历史潮流浩浩荡荡,顺之则昌,逆之则亡。——孙中山

Java生产者消费者模型实践四

JAVA 徐承恩 929℃

我们要保证理解wait && notify机制。实现时可以使用Object类提供的wait()方法与notifyAll()方法,但更推荐的方式是使用java.util.concurrent包提供的Lock && Condition

package com.github.xuchengen.concurrent.impl;

import com.github.xuchengen.concurrent.AbsConsumer;
import com.github.xuchengen.concurrent.AbsProducer;
import com.github.xuchengen.concurrent.Model;
import com.github.xuchengen.concurrent.Task;

import java.util.LinkedList;
import java.util.Queue;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
 * 基于锁条件实现
 * 作者:徐承恩
 * 邮箱:xuchengen@gmail.com
 * 日期:2019/12/12
 */
public class LockConditionModel1 implements Model {

    private final Lock BUFFER_LOCK = new ReentrantLock();

    private final Condition BUFFER_COND = BUFFER_LOCK.newCondition();

    private final Queue<Task> buffer = new LinkedList<>();

    private final int cap;

    private final AtomicInteger increTaskNo = new AtomicInteger(0);

    public LockConditionModel1(int cap) {
        this.cap = cap;
    }

    @Override
    public Runnable newRunnableConsumer() {
        return new ConsumerImpl();
    }

    @Override
    public Runnable newRunnableProducer() {
        return new ProducerImpl();
    }

    private class ConsumerImpl extends AbsConsumer {
        @Override
        public void consume() throws InterruptedException {
            BUFFER_LOCK.lockInterruptibly();
            try {
                while (buffer.size() == 0) {
                    // 当缓冲中元素为空则阻塞该线程与此同时会唤醒生产者线程进行生产
                    BUFFER_COND.await();
                }
                Task task = buffer.poll();
                assert task != null;
                // 固定时间范围的消费,模拟相对稳定的服务器处理过程
                Thread.sleep(500 + (long) (Math.random() * 500));
                System.out.println("consume: " + task.no);
                // 消费后唤醒生产者线程进行生产
                BUFFER_COND.signalAll();
            } finally {
                BUFFER_LOCK.unlock();
            }
        }
    }

    private class ProducerImpl extends AbsProducer {
        @Override
        public void produce() throws InterruptedException {
            // 不定期生产,模拟随机的用户请求
            Thread.sleep((long) (Math.random() * 1000));
            BUFFER_LOCK.lockInterruptibly();
            try {
                while (buffer.size() == cap) {
                    // 当缓冲中元素已满则阻塞该线程与此同时会唤醒消费者线程进行消费
                    BUFFER_COND.await();
                }
                Task task = new Task(increTaskNo.getAndIncrement());
                buffer.offer(task);
                System.out.println("produce: " + task.no);
                // 生产后唤醒消费者线程进行消费
                BUFFER_COND.signalAll();
            } finally {
                BUFFER_LOCK.unlock();
            }
        }
    }

    public static void main(String[] args) {
        Model model = new LockConditionModel1(3);
        for (int i = 0; i < 2; i++) {
            new Thread(model.newRunnableConsumer()).start();
        }
        for (int i = 0; i < 5; i++) {
            new Thread(model.newRunnableProducer()).start();
        }
    }

}

该写法的思路与实现二的思路完全相同,仅仅将锁与条件变量换成了Lock和Condition。

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