生产者消费者

核心思想：

组成：1、生产者；2、消费者；3、主题队列；
互助：生产者生产主题加入主题队列；消费者从主题队列中取出主题，消费主题；
互斥：生产者和消费者都持有主题队列，当队列中主题数达到队列上限，生产者停止生产，等待消费者消费；当队列中没有主题，消费者停止消费，等待生产者生产。

wait()和notifyAll()

wait()/ nofity()方法是基类Object的两个方法，也就意味着所有Java类都会拥有这两个方法，我们可以为任何对象实现同步机制。

wait()：当主题队列已满/空时，生产者/消费者线程停止自己的执行，放弃锁，使自己处于等待状态，让其他线程执行。
notify()：当生产者/消费者向生产队列放入/取出一个产品后，向其他等待的线程发出可执行的通知，同时放弃锁，使自己处于等待状态。

public class ProducerAndConsumerByObject {

    public static void main(String[] args) {
        ProducerAndConsumerByObject producerAndConsumerByObject = new ProducerAndConsumerByObject();
    }

    private static final int MAX_SIZE = 10;
    final LinkedList<Integer> subjects = new LinkedList<>();

    ProducerAndConsumerByObject() {
        doExample();

    }

    private void doExample() {
        Subject subject = new Subject();
        Producer p1 = new Producer(subject, "P1");
        Producer p2 = new Producer(subject, "P2");
        Producer p3 = new Producer(subject, "P3");
        Customer c1 = new Customer(subject, "C1");
        Customer c2 = new Customer(subject, "C2");
        p1.start();
        p2.start();
        p3.start();
        c1.start();
        c2.start();
    }



    public class Subject {
        private int i;
        Subject() {
        }
       // 生产者生产主题，加入队列
        void produce(String name) {
            while(true) {
                synchronized (subjects) {
                    while (subjects.size() == MAX_SIZE) {
                        try {
                            subjects.wait();
                            System.out.println("Queue is full, Producer wait");
                        } catch (Exception ex) {
                            ex.printStackTrace();
                        }
                    }
                    System.out.println(name + " Producer produces " + i);
                    subjects.offer(i++);
                    subjects.notifyAll();
                }
                try {
                    Thread.sleep(100);
                } catch (Exception ex) {
                    ex.printStackTrace();
                }
            }
        }

        // 消费者消费主题，取出队列
        void customer(String name) {
            while(true) {
                synchronized (subjects) {
                    while (subjects.isEmpty()) {
                        try {
                            subjects.wait();
                            System.out.println("Queue is empty, Customer wait");
                        } catch (Exception ex) {
                            ex.printStackTrace();
                        }
                    }

                    Integer i = subjects.poll();
                    subjects.notifyAll();
                    System.out.println(name + " Customer cust " + i);
                }
                try {
                    Thread.sleep(100);
                } catch (Exception ex) {
                    ex.printStackTrace();
                }
            }
        }
    }

    // 生产者，独立线程，在run方法中生产 
    public class Producer extends Thread {
        private Subject subject;
        private String name;
        Producer(Subject subject, String name) {
            this.subject = subject;
            this.name = name;
        }

        @Override
        public void run() {
            System.out.println(name + " is running");
            subject.produce(name);
        }
    }

    // 消费者，独立线程，在run方法中消费
    public class Customer extends Thread {
        private Subject subject;
        private String name;
        Customer(Subject subject, String name) {
            this.subject = subject;
            this.name = name;
        }

        @Override
        public void run() {
            System.out.println(name + " is running");
            subject.customer(name);
        }
    }
}

await()和signalAll()

上面的方式实现进程间同步依赖于synchronized，在简单场景下可以满足要求，但是在复杂场景下，对于锁需要更加细致的操作（条件满足，及时释放锁），因此需要用到lock.
await()和signalAll()是lock中实现同步的一种方式，基本和上述的wait()和notifyAll()方法相同。通过lock.newCondition()获取condition，通过condition的await()和signlaAll()实现同步。

public class ProducerConsumerByLock {

    public static void main(String[] args) {
        ProducerConsumerByLock producerConsumerByLock = new ProducerConsumerByLock();
    }

    private static final int MAX_SIZE = 5;
    private static final Lock lock = new ReentrantLock();
    private static final Condition emptyCondition = lock.newCondition();
    private static final Condition fullCondition = lock.newCondition();
    private Queue<Integer> subject = new LinkedList<>();

    ProducerConsumerByLock() {
        doExample();
    }

    private void doExample() {
        Subject subject = new Subject();
        Producer p1 = new Producer(subject, "P1");
        Producer p2 = new Producer(subject, "P2");
        Producer p3 = new Producer(subject, "P3");
        Consumer c1 = new Consumer(subject, "C1");
        Consumer c2 = new Consumer(subject, "C2");
        p1.start();
        p2.start();
        p3.start();
        c1.start();
        c2.start();

