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();
        }
    }