Java多线程

2023-12-14 17:34:58

多线程

程序是指令和数据的有序集合,起本升本没有任何运行的含义,是一个静态的概念
进程是执行程序的一次执行过程,他是一个动态的概念,是系统资源分配的单位
通常在一个进程中,可以包含若干个线程,当然一个进程中至少有一个线程,不然没有存在的意义,线程是cpu调度和执行的单位

线程的创建

三种创建方式

继承Thread类(重点)

//创建线程方式1:继承Thread类,重写run,调用start开启线程
public class TestThread1 extends Thread{
    @Override
    public void run() {
        for (int i = 0; i < 20; i++) {
            System.out.println("-----");
        }
    }

    public static void main(String[] args) {
        //创建一个线程对象
        TestThread1 testThread1 = new TestThread1();
        //调用start方法,开启线程
        testThread1.start();
        //main线程,主线程
        for (int i = 0; i < 20; i++) {
            System.out.println("主线程");
        }
    }
}
//两个线程是同时执行的,线程开启后不一定立即执行,按照cpu安排调度

实现图片同步下载

package org.example;

import org.apache.commons.io.FileUtils;

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

//实现多线程同步下载图片
public class TestThread2 extends Thread{
    private String url;
    private String path;
    public TestThread2(String url,String name){
        this.url =url;
        this.path =name;
    }
    @Override
    public void run() {
        WebDownloader webDownloader = new WebDownloader();
        webDownloader.downloader(url, path);
        System.out.println("下载了文件名为:"+path);
    }
    public static void main(String[] args) {
        String url ="https://img-blog.csdnimg.cn/3199ad8ae6974b33953faa7a233a763a.png";
        String path = "test.jpg";
        TestThread2 t1 = new TestThread2(url, path);
        TestThread2 t2 = new TestThread2("https://img-blog.csdnimg.cn/cd63b3bdaa6d4c468238922c197bd2f7.png", "2.jpg");
        TestThread2 t3 = new TestThread2("https://img-blog.csdnimg.cn/ae7b9b2c89fb4069802660a4d6bbd691.png", "3.jpg");
        t1.start();
        t2.start();
        t3.start();
    }
}

class WebDownloader{
    public void downloader(String url, String name){
        try {
            FileUtils.copyURLToFile(new URL(url),new File(name));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

实现Runnable接口(重点)

package org.example;

public class TestRunnable1 implements Runnable{
    @Override
    public void run() {
        for (int i = 0; i < 20; i++) {
            System.out.println("多线程启动");
        }
    }

    public static void main(String[] args) {
        TestRunnable1 testRunnable1 = new TestRunnable1();
         new Thread(testRunnable1).start();
        for (int i = 0; i < 30; i++) {
            System.out.println("主线程");
        }
    }
}

package org.example;
//龟兔赛跑
public class Race implements Runnable{
   private String winner;
    @Override
    public void run() {
        for (int i = 0; i <=100; i++) {
            if(Thread.currentThread().getName().equals("兔子") && i %10 ==0){
                try {
                    Thread.sleep(1);
                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                }
            }
            if(gameOver(i)) break;
            System.out.println(Thread.currentThread().getName()+"跑了"+i+"步");
            gameOver(i);
        }
    }
    private boolean gameOver(int step){
        if(winner != null){
            return true;
        }else {
            if(step == 100){
                winner = Thread.currentThread().getName();
                System.out.println("winer 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();
    }
}

实现Callable接口(了解)

静态代理模式

代理对象可以做额外的事情

真实对象只需要做要做的事情

package org.example;
//静态代理模式:真实对象和代理对象都要实现同一个接口,代理对象要代理真实角色,
public class StaticProxy {
    public static void main(String[] args) {
        Person person = new Person();
        WeddingCompany weddingCompany = new WeddingCompany(person);
        weddingCompany.marry();
    }
}
interface Marry{
    void marry();

