// run in server JVM to show effect of hoisting non-volatile _flag into t2.
public class VolatileDemo {
  volatile boolean _flag = false;
  
  void run() {
    Thread t1 = new Thread(new Runnable() {
      public void run() {
        try {
          Thread.sleep(1000);
          _flag = true;
        }
        catch(InterruptedException ie) { /* ignore */ }
      }
    });
    Thread t2 = new Thread(new Runnable() {
      public void run() {
        System.out.println("_flag = "+_flag);
        while(!_flag) {
          // this may become an infinite loop
        }
        System.out.println("_flag = "+_flag);
      }
    });
    t1.start();
    t2.start();
    try {
      t1.join();
      t2.join();
    }
    catch(InterruptedException ie) { /* ignore */ }
  }
  
  public static void main(String[] args) {
    (new VolatileDemo()).run();
  }
}