多线程知识_Java

多线程 1.概述

多线程指的是在单个程序中可以同时运行多个不同的线程，执行不同的任务

2.线程，进程，多线程

**程序：**是指令和数据的有序集合。

**进程：**是执行程序的一次执行过程。

线程：在一个进程中可以包含若干个线程。

3.继承Thread类

自定义线程类。

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

//创建线程方式1：继承Thread类，重写run()方法，调用start开启线程
	//总结：注意，线程开启不一定立即执行，由CPU调度执行
public class ThreadTest extends Thread{
	//线程入口点
    @Override
    public void run() {
        //run方法线程体
        for (int i = 0; i < 20; i++) {
            System.out.println("我在看代码！！！");
        }
    }

    public static void main(String[] args) {
        //main线程，主线程
        //创建一个线程对象
        ThreadTest threadTest1 = new ThreadTest();

        //调用start()方法开启线程
        threadTest1.start();

        for (int i = 0; i < 200;i++) {
            System.out.println("我在学习多线程--"+i);
        }
    }
}

4.网图下载

//练习Thread，实现多线程同步下载图片
public class ThreadDemo extends Thread{

    private String url; //网络图片地址
    private String name; //保存的文件名

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

    //下载图片的执行体
    @Override
    public void run() {
        WebDownloader webDownloader = new WebDownloader();
        webDownloader.downloader(url,name);
        System.out.println("下载的文件名为："+ name);
    }

    public static void main(String[] args) {
        ThreadDemo threadDemo1 = new ThreadDemo("https://nimg.ws.126.net/?url=http%3A%2F%2Fdingyue.ws.126.net%2F2021%2F1015%2F793bfdcaj00r0zwsy002jc000dw0076m.jpg&thumbnail=650x2147483647&quality=80&type=jpg","热巴1.jpg");
        ThreadDemo threadDemo2 = new ThreadDemo("https://nimg.ws.126.net/?url=http%3A%2F%2Fdingyue.ws.126.net%2F2021%2F1015%2F793bfdcaj00r0zwsy002jc000dw0076m.jpg&thumbnail=650x2147483647&quality=80&type=jpg","热巴2.jpg");
        ThreadDemo threadDemo3 = new ThreadDemo("https://nimg.ws.126.net/?url=http%3A%2F%2Fdingyue.ws.126.net%2F2021%2F1015%2F793bfdcaj00r0zwsy002jc000dw0076m.jpg&thumbnail=650x2147483647&quality=80&type=jpg","热巴3.jpg");

        //先下载了1
        threadDemo1.start();
        //然后是2
        threadDemo2.start();
        //最后是3
        threadDemo3.start();
    }
}


class WebDownloader {
    //下载方法
    public void downloader(String url,String name) {
        try {
            //Commons IO是针对开发IO流功能的工具类库。
            //FileUtils文件工具，复制url到文件。
            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");
        }
    }
}

5.实现Runnable接口

实现Runable接口

实现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

//创建线程方式2：实现runnable接口，重写run()方法，执行线程需要丢入runnable接口实现类，调用start方法
public class Thread3 implements Runnable{
    @Override
    public void run() {
        //run()方法线程体
        for (int i = 0; i < 200; i++) {
            System.out.println("我在看代码"+i);
        }
    }

    public static void main(String[] args) {
        //创建runnable接口的实现类对象
        Thread3 thread3 = new Thread3();

        //创建线程对象，通过线程对象来开启我们的线程，代理
//        Thread thread = new Thread(thread3);
//        thread.start();
        //简化写
        new Thread(thread3).start();

        for (int i = 0; i < 1000; i++) {
            System.out.println("我在学习多线程--"+i);
        }
    }
}

6.并发

//买火车票的例子
//多线程操作同一个对象
    //问题：多个线程操作同一个资源的时候，线程不安全，数据紊乱
public class Thread4 implements Runnable{
    //票数
    private int ticketNums = 10;

    @Override
    public void run() {
        while (true) {
            if (ticketNums <= 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"+ticketNums-- +"票。");
        }
    }

    public static void main(String[] args) {
        Thread4 ticket = new Thread4();

        new Thread(ticket,"小明").start();
        new Thread(ticket,"小花").start();
        new Thread(ticket,"小天").start();
    }
}

