JUC并发编程学习笔记（三）生产者和消费者问题

生产者和消费者问题

synchronized版-> wait/notify

juc版->Lock

面试：单例模式、排序算法、生产者和消费者、死锁

生产者和消费者问题 Synchronized版

package org.example.pc;

public class A {
    public static void main(String[] args) {
        Date date = new Date();
        new Thread(()->{
            for (int i = 0; i < 20; i++) {
                date.increment();
            }
        },"A").start();
        new Thread(()->{
            for (int i = 0; i < 20; i++) {
                date.decrement();
            }
        },"B").start();
    }
}
//判断等待、业务、通知
class Date{
    private int number = 0;

    public synchronized void increment(){
        if (number!=0){
            try {
                //不等于0就让该线程等待
                this.wait();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        }

        number++;
//        打印加完后的值
        System.out.println(Thread.currentThread().getName()+"=>"+number);
//        通知其他线程，我完成了
        this.notify();
    }
    public synchronized void decrement(){
        if (number!=1){
            try {
                this.wait();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        }
        number--;
        System.out.println(Thread.currentThread().getName()+"=>"+number);
        this.notify();
    }

}

存在的问题:A、B、C、D四个线程

在线程中判断业务完成唤醒等待应该使用while循环判断，而非if判断，因为if判断值判断一次，在线程中存在一种状态叫虚假唤醒。

JUC版生产者和消费者问题

代码实现

package org.example.pc;

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

//判断等待、业务、通知
public class Date {
    private int number = 0;
    private Lock lock = new ReentrantLock();
    private Condition inCondition = lock.newCondition();

    public void increment() {

        try {
            lock.lock();
            while (number != 0) {
                inCondition.await();
            }
            number++;
//        打印加完后的值
            System.out.println(Thread.currentThread().getName() + "=>" + number);
//        通知其他线程，我完成了

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

    }

    public void decrement() {

        try {
            lock.lock();
            while (number != 1) {
                inCondition.await();
            }
            number--;
            System.out.println(Thread.currentThread().getName() + "=>" + number);
            inCondition.signalAll();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }

    }

}

Condition 精准的通知唤醒线程

在传统并发编程中，通过notifily唤醒线程后所有线程都是随机获取到资源的，JUC中可以通过Condition来精准的控制要唤醒哪一个线程资源。任何一个新技术的出现都不会只是为了实现之前已有的效果

代码实现

package org.example.pc;

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

public class C {
    public static void main(String[] args) {
        DateC dateC = new DateC();
        new Thread(()->{
            for (int i = 0; i < 10; i++) dateC.plantA();
        },"A").start();
        new Thread(()->{
            for (int i = 0; i < 10; i++) dateC.plantB();
        },"B").start();
        new Thread(()->{
            for (int i = 0; i < 10; i++) dateC.plantC();
        },"C").start();
    }

}

class DateC {
    private int number = 1;
    private Lock lock = new ReentrantLock();
    private Condition inCondition1 = lock.newCondition();
    private Condition inCondition2 = lock.newCondition();
    private Condition inCondition3 = lock.newCondition();

   public void plantA(){
       try {
           lock.lock();
           while (number!=1){
               inCondition1.await();
           }
           System.out.println(Thread.currentThread().getName());
           number=2;
           inCondition2.signal();
       }catch (Exception e){
           e.printStackTrace();
       }finally {
           lock.unlock();
       }
   }
    public void plantB(){
        try {
            lock.lock();
            while (number!=2){
                inCondition2.await();
            }
            System.out.println(Thread.currentThread().getName());
            number=3;
            inCondition3.signal();
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            lock.unlock();
        }
    }
    public void plantC(){
        try {
            lock.lock();
            while (number!=3){
                inCondition3.await();
            }
            System.out.println(Thread.currentThread().getName());
            number=1;
            inCondition1.signal();
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            lock.unlock();
        }
    }
}