GuardedObject.java

class GuardedObject<T> {
  // 受保护的对象
  T obj;
  final Lock lock = new ReentrantLock();
  final Condition done = lock.newCondition();
  final int timeout = 1;
  
  T get(Predicate<T> p) {
    lock.lock();
    try{
      // MESA管程推荐写法
      while(!p.test(obj)){
        done.await(timeout, TimeUnit.SECONDS);
      }
    }finally{
      lock.unlock();
    }
    return obj;
  }
 
  void onChange(T obj){
    lock.lock();
    try{
      this.obj = obj;
      done.signalAll();
    }finally{
      lock.unlock();
    }
  }
}