生产者消费者模型Java实现


生产者消费者模型

生产者消费者模型可以描述为:
①生产者持续生产,直到仓库放满产品,则停止生产进入等待状态;仓库不满后继续生产;
②消费者持续消费,直到仓库空,则停止消费进入等待状态;仓库不空后,继续消费;
③生产者可以有多个,消费者也可以有多个;

生产者消费者模型

对应到程序中,仓库对应缓冲区,可以使用队列来作为缓冲区,并且这个队列应该是有界的,即最大容量是固定的;进入等待状态,则表示要阻塞当前线程,直到某一条件满足,再进行唤醒。

常见的实现方式主要有以下几种。
①使用wait()notify()
②使用LockCondition
③使用信号量Semaphore
④使用JDK自带的阻塞队列
⑤使用管道流


使用wait()和notify()实现

前提是要熟悉Object的几个方法:

  • wait():当前线程释放锁,直到等到通知,再去获取锁
  • sleep():当前线程休眠,但不释放锁
  • notify():唤醒其他正在wait的线程

参考代码如下:

public class ProducerConsumer1 {

    class Producer extends Thread {
        private String threadName;
        private Queue<Goods> queue;
        private int maxSize;

        public Producer(String threadName, Queue<Goods> queue, int maxSize) {
            this.threadName = threadName;
            this.queue = queue;
            this.maxSize = maxSize;
        }

        @Override
        public void run() {
            while (true) {
                //模拟生产过程中的耗时操作
                Goods goods = new Goods();
                try {
                    Thread.sleep(new Random().nextInt(1000));
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

                synchronized (queue) {
                    while (queue.size() == maxSize) {
                        try {
                            System.out.println("队列已满,【" + threadName + "】进入等待状态");
                            queue.wait();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }

                    queue.add(goods);
                    System.out.println("【" + threadName + "】生产了一个商品:【" + goods.toString() + "】,目前商品数量:" + queue.size());
                    queue.notifyAll();
                }
            }
        }
    }

    class Consumer extends Thread {
        private String threadName;
        private Queue<Goods> queue;

        public Consumer(String threadName, Queue<Goods> queue) {
            this.threadName = threadName;
            this.queue = queue;
        }

        @Override
        public void run() {
            while (true) {
                Goods goods;
                synchronized (queue) {
                    while (queue.isEmpty()) {
                        try {
                            System.out.println("队列已空,【" + threadName + "】进入等待状态");
                            queue.wait();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                    goods = queue.remove();
                    System.out.println("【" + threadName + "】消费了一个商品:【" + goods.toString() + "】,目前商品数量:" + queue.size());
                    queue.notifyAll();
                }
                //模拟消费过程中的耗时操作
                try {
                    Thread.sleep(new Random().nextInt(1000));
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }


    @Test
    public void test() {

        int maxSize = 5;
        Queue<Goods> queue = new LinkedList<>();

        Thread producer1 = new Producer("生产者1", queue, maxSize);
        Thread producer2 = new Producer("生产者2", queue, maxSize);
        Thread producer3 = new Producer("生产者3", queue, maxSize);

        Thread consumer1 = new Consumer("消费者1", queue);
        Thread consumer2 = new Consumer("消费者2", queue);


        producer1.start();
        producer2.start();
        producer3.start();
        consumer1.start();
        consumer2.start();

        while (true) {

        }
    }
}

几个注意的地方:

①确定锁的对象是队列queue

②不要把生产过程和消费过程写在同步块中,这些操作无需同步,同步的仅仅是放入和取出这两个动作;

③因为是持续生产,持续消费,要用while(true){...}的方式将【生产、放入】或【取出、消费】的操作都一直进行。

④但由于是对队列使用synchronized的方式加锁,同一时刻,要么在放入,要么在取出,两者不能同时进行。


使用Lock和Condition实现

前提是要熟悉Lock接口以及常用实现类ReentrantLock,以及Condition的两个常用方法:

  • await():等待Condition的满足,会释放锁
  • signal():唤醒其他正在等待该Condition的线程
    参考代码如下:
public class ProducerConsumer2 {

    class Producer extends Thread {

        private String threadName;
        private Queue<Goods> queue;
        private Lock lock;
        private Condition notFullCondition;
        private Condition notEmptyCondition;
        private int maxSize;

        public Producer(String threadName, Queue<Goods> queue, Lock lock, Condition notFullCondition, Condition notEmptyCondition, int maxSize) {
            this.threadName = threadName;
            this.queue = queue;
            this.lock = lock;
            this.notFullCondition = notFullCondition;
            this.notEmptyCondition = notEmptyCondition;
            this.maxSize = maxSize;

