3. 生产者和消费者问题

生产者和消费者问题：Synchronized 版

Synchronized：wait 、notify

package pers.vincent.matrix.subject.juc;

public class JucTest3 {
    public static void main(String[] args) {

        NoTest noTest = new NoTest();

        new Thread(()->{
            for (int i = 0; i < 60; i++) {
                try {
                    noTest.add();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }, "A").start();

        new Thread(()->{
            for (int i = 0; i < 60; i++) {
                try {
                    noTest.del();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }, "B").start();
    }
}

//
class NoTest{

    private int num = 0 ;

    public synchronized void add() throws InterruptedException {
        if(num!=0){
            this.wait();
        }
        num++;
        this.notifyAll();
    }


    public synchronized void del() throws InterruptedException {
        if(num==0){
            this.wait();
        }
        num--;
        this.notifyAll();
    }
}

问题存在：if 在更多线程的情况下会存在虚假唤醒问题

if 拿到之后不会等待，while 会等待，所以当多个线程操作的时候，循环需要时候 while()

JUC 版 生产者和消费者问题

package pers.vincent.matrix.subject.juc;

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

public class JucTest4 {
    public static void main(String[] args) {
        Data data = new Data();

        new Thread(()->{
            for (int i = 0; i < 5; i++) {
                data.in();
            }
        }, "A").start();

        new Thread(()->{
            for (int i = 0; i < 5; i++) {
                data.out();
            }
        }, "B").start();

        new Thread(()->{
            for (int i = 0; i < 5; i++) {
                data.in();
            }
        }, "C").start();

        new Thread(()->{
            for (int i = 0; i < 5; i++) {
                data.out();
            }
        }, "D").start();
    }
}

class Data{

    private int num = 0;

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

    public void in(){

        try {
            lock.lock();

            while(num!=0){
                condition.await();
            }
            num++;
            condition.signalAll();
            System.out.println(Thread.currentThread().getName()+num);

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

    }

    public void out(){

        try {
            lock.lock();

            while(num==0){
                condition.await();
            }
            num--;
            condition.signalAll();
            System.out.println(Thread.currentThread().getName()+num);

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

    }
}

Condition 的作用**： **精准的通知和唤醒线程