*
 *   public V get() throws InterruptedException {
 *     monitor.enterWhen(valuePresent);
 *     try {
 *       V result = value;
 *       value = null;
 *       return result;
 *     } finally {
 *       monitor.leave();
 *     }
 *   }
 *
 *   public void set(V newValue) throws InterruptedException {
 *     monitor.enterWhen(valueAbsent);
 *     try {
 *       value = newValue;
 *     } finally {