7.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++) {
            //模拟兔子休息
            if (Thread.currentThread().getName().equals("兔子")&& i%10==0) {
                try {
                    Thread.sleep(1);
                } 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+"圈。");
        }
    }

    //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();
    }
}

8.实现Callable接口

1.实现Callable接口，需要返回值类型

2.重写call方法，需要抛出异常

3.创建目标对象

4.创建执行服务：ExecutorService executorService = Executors.newFixedThreadPool(3);

5.提交执行：Future submit1 = executorService.submit(thread1);

6.获取结果：Boolean rs1 = submit1.get();

7.关闭服务：executorService.shutdownNow();

public class Thread5 implements Callable {

    private String url; //网络图片地址
    private String name; //保存的文件名

    public Thread5(String url,String name) {
        this.url = url;
        this.name = name;
    }

    //下载图片的执行体
    @Override
    public Boolean call() {
        WebDownloader5 webDownloader5 = new WebDownloader5();
        webDownloader5.downloader(url,name);
        System.out.println("下载的文件名为："+ name);
        return true;
    }

    public static void main(String[] args) throws ExecutionException, InterruptedException {
        Thread5 thread1 = new Thread5("https://nimg.ws.126.net/?url=http%3A%2F%2Fdingyue.ws.126.net%2F2021%2F1015%2F793bfdcaj00r0zwsy002jc000dw0076m.jpg&thumbnail=650x2147483647&quality=80&type=jpg","热巴4.jpg");
        Thread5 thread2 = new Thread5("https://nimg.ws.126.net/?url=http%3A%2F%2Fdingyue.ws.126.net%2F2021%2F1015%2F793bfdcaj00r0zwsy002jc000dw0076m.jpg&thumbnail=650x2147483647&quality=80&type=jpg","热巴5.jpg");
        Thread5 thread3 = new Thread5("https://nimg.ws.126.net/?url=http%3A%2F%2Fdingyue.ws.126.net%2F2021%2F1015%2F793bfdcaj00r0zwsy002jc000dw0076m.jpg&thumbnail=650x2147483647&quality=80&type=jpg","热巴6.jpg");

        //创建执行服务
        ExecutorService executorService = Executors.newFixedThreadPool(3);

        //提交执行
        Future submit1 = executorService.submit(thread1);
        Future submit2 = executorService.submit(thread2);
        Future submit3 = executorService.submit(thread3);

        //获取结果
        Boolean rs1 = submit1.get();
        Boolean rs2 = submit2.get();
        Boolean rs3 = submit3.get();

        //关闭服务
        executorService.shutdownNow();
    }

}


class WebDownloader5 {
    //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");
        }
    }
}

9.静态代理

//静态代理模式：
    //真实对象和代理对象都要实现同一个接口
    //代理对象要真是角色
//好处：代理对象可以做好多对象做不了的事，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();
//        you.HappyMarry();
        WebdingCompany company = new WebdingCompany(you);
        company.HappyMarry();
    }
}

interface Marry{
    //人间四喜
        //久旱逢甘露
        //他乡遇故知
        //洞房花烛夜
        //金榜题名时
    public void HappyMarry();
}

//真实角色，你去结婚
class You implements Marry{
    @Override
    public void HappyMarry() {
        System.out.println("我要结婚了！");
    }
}

//代理角色，帮助你结婚
class WebdingCompany implements Marry{
    //代理谁--> 真是目标角色
    private Marry marry;

    public WebdingCompany(Marry marry){
        this.marry = marry;
    }
    @Override
    public void HappyMarry() {
        before();
        this.marry.HappyMarry();//这就是真实对象
        after();
    }

    private void before(){
        System.out.println("结婚前。");
    }

    private void after(){
        System.out.println("结婚后。");
    }

}

10.Lamda表达式

为什么使用Lamda表达式

避免匿名内部类定义过多

简洁代码

//Lambda表达式
public class LambdaDemo {
    //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();

        Like2 like2 = new Like2();
        like2.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，必须借助接口或父类
        ILike iLike = 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{
    public void lambda();
}

