java实现生产者消费者问题

Posted 2020-08-08

引言

　　生产者和消费者问题是线程模型中的经典问题：生产者和消费者在同一时间段内共用同一个存储空间，如下图所示，生产者向空间里存放数据，而消费者取用数据，如果不加以协调可能会出现以下情况：

生产者消费者图

　　存储空间已满，而生产者占用着它，消费者等着生产者让出空间从而去除产品，生产者等着消费者消费产品，从而向空间中添加产品。互相等待，从而发生死锁。

JAVA解决线程模型的三种方式

 

1、wait()和notify()

import java.util.LinkedList;

public class ProducerConsumer {
    private LinkedList<Object> storeHouse = new LinkedList<Object>();
    private int MAX = 10;

    public ProducerConsumer() {
    }

    public void start() {
        new Producer().start();
        new Comsumer().start();
    }

    class Producer extends Thread {
        public void run() {
            while (true) {
                synchronized (storeHouse) {
                    try {
                        while (storeHouse.size() == MAX) {
                            System.out.println("storeHouse is full , please wait");
                            storeHouse.wait();
                        }
                        Object newOb = new Object();
                        if (storeHouse.add(newOb)) {
                            System.out.println("Producer put a Object to storeHouse");
                            Thread.sleep((long) (Math.random() * 3000));
                            storeHouse.notify();
                        }
                    } catch (InterruptedException ie) {
                        System.out.println("producer is interrupted!");
                    }

                }
            }
        }
    }

    class Comsumer extends Thread {
        public void run() {
            while (true) {
                synchronized (storeHouse) {
                    try {
                        while (storeHouse.size() == 0) {
                            System.out.println("storeHouse is empty , please wait");
                            storeHouse.wait();
                        }
                        storeHouse.removeLast();
                        System.out.println("Comsumer get  a Object from storeHouse");
                        Thread.sleep((long) (Math.random() * 3000));
                        storeHouse.notify();
                    } catch (InterruptedException ie) {
                        System.out.println("Consumer is interrupted");
                    }

                }
            }

        }
    }

    public static void main(String[] args) throws Exception {
        ProducerConsumer pc = new ProducerConsumer();
        pc.start();
    }
}

 

　　2、await()和signal()，即线程锁的方式

package sort;

import java.util.LinkedList;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class ProducerConsumer {
    private LinkedList<Object> myList = new LinkedList<Object>();
    private int MAX = 10;
    private final Lock lock = new ReentrantLock();
    private final Condition full = lock.newCondition();
    private final Condition empty = lock.newCondition();

    public ProducerConsumer() {
    }

    public void start() {
        new Producer().start();
        new Consumer().start();
    }

    public static void main(String[] args) throws Exception {
        ProducerConsumer s2 = new ProducerConsumer();
        s2.start();
    }

    class Producer extends Thread {
        public void run() {
            while (true) {
                lock.lock();
                try {
                    while (myList.size() == MAX) {
                        System.out.println("warning: it‘s full!");
                        full.await();
                    }
                    Object o = new Object();
                    if (myList.add(o)) {
                        System.out.println("Producer: " + o);
                        empty.signal();
                    }
                } catch (InterruptedException ie) {
                    System.out.println("producer is interrupted!");
                } finally {
                    lock.unlock();
                }
            }
        }
    }

    class Consumer extends Thread {
        public void run() {
            while (true) {
                lock.lock();
                try {
                    while (myList.size() == 0) {
                        System.out.println("warning: it‘s empty!");
                        empty.await();
                    }
                    Object o = myList.removeLast();
                    System.out.println("Consumer: " + o);
                    full.signal();
                } catch (InterruptedException ie) {
                    System.out.println("consumer is interrupted!");
                } finally {
                    lock.unlock();
                }
            }
        }
    }

}

 

　　3、阻塞队列的方式

import java.util.concurrent.*;

public class ProducerConsumer {
    // 建立一个阻塞队列
    private LinkedBlockingQueue<Object> queue = new LinkedBlockingQueue<Object>(10);

    public ProducerConsumer() {
    }

    public void start() {
        new Producer().start();
        new Consumer().start();
    }

    public static void main(String[] args) throws Exception {
        ProducerConsumer s3 = new ProducerConsumer();
        s3.start();
    }

    class Producer extends Thread {
        public void run() {
            while (true) {
                try {
                    Object o = new Object();
                    // 取出一个对象
                    queue.put(o);
                    System.out.println("Producer: " + o);
                } catch (InterruptedException e) {
                    System.out.println("producer is interrupted!");
                }
                // }
            }
        }
    }

    class Consumer extends Thread {
        public void run() {
            while (true) {
                try {
                    // 取出一个对象
                    Object o = queue.take();
                    System.out.println("Consumer: " + o);
                } catch (InterruptedException e) {
                    System.out.println("producer is interrupted!");
                }
                // }
            }
        }
    }

}

结论

  三种方式原理一致，都是对独占空间加锁，阻塞和唤醒线程，第一种方式比较传统，第三种方式最简单，只需存储和取用，线程同步的操作交由LinkedBlockingQueue全权处理。