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

Answer 1

你这里3个线程都是要写数据 怎么可能会并发执行，Thread-0 调用put的时候占用了write锁，Thread-1和Thread-2都被挡在外面了；锁降级的意义是当前线程由write降为read，其他只需要read锁的线程可以去获取read锁，达到并发读的目的。