}
class Person implements Marry{

    @Override
    public void marry() {
        System.out.println("要结婚了超开心");
    }
}
class WeddingCompany implements Marry{
    private Marry target;
    public WeddingCompany(Marry target){
        this.target =target;
    }

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

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

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

线程状态

在这里插入图片描述

线程停止

不退将jdk提供的stop(),destory()方法
推荐线程自己停下来
金阿姨使用一个标志位进行终止变量

package org.example;

import jdk.internal.org.objectweb.asm.tree.analysis.SourceInterpreter;

public class TestStop implements Runnable{
    private boolean flag =true;
    @Override
    public void run() {
        while (flag){
            System.out.println("线程在执行");
        }
    }
    public void stop(){
        flag = false;
    }

    public static void main(String[] args) {
        TestStop testStop = new TestStop();
        new Thread(testStop).start();
        for (int i = 0; i < 1000; i++) {
            System.out.println(i);
            if( i== 900){
                testStop.stop();
                System.out.println("线程停止了" );
                break;
            }
        }
    }
}

线程休眠

sleep(time) 毫秒

存在InterruptedException

sleep可以模拟网络延迟倒计时

每个对象都有锁,sleep不会释放锁

线程礼让

礼让线程,让当前正在执行的线程暂停,但不阻塞
将线程从运行状态转为就绪状态
让cpu重新调度,礼让不一定成功,看cpu心情

package org.example;

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");
    }
}

join

Join线程合并,待此线程执行完成后,再执行其他线程,其他线程阻塞

package org.example;

public class TestJoin {
    public static void main(String[] args) {
        MyJoin myJoin = new MyJoin();
        Thread thread = new Thread(myJoin);
        thread.start();
        for (int i = 0; i < 500; i++) {
            if(i ==200){
                try {
                    thread.join();
                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                }
            }
            System.out.println("main"+i);
        }
    }
}
class MyJoin implements Runnable{

    @Override
    public void run() {
        for (int i = 0; i < 1000; i++) {
            System.out.println("线程vip来了"+i);
        }
    }
}

检测线程状态

package org.example;

public class TestStatus {
    public static void main(String[] args) {
        Thread r =  new Thread(()->{
            for (int i = 0; i < 5; i++) {
                try {
                    Thread.sleep(1000);
                    System.out.println("---");
                } catch (InterruptedException e) {

                }
            }
        });
        System.out.println(r.getState());
        r.start();
        System.out.println(r.getState());
    }

}

线程的优先级

先设置优先级在启动,大的先执行,但是还是由cpu决定

package org.example;

public class TestPriority {
    public static void main(String[] args) {
        System.out.println(Thread.currentThread().getName()+" "+Thread.currentThread().getPriority());
        Thread t1 = new Thread(new myPriority());
        Thread t2 = new Thread(new myPriority());
        Thread t3 = new Thread(new myPriority());
        t1.start();
        t2.setPriority(1);
        t2.start();
        t3.setPriority(8);
        t3.start();
    }
}
class myPriority implements Runnable{

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

守护线程

线程分为用户线程和守护线程
虚拟机确保用户线程执行完毕
虚拟机不用等待守护线程执行完毕

package org.example;

public class TestDaemon {
    public static void main(String[] args) {
        god god = new god();
        You you = new You();
        Thread thread = new Thread(god);
        //设置守护县城
        thread.setDaemon(true);
        thread.start();
        new Thread(you).start();
    }
}
class god implements Runnable{

    @Override
    public void run() {
        while (true){
            System.out.println("上帝保佑着你");
        }
    }
}
class You implements Runnable{
    @Override
    public void run() {
        for (int i = 0; i < 36500; i++) {
            System.out.println("happy everyDay");
        }
        System.out.println("goodBye world");
    }
}

