java基础>线程 生产者消费者问题 小强斋

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：

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。

存储空间为空，而消费者占用着它，生产者等着消费者让出空间从而添加产品，消费者等着生产者生产产品，从而从空间中去除产品。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!");
                }
                // }
            }
        }
    }

}

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。

wait()和notify()其他例子

产品类

//生产的产品
public class Product {
	private  int productId;

	public Product(int productId) {
		this.productId = productId;
	}

	public int getProductId() {
		return productId;
	}

	public void setProductId(int productId) {
		this.productId = productId;
	}

	@Override
	public String toString() {
		return "product_"+productId;
	}
}

仓库类

import java.util.ArrayList;
import java.util.List;

public class StoreHouse {
	private static final Integer initialSize = 10;
	private List<Product> list = null;

	public StoreHouse() {

		this.list = new ArrayList<Product>(initialSize);

	}

	public synchronized void put(Product product) {
		if (list.size() == StoreHouse.initialSize) {
			try {
				System.out.println("仓库已满，等待消费者消费");
				this.wait();
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}

		list.add(product);
		System.out.println("放入仓库" + product);
		notifyAll();

	}

	public synchronized void get() {
		if (list.size() == 0) {
			try {
				System.out.println("仓库为空，等待生产者生产");
				this.wait();
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
		Product product = list.get(list.size()-1);
		System.out.println("从仓库取出" + product);
		list.remove(list.size()-1);
		notifyAll();
	}

}

生产者

public class Producer implements Runnable {

	StoreHouse storeHouse = null;

	public Producer(StoreHouse storeHouse) {
		this.storeHouse = storeHouse;
	}

	@Override
	public void run() {
		int i = 0;
		while (true) {

			Product product = new Product(++i);
			storeHouse.put(product);
			 try { 
	                Thread.sleep(1000); 
	            } catch (InterruptedException e) { 
	                return; 
	            } 

		}
	}

}

消费者

public class Consumer implements Runnable {

	StoreHouse storeHouse = null;

	public Consumer(StoreHouse storeHouse) {
		this.storeHouse = storeHouse;
	}

	@Override
	public void run() {
		int i = 0;
		while (true) {
			storeHouse.get();
			 try { 
	                Thread.sleep(1500); 
	            } catch (InterruptedException e) { 
	                return; 
	            } 
		}
	}

}

客户端测试

public class Client {

	public static void main(String[] args) {
		StoreHouse storeHouse = new StoreHouse();

		Runnable producer = new Producer(storeHouse);
		Runnable consumer = new Consumer(storeHouse);
		Thread produceThread = new Thread(producer);
		Thread consumeThread = new Thread(consumer);
		produceThread.start();
		consumeThread.start();
	}

}