实现生产者消费者模式的方法

1、使用 BlockingQueue

ArrayBlockingQueue 完成了很多工作，比如队列满了就去阻塞生产者线程，队列有空就去唤醒生产者线程等。

import java.util.concurrent.*;

public class MyProdCons {
    public static void main(String[] args){
        BlockingQueue<Object> queue = new ArrayBlockingQueue<>(10);
        
        Runnable producer = () ->{
            int num1 = 0;
            while(true) {
                try {
                    queue.put(new Object());
                    System.out.println("生产个数:  " + num1++);
                }catch(InterruptedException e){
                    e.printStackTrace();
                }
            }
        };
        new Thread(producer).start();
        new Thread(producer).start();
        
        Runnable consumer = () ->{
            int num2 = 0;
            while(true) {
                try {
                    queue.take();
                    System.out.println("消费个数:  " + num2++);
                }catch(InterruptedException e) {
                    e.printStackTrace();
                }
            }
        };
        new Thread(consumer).start();
        new Thread(consumer).start();
    }
}

2、使用 Condition

import java.util.*;
import java.util.concurrent.*;
import java.util.concurrent.locks.*;

public class MyBlockingQueueForCondition {
    private Queue<Object> queue;
    private int max = 16;
    private ReentrantLock lock = new ReentrantLock();
    private Condition notEmpty = lock.newCondition();
    private Condition notFull = lock.newCondition();
    
    public MyBlockingQueueForCondition(int size) {
        this.max = size;
        queue = new LinkedList();
    }
    public void put(Object o) throws InterruptedException{
        lock.lock();
        try {
            while(queue.size() == max) {
                notFull.await();
            }
            queue.add(o);
            notEmpty.signalAll();
        }finally{
            lock.unlock();
        }
    }
    
    public Object take() throws InterruptedException{
        lock.lock();
        try {
            while(queue.size() == 0) {
                notEmpty.await();
            }
            Object item = queue.remove();
            notFull.signalAll();
            return item;
        }finally {
            lock.unlock();
        }
    }
}

3、使用 wait/notify

public class WaitStyle {

    public static void main(String[] args) {
        MyBlockingQueue myBlockingQueue = new MyBlockingQueue(5);
        Producer producer = new Producer(myBlockingQueue);
        Consumer consumer = new Consumer(myBlockingQueue);
        new Thread(producer).start();
        new Thread(consumer).start();
    }
}

class Producer implements Runnable{
    private MyBlockingQueue storage;
    public Producer(MyBlockingQueue storage) {
        this.storage = storage;            
    }
    public void run() {
        for(int i=0;i<10;i++) {
            try {
                storage.put();
            }catch(InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

class Consumer implements Runnable{
    private MyBlockingQueue storage;
    public Consumer(MyBlockingQueue storage) {
        this.storage = storage;
    }
    public void run() {
        for(int i=0;i<10;i++) {
            try {
                storage.take();
            }catch(InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}



import java.util.*;

public class MyBlockingQueue {
    private int maxSize;
    private LinkedList<Object> storage;
    
    public MyBlockingQueue(int size) {
        this.maxSize = size;
        storage = new LinkedList<>();
    }
    
    public synchronized void put() throws InterruptedException{
        while(storage.size() == maxSize) {
            wait();
        }
        storage.add(new Object());
        System.out.println("放入后个数 " + storage.size());
        notifyAll();
    }
    
    public synchronized void take() throws InterruptedException{
        while(storage.size() == 0) {
            wait();
        }
        //System.out.println(storage.remove());
        storage.remove();
        System.out.println("取出后个数 " + storage.size());
        notifyAll();
    }
}

以上是三种实现生产者消费者模式的方法，其中，第一种 BlockingQueue 模式实现比较简单，但其背后的实现原理在第二种、第三种实现方法中得以体现，第二种、第三种实现方法本质上是我们自己实现了 BlockingQueue 的一些核心逻辑，供生产者与消费者使用。

ref:

拉勾课堂 徐隆曦  《Java 并发编程 78 讲》