what is wrong with volatile variables?

[jalligator]

Guys,

What is wrong with snippet below? Why both conditions sometimes are true at the same time:
if ( fine != suspect ) {
if ( fine == suspect ) {
Why foobar is printed out? I had a long time arguments, but failed to prove anything. Could you help me please? What do you think?

Code:

public class VWC {
  private volatile boolean  suspect;
  private boolean            fine;
  private boolean            anotherFine;
  private Object             lock = new Object();
  private int                   failures;
  private int                   iterations;
 
  private VWC() {
    new Thread() {
      public void run() {
        while( true ) {
          synchronized( lock ) {
            try {
              lock.wait();
            } catch ( Exception exception ) {
            }
          }
          synchronized( lock ) {
            if ( fine != suspect ) {
              System.err.println( "foo" );
              if ( fine == suspect ) {
                System.err.println( "bar" );
              }
            }
            if ( fine != anotherFine ) {
              System.err.println( "baz" );
            }
          }
        }
      }
    }.start();
  }
 
  private void run() {
    while( true ) {
      synchronized( lock ) {
        ++iterations;
        fine = ! fine;
        anotherFine = ! anotherFine;
      }
      suspect = ! suspect;
      synchronized( lock ) {
        lock.notify();
      }
    }
  }
 
  public static void main(String[] args) {
    new VWC().run();
  }
}

[fishtoprecords]

How about cleaning up your code some.

Code:

            if ( fine != suspect ) {
              System.err.println( "foo" );
              if ( fine == suspect ) {
                System.err.println( "bar" );
              }
            }

should really be written clearly, which means make the test obvious.

Code:

 
           if ( fine == suspect ) {
                System.err.println( "is same" );
           else {
                System.err.println( "not same at all" );
           }

Your code is not obvious, and non-obvious code can hide many bugs