        }

        @Override
        public void run() {
            while (true) {
                //模拟生产过程中的耗时操作
                Goods goods = new Goods();
                try {
                    Thread.sleep(new Random().nextInt(100));
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

                lock.lock();
                try {
                    while (queue.size() == maxSize) {
                        try {
                            System.out.println("队列已满,【" + threadName + "】进入等待状态");
                            notFullCondition.await();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }

                    queue.add(goods);
                    System.out.println("【" + threadName + "】生产了一个商品:【" + goods.toString() + "】,目前商品数量:" + queue.size());
                    notEmptyCondition.signalAll();

                } finally {
                    lock.unlock();
                }
            }
        }
    }

    class Consumer extends Thread {
        private String threadName;
        private Queue<Goods> queue;
        private Lock lock;
        private Condition notFullCondition;
        private Condition notEmptyCondition;

        public Consumer(String threadName, Queue<Goods> queue, Lock lock, Condition notFullCondition, Condition notEmptyCondition) {
            this.threadName = threadName;
            this.queue = queue;
            this.lock = lock;
            this.notFullCondition = notFullCondition;
            this.notEmptyCondition = notEmptyCondition;
        }

        @Override
        public void run() {
            while (true) {
                Goods goods;
                lock.lock();
                try {
                    while (queue.isEmpty()) {
                        try {
                            System.out.println("队列已空,【" + threadName + "】进入等待状态");
                            notEmptyCondition.await();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                    goods = queue.remove();
                    System.out.println("【" + threadName + "】消费了一个商品:【" + goods.toString() + "】,目前商品数量:" + queue.size());
                    notFullCondition.signalAll();

                } finally {
                    lock.unlock();
                }

                //模拟消费过程中的耗时操作
                try {
                    Thread.sleep(new Random().nextInt(100));
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    @Test
    public void test() {

        int maxSize = 5;
        Queue<Goods> queue = new LinkedList<>();
        Lock lock = new ReentrantLock();
        Condition notEmptyCondition = lock.newCondition();
        Condition notFullCondition = lock.newCondition();

        Thread producer1 = new ProducerConsumer2.Producer("生产者1", queue, lock, notFullCondition, notEmptyCondition, maxSize);
        Thread producer2 = new ProducerConsumer2.Producer("生产者2", queue, lock, notFullCondition, notEmptyCondition, maxSize);
        Thread producer3 = new ProducerConsumer2.Producer("生产者3", queue, lock, notFullCondition, notEmptyCondition, maxSize);

        Thread consumer1 = new ProducerConsumer2.Consumer("消费者1", queue, lock, notFullCondition, notEmptyCondition);
        Thread consumer2 = new ProducerConsumer2.Consumer("消费者2", queue, lock, notFullCondition, notEmptyCondition);
        Thread consumer3 = new ProducerConsumer2.Consumer("消费者3", queue, lock, notFullCondition, notEmptyCondition);


        producer1.start();
        producer2.start();
        producer3.start();
        consumer1.start();
        consumer2.start();
        consumer3.start();
        while (true) {

        }
    }
}

要注意的地方:

放入和取出操作均是用的同一个锁,所以在同一时刻,要么在放入,要么在取出,两者不能同时进行。因此,与使用wait()和notify()实现类似,这种方式的实现并不能最大限度地利用缓冲区(即例子中的队列)。如果要实现同一时刻,既可以放入又可以取出,则要使用两个重入锁,分别控制放入和取出的操作,具体实现可以参考LinkedBlockingQueue


使用信号量Semaphore实现

前提是熟悉信号量Semaphore的使用方式,尤其是release()方法,Semaphorerelease之前不必一定要先acquire。(如果不熟悉Semaphore,可以参考阅读【多线程与并发】Java并发工具类)

There is no requirement that a thread that releases a permit must
have acquired that permit by calling acquire.
Correct usage of a semaphore is established by programming convention
in the application.