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

public class LambdaDemo2 {
    public static void main(String[] args) {
        ILove love = null;
        //1.lambda表示简化
//        ILove love = (int a)-> {
//            System.out.println("i love you!"+ a);
//        };
//        //简化1.参数类型
//        love = (a) -> {
//            System.out.println("i love you!"+ a);
//        };
        //简化2.简化括号
//        love = a -> {
//            System.out.println("i love you!-->"+ a);
//            System.out.println("i love you too!-->"+ a);
//        };
        //简化3.去掉花括号
        love = a -> System.out.println("i love you!-->"+ a);
//总结：1.lambda表达式只能由一行代码的情况下才能简化成一行，如果多行则必须用代码块包裹。
    // 前提是接口为函数式接口。
    // 多个参数也可以去掉参数类型，要去掉就都去掉。必须加上括号
        love.love(521);
    }
}

interface ILove{
    public void love(int a);
}

class Love implements ILove{
    @Override
    public void love(int a) {
        System.out.println("I Love You!-->"+ a);
    }
}

11.线程停止线程的状态

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线程方法

方法	说明
setPriority(int newPriority)	更改线程的优先级
static void sleep(long millis)	在指定的毫秒数内让当前正在执行的线程休
void join()	等待线程终止
static void yield()	暂停当前正在执行的线程的对象，并且执行其他的线程
void interrupt()	中断线程，别用这个
boolean isAlive()	测试线程是否处于活动状态

推荐线程自动停止。

public class StopThread implements Runnable{
    //1.设置一个标识位
    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，转换标识位
    public void stop(){
        this.flag = false;
    }

    public static void main(String[] args) {
        StopThread stopThread = new StopThread();
        new Thread(stopThread).start();
        for (int i = 0;i < 1000; i++) {
            System.out.println("main:"+i);
            if (i == 900) {
                //调用stop方法切换标志位，让线程停止
                stopThread.stop();
                System.out.println("线程该停止了");
            }
        }
    }
}

12.线程休眠——sleep

sleep(时间)指定当前线程阻塞的毫秒数；

sleep存在异常InterruptedException；

sleep时间到达后线程进入就绪状态；

sleep可以模拟延时，倒计时等；

每一个对象都有一个锁，sleep不会释放锁。

//模拟网络延时：是为了放大问题的发生性
public class SleepThread implements Runnable{
    //票数
    private int ticketNums = 100;
    @Override
    public void run() {
        while (true) {
            if (ticketNums <= 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"+ticketNums-- +"张票。");
        }
    }

    public static void main(String[] args) {
        SleepThread sleepThread = new SleepThread();
        new Thread(sleepThread,"小明").start();
        new Thread(sleepThread,"小里").start();
        new Thread(sleepThread,"小五").start();
    }
}

public class SleepThread2 {
    //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;
            }
        }
    }

    public static void main(String[] args) throws InterruptedException {
        //模拟倒计时
//        tenDown();
        //打印当前系统时间
        Date startTime = new Date(System.currentTimeMillis()); //获取系统当前时间
        while (true) {
            Thread.sleep(1000);
            System.out.println(new SimpleDateFormat("HH:mm:ss").format(startTime));
            startTime = new Date(System.currentTimeMillis());//更新当前时间
        }
    }
}

13.线程礼让_yield

让当前正在执行的线程暂停，但不阻塞。

让线程从运行状态转换成就绪状态

//测试礼让线程
//礼让不一定成功，看CPU心情
public class YieldThread {
    public static void main(String[] args) {
        MyYield myYield = new MyYield();
        new Thread(myYield,"a").start();
        new Thread(myYield,"b").start();
        new Thread(myYield,"c").start();
    }
}

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

14.线程强制执行_join

Join合并线程，待此线程执行完成之后，再执行其他线程，其他线程阻塞。

//测试join方法，想象成插队。
public class JoinThread implements Runnable{
    @Override
    public void run() {
        for (int i = 0; i < 100; i++) {
            System.out.println("线程VIP来了"+i);
        }
    }

    public static void main(String[] args) throws InterruptedException {
        //启动线程
        JoinThread joinThread = new JoinThread();
        Thread thread = new Thread(joinThread);
        thread.start();
        //主线程
        for (int i = 0; i < 1000; i++) {
            if (i == 200) {
                thread.join();//插队
            }
            System.out.println("main:"+i);
        }
    }
}

15.观测线程状态

//观察测试线程状态
public class StateThread {
    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("输出状态："+ state);
        }
    }
}

16.线程的优先级

Java提供一个线程调度器来监控程序中启动后进入就绪状态的所有线程，线程调度器按照优先级决定应该调度那个线程来执行。

线程的优先级用数字表示：范围从1~10.

