30. Example: wait() -- notifyAll()

• 
      boolean taken = false;
      public
          synchronized
          void grab() throws InterruptedException
          {
              while ( taken ) {
                  wait(); // wait unti my turn
              }
              taken = true; // okay, my turn!
          }
  
      public 
          synchronized
          void drop()
          {
              taken = false;
              notifyAll() // wake up all waiting threads
          }
  
  
      // Client code:
      resource.grab();
      // Critical section: do something with the resource
      resource.drop();