生产者和消费者

生产者和消费者 synchroinzed 版

package juc;
/* 线程之间的通信问题： 生产者消费者问题！ 等待唤醒，通知唤醒 线程交替执行 A B  操作同一变量 num=0
A num+1
B num-1
* */
public class A {
    public static void main(String[] args) {
        Data data = new Data();
        new Thread(()->{
            for (int i = 0; i <10 ; i++) {
                try {
                    data.increment();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

            }

        },"A").start();

        new Thread(()->{
            for (int i = 0; i <10 ; i++) {
                try {
                    data.decrement();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

        },"B").start();

    }
}

//判断等待，业务，通知
class Data{
    private int number =0;
    //+1
    public synchronized void increment() throws InterruptedException {
        if(number!=0){
            //等待
            this.wait();
        }
        number++;
        System.out.println(Thread.currentThread().getName()+"=>"+number);
        //通知其他线程，我+1完了
        this.notifyAll();
    }

    public synchronized void decrement() throws InterruptedException {
        if(number==0){
            //等待
            this.wait();
        }
        number--;
        System.out.println(Thread.currentThread().getName()+"=>"+number);
        //通知其他线程，我-1完了
        this.notifyAll();
    }
}

输出：
问题升级：防止虚假唤醒，4个线程，两个加，两个减

if 改成 while

新版生产者和消费者写法

package juc;

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

public class B {
    public static void main(String[] args) {
        Data2 data = new Data2();
        new Thread(()->{
            for (int i = 0; i <10 ; i++) {
                try {
                    data.increment();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

            }

        },"A").start();

        new Thread(()->{
            for (int i = 0; i <10 ; i++) {
                try {
                    data.decrement();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

        },"B").start();

        new Thread(()->{
            for (int i = 0; i <10 ; i++) {
                try {
                    data.decrement();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

        },"C").start();

        new Thread(()->{
            for (int i = 0; i <10 ; i++) {
                try {
                    data.decrement();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

        },"D").start();



    }
}

//判断等待，业务，通知
class Data2{
    private int number =0;
    Lock lock=new ReentrantLock();
    Condition condition=lock.newCondition();
    //+1
    public  void increment() throws InterruptedException {
        lock.lock();
        try {
            while (number!=0){
                condition.await();
            }
            number++;
            System.out.println(Thread.currentThread().getName()+"=>"+number);
            condition.signalAll();

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }

    }

    public  void decrement() throws InterruptedException {
       lock.lock();
        try {
            while (number==0){
                condition.await();
            }
            number--;
            System.out.println(Thread.currentThread().getName()+"=>"+number);
            condition.signalAll();

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }


}