多线程详解---狂神说

最新推荐文章于 2025-03-08 10:28:30 发布

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最新推荐文章于 2025-03-08 10:28:30 发布

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文章标签：多线程

本文链接：https://blog.youkuaiyun.com/weixin_48666874/article/details/121492974

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本文深入探讨了Java中的多线程概念，包括进程与线程的区别、线程的创建（Thread类、Runnable接口、Callable接口）以及线程的运行状态。通过示例展示了线程同步的重要性，如并发问题、死锁、线程礼让、线程优先级等，并介绍了线程池的概念，最后回顾了线程的创建方式。内容覆盖了线程的基本操作和高级用法，适合Java开发者学习。

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多线程详解

进程：

在操作系统中运行的程序就是进程，比如你的QQ，播放器，游戏，IDE等等

线程：

一个进程可以有多个线程，如视频中同时听声音，看图像，看弹幕，，等等

线程就是独立的执行路径
在程序运行时，即使没有自己创建线程，后台也会有多个线程，如主线程、gc线程
main（）称之为主线程，为程序的入口，用于执行整个程序
在一个进程中，如果开辟了多个线程，线程的运行由调度器安排调度，调度器是与操作系统紧密相关的，先后顺序是不能人为的干预的
对同一份资源操作时，会存在资源抢夺问题，需要加入并发控制
线程会带来额外的开销，如cpu调度时间，并发控制开销
每个线程在自己的工作内存交互，内存控制不当会造成数据不一致

线程创建

Thread

Runnable

Callable

重点：Thread class 继承Thread类

重点：Runnable 接口实现Runnable 接口

了解：Callable接口

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Thread

自定义线程类继承Thread类
重写run()方法，编写线程执行体

创建线程对象，调用start()方法启动线程

//创建一个线程对象
TestThread1 testThread1 = new TestThread1();
//调用start方法开启线程
testThread1.start();

线程不一定立即执行，由cpu安排调度

Runnable

定义MyRunnable类实现Runnable接口
实现run()方法，编写编程执行体
创建编程对象，调用start()方法启动线程

推荐使用Runnable对象，因为java单继承的局限性

//创建runnable 接口实现类对象
TestThread3 testThread3 = new TestThread3();
//创建代理类对象，通过线程对象来开启我们的线程，代理
Thread thread = new Thread(testThread3);
//启动
thread.start();

两种方式实现网图下载

package com.kuang.demo01;

import org.apache.commons.io.FileUtils;
import sun.misc.FileURLMapper;

import java.io.File;
import java.io.IOException;
import java.net.URL;

//练习Thread，实现多线程同步下载图片
public class TestThread2 extends Thread {
    private String url;
    private String name;

    public TestThread2(String url, String name) {
        this.url = url;
        this.name = name;
    }

    @Override
    public void run() {
        WebDownloader webDownloader = new WebDownloader();
        webDownloader.downloader(url, name);
        System.out.println("下载了文件名为：" + name);

    }

    public static void main(String[] args) {
        TestThread2 t1 = new TestThread2("https://img-home.csdnimg.cn/images/20211118020207.jpg","1.png");
        TestThread2 t2 = new TestThread2("https://img-home.csdnimg.cn/images/20211118020207.jpg","2.png");
        TestThread2 t3 = new TestThread2("https://img-home.csdnimg.cn/images/20211118020207.jpg", "3.png");

        t1.start();
        t2.start();
        t3.start();
    }


}

//下载器
class WebDownloader {
    //下载方法
    public void downloader(String url, String name) {
        try {
            FileUtils.copyURLToFile(new URL(url), new File(name));
        } catch (IOException e) {
            e.printStackTrace();
            System.out.println("IO异常，downloader方法出现问题");
        }
    }
}

package com.kuang.demo01;

import org.apache.commons.io.FileUtils;

import java.io.File;
import java.io.IOException;
import java.net.URL;

public class TestThread4 implements Runnable{

    private String url;
    private String name;

    public TestThread4(String url, String name) {
        this.url = url;
        this.name = name;
    }

    @Override
    public void run() {
        WebDownloader webDownloader = new WebDownloader();
        webDownloader.downloader(url, name);
        System.out.println("下载了文件名为：" + name);

    }

    public static void main(String[] args) {
        TestThread4 t1 = new TestThread4("https://img-home.csdnimg.cn/images/20211118020207.jpg","1.png");
        TestThread4 t2 = new TestThread4("https://img-home.csdnimg.cn/images/20211118020207.jpg", "1.png");
        TestThread4 t3 = new TestThread4("https://img-home.csdnimg.cn/images/20211118020207.jpg", "1.png");
        new Thread(t1).start();
        new Thread(t2).start();
        new Thread(t3).start();

