JAVA轮训线程 java线程编程

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mob64ca1414098d 2023-08-16 20:19:14

文章标签 JAVA轮训线程 java 多线程 thread 并发编程 文章分类 Java 后端开发

首先，我们我们要进行多线程编程，最少线程怎么创建时最基本的知识。

创建线程由四种方式

1.继承Thread类创建线程（重写run方法，用start()开启线程）

2.实现Runable接口创建线程（重写run方法，也是start来开启线程）

3.使用Callable和Future创建线程（用Lambda表达式创建Callable<Integer>对象，用Future来包装该对象，可以有返回值）

4.使用线程池（Executore框架）

我们创建一个场景，有三个站台再卖20张票，再一个站台卖某张票的时候，其他站台不能同时卖这张票。

线程创建方式知道了，那么多线程编程还有一个很重要的就是怎么同步

1.synchronized关键字

2.Atomic实现原子性

3.lock锁

1、继承Thread类创建线程

synchronized关键字

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.atomic.AtomicInteger;

public class TestThread2 {
    public static void main(String[] args) throws InterruptedException {
        CountDownLatch countDownLatch = new CountDownLatch(3);
        Station1 st1 = new Station1("station 1",countDownLatch);
        Station1 st2 = new Station1("station 2",countDownLatch);
        Station1 st3 = new Station1("station 3",countDownLatch);
        long time = System.currentTimeMillis();
        st1.start();
        st2.start();
        st3.start();
        countDownLatch.await();
        System.out.println((System.currentTimeMillis() - time));

    }
}
class Station1 extends Thread {
    static CountDownLatch countDownLatch;
    Object lock  = "lock";
    static int tick = 20;//保持多个站台线程间票量一直要用static
    public Station1(String name, CountDownLatch countDownLatch){
        super(name);//给线程命名
        this.countDownLatch = countDownLatch;
    }


    @Override
    public void run(){
        while(tick > 0){
            synchronized (lock){
                if(tick > 0){
                    System.out.println(getName() + " 卖出了第" + tick  + "张票" );
                    tick--;
                    //System.out.println("剩下 " + tick + " 张票" );
                }else {
                    System.out.println("票卖完了");
                }
                try {
                    sleep(1000);
                }catch (InterruptedException e){
                    e.printStackTrace();
                }
            }
        }
        countDownLatch.countDown();
    }
}

输出结果，可以看到卖20张票因为synchronized锁的缘故，时间非常慢，要用20多秒，synchronized的效率问题已经很直观了。

JAVA轮训线程 java线程编程_thread

Atomic实现原子性

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.atomic.AtomicInteger;

public class TestThread {
    public static void main(String[] args) throws InterruptedException {
        CountDownLatch countDownLatch = new CountDownLatch(3);
        Station st1 = new Station("station 1",countDownLatch);
        Station st2 = new Station("station 2",countDownLatch);
        Station st3 = new Station("station 3",countDownLatch);
        long time = System.currentTimeMillis();
        st1.start();
        st2.start();
        st3.start();
        countDownLatch.await();
        System.out.println((System.currentTimeMillis() - time));

    }
}
class Station extends Thread {
    static CountDownLatch countDownLatch;
    static AtomicInteger tick = new AtomicInteger(20);//保持多个站台线程间票量一直要用static
    public Station(String name, CountDownLatch countDownLatch){
        super(name);//给线程命名
        this.countDownLatch = countDownLatch;
    }


    @Override
    public void run(){
        while(tick.get() > 0){
            if(tick.get() > 0){
                int i = tick.getAndDecrement();
                System.out.println(getName() + " 卖出了第" + i  + "张票" );
                //System.out.println("剩下 " + tick + " 张票" );
            }else {
                System.out.println("票卖完了");
            }
            try {
                sleep(1000);
            }catch (InterruptedException e){
                e.printStackTrace();
            }
        }
        countDownLatch.countDown();
    }
}

JAVA轮训线程 java线程编程_JAVA轮训线程_02

lock锁

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class TestThread3 {
    public static void main(String[] args) throws InterruptedException {
        CountDownLatch countDownLatch = new CountDownLatch(3);
        Station st1 = new Station("station 1",countDownLatch);
        Station st2 = new Station("station 2",countDownLatch);
        Station st3 = new Station("station 3",countDownLatch);
        long time = System.currentTimeMillis();
        st1.start();
        st2.start();
        st3.start();
        countDownLatch.await();
        System.out.println((System.currentTimeMillis() - time));

    }
}
class Station3 extends Thread {
    static CountDownLatch countDownLatch;
    static int tick = 20;//保持多个站台线程间票量一直要用static
    private Lock lock = new ReentrantLock();
    public Station3(String name, CountDownLatch countDownLatch){
        super(name);//给线程命名
        this.countDownLatch = countDownLatch;
    }


    @Override
    public void run(){

        while(tick > 0){
            lock.lock();
            if(tick > 0){
                System.out.println(getName() + " 卖出了第" + tick  + "张票" );
                tick --;
                //System.out.println("剩下 " + tick + " 张票" );
            }else {
                System.out.println("票卖完了");
            }
            lock.unlock();
            try {
                sleep(1000);
            }catch (InterruptedException e){
                e.printStackTrace();
            }
        }
        countDownLatch.countDown();
    }
}

