并发实践-生产者消费者问题

　　Java中实现生产者消费者通常有以下几种方式：

1. 用object原生的wait() 和 notify()做同步，并用synchronized对存储加锁
2. 用condition的await() 和signal()做同步。并用concurrent.locks.Lock，
3. 直接使用concurrent.BlockingQueue。
4. 使用PipedInputStream/PipedOutputStream。
5. 使用信号量semaphore。　

　　解决问题的核心

   保证同一资源被多个线程并发访问时的完整性。常用的同步方法是采用信号或加锁机制，保证资源在任意时刻至多被一个线程访问。

　　

public class ProducerAndConsumer {
    private final int MAX_LEN = 10;
    private Queue<Integer> queue = new LinkedList<Integer>();
    class Producer extends Thread {
        @Override
        public void run() {
            producer();
        }
        private void producer() {
            while(true) {
                synchronized (queue) {
                    while (queue.size() == MAX_LEN) {
                        queue.notify();
                        System.out.println("当前队列满");
                        try {
                            queue.wait();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                    queue.add(1);
                    queue.notify();
                    System.out.println("生产者生产一条任务，当前队列长度为" + queue.size());
                    try {
                        Thread.sleep(500);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        }
    }
    class Consumer extends Thread {
        @Override
        public void run() {
            consumer();
        }
        private void consumer() {
            while (true) {
                synchronized (queue) {
                    while (queue.size() == 0) {
                        queue.notify();
                        System.out.println("当前队列为空");
                        try {
                            queue.wait();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                    queue.poll();
                    queue.notify();
                    System.out.println("消费者消费一条任务，当前队列长度为" + queue.size());
                    try {
                        Thread.sleep(500);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        }
    }
    public static void main(String[] args) {
        ProducerAndConsumer pc = new ProducerAndConsumer();
        Producer producer = pc.new Producer();
        Consumer consumer = pc.new Consumer();
        producer.start();
        consumer.start();
    }
}

 

 

public class ProducerAndConsumer1 {
    private final int MAX_LEN = 10;
    private Queue<Integer> queue = new LinkedList<Integer>();
    private final Lock lock = new ReentrantLock();
    private final Condition condition = lock.newCondition();
    class Producer extends Thread {
        @Override
        public void run() {
            producer();
        }
        private void producer() {
            while(true) {
                lock.lock();
                try {
                    while (queue.size() == MAX_LEN) {
                        System.out.println("当前队列满");
                        try {
                            condition.await();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                    queue.add(1);
                    condition.signal();
                    System.out.println("生产者生产一条任务，当前队列长度为" + queue.size());
                    try {
                        Thread.sleep(500);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                } finally {
                    lock.unlock();
                }
            }
        }
    }
    class Consumer extends Thread {
        @Override
        public void run() {
            consumer();
        }
        private void consumer() {
            while (true) {
                lock.lock();
                try {
                    while (queue.size() == 0) {
                        System.out.println("当前队列为空");
                        try {
                            condition.await();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                    queue.poll();
                    condition.signal();
                    System.out.println("消费者消费一条任务，当前队列长度为" + queue.size());
                    try {
                        Thread.sleep(500);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                } finally {
                    lock.unlock();
                }
            }
        }
    }
    public static void main(String[] args) {
        ProducerAndConsumer pc = new ProducerAndConsumer();
        Producer producer = pc.new Producer();
        Consumer consumer = pc.new Consumer();
        producer.start();
        consumer.start();
    }
}

 

 

public class ProducerAndConsumer {
    private BlockingQueue<Integer> queue = new LinkedBlockingQueue<Integer>(10);
    class Producer extends Thread {
        @Override
        public void run() {
            producer();
        }
        private void producer() {
            while(true) {
                try {
                    queue.put(1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("生产者生产一条任务，当前队列长度为" + queue.size());
                try {
                    Thread.sleep(new Random().nextInt(1000)+500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }
    class Consumer extends Thread {
        @Override
        public void run() {
            consumer();
        }
        private void consumer() {
            while (true) {
                try {
                    queue.take();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("消费者消费一条任务，当前队列长度为" + queue.size());
                try {
                    Thread.sleep(new Random().nextInt(1000)+500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }
    public static void main(String[] args) {
        ProducerAndConsumer pc = new ProducerAndConsumer();
        Producer producer = pc.new Producer();
        Consumer consumer = pc.new Consumer();
        producer.start();
        consumer.start();
    }
}

 

 

class Stock {
    List<String> stock = new LinkedList();
    // 互斥量，控制共享数据的互斥访问
    private Semaphore mutex = new Semaphore(1);

    // canProduceCount可以生产的总数量。 通过生产者调用acquire，减少permit数目
    private Semaphore canProduceCount = new Semaphore(10);

    // canConsumerCount可以消费的数量。通过生产者调用release，增加permit数目
    private Semaphore canConsumerCount = new Semaphore(0);

    public void put(String computer) {
        try {
            // 可生产数量 -1
            canProduceCount.acquire();
            mutex.acquire();
            // 生产一台电脑
            stock.add(computer);
            System.out.println(computer + " 正在生产数据" + " -- 库存剩余：" + stock.size());
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            // 释放互斥锁
            mutex.release();
            // 释放canConsumerCount，增加可以消费的数量
            canConsumerCount.release();
        }
        // 无逻辑作用，放慢速度
        try {
            Thread.sleep(500);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public void get(String consumerName) {
        try {
            // 可消费数量 -1
            canConsumerCount.acquire();
            mutex.acquire();
            // 从库存消费一台电脑
            String removedVal = stock.remove(0);
            System.out.println(consumerName + " 正在消费数据：" + removedVal + " -- 库存剩余：" + stock.size());
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            mutex.release();
            // 消费后释放canProduceCount，增加可以生产的数量
            canProduceCount.release();
        }
    }
}


public class SemaphoreTest {
    public static void main(String[] args) {
        // 用于多线程操作的库存变量
        final Stock stock = new Stock();
        // 定义两个生产者和两个消费者
        Thread dellProducer = new Thread(new Runnable() {
            @Override
            public void run() {
                while (true) {
                    stock.put("Del");
                }
            }
        });
        Thread macProducer = new Thread(new Runnable() {
            @Override
            public void run() {
                while (true) {
                    stock.put("Mac");
                }
            }
        });
        Thread consumer1 = new Thread(new Runnable() {
            @Override
            public void run() {
                while (true) {
                    stock.get("zhangsan");
                }
            }
        });
        Thread consumer2 = new Thread(new Runnable() {
            @Override
            public void run() {
                while (true) {
                    stock.get("李四");
                }
            }
        });
        dellProducer.start();
        macProducer.start();
        consumer1.start();
        consumer2.start();
    }
}