    }
}


//下载器
class WebDownloader1 {
    //下载方法
    public void downloader(String url, String name) {
        try {
            FileUtils.copyURLToFile(new URL(url), new File(name));
        } catch (IOException e) {
            e.printStackTrace();
            System.out.println("IO异常，downloader方法出现问题");
        }
    }
}

小结

继承Thread 类
- 子类继承Thread 类具备多线程能力
- 启动线程：子类对象.start（）
- 不建议使用：避免OOP单继承的局限性
实现Runnable接口
- 实现Runnable接口具有多线程能力
- 启动线程：传入目标对象+Thread对象.start（）
- 推荐使用：避免单继承局限性，灵活方便，方便同一个对象呗多个线程使用

初始并发问题

问题：多个线程操作同一个资源的情况下，线程不安全，数据紊乱

package com.kuang.demo01;

//多个线程同时操作同一个对象
//买火车票的例子

//发现问题：多个线程操作同一个资源的情况下，线程不安全，数据紊乱
public class TestThread5 implements Runnable{
    //票数
    private int tickeNum = 10;
    @Override
    public void run() {
        while(true) {
            if(tickeNum <= 0) {
                break;
            }
            //模拟延时
            try {
                Thread.sleep(200);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName() + "--->拿到了第" + tickeNum + "张票");
        }
    }

    public static void main(String[] args) {

        TestThread5 ticket = new TestThread5();

        new Thread(ticket, "小明").start();
        new Thread(ticket, "老师").start();
        new Thread(ticket, "黄牛党").start();
    }
}

龟兔赛跑

package com.kuang.demo01;

//模拟龟兔赛跑
public class Race implements Runnable{
    //胜利者
    private static String winner;

    @Override
    public void run() {
        for (int i = 0; i <= 100; i++) {
            //模拟兔子睡觉
            if(Thread.currentThread().getName() == "兔子" && i % 10 == 0) {
                try {
                    Thread.sleep(200);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            //判断比赛是否结束
            boolean flag = gameOver(i);
            //如果比赛结束了，就停止程序
            if(flag) {
                break;
            }
            System.out.println(Thread.currentThread().getName() + "--->跑了" + i + "步");

        }
    }
    //判断是否完成比赛
    private boolean gameOver(int steps){
        //判断是否有胜利者
        if(winner != null) {
            //已经存在胜利者
            return true;
        }{
            if(steps >= 100) {
                winner = Thread.currentThread().getName();
                System.out.println("winner is:" + winner);
                return true;
            }
        }
        return false;
    }

    public static void main(String[] args) {
        Race race = new Race();

        new Thread(race, "兔子").start();
        new Thread(race, "乌龟").start();
    }
}

静态代理模式

package com.kuang.demo01;

import sun.awt.windows.WEmbeddedFrame;

/**
 * 静态代理模式总结：
 * 真是对象和代理对象都要实现同一个接口
 * 代理对象要代理真实角色
 * 好处：代理对象可以做好多真是对象做不了的事情
 * 真实对象专注做自己的事情
 */


public class StaticProxy {
    public static void main(String[] args) {
        You you = new You();
        new Thread(() -> System.out.println("我爱你")).start();
        //
//        WeddingCompany weddingCompany = new WeddingCompany(new You());
//        weddingCompany.HappyMarry();
        new WeddingCompany(new You()).HappyMarry();
    }
}

interface Marry{
    void HappyMarry();
}

//真是角色：你
class You implements Marry {
    @Override
    public void HappyMarry() {
        System.out.println("老师要结婚了，超开心");
    }
}

//代理角色：帮助你结婚
class WeddingCompany implements Marry {
    private Marry target;

    public WeddingCompany(Marry target) {
        this.target = target;
    }

    @Override
    public void HappyMarry() {
        before();
        this.target.HappyMarry();
        after();
    }

    private void before() {
        System.out.println("结婚之前布置现场");
    }

    private void after() {
        System.out.println("结婚之后收尾款");
    }
}

lambda表达式

package com.kuang.lambda;

/*
推导lambda表达式
 */

public class TestLambda1 {
    // 3. 静态内部类
    static class Like2 implements ILike{
        @Override
        public void lambda() {
            System.out.println("I Like Lambda2");
        }
    }
    public static void main(String[] args) {
        ILike like = new Like();
        like.lambda();

        like = new Like2();
        like.lambda();