线程同步

多个线程操作同一个资源

不安全

package syn;

import sun.rmi.runtime.NewThreadAction;

public class UnsafeBuyTicket {
    public static void main(String[] args) {
        BuyTicket buyTicket = new BuyTicket();
         new Thread(buyTicket,"1").start();
         new Thread(buyTicket,"2").start();
         new Thread(buyTicket,"3").start();
         new Thread(buyTicket,"4").start();
    }
}
class BuyTicket implements Runnable{
    private int ticket =10;
    private boolean flag = true;
    @Override
    public void run() {
        while (flag){
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
            buy();
        }
    }
    private void buy(){
        if(ticket <= 0) {
            stop();
            return;
        }
        System.out.println(Thread.currentThread().getName()+"拿到第"+ticket--+"张票");
    }
    public void stop(){
        flag =false;
    }
}

线程同步

使用synchronized

synchronized方法控制对"对象的访问",每个对象对应一把锁,每个sync方法都必须获得调用该方法的对象的锁才能执行,否则会线程阻塞

方法一旦执行,就独占该锁,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

package syn;
public class UnsafeBuyTicket {
    public static void main(String[] args) {
        BuyTicket buyTicket = new BuyTicket();
         new Thread(buyTicket,"1").start();
         new Thread(buyTicket,"2").start();
         new Thread(buyTicket,"3").start();
         new Thread(buyTicket,"4").start();
    }
}
class BuyTicket implements Runnable{
    private int ticket =10;
    private boolean flag = true;
    @Override
    public void run() {
        while (flag){
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
            buy();
        }
    }
    private synchronized void buy(){
        if(ticket <= 0) {
            stop();
            return;
        }
        System.out.println(Thread.currentThread().getName()+"拿到第"+ticket--+"张票");
    }
    public void stop(){
        flag =false;
    }
}

同步块

sycn(obj){}

obj称之为同步监视器

obj可以是任何对象,但是推荐使用共享资源作为同步监视器
同步方法中无需指定同步监视器,因为同步方法的同步器就是thism就是这个对象本身,或者是class

同步监视器执行过程

第一个线程访问,锁定同步监视器,执行方法
第二个线程访问,发现同步监视器被锁定,无法访问
第一个线程访问完毕,解锁同步监视器
第二个线程访问,发现没有被锁定,锁定监视器,执行代码.

package syn;

import java.util.ArrayList;

public class UnSafeList {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();
        for (int i = 0; i < 1000; i++) {
            new Thread(()->{
                synchronized (list){
                    list.add(Thread.currentThread().getName());
                }
            }).start();
        }
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {


        }
        System.out.println(list.size());
    }
}

juc下的线程安全集合

package syn;

import java.util.concurrent.CopyOnWriteArrayList;

public class TestJUC {
    public static void main(String[] args) {
        //测试juc安全数组
        CopyOnWriteArrayList<String> list = new CopyOnWriteArrayList<>();
        for (int i = 0; i < 1000; i++) {
            new Thread(()->{
                list.add(Thread.currentThread().getName());
            }).start();
        }
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
        System.out.println(list.size());
    }
}

死锁

多个线程各自占有一些共享资源,并且互相等待其他线程占有的支援才能运行,而导致两个或多个线程都在等待对方释放资源,都停止执行的场景,某个同步块同时拥有"两个以上对象的锁"时就有可能会发生死锁问题.

package syn;

//死锁:多个线程互相占有对方的支援,形成僵持
public class Lock {
    public static void main(String[] args) {
        MakeUp m1= new MakeUp(0, "1");
        MakeUp m2= new MakeUp(0, "2");
        m1.start();
        m2.start();
    }
}
//口红
class Lipstick{}
//镜子
class Mirror{}
class MakeUp extends Thread{
     static Lipstick lipstick =new Lipstick();
     static Mirror mirror = new Mirror();
     int choice;
     String girlName;
     MakeUp(int choice,String girlName){
         this.choice = choice;
         this.girlName = girlName;
     }
    @Override
    public void run() {
        //化妆
        try {
            makeup();
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
    }
    //互相拿到对方的锁
    private void makeup() throws InterruptedException {
         if(choice == 0){
             synchronized (lipstick){
                 System.out.println(this.girlName+"获得口红的锁");
                 Thread.sleep(5000);
                 synchronized (mirror){
                     System.out.println("获得镜子的锁");
                 }
             }
         }else {
             synchronized (mirror){
                 System.out.println(this.girlName+"获得口红的锁");
                 Thread.sleep(4000);
                 synchronized (lipstick){
                     System.out.println("获得镜子的锁");
                 }
             }
         }
    }
}