Thread.MIN_PRIORITY = 1;

Thread.MAX_PRIORITY = 10;

Thread.NORM_PRIORITY = 5;

使用以下方式改变获取优先级

getPriority(). setPriority(int xxx)

//线程的优先级
public class PriorityThread {
    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 thread1 = new Thread(MyPriority);
        Thread thread2 = new Thread(MyPriority);
        Thread thread3 = new Thread(MyPriority);
        Thread thread4 = new Thread(MyPriority);
        Thread thread5 = new Thread(MyPriority);
        Thread thread6 = new Thread(MyPriority);

        //先设置优先级，在启动
        thread1.start();

        thread2.setPriority(1);
        thread2.start();

        thread3.setPriority(4);
        thread3.start();

        thread4.setPriority(Thread.MAX_PRIORITY); // MAX_PRIORITY = 10
        thread4.start();

    }
}

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

17.守护线程

线程分成用户线程和守护线程

//测试守护线程
    //上帝守护你
public class DaemonThread {
    public static void main(String[] args) {
        God god = new God();
        You you = new You();

        Thread thread = new Thread(god);
        thread.setDaemon(true); //默认时false表示是用户线程，正常的线程都是用户线程。。。

        thread.start();//上帝守护线程启动

        new Thread(you).start(); //你  用户线程启动。。。
    }
}

//上帝
class God implements Runnable {
    @Override
    public void run() {
        while (true) {
            System.out.println("上帝保佑你！");
        }
    }
}

//你
class You implements Runnable {
    @Override
    public void run() {
        for (int i = 0; i < 36500; i++) {
            System.out.println("你一生都开心的活着。");
        }
        System.out.println("============googbye! world!============");
    }
}

18.线程同步机制

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

线程同步需要：队列加锁 synchronized

19.三大不安全案例

//不安全取钱
    //两个人去银行取钱，账户
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 girlFriend = new Drawing(account, 100, "girlFriend");

        you.start();
        girlFriend.start();
    }
}

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

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

//银行
class Drawing extends Thread {
    Account account;//账户
    //取了多少钱
    int drawingMoney;
    //现在手里有多少钱
    int nowMoney;
    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
        account.money = account.money - drawingMoney;
        //你手里的钱
        nowMoney = nowMoney + drawingMoney;

        System.out.println(account.name+"余额为："+account.money);
        System.out.println(this.getName()+"手里的钱："+nowMoney);
    }
}

//不安全买票
public class UnsafeBuyTicket {
    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 = 50;
    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(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

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

//线程不安全集合
public class UnsafeList {
    public static void main(String[] args) {
        ArrayList list = new ArrayList<>();
        for (int i = 0; i < 10000; i++) {
            new Thread(()->{
                    list.add(Thread.currentThread().getName());
            }).start();
        }
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(list.size());
    }
}

20.同步方法以及同步块

由于我们可以通过private关键字来保证数据对象只能被方法访问，所以我们只需要针对方法提出一套机制，这套机制就是synchronized关键字，它包括synchronized方法，synchronized块。

同步方法：public synchronized void method(int args){}

synchronized方法控制对"对象"的访问，每个对象对应一把锁，每个synchronized方法都必须获得调用该方法的对象的锁才能执行，否则线程会阻塞，方法一旦执行，就独占锁，直到该方法返回才释放锁，后面被阻塞的线程才能获得这个锁，继续执行。

缺陷：若将一个大的方法申明为synchronized将会影响效率。

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public class UnsafeBuyTicket {
    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; //外部停止方式
    @Override
    public void run() {
        //买票
        while (flag) {
            buy();
        }
    }

