线程间通信

 对于两个线程a，b；

首先线程a：

(1) 判断：变量值如果为0

(2) 干活：变量值+1

(3) 通知：a线程通知b线程对变量-1

其次线程b：

(1) 判断：变量值如果为1

(2) 干活：变量值-1

(3) 通知：b线程通知a线程对变量+1

依次类推。。。

代码实现：方式一：synchronized关键字

package JUC.sync;

//第一步 创建资源类，定义属性和操作方法
class Share {
    //初始值
    private int number = 0;
    //+1的方法
    public synchronized void incr() throws InterruptedException {
        //第二步 判断 干活 通知
        if (number != 0) { //判断number值是否为0，如果不是0，等待
            this.wait();
        }
        //如果number值是0，就+1操作
        number++;
        System.out.println(Thread.currentThread().getName()+" :: "+number);
        //通知其他线程
        this.notifyAll();
    }

    //-1的方法
    public synchronized void decr() throws InterruptedException {
        //第二步 判断 干活 通知
        if (number != 1) { //判断number值是否为1，如果不是1，等待
            this.wait();
        }
        //如果number值是1，就-1操作
        number--;
        System.out.println(Thread.currentThread().getName()+" :: "+number);
        //通知其他线程
        this.notifyAll();
    }
}

public class ThreadDemo1 {
    //第三步 创建多个线程，调用资源类的操作方法
    public static void main(String[] args) {
        Share share = new Share();
        //创建线程
        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                try {
                    share.incr();//+1
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        },"AA").start();

        new Thread(()->{
            for (int i = 0; i < 10; i++) {
                try {
                    share.decr();//-1
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        },"BB").start();
    }

}

如果线程为4个，会出现 虚假唤醒 的问题

 解决方案：

判断语句由 if 改为 while。while条件不管wait什么时候睡，什么时候醒，都要经过判断条件。

代码实现：方式二：Lock接口

package JUC.lock;

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

//第一步 创建资源类，定义属性和操作方法
class Share {
    private int number = 0;

    //创建Lock
    final Lock lock = new ReentrantLock();
    final Condition condition  = lock.newCondition();

    //+1
    public void incr() throws InterruptedException {
        //上锁
        lock.lock();
        try{
            //判断
            while(number != 0){
                condition.await();
            }
            //干活
            number++;
            System.out.println(Thread.currentThread().getName()+" :: "+number);
            //通知
            condition.signalAll();
        } finally {
            //解锁
            lock.unlock();
        }

    }

    //-1
    public void decr() throws InterruptedException {
        //上锁
        lock.lock();
        try{
            //判断
            while(number != 1){
                condition.await();
            }
            //干活
            number--;
            System.out.println(Thread.currentThread().getName()+" :: "+number);
            //通知
            condition.signalAll();
        } finally {
            //解锁
            lock.unlock();
        }

    }
}

public class ThreadDemo2 {

    public static void main(String[] args) {
        Share share = new Share();
        new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                try {
                    share.incr();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        },"AA").start();

        new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                try {
                    share.decr();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        },"BB").start();

        new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                try {
                    share.incr();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        },"CC").start();

        new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                try {
                    share.decr();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        },"DD").start();
    }

}

线程定制化通信

方案：给每个线程定义一个标志位。

package JUC.lock;

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

//第一步 创建资源类，定义属性和操作方法
class ShareResource {
    //定义标志位
    private int flag = 1;// 1 AA 2 BB 3 CC

    //创建Lock锁
    final Lock lock = new ReentrantLock();

    //创建三个condition
    final Condition c1  = lock.newCondition();
    final Condition c2  = lock.newCondition();
    final Condition c3  = lock.newCondition();

    //打印5次，参数第几轮
    public void print5(int loop) throws InterruptedException {
        //上锁
        lock.lock();
        try{
            //判断
            while(flag != 1){
                c1.await();
            }
            //干活
            for (int i = 1; i <= 5; i++) {
                System.out.println(Thread.currentThread().getName()+" :: "+i+" :轮数: "+loop);
            }
            //修改标志位
            flag = 2;
            //通知
            c2.signalAll();
        } finally {
            //解锁
            lock.unlock();
        }
    }

    //打印10次，参数第几轮
    public void print10(int loop) throws InterruptedException {
        //上锁
        lock.lock();
        try{
            //判断
            while(flag != 2){
                c2.await();
            }
            //干活
            for (int i = 1; i <= 10; i++) {
                System.out.println(Thread.currentThread().getName()+" :: "+i+" :轮数: "+loop);
            }
            //修改标志位
            flag = 3;
            //通知
            c3.signalAll();
        } finally {
            //解锁
            lock.unlock();
        }
    }

    //打印15次，参数第几轮
    public void print15(int loop) throws InterruptedException {
        //上锁
        lock.lock();
        try{
            //判断
            while(flag != 3){
                c3.await();
            }
            //干活
            for (int i = 1; i <= 15; i++) {
                System.out.println(Thread.currentThread().getName()+" :: "+i+" :轮数: "+loop);
            }
            //修改标志位
            flag = 1;
            //通知
            c1.signalAll();
        } finally {
            //解锁
            lock.unlock();
        }
    }
}

public class ThreadDemo3 {

    public static void main(String[] args) {
        ShareResource shareResource = new ShareResource();
        new Thread(() -> {
            for (int i = 1; i <= 10; i++) {
                try {
                    shareResource.print5(i);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        },"AA").start();

        new Thread(() -> {
            for (int i = 1; i <= 10; i++) {
                try {
                    shareResource.print10(i);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        },"BB").start();

        new Thread(() -> {
            for (int i = 1; i <= 10; i++) {
                try {
                    shareResource.print15(i);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        },"CC").start();

    }

}