Lock

package gaoji;

import java.util.concurrent.locks.ReentrantLock;

//测试lock
public class TestLock {
    public static void main(String[] args) {
        testLock2 t2 = new testLock2();
        new Thread(t2).start();
        new Thread(t2).start();
        new Thread(t2).start();
    }
}
class testLock2 implements Runnable{
    int tickNum =10;
   private final ReentrantLock lock = new ReentrantLock();

    @Override
    public void run() {
        while (true){
            try {
                //放到try里面
                lock.lock();
                if(tickNum >0){
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        throw new RuntimeException(e);
                    }
                    System.out.println(tickNum--);
                }else {
                    break;
                }
            }finally {
                //一般写到finally
                lock.unlock();
            }

        }
    }
}

在这里插入图片描述

线程协作

Java提供了几个方法解决线程之间的通信问题

package gaoji;

//测试生产者消费者模型
public class TestPC {
    public static void main(String[] args) {
        SyncContainer syncContainer = new SyncContainer();
        Producer producer = new Producer(syncContainer);
        Consumer consumer = new Consumer(syncContainer);
        producer.start();
        consumer.start();
    }
}
class Producer extends Thread{
    SyncContainer container;
    public Producer(SyncContainer container){
        this.container = container;
    }

    @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");
        }
    }
}
class Consumer extends Thread{
    SyncContainer container;
    public Consumer(SyncContainer container){
        this.container = container;
    }

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

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

    @Override
    public String toString() {
        return "Chicken{" +
                "id=" + id +
                '}';
    }
}
//缓冲区
class SyncContainer{
    Chicken[] chickens = new Chicken[10];
    //容器计数器
    int cnt = 0;
    //生产者放入产品
    public synchronized void push(Chicken product) {
        if (cnt == 10) {
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        chickens[cnt] = product;
        cnt++;
        this.notifyAll();
    }

    public synchronized Chicken pop() {
        if (cnt == 0) {
            try {
                this.wait();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        cnt--;
        Chicken product = chickens[cnt];
        this.notifyAll();
        return product;
    }
}

线程池

提前创建好多个线程,放入线程池,使用时直接获取,使用完放回池中

在这里插入图片描述

package gaoji;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class TestPool {
    public static void main(String[] args) {
        //创建线程池,参数为大小
        ExecutorService executorService = Executors.newFixedThreadPool(10);
        executorService.execute(new myThread());
        executorService.execute(new myThread());
        executorService.execute(new myThread());
        executorService.execute(new myThread());
    }
}
class myThread implements Runnable{

    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName());
    }
}

roduct;
}
}


## 线程池

提前创建好多个线程,放入线程池,使用时直接获取,使用完放回池中

[外链图片转存中...(img-4V6tDQBC-1702542956181)]

[外链图片转存中...(img-9qAWm6xK-1702542956181)]

```java
package gaoji;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class TestPool {
    public static void main(String[] args) {
        //创建线程池,参数为大小
        ExecutorService executorService = Executors.newFixedThreadPool(10);
        executorService.execute(new myThread());
        executorService.execute(new myThread());
        executorService.execute(new myThread());
        executorService.execute(new myThread());
    }
}
class myThread implements Runnable{

    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName());
    }
}

文章来源:https://blog.csdn.net/m0_74347016/article/details/134999054
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