    //synchronized 同步方法：锁的是this   (锁住对象才能实现)
    private synchronized void buy() {
        //判断是否有票
        if (ticketNums <= 0) {
            flag = false;
            return;
        }
            //模拟延时
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

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

同步块：synchronized(Obj){}

**obj:**称为同步监视器，obj可以是任何对象。

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 girlFriend = new Drawing(account, 100, "girlFriend");

        you.start();
        girlFriend.start();
    }
}

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

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

//银行
class Drawing extends Thread {
    Account account;//账户
    //取了多少钱
    int drawingMoney;
    //现在手里有多少钱
    int nowMoney;
    public Drawing(Account account,int drawingMoney,String name) {
        super(name);
        this.account = account;
        this.drawingMoney = drawingMoney;
    }

    //取钱
    //synchronized 默认锁的是this
    @Override
    public void run() {
        synchronized (account) {
            //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
            account.money = account.money - drawingMoney;
            //你手里的钱
            nowMoney = nowMoney + drawingMoney;

            System.out.println(account.name+"余额为："+account.money);
            System.out.println(this.getName()+"手里的钱："+nowMoney);
        }

    }
}

21.CopyonWrite

//测试JUC安全类型的集合
public class JUCDemo {
    public static void main(String[] args) {
        CopyOnWriteArrayList list = new CopyOnWriteArrayList<>();
        for (int i = 0; i < 1000; i++) {
            new Thread(()->{
                list.add(Thread.currentThread().getName());
            }).start();
        }
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(list.size());
    }
}

22.死锁

多个线程各自占有一些共享资源，并且相互等待其他线程占有的资源才能运行，从而导致两个或多个线程都等待对方释放资源，都停止执行的情形。某个同步块同时拥有“两个以上对象的锁”。就可能会发生死锁问题。

产生死锁的四个必要条件：

1.互斥条件：一个资源每次只能被一个进程使用

2.请求与保持条件：一个进程因请求资源而阻塞时，对已经获取到的资源保持不放。

3.不剥夺条件：进程已经获得的资源，在未使用完成之前，不能强行剥夺。

4.循环等待条件：若干进程之间形成一种头尾相接的循环等待资源关系。

//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 makeup0 = new Makeup(0, "00");
        Makeup makeup1 = new Makeup(1, "11");
        makeup0.start();
        makeup1.start();
    }
}

//口红
class Lipstick{}
//镜子
class Mirror{}

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();
        }
    }

    //化妆方法
    private void makeUp() throws InterruptedException {
        if (choice == 0) {
            synchronized (lipstick) {//获得口红的锁
                System.out.println(this.girlName+"获取口红的锁");
                Thread.sleep(1000);
            }
            synchronized (mirror) { //一秒后获得镜子的锁
                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+"获取镜子的锁");
                Thread.sleep(2000);
            }
            synchronized (lipstick) { //两秒后获得口红的锁
                System.out.println(this.girlName+"获得口红的锁");
            }
        }
    }
}

23.Lock锁

Java提供了更强大的线程同步机制----->显式定义同步锁对象来实现同步。同步锁使用Lock对象来充当。

class A{
		private final ReentrantLock lock = new ReentrantLock();
		public void m(){
			lock.lock();
			try{
				//保证线程安全的代码
			}finally{
				lock.unlock();
				//如果同步代码块有异常，要将unlock()写入finally语句块
			}
		}
}

//测试lock锁。
public class LockDemo {
    public static void main(String[] args) {
        LockDemo2 lockDemo2 = new LockDemo2();
        new Thread(lockDemo2).start();
        new Thread(lockDemo2).start();
        new Thread(lockDemo2).start();
    }
}

class LockDemo2 extends Thread{
    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 {
                lock.unlock();//解锁
            }