        // 4. 局部内部类
        class Like3 implements ILike{
            @Override
            public void lambda() {
                System.out.println("I Like Lambda3");
            }
        }

        like = new Like3();
        like.lambda();

        //5.匿名内部类，没有类的名称，必须借助接口或者父类
        like = new ILike() {
            @Override
            public void lambda() {
                System.out.println("I Like Lambda4");
            }
        };
        like.lambda();

        //6. 用lambda简化
        like = () -> {
            System.out.println("I Like Lambda5");
        };
        like.lambda();


    }
}

// 1.定义一个函数式接口
interface ILike{
    void lambda();
}

// 2.实现类
class Like implements ILike{
    @Override
    public void lambda() {
        System.out.println("I Like Lambda");
    }
}

线程状态

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线程停止

package com.kuang.state;

/***
 * 测试stop
 * 1.建议线程正常停止---->利用次数，不建议死循环
 * 2.建议使用标志位----->设置一个标志位
 * 3.不要使用stop或者destroy等过时或者JDK不建议使用的方法
 */
public class TestStop implements Runnable{

    //1.设置一个标志位
    private boolean flag = true;

    @Override
    public void run() {
        int i = 0;
        while(flag) {
            System.out.println("run.....Thread" + i++);
        }

    }

    //2.设置一个公开的方法停止线程，转换标志位
    public void stop() {
        this.flag = false;
    }

    public static void main(String[] args) {
        TestStop testStop = new TestStop();
        new Thread(testStop).start();

        for (int i = 0; i < 100; i++) {
            System.out.println("main" + i);
            if(i == 900) {
                //调用stop方法切换标志位，让线程停止
                testStop.stop();
                System.out.println("该线程该停止了");
            }
        }

    }
}

线程休眠

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package com.kuang.state;

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.logging.SimpleFormatter;

public class TestSleep2 {
    public static void main(String[] args) {
//        try {
//            tenDown();
//        } catch (InterruptedException e) {
//            e.printStackTrace();
//        }

        //打印系统当前时间
        Date startTime = new Date(System.currentTimeMillis());//获取当前时间
        while(true) {
            try {
                Thread.sleep(1000);
                System.out.println(new SimpleDateFormat("HH:mm:ss").format(startTime));
                startTime = new Date(System.currentTimeMillis());//更新当前时间
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    //模拟倒计时
    public static void tenDown() throws InterruptedException{
        int num = 10;
        while(true) {
            Thread.sleep(1000);
            System.out.println(num--);
            if(num <= 0) {
                break;
            }
        }
    }
}

线程礼让

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yield：礼让

package com.kuang.state;

//测试礼让
//礼让不一定成功，看CPU心情
public class TestYield {
    public static void main(String[] args) {
        MyYield myYield = new MyYield();
        new Thread(myYield, "A").start();
        new Thread(myYield, "B").start();
    }

}

class MyYield implements Runnable {

    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName() + "线程开始执行");
        Thread.yield();
        System.out.println(Thread.currentThread().getName() + "线程停止执行");
    }
}

线程强制执行

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线程状态观测

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package com.kuang.state;

//观察测试线程的状态
public class TestState {
    public static void main(String[] args) throws InterruptedException {
        Thread thread = new Thread(() -> {
            for (int i = 0; i < 5; i++) {
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            System.out.println("==========");
        });

        //观察状态
        Thread.State state = thread.getState();
        System.out.println(state); //new

        //观察启动后
        thread.start();//启动线程
        state = thread.getState();
        System.out.println(state); //run

        while(state != Thread.State.TERMINATED) {//只要线程不终止，就一直输出状态
            Thread.sleep(100);
            state = thread.getState();//更新线程状态
            System.out.println(state);

        }
    }
}

线程优先级

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package com.kuang.state;

public class TestPriority {
    public static void main(String[] args) {
        //主线程默认优先级
        System.out.println(Thread.currentThread().getName() + "--->" + Thread.currentThread().getPriority());


        MyPriority myPriority = new MyPriority();
        Thread t0 = new Thread(myPriority);
        Thread t1 = new Thread(myPriority);
        Thread t2 = new Thread(myPriority);
        Thread t3 = new Thread(myPriority);
        Thread t4 = new Thread(myPriority);
        Thread t5 = new Thread(myPriority);

        //先设置优先级，在启动
        t0.start();

        t1.setPriority(2);
        t1.start();

        t2.setPriority(7);
        t2.start();

        t3.setPriority(Thread.MAX_PRIORITY);
        t3.start();

        t4.setPriority(8);
        t4.start();

        t5.setPriority(1);
        t5.start();
        
