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This noncompliant code example uses a shutdown() method to set a non-volatile done flag that is checked in the run() method. If some one thread invokes the shutdown() method to set the flag, it is possible that another thread might not observe this change. Consequently, it may be forced to sleep even though the condition variable (or flag) disallows thisthe second thread may still observe that done if false and incorrectly invoke the sleep() method.

final class ControlledStop implements Runnable {
  private boolean done = false;
 
  public void run() {
    while(!done) {
      try {
        // ...
        Thread.currentThread().sleep(1000); // Do something
      } catch(InterruptedException ie) { 
        // handle exception
      } 
    } 	 
  }

  protected void shutdown(){
    done = true;
  }
}

Compliant Solution

This compliant solution declares qualifies the done flag as volatile so that updates by one thread are immediately visible to another thread.

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