参考代码如下:

public class ProducerConsumer4 {


    class Producer extends Thread {
        private String threadName;
        private Queue<Goods> queue;
        private Semaphore queueSizeSemaphore;
        private Semaphore concurrentWriteSemaphore;
        private Semaphore notEmptySemaphore;

        public Producer(String threadName, Queue<Goods> queue, Semaphore concurrentWriteSemaphore, Semaphore queueSizeSemaphore, Semaphore notEmptySemaphore) {
            this.threadName = threadName;
            this.queue = queue;
            this.concurrentWriteSemaphore = concurrentWriteSemaphore;
            this.queueSizeSemaphore = queueSizeSemaphore;
            this.notEmptySemaphore = notEmptySemaphore;
        }

        @Override
        public void run() {
            while (true) {
                //模拟生产过程中的耗时操作
                Goods goods = new Goods();
                try {
                    Thread.sleep(new Random().nextInt(100));
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

                try {
                    queueSizeSemaphore.acquire();//获取队列未满的信号量
                    concurrentWriteSemaphore.acquire();//获取读写的信号量
                    queue.add(goods);
                    System.out.println("【" + threadName + "】生产了一个商品:【" + goods.toString() + "】,目前商品数量:" + queue.size());
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }finally {
                    concurrentWriteSemaphore.release();
                    notEmptySemaphore.release();
                }
            }
        }
    }

    class Consumer extends Thread {
        private String threadName;
        private Queue<Goods> queue;
        private Semaphore queueSizeSemaphore;
        private Semaphore concurrentWriteSemaphore;
        private Semaphore notEmptySemaphore;

        public Consumer(String threadName, Queue<Goods> queue, Semaphore concurrentWriteSemaphore, Semaphore queueSizeSemaphore, Semaphore notEmptySemaphore) {
            this.threadName = threadName;
            this.queue = queue;
            this.concurrentWriteSemaphore = concurrentWriteSemaphore;
            this.queueSizeSemaphore = queueSizeSemaphore;
            this.notEmptySemaphore = notEmptySemaphore;
        }

        @Override
        public void run() {
            while (true) {
                Goods goods;
                try {
                    notEmptySemaphore.acquire();
                    concurrentWriteSemaphore.acquire();
                    goods = queue.remove();
                    System.out.println("【" + threadName + "】生产了一个商品:【" + goods.toString() + "】,目前商品数量:" + queue.size());
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }finally {
                    concurrentWriteSemaphore.release();
                    queueSizeSemaphore.release();
                }

                //模拟消费过程中的耗时操作
                try {
                    Thread.sleep(new Random().nextInt(100));
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }


    @Test
    public void test() {

        int maxSize = 5;
        Queue<Goods> queue = new LinkedList<>();
        Semaphore concurrentWriteSemaphore = new Semaphore(1);
        Semaphore notEmptySemaphore = new Semaphore(0);
        Semaphore queueSizeSemaphore = new Semaphore(maxSize);


        Thread producer1 = new ProducerConsumer4.Producer("生产者1", queue, concurrentWriteSemaphore, queueSizeSemaphore, notEmptySemaphore);
        Thread producer2 = new ProducerConsumer4.Producer("生产者2", queue, concurrentWriteSemaphore, queueSizeSemaphore, notEmptySemaphore);
        Thread producer3 = new ProducerConsumer4.Producer("生产者3", queue, concurrentWriteSemaphore, queueSizeSemaphore, notEmptySemaphore);

        Thread consumer1 = new ProducerConsumer4.Consumer("消费者1", queue, concurrentWriteSemaphore, queueSizeSemaphore, notEmptySemaphore);
        Thread consumer2 = new ProducerConsumer4.Consumer("消费者2", queue, concurrentWriteSemaphore, queueSizeSemaphore, notEmptySemaphore);
        Thread consumer3 = new ProducerConsumer4.Consumer("消费者3", queue, concurrentWriteSemaphore, queueSizeSemaphore, notEmptySemaphore);


        producer1.start();
        producer2.start();
        producer3.start();
        consumer1.start();
        consumer2.start();
        consumer3.start();
        while (true) {
        }
    }
}

要注意的地方:

①理解代码中的三个信号量的含义
queueSizeSemaphore:(其中的许可证数量,可以理解为队列中可以再放入多少个元素),该信号量的许可证初始数量为仓库大小,即maxSize;生产者每放置一个商品,则该信号量-1,即执行acquire(),表示队列中已经添加了一个元素,要减少一个许可证;消费者每取出一个商品,该信号量+1,即执行release(),表示队列中已经少了一个元素,再给你一个许可证。
notEmptySemaphore:(其中的许可证数量,可以理解为队列中可以取出多少个元素),该信号量的许可证初始数量为0;生产者每放置一个商品,则该信号量+1,即执行release(),表示队列中添加了一个元素;消费者每取出一个商品,该信号量-1,即执行acquire(),表示队列中已经少了一个元素,要减少一个许可证;
concurrentWriteSemaphore,相当于一个写锁,在放入或取出商品的时候,都需要先获取再释放许可证。