    }

}

class MyPriority implements Runnable {

    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName() + "--->" + Thread.currentThread().getPriority());
    }
}

守护线程

daemon:守护

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线程同步

多个线程操作同一个资源

并发：同一个对象被多个线程同时操作
形成条件：队列 + 锁

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三大不安全案例

买票

package com.kuang.syn;

//不安全的买票
public class UnsafeBuyTicket {
    public static void main(String[] args) {
        BuyTicket station = new BuyTicket();
        new Thread(station, "苦逼的你们").start();
        new Thread(station, "牛逼的我").start();
        new Thread(station, "可恶的黄牛党").start();


    }
}

class BuyTicket implements Runnable {
    private int ticketNums = 10;
    boolean flag = true;//外部停止方式

    @Override
    public void run() {
        //买票
        while(flag) {
            buy();
        }
    }

    private void buy() {
        //判断是否有票
        if(ticketNums <= 0) {
            flag= false;
            return;
        }

        //模拟延时
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        //买票
        System.out.println(Thread.currentThread().getName() + "拿到了" + ticketNums--);
    }
}

取钱

package com.kuang.syn;

//不安全的取钱
//两个人去银行取钱
public class UnsafeBank {
    public static void main(String[] args) {
        //账户
        Account account = new Account(100,"结婚基金");

        Drawing you = new Drawing(account, 50, "你");
        Drawing yourWife = new Drawing(account, 100 , "妻子");

        you.start();
        yourWife.start();
    }
}


class  Account {
    int money;//余额
    String name;//账户

    public Account(int money, String name) {
        this.money = money;
        this.name = name;
    }
}

//银行：模拟取款‘
class Drawing extends Thread {
    Account account;//账户
    int drawingMoney;//取了多少钱
    int nowMoney;//现在手里有多少钱

    public Drawing(Account account, int drawingMoney, String name) {
        super(name);
        this.account = account;
        this.drawingMoney = drawingMoney;

    }

    //取钱
    @Override
    public void run() {
        //判断有没有钱
        if(account.money - drawingMoney < 0) {
            System.out.println(Thread.currentThread().getName() + "钱不够，取不了");
            return;
        }

//        //sleep可以放大问题的发生性
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        //卡内余额 = 余额 - 你取的钱
        account.money = account.money - drawingMoney;
        //你手里的钱
        nowMoney = nowMoney + drawingMoney;
        System.out.println(account.name + "余额为：" + account.money);
        //this.getName() = Thread.currentThread().getName()
        System.out.println(this.getName() + "手里的钱为：" + nowMoney);
    }
}

同步方法及同步块

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死锁

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package com.kuang.thread;

//死锁：多个线程互相抱着对方需要的资源，然后形成僵持
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 {

}

//化妆
class Makeup extends Thread {
    //需要的资源只有一份，用static来保证只有一份
    static  Lipstick lipstick = new Lipstick();
    static  Mirror mirror = new Mirror();

    int choice;//选择
    String girlName;// 使用化妆品的人

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

    @Override
    public void run() {
        //化妆
        try {
            makeup();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    //化妆，互相持有对方的锁，就是需要拿到对方的资源
    private void makeup() throws InterruptedException {
        if(choice == 0) {
            synchronized (lipstick) {
                System.out.println(this.girlName + "获得口红的锁");
                Thread.sleep(1000);//1s之后想要镜子的锁

            }
            synchronized (mirror) {
                System.out.println(this.girlName + "获得镜子的锁");
            }
        }else {
            synchronized (mirror) {
                System.out.println(this.girlName + "获得镜子的锁");
                Thread.sleep(2000);//2s之后想要获得口红的锁

            }
            synchronized (lipstick) {
                System.out.println(this.girlName + "获得口红的锁");
            }
        }
    }
}

Lock锁

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package com.kuang.senior;

import java.util.concurrent.locks.ReentrantLock;

//测试lock锁
public class TestLock {
    public static void main(String[] args) {
        TestLock2 testLock2 = new TestLock2();
        new Thread(testLock2).start();
        new Thread(testLock2).start();
        new Thread(testLock2).start();


    }

}

class  TestLock2 implements Runnable {
    int ticketNum = 10;

    //定义Lock锁
    private final ReentrantLock lock = new ReentrantLock();


