3.1.4 读写锁

Posted 2020-10-23 anxbb

一、分为两种：公平和非公平

线程 a b c d e
公平：按顺序执行：a,b,d,e 读锁 c 写锁
      1.a,b 执行 c 堵塞，d,e 等待
      2.a,b执行结束 c获取锁 d,e堵塞等待
      3.c执行结束 d开始执行，然后在唤醒e

非公平：
      1，2步骤相同
      3，c执行结束的时候，新来个线程 f读锁，在d没有唤醒的情况下，会获取读锁，然后在唤醒d，e

package 第三章.读写锁;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.locks.ReentrantReadWriteLock;

/**
 * Created by zzq on 2018/1/23.
 */
public class WebTestReadAndWriteLock {
    ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
    public static void main(String[] args) {
        final WebTestReadAndWriteLock lock = new WebTestReadAndWriteLock();
        // 建N个线程，同时读
        ExecutorService service = Executors.newCachedThreadPool();
        service.execute(new Runnable() {
            public void run() {
                lock.readFile(Thread.currentThread());
            }
        });
        service.execute(new Runnable() {
            public void run() {
                lock.readFile(Thread.currentThread());
            }
        });
        // 建N个线程，同时写
        ExecutorService service1 = Executors.newCachedThreadPool();
        service1.execute(new Runnable() {
            public void run() {
                lock.writeFile(Thread.currentThread());
            }
        });
        service.execute(new Runnable() {
            public void run() {
                lock.readFile(Thread.currentThread());
            }
        });
        service.execute(new Runnable() {
            public void run() {
                lock.readFile(Thread.currentThread());
            }
        });
        service1.execute(new Runnable() {
            public void run() {
                lock.writeFile(Thread.currentThread());
            }
        });
    }
    // 读操作
    public void readFile(Thread thread){
        lock.readLock().lock();
        boolean readLock = lock.isWriteLocked();
        if(!readLock){
            System.out.println("当前为读锁！");
        }
        try{
            for(int i=0; i<5; i++){
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(thread.getName() + ":正在进行读操作……");
            }
            System.out.println(thread.getName() + ":读操作完毕！");
        }finally{
            System.out.println("释放读锁！");
            lock.readLock().unlock();
        }
    }
    // 写操作
    public void writeFile(Thread thread){
        lock.writeLock().lock();
        boolean writeLock = lock.isWriteLocked();
        if(writeLock){
            System.out.println("当前为写锁！");
        }
        try{
            for(int i=0; i<5; i++){
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(thread.getName() + ":正在进行写操作……");
            }
            System.out.println(thread.getName() + ":写操作完毕！");
        }finally{
            System.out.println("释放写锁！");
            lock.writeLock().unlock();
        }
    }
}