结果

JAVA轮训线程 java线程编程_多线程_03

可以看到，Atomic和lock的时间差不多，因为底层实现都是CAS，所以比synchronized要快很多，AtomicInteger用起来比较方便，所以后面的例子值用AtomicInteger来实现。

2、实现Runable接口创建线程

可以看到，第一个不同是实现了Runnable接口的Station类并不是一个Thread对象，所以在start的时候需要new一个Thread对象然后执行，这一步，没有Thread方便。

第二个是给线程命名需要自己手动写，所以也麻烦了不少。

Runnable接口的好处就是实现了Runnable接口还可以实现别的接口，但是继承了Thread类就只能继承这一个类了，所以可以根据情况进行选择。

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.atomic.AtomicInteger;

import static java.lang.Thread.sleep;

public class TestThread {
    public static void main(String[] args) throws InterruptedException {
        CountDownLatch countDownLatch = new CountDownLatch(3);
        Station st1 = new Station("station 1",countDownLatch);
        Station st2 = new Station("station 2",countDownLatch);
        Station st3 = new Station("station 3",countDownLatch);
        long time = System.currentTimeMillis();
        new Thread(st1).start();
        new Thread(st2).start();
        new Thread(st3).start();
        countDownLatch.await();
        System.out.println((System.currentTimeMillis() - time));

    }
}
class Station implements Runnable {
    static CountDownLatch countDownLatch;
    static AtomicInteger tick = new AtomicInteger(20);//保持多个站台线程间票量一直要用static
    String name;
    public Station(String name, CountDownLatch countDownLatch){
        this.name = name;//给线程命名
        this.countDownLatch = countDownLatch;
    }

    public String getName() {
        return name;
    }

    @Override
    public void run(){
        while(tick.get() > 0){
            if(tick.get() > 0){
                int i = tick.getAndDecrement();
                System.out.println(getName() + " 卖出了第" + i  + "张票" );
                //System.out.println("剩下 " + tick + " 张票" );
            }else {
                System.out.println("票卖完了");
            }
            try {
                sleep(1000);
            }catch (InterruptedException e){
                e.printStackTrace();
            }
        }
        countDownLatch.countDown();
    }
}

JAVA轮训线程 java线程编程_java_04

3、使用Callable和Future创建线程

在JDK8出来后，使用Callable和Future创建线程可以用Lambda表达式来创建线程

import java.awt.*;
import java.util.concurrent.Callable;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.FutureTask;
import java.util.concurrent.atomic.AtomicInteger;

import static java.lang.Thread.sleep;

public class TestThread {
    public static void main(String[] args) throws InterruptedException {
        CountDownLatch countDownLatch = new CountDownLatch(3);
        long time = System.currentTimeMillis();

        AtomicInteger tick = new AtomicInteger(20);
        for(int i  = 0; i < 3 ;++ i){
            FutureTask<Integer> station = new FutureTask<>((Callable<Integer>)()->{
                while(tick.get() > 0){
                    if(tick.get() > 0){
                        int j = tick.getAndDecrement();
                        System.out.println(Thread.currentThread().getName() + " 卖出了第" + j  + "张票" );
                        //System.out.println("剩下 " + tick + " 张票" );
                    }else {
                        System.out.println("票卖完了");
                    }
                    try {
                        sleep(1000);
                    }catch (InterruptedException e){
                        e.printStackTrace();
                    }
                }
                countDownLatch.countDown();
                return tick.get();
            });
            new Thread(station, "station" + i).start();
        }
        countDownLatch.await();
        System.out.println((System.currentTimeMillis() - time));

    }
}

结果

JAVA轮训线程 java线程编程_JAVA轮训线程_05

4、使用线程池（Executore框架）

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.Executor;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

import static java.lang.Thread.sleep;

public class TestThread3 {
    public static void main(String[] args) throws InterruptedException {
        CountDownLatch countDownLatch = new CountDownLatch(3);
        ExecutorService executorService = Executors.newCachedThreadPool();
        long time = System.currentTimeMillis();
        for (int i = 0; i < 3; ++i){
            String name = "station" + i;
            executorService.execute(new Station(name,countDownLatch));
        }
        countDownLatch.await();
        System.out.println((System.currentTimeMillis() - time));

        executorService.shutdown();
    }
}
class Station implements Runnable {
    static CountDownLatch countDownLatch;
    static AtomicInteger tick = new AtomicInteger(20);//保持多个站台线程间票量一直要用static
    private final String name;

    public Station(String name, CountDownLatch countDownLatch){
        this.name = name;//给线程命名
        this.countDownLatch = countDownLatch;
    }

    public String getName() {
        return name;
    }

    @Override
    public void run(){
        while(tick.get() > 0){
            if(tick.get() > 0){
                System.out.println(getName() + " 卖出了第" + tick.getAndDecrement() + "张票" );
                //System.out.println("剩下 " + tick + " 张票" );
            }else {
                System.out.println("票卖完了");
            }
            try {
                sleep(1000);
            }catch (InterruptedException e){
                e.printStackTrace();
            }

        }
        countDownLatch.countDown();
    }
}

结果

JAVA轮训线程 java线程编程_JAVA轮训线程_06