    @Override
    public void run() {
        while(true) {
            try {
                lock.lock();//加锁
                if(ticketNum > 0) {
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println(ticketNum--);
                }else {
                    break;
                }
            }finally {
                //解锁
                lock.unlock();
            }
        }
    }

}

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线程协作

生产者消费者问题

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管程法

利用缓冲区解决生产者消费者模式问题

package com.kuang.senior;

//测试：生产者消费者模型————>利用缓冲区解决:管程法

//生产者、消费者、产品、缓冲区
public class TestPC {
    public static void main(String[] args) {
        SynContainer container = new SynContainer();

        new Productor(container).start();
        new Consumer(container).start();
    }

}


//生产者
class Productor extends Thread {
    SynContainer container;
    public Productor(SynContainer container) {
        this.container = container;
    }

    //生产
    @Override
    public void run() {
        for (int i = 0; i < 100; i++) {
            container.push(new Chicken(i));
            System.out.println("生产了" + i + "只鸡");
        }
    }
}

//消费者
class Consumer extends Thread {
    SynContainer container;
    public Consumer(SynContainer container) {
        this.container = container;
    }

    //消费
    @Override
    public void run() {
        for (int i = 0; i < 100; i++) {
            System.out.println("消费了--->" +container.pop().id + "只鸡");
        }
    }
}
//产品
class Chicken {
    int id;

    public Chicken(int id) {
        this.id = id;
    }
}

//缓冲区
class SynContainer {
    //需要一个容器大小
    Chicken[] chickens = new Chicken[10];

    //容器计数器
    int count = 0;

    //生产者放入产品
    public synchronized void push(Chicken chicken) {
        //如果容器满了，就需要等待消费者消费
        if(count == chickens.length) {
            //通知消费者消费，生产者等待
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

        //如果没有满，我们就需要丢入产品
        chickens[count] = chicken;
        count++;

        //可以通知消费者消费了
        this.notifyAll();

    }


    //消费者消费产品
    public synchronized Chicken pop() {
        //判断能否消费
        if(count == 0) {
            //等待生产者生产，消费者等待
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        //如果可以消费
        count--;
        Chicken chicken = chickens[count];

        //吃完了，通知生产者生产
        this.notifyAll();
        return chicken;
    }



}

信号灯法

package com.kuang.senior;


//测试生产者消费者问题2：信号灯法，标志位解决
public class TestPC2 {
    public static void main(String[] args) {
        TV tv = new TV();
        new Player(tv).start();
        new Watcher(tv).start();

    }
}

//生产者：演员
class Player extends Thread {
    TV tv;
    public Player(TV tv) {
        this.tv = tv;
    }

    @Override
    public void run() {
        for (int i = 0; i < 20; i++) {
            if(i % 2 == 0) {
                this.tv.play("快乐大本营");
            }else {
                this.tv.play("抖音：记录美好生活");
            }
        }
    }
}

//消费者：观众
class Watcher extends Thread {
    TV tv;
    public Watcher(TV tv) {
        this.tv = tv;
    }

    @Override
    public void run() {
        for (int i = 0; i < 20; i++) {
            tv.watch();
        }
    }
}

//产品：节目
class TV{
    //演员表演，观众等待 T
    //观众观看，演员等待 F
    String voice;
    boolean flag = true;

    //演员表演
    public synchronized void play(String voice) {
        if(!flag) {
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println("演员表演了： " + voice);
        //通知观众观看
        this.notifyAll();// 通知唤醒
        this.voice = voice;
        this.flag = !this.flag;
    }

    //观众观看
    public synchronized void watch() {
        if(flag) {
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println("观看了： " + voice);
        //通知演员表演
        this.notifyAll();
        this.flag = !this.flag;
    }
}

线程池

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线程总结

package com.kuang.senior;

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;

//回顾总结线程的创建
public class ThreadNew {
    public static void main(String[] args) {
        new MyThread1().start();

        new Thread(new MyThread2()).start();

        FutureTask<Integer> futureTask = new FutureTask<Integer>(new MyThread3());
        new Thread(futureTask).start();
        try {
            Integer integer = futureTask.get();
            System.out.println(integer);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }

    }
}

// 1.继承Thread类
class MyThread1 extends Thread{
    @Override
    public void run() {
        System.out.println("MyThread1");
    }
}

// 2.实现Runnable接口
class MyThread2 implements Runnable {
    @Override
    public void run() {
        System.out.println("MyThread2");
    }
}

// 3.实现
class MyThread3 implements Callable<Integer> {

    @Override
    public Integer call() throws Exception {
        System.out.println("MyThread3");
        return 100;
    }
}