②由于实现中,使用了concurrentWriteSemaphore实现了对队列并发写的控制,在同一时刻,只能对队列进行一种操作:放入或取出。假如把concurrentWriteSemaphore中的信号量初始化为2或者2以上的值,就会出现多个生产者同时放入或多个消费者同时消费的情况,而使用的LinkedList是不允许并发进行这种修改的,否则会出现溢出或取空的情况。所以,concurrentWriteSemaphore只能设置为1,也就导致性能与使用wait() / notify()方式类似,性能不高。


使用jdk自带的阻塞队列实现

前提是要记住两个阻塞取放方法,因为阻塞队列提供了很多存取元素的方法,几种存取方式在队列已满/已空时采取的措施如下:

方法/方式处理 抛出异常 返回特殊值 一直阻塞 超时退出
插入 add(e) offer(e) put(e) offer(e, time, unit)
移除 remove() poll() take() poll(time, unit)
检查 element() peek() 不可用 不可用

所以,在这里,要选用put()take()这两个会阻塞的方法。

参考代码如下:

public class ProducerConsumer3 {

    class Producer extends Thread {
        private String threadName;
        private BlockingQueue<Goods> queue;

        public Producer(String threadName, BlockingQueue<Goods> queue) {
            this.threadName = threadName;
            this.queue = queue;
        }

        @Override
        public void run() {
            while (true){
                Goods goods = new Goods();
                try {
                    //模拟生产过程中的耗时操作
                    Thread.sleep(new Random().nextInt(100));
                    queue.put(goods);
                    System.out.println("【" + threadName + "】生产了一个商品:【" + goods.toString() + "】,目前商品数量:" + queue.size());
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    class Consumer extends Thread {
        private String threadName;
        private BlockingQueue<Goods> queue;

        public Consumer(String threadName, BlockingQueue<Goods> queue) {
            this.threadName = threadName;
            this.queue = queue;
        }

        @Override
        public void run() {
            while (true){
                try {
                    Goods goods = queue.take();
                    System.out.println("【" + threadName + "】消费了一个商品:【" + goods.toString() + "】,目前商品数量:" + queue.size());
                    //模拟消费过程中的耗时操作
                    Thread.sleep(new Random().nextInt(100));
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    @Test
    public void test() {

        int maxSize = 5;
        BlockingQueue<Goods> queue = new LinkedBlockingQueue<>(maxSize);

        Thread producer1 = new ProducerConsumer3.Producer("生产者1", queue);
        Thread producer2 = new ProducerConsumer3.Producer("生产者2", queue);
        Thread producer3 = new ProducerConsumer3.Producer("生产者3", queue);

        Thread consumer1 = new ProducerConsumer3.Consumer("消费者1", queue);
        Thread consumer2 = new ProducerConsumer3.Consumer("消费者2", queue);


        producer1.start();
        producer2.start();
        producer3.start();
        consumer1.start();
        consumer2.start();

        while (true) {
        }
    }
}

要注意的地方:

如果使用LinkedBlockingQueue作为队列实现,则可以实现:在同一时刻,既可以放入又可以取出,因为LinkedBlockingQueue内部使用了两个重入锁,分别控制取出和放入。
如果使用ArrayBlockingQueue作为队列实现,则在同一时刻只能放入或取出,因为ArrayBlockingQueue内部只使用了一个重入锁来控制并发修改操作。


使用管道流实现

//TODO


无锁的缓存框架: Disruptor

BlockingQueue 实现生产者和消费者模式简单易懂,但是BlockingQueue并不是一个高性能的实现:它完全使用锁和阻塞来实现线程之间的同步。在高并发的场合,它的性能并不是特别的优越。(ConconcurrentLinkedQueue是一个高性能的队列,但并不没有实现BlockingQueue接口,即不支持阻塞操作)。

Disruptor是LMAX公司开发的高效的无锁缓存队列。它使用无锁的方式实现了一个环形队列,非常适合于实现生产者和消费者模式,如:事件和消息的发布。

//TODO 应用场景的代码实现


参考

Java 实现生产者 – 消费者模型:各种实现方式的性能
高性能的生产者-消费者:无锁的实现:无锁实现
Java生产者和消费者模型的5种实现方式
生产者/消费者问题的多种Java实现方式
Java阻塞队列ArrayBlockingQueue和LinkedBlockingQueue实现原理分析:两种常用阻塞队列的区别

完整代码示例在此