实现两条线程交替打印奇偶数的两种简单方法

Posted 2020-12-17 dwwzone

实现两条线程交替打印奇偶数的两种简单方法

使用Synchronized

public class Main {

    private int count = 0;

    public static void main(String[] args) throws InterruptedException {
        Main main = new Main();
        new Thread(()->{
            for (int i = 0; i < 50; i++) {
                try {
                    main.printEven();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        },"A").start();

        new Thread(()->{
            for (int i = 0; i < 50; i++) {
                try {
                    main.printOdd();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        },"B").start();
    }
	
   	//打印奇数方法
    public  synchronized void printOdd() throws InterruptedException {
        while (this.count % 2 == 0) {//如果是偶数，则阻塞，释放锁
            this.wait();
        }
        System.out.println(Thread.currentThread().getName() + this.count++);
        this.notifyAll();//唤醒阻塞线程
    }
	
    //打印偶数方法
    public  synchronized void printEven() throws InterruptedException {
        while (this.count % 2 != 0) {//如果是奇数，则阻塞，释放锁
            this.wait();
        }
        System.out.println(Thread.currentThread().getName() + this.count++);
        this.notifyAll();//唤醒阻塞线程
    }
}

此方法不容易扩展到多条线程，越多的线程在唤醒时会经历越多的竞争，加大CPU资源浪费，同时也增加耗时

使用ReetrantLock+Condition实现精准唤醒

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;

public class Turning {

    public static void main(String[] args) throws InterruptedException {
        Turning turning = new Turning();
        new Thread(()->{
            for (int i = 0; i < 50; i++) {
                turning.printO();
            }
        },"A").start();
        Thread.sleep(1000);
        new Thread(()->{
            for (int i = 0; i < 50; i++) {
                turning.printJ();
            }
        },"B").start();
    }

    private ReentrantLock lock = new ReentrantLock();
    private Condition condition1 = lock.newCondition();
    private Condition condition2 = lock.newCondition();

    private int number = 0;

    public void printJ() {
        lock.lock();
        try {
            while (number % 2 == 0) {
                condition1.await(); //如果是偶数，在此处阻塞
            }
            System.out.println(Thread.currentThread().getName()+number++);
            condition2.signal(); //唤醒在2处阻塞的线程
        }catch (Exception e) {
            e.printStackTrace();
        }finally {
            lock.unlock();
        }
    }

    public void printO() {
        lock.lock();
        try{
            while (number % 2 != 0) { 
                condition2.await(); //如果是奇数，在此处阻塞
            }
            System.out.println(Thread.currentThread().getName()+number++);
            condition1.signal(); //唤醒在1处阻塞的线程
        }catch (Exception e) {
            e.printStackTrace();
        }finally {
            lock.unlock();
        }
    }
}

此方法容易扩展到多条线程交替，且为精准唤醒，减少线程竞争带来的消耗