ReadWriteLock读写锁

ReadWriteLock维护了一对锁，读锁可允许多个读线程并发使用，写锁是独占的。

下面通过一个简单的例子来了解ReadWriteLock。

 package com.ccfdod.juc;

 import java.util.concurrent.locks.ReadWriteLock;
 import java.util.concurrent.locks.ReentrantReadWriteLock;

 /**
  * 写写/读写，需要互斥
  * 读读，不需要互斥
  */
 public class TestReadWriteLock {

     public static void main(String[] args) {
         ReadWriteLockDemo rw = new ReadWriteLockDemo();
         new Thread(new Runnable() {

             @Override
             public void run() {
                 rw.set((int) (Math.random() * 101));
             }

         }, "Write:").start();

         for (int i = 0; i < 100; i++) {
             new Thread(new Runnable() {

                 @Override
                 public void run() {
                     rw.get();
                 }

             }, "Read:").start();
         }
     }
 }

 class ReadWriteLockDemo {

     private int number = 0;

     private ReadWriteLock lock = new ReentrantReadWriteLock();

     //读
     public void get() {
         lock.readLock().lock();    //上锁
         try {
             System.out.println(Thread.currentThread().getName() + " : " + number);
         } finally {
             lock.readLock().unlock();    //释放锁
         }
     }

     //写
     public void set(int number) {
         lock.writeLock().lock();    //上锁
         try {
             System.out.println(Thread.currentThread().getName());
             this.number = number;
         } finally {
             lock.writeLock().unlock();    //释放锁
         }
     }
 }