读写锁ReentrantReadWriteLock锁降级的意义是什么啊

Question

比如如下代码，降级了并没有并发执行啊？

  public void put(Object data){

            rwl.writeLock().lock();
            rwl.readLock().lock();
            System.out.println(Thread.currentThread().getName() + " be ready to write data!");                    
            try {
                Thread.sleep((long)(Math.random()*1000));
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            this.data = data;        
            System.out.println(Thread.currentThread().getName() + " have write data: " + data);                    
            rwl.readLock().unlock();
            rwl.writeLock().unlock();

        }

输出：
Thread-0 be ready to write data!
Thread-0 have write data: 1103
Thread-2 be ready to write data!
Thread-2 have write data: 4531
Thread-1 be ready to write data!
Thread-1 have write data: 2188
也并没有并发执行啊

Answer 1

是写的线程用writelock，读的线程用readlock