        }
    }
}

synchronized与Lock的对比

Lock时显式锁（手动开启和关闭锁，别忘记关闭锁）synchronized是隐式锁，出了作用域自动释放。

Lock只有代码块锁，synchronized有代码块锁和方法锁

使用Lock锁，JVM将花费较少的时间来调度线程，性能更好。并且具有更好的扩展性（提供更多的子类）

优先使用顺序：

Lock　＞　同步代码块（已经进入方法体，分配了相应资源）　＞　同步方法（在方法体之外）

24.生产者消费者

在生产者消费者问题中，仅有synchronized是不够的

synchronized　可阻止并发更新同一个共享资源，实现了同步。

synchronized　不能用来实现不同线程之间的消息传递（通信）

Java提供了几个方法解决线程之间的通信问题

方法名	作用
wait()	表示线程一直等待，直到其他线程通知，与sleep不同，会释放锁
wait(long timeout)	指定等待的毫秒数
notify()	唤醒一个处于等待状态的线程
notifyAll()	唤醒同一个对象上所有调用wait()方法的线程，优先级别高的线程优先调度

25.管程法

//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 PCDemo {
    public static void main(String[] args) {
        SynContainer synContainer = new SynContainer();
        new Productor(synContainer).start();
        new Consumer(synContainer).start();
    }
}

//生产者
class Productor extends Thread{
    SynContainer synContainer;
    public Productor(SynContainer synContainer){
        this.synContainer = synContainer;
    }
    //生产
    @Override
    public void run() {
        for (int i = 0; i < 100; i++) {
            synContainer.push(new Chicken(i));
            System.out.println("生产了"+i+"只鸡。");
        }
    }
}

//消费者
class Consumer extends Thread{
    SynContainer synContainer;
    public Consumer(SynContainer synContainer){
        this.synContainer = synContainer;
    }
    //消费
    @Override
    public void run() {
        for (int i = 0; i < 1000; i++) {
            System.out.println("消费者消费了-->"+synContainer.pop().id+"只鸡！");
        }
    }
}

//产品
class Chicken{
    int id;//产品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();
            }
        }
        //如果没满，就需要添加产品
        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(){
        //判断是否能消费
        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;
    }
}

26.信号灯法

//测试生产者消费者问题2：信号灯法，标志位解决。
public class PcDemo2 {
    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("节目1");
            }else {
                this.tv.play("节目2");
            }
        }
    }
}
//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，true
    //观众观看演员等待  false
    String voice;//表演的节目
    boolean flag = true;
    //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;
    }
}

27.线程池

线程池相关API：ExecutorService和Executors

ExecutorService：真正的线程池接口，常见子类ThreadPoolExecutors

void execute(Runnable command)：执行任务，有返回值，一般用来执行Runable

Future submit(Callable task)：执行任务，有返回值，一般又来执行Callable

void shutdown()：关闭线程池

Executors：工具类、线程池的工厂类，用于创建并返回不同类型的线程池。

//测试线程池
public class PoolDemo {
    public static void main(String[] args) {
        // 1.创建服务，创建线程池
        // newFixedThreadPool 参数为：线程池的大小
        ExecutorService service = Executors.newFixedThreadPool(10);
        service.execute(new MyThread());
        service.execute(new MyThread());
        service.execute(new MyThread());
        service.execute(new MyThread());
        //2.关闭连接
        service.shutdown();
    }
}

class MyThread implements Runnable{
    @Override
    public void run() {
//        for (int i = 0; i < 100; i++) {
            System.out.println(Thread.currentThread().getName());
//        }
    }
}

28.总结

//线程总结
public class ThreadSummary {
    public static void main(String[] args) {
        new MyThread().start();

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

        FutureTask futureTask = new FutureTask(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
class MyThread 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Callable接口
class MyThread3 implements Callable{
    @Override
    public Integer call() throws Exception {
        System.out.println("MyThread3");
        return 100;
    }
}

FixedThreadPool(10);
service.execute(new MyThread());
service.execute(new MyThread());
service.execute(new MyThread());
service.execute(new MyThread());
//2.关闭连接
service.shutdown();
}
}

class MyThread implements Runnable{
@Override
public void run() {
// for (int i = 0; i < 100; i++) {
System.out.println(Thread.currentThread().getName());
// }
}
}



## 28.总结

```java
//线程总结
public class ThreadSummary {
    public static void main(String[] args) {
        new MyThread().start();

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

        FutureTask futureTask = new FutureTask(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
class MyThread 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Callable接口
class MyThread3 implements Callable{
    @Override
    public Integer call() throws Exception {
        System.out.println("MyThread3");
        return 100;
    }
}

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