    }


    public class Subject {
        int i = 0;

        public Subject(){
        }

        public void produce(String name) {
            while(true) {
                lock.lock();
                while (subject.size() == MAX_SIZE) {
                    try {
                        fullCondition.await();
                        System.out.println( name + " Queue is full");
                    } catch (InterruptedException ex) {
                        ex.printStackTrace();
                    }
                }
                System.out.println(name + " produce " + i);
                subject.offer(i++);
                fullCondition.signalAll();
                emptyCondition.signalAll();
                lock.unlock();
                try {
                    Thread.sleep(100);
                } catch (Exception ex) {
                    ex.printStackTrace();
                }
            }
        }


        public void consume(String name) {
            while (true) {
                lock.lock();
                while (subject.size() == 0) {
                    try {
                        emptyCondition.await();
                        System.out.println(name + " Queue is empty");
                    } catch (InterruptedException ex) {
                        ex.printStackTrace();
                    }
                }
                int x = subject.poll();
                System.out.println(name + " consume " + x);
                fullCondition.signalAll();
                emptyCondition.signalAll();
                lock.unlock();
                try {
                    Thread.sleep(100);
                } catch (Exception ex) {
                    ex.printStackTrace();
                }
            }
        }
    }


    public class Producer extends Thread {
        private Subject subject;
        private String name;
        Producer(Subject subject, String name) {
            this.subject = subject;
            this.name = name;
        }

        @Override
        public void run() {
            System.out.println(name + " is running");
            subject.produce(name);
        }
    }

    public class Consumer extends Thread {
        private Subject subject;
        private String name;
        Consumer(Subject subject, String name) {
            this.subject = subject;
            this.name = name;
        }

        @Override
        public void run() {
            System.out.println(name + " is running");
            subject.consume(name);
        }
    }
}

BlockingQueue

LinkedBlockingQueue是一个已经在内部实现了同步的队列，它可以在生成对象时指定容量大小。它利用await()和signalAll()实现阻塞的入队出队操作，具体的方法为：

put()方法：容量达到最大时，自动阻塞，生产者。
take()方法：容量为0时，自动阻塞，消费者。

public class ProducerConsumerByBlockingQueue {


    public static void main(String[] args) {
        ProducerConsumerByBlockingQueue producerConsumerByBlockingQueue = new ProducerConsumerByBlockingQueue();
    }


    private static final int MAX_SIZE = 5;
    private LinkedBlockingQueue<Integer> subject = new LinkedBlockingQueue<>(MAX_SIZE);


    ProducerConsumerByBlockingQueue() {
        doExample();
    }

    private void doExample() {
        Subject subject = new Subject();
        Producer p1 = new Producer(subject, "P1");
        Producer p2 = new Producer(subject, "P2");
        Producer p3 = new Producer(subject, "P3");
        Consumer c1 = new Consumer(subject, "C1");
        Consumer c2 = new Consumer(subject, "C2");
        p1.start();
        p2.start();
        p3.start();
        c1.start();
        c2.start();

    }


    public class Subject {
        int i = 0;

        public Subject(){
        }

        public void produce(String name) {
            while(true) {
                try {
                    System.out.println(name + " produce " + i + " with size = " + subject.size());
                    subject.put(i++);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                try {
                    Thread.sleep(100);
                } catch (Exception ex) {
                    ex.printStackTrace();
                }
            }
        }


        public void consume(String name) {
            while (true) {
                try {
                    int x = subject.take();
                    System.out.println(name + " consumer " + x + " with size = " + subject.size());
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                try {
                    Thread.sleep(100);
                } catch (Exception ex) {
                    ex.printStackTrace();
                }
            }
        }
    }


    public class Producer extends Thread {
        private Subject subject;
        private String name;
        Producer(Subject subject, String name) {
            this.subject = subject;
            this.name = name;
        }

        @Override
        public void run() {
            System.out.println(name + "is running");
            subject.produce(name);
        }
    }

    public class Consumer extends Thread {
        private Subject subject;
        private String name;
        Consumer(Subject subject, String name) {
            this.subject = subject;
            this.name = name;
        }

        @Override
        public void run() {
            System.out.println(name + "is running");
            subject.consume(name);
        }
    }
}

Tips

需要注意到，生产者Producer和消费者Consumer在上述三种实现方式中完全一样，不同的只是Subject，这就做的好处：

使得生产者和消费者只有生产和消费的功能，而不需要知道如何生产和消费，提高了生产者和消费者的复用率（可以将Subject抽象化，传入不同的Subject子类）
使得Subject的逻辑变得完整，增加代码可读性，如何生产出，如何消费掉，一目了然。

最后编辑于：2018.10.01 01:14:39

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