int count = COUNT;
   6         volatile static AtomicBoolean lock = new AtomicBoolean(false);
   7         static int a = 0;
   8         static int b = 0;
   9
  10         public static void main(String args[]) {
  11
  12                 new Thread() {
  13
  14                         @Override
  15                         public void run() {
  16                                 while(count > 0) {
  17                                         if (lock.get()) continue;
  18                                         lock.set(true);
  19                                         decreaseCount();
  20                                         a++;
  21                                         lock.set(false);
  22
  23
  24                                 }
  25                         }
  26                 }.start();
  27
  28         new Thread() {
  29
  30                         @Override
  31                         public void run() {
  32                                 while(count > 0) {
  33                                         if (lock.get()) continue;
  34                                         lock.set(true);
  35                                         decreaseCount();
  36                                         b++;
  37                                         lock.set(false);
  38
  39
  40                                 }
  41                         }
  42                 }.start();
  43
  44                 while(count > 0);
  45                 //System.out.println("a = " + a);
  46                 //System.out.println("b = " + b);
  47                 //System.out.println("a + b = " + (a + b));
  48                 //System.out.println("count = " + count);
  49
  50                 //Checks for concurrency error (which should be found when using model checking)
  51                 assert a + b == COUNT;
  52         }
  53
  54         private static synchronized void decreaseCount() {
  55                 count--;
  56         }
  57
  58 }
  59