多线程的实现方式

通过实现 Runnable 接口

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package com.ruanyuan;

/**
 * TODO
 *
 * @ClassName TestThread
 * @Author Alfa
 * @Data 2022/7/14 15:43
 * @Version 1.0
 **/
public class TestThread{
    public static void main(String[] args) {
        RunnableDemo demo = new RunnableDemo();
        new Thread(demo).start();
        for (int i = 0; i < 1000; i++) {
            System.out.println("主线程");
        }
    }
}
class RunnableDemo implements Runnable {
    public void run() {
        for (int i = 0; i < 1000; i++) {
            System.out.println("子线程--"+Thread.currentThread().getName());
        }
    }
}

推荐使用Runnable对象,因为Java单继承的局限性

通过继承 Thread 类本身

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package com.ruanyuan;

/**
 * TODO
 *
 * @ClassName TestThread
 * @Author Alfa
 * @Data 2022/7/14 15:43
 * @Version 1.0
 **/
public class TestThread{
    public static void main(String[] args) {
        ThreadRDemo demo = new ThreadRDemo();
        demo.start();
        for (int i = 0; i < 1000; i++) {
            System.out.println("主线程");
        }
    }
}
class ThreadRDemo extends Thread {
    public void run() {
        for (int i = 0; i < 1000; i++) {
            System.out.println("子线程--"+Thread.currentThread().getName());
        }
    }
}

线程同步

线程安全案例一

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package com.ruanyuan;

import java.util.ArrayList;
import java.util.List;

/**
 * TODO
 *
 * @ClassName TestThread
 * @Author Alfa
 * @Data 2022/7/14 15:43
 * @Version 1.0
 **/
public class TestThread{
    public static void main(String[] args) {
        //ArrayList线程不安全案例
        List<String> list = new ArrayList<>();
        //开启一万个线程操作list
        for (int i = 0; i < 10000; i++) {
            new Thread(() -> {
                list.add(Thread.currentThread().getName());
            }).start();
        }
        // 主线程睡眠三秒，等待一万个子线程执行完毕
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(list.size());
    }
}

image-20220714163801117

并发太快，对集合的操作有的重复在了一个位置。

同步代码块

image-20220714171307635

线程安全案例二

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package com.ruanyuan;

//不安全买票
public class TestThread {
    public static void main(String[] args) {
        BuyTicket buyTicket = new BuyTicket();
        new Thread(buyTicket, "张三").start();
        new Thread(buyTicket, "李四").start();
        new Thread(buyTicket, "王五").start();
    }
}

class BuyTicket implements Runnable {
    //票
    private int ticketNums = 10;
    boolean flag = true;

    @Override
    public void run() {
        //买票
        while (flag) {
            try {
                buy();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    //买票
    private void buy() {
        //判断是否有票
        if (ticketNums <= 0) {
            flag = false;
            return;
        }
        //延迟
        try {
            Thread.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        //买票
        System.out.println(Thread.currentThread().getName() + "拿到" + ticketNums--);
    }
}

image-20220714172648484

同步方法

image-20220714173011580

死锁

案例

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package com.ruanyuan;

/**
 * 死锁:多个线程互相抱着对方需要的资源,然后形成僵持
 * 解决:一个锁只锁一个对象
 */
public class DeadLock {
    public static void main(String[] args) {
        MakeUp g1 = new MakeUp(0, "灰姑娘");
        MakeUp g2 = new MakeUp(1,"白雪公主");

        g1.start();
        g2.start();
    }
}

//口红
class LipStick{

}

//镜子
class Mirror{

}

class MakeUp extends Thread{
	//需要的资源只有一份,用static保证只有一份
    static LipStick lipStick = new LipStick();
    static Mirror mirror = new Mirror();
	
    //选择
    int choice;
    //使用化妆品的人	
    String girlName;

    public MakeUp(int choice, String girlName) {
        this.choice = choice;
        this.girlName = girlName;
    }

    @Override
    public void run() {
        //化妆
        makeup();
    }

    //化妆，互相持有对方的锁
    private void makeup(){
        if (choice == 0)
        {
            synchronized (lipStick) {
                // 获得口红的锁
                System.out.println(this.girlName+"获得口红的锁");
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                synchronized (mirror) {
                    //一秒钟后想要获得镜子
                    System.out.println(this.girlName+"获得镜子的锁");
                }
            }
        } else {
            synchronized (mirror) {
                // 获得镜子的锁
                System.out.println(this.girlName+"获得镜子的锁");
                try {
                    Thread.sleep(2000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                synchronized (lipStick) {
                    //两秒钟后想要获得镜子
                    System.out.println(this.girlName+"获得口红的锁");
                }
            }
        }
    }
}

解决

image-20220715092321508

image-20220715092603663