java锁：第二章：可重入锁和递归锁

可重入锁是什么？

可以防止死锁，是同一把锁

代码：

package com.javaliao.backstage;

class Phone{

    public synchronized void sendSMS(){
        System.out.println(Thread.currentThread().getName()+"\t 发短信");
        sendEmail();
    }
    public synchronized void sendEmail(){
        System.out.println(Thread.currentThread().getName()+"\t 发邮件");
    }
}
public class Demo {
    public static void main(String[] args) {
        Phone phone = new Phone();
        new Thread(()->{
            phone.sendSMS();
        },"t1").start();
        new Thread(()->{
            phone.sendSMS();
        },"t2").start();
    }
}

控制台：

生活案例：

家里的大门有一把锁，厕所没有上锁。我进了大门了，就不用在厕所上锁了。

ReentrantLock就是把可重入锁

package com.javaliao.backstage;


import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

class Phone implements Runnable{

    Lock lock = new ReentrantLock();
    @Override
    public void run() {
        sendSMS();
    }

    public void sendSMS(){
        //加几把就要解锁几次
        lock.lock();
        lock.lock();
        try {
            System.out.println(Thread.currentThread().getName()+"\t 发短信");
            sendEmail();
        } finally {
            lock.unlock();
            lock.unlock();
        }
    }
    public void sendEmail(){
        lock.lock();
        try {
            System.out.println(Thread.currentThread().getName()+"\t 发邮件");
        } finally {
            lock.unlock();
        }
    }


}
public class Demo {
    public static void main(String[] args) {
        Phone phone = new Phone();
        Thread t1 = new Thread(phone,"t1");
        Thread t2 = new Thread(phone,"t2");
        t1.start();
        t2.start();
    }
}