多线程交替打印奇偶数

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LockSupport

原理

贴一个之前的笔记，字迹比较潦草zz 有空的时候这里会补上说明

实现1

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.LockSupport;

class Main{
    static Thread a = null, b=null;

    public static void main(String[] args){
        a = new Thread(new Runnable() {
            @Override
            public void run() {
                for(int i = 1;i<=99;i+=2){
                    System.out.println(i);
                    LockSupport.unpark(b);
                    LockSupport.park();
                }
            }
        });

        b = new Thread(new Runnable() {
            @Override
            public void run() {
                for(int i = 2;i<=100;i+=2){
                    LockSupport.park();
                    System.out.println(i);
                    LockSupport.unpark(a);
                }
            }
        });

        a.start();
        b.start();
    }
}

实现2

import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.LockSupport;

public class Main {

    static AtomicInteger num = new AtomicInteger(1);

    public static void main(String[] args) throws InterruptedException {

        Print p1 = new Print();
        Print p2 = new Print();
        Thread t1 = new Thread(p1); //t1对应p1任务 但p1任务的线程挂在t2上方便t1唤醒它
        Thread t2 = new Thread(p2);
        t1.setName("thread-cc-1");
        t2.setName("thread-cc-2");

        p1.setT(t2);//给p1的Thread设置为t2方便t1唤醒它
        p2.setT(t1);
        t1.start();
        t2.start();

        // 唤醒线程t1打印奇数，线程1打印奇数，线程2打印偶数
        LockSupport.unpark(t1);

    }

    static class Print implements Runnable {
        private volatile Thread t;

        @Override
        public void run() {
            while (true) {
                // 进入之后立即阻塞
                LockSupport.park();
                if (num.get() > 100) {
                    LockSupport.unpark(t);
                    return;
                }
                System.out.println(Thread.currentThread().getName() + " : " + num.getAndIncrement());
        // 这里的t实际上是与currentThread不同的另一个线程
        // 因此实现了 奇数唤醒偶数线程，偶数唤醒奇数线程
                LockSupport.unpark(t);
            }
        }

        public void setT(Thread t) {
            this.t = t;
        }
    }
}

点评：可拓展性实现2相对较差一些(实现3个线程交替打印etc)

Synchronized + wait/notify实现

public class Main{
    public static void main(String[] args){
        MyPrint print = new MyPrint();
        Thread thread1 = new Thread(print,"A");
        Thread thread2 = new Thread(print,"B");
        thread1.start();
        thread2.start();

    }
}


class MyPrint implements Runnable{
    int i = 1;
    @Override
    public void run() {
        while (true){
            synchronized (this){
                this.notify();//在这里唤醒的目的是为保证拿到锁的线程只有一个
                // 不会立即释放锁 退出代码块才会释放锁
                if (i <= 100){
                    System.out.println(Thread.currentThread().getName()+" "+i++);
                }else {
                    return;
                }
                try {
                    this.wait();//打印过数据的线程等待 必须等到没打印过数字的拿到锁了才能唤醒
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}