线程同步--生产者消费者

最新推荐文章于 2024-08-27 07:44:43 发布

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文章标签：

#多线程 #同步 #通信 #生产者 #消费者

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当同时有很多生产者和消费者往仓库里面增加产品减少产品，会产生以下两个问题：

1当生产者和消费者同时改变仓库对象的属性，最后打印出的结果不能反映仓库的情况

2当生产者过多或者消费者过多会使仓库满或者空，如果不把线程从运行态变成就阻塞态的话，会出现异常

解决方式：

问题1：在改变对象的方法加入同步锁，该方法运行时将对象或者对象的属性锁定，当方法运行完才可以访问该对象或者对象的属性

问题2：在方法头部加入判断条件，如果仓库满或空，则调用wait()方法。线程将交出对象锁，并进入阻塞状态。而当其他的生产或者消费方法执行过后，仓库不满或不空则调用notifyall()方法，将线程池中阻塞的方法变成就绪态。

下面我利用三种方法实现了生产者和消费者

方法一：

线程同步synchronized+线程通信wait()，notify()

import java.util.LinkedList;
import java.util.List;

/**
 * Created by marsares on 15/7/7.
 */
public class ProducerAndCustomer1 {
    public static void main(String[]args){
        Storage storage=new Storage();
        Producer1 p1=new Producer1(storage,"p1",10);
        Producer1 p2=new Producer1(storage,"p2",10);
        Producer1 p3=new Producer1(storage,"p3",10);
        Producer1 p4=new Producer1(storage,"p4",10);
        Producer1 p5=new Producer1(storage,"p5",10);
        Customer1 c1=new Customer1(storage,"c1",10);
        Customer1 c2=new Customer1(storage,"c2",10);
        p1.start();
        p2.start();
        p3.start();
        p4.start();
        p5.start();
        c1.start();
        c2.start();
    }
}
class Storage{
    private static final int max=30;
    private int size=0;
    private int count=0;
    LinkedList<String>storage=new LinkedList<String>();
    public synchronized void add(int num){
        notifyAll();
        while(size+num>max){
            System.out.println(Thread.currentThread().getName()+"wait for customer");
            try{
                wait();
            }catch(InterruptedException e){
                throw new RuntimeException(e);
            }
        }
        for(int i=0;i<num;i++){
            storage.add("apple" + count);
            count++;
            size++;
        }
        System.out.println(Thread.currentThread().getName()+" add "+num+" products,"+" size="+size);
    }
    public synchronized void delete(int num){
        notifyAll();
        while(size-num<0){
            System.out.println(Thread.currentThread().getName()+"wait for producer");
            try{
                wait();
            }catch(InterruptedException e){
                throw new RuntimeException(e);
            }
        }
        for(int i=0;i<num;i++){
            storage.remove();
            size--;
        }
        System.out.println(Thread.currentThread().getName()+" delete "+num+" products,"+" size="+size);
    }
}
class Producer1 extends Thread{
    Storage storage;
    String name;
    int num;
    public Producer1(Storage storage,String name,int num){
        this.storage=storage;
        this.name=name;
        this.num=num;
    }
    public void produce(int num){
        storage.add(num);
    }
    public void run(){
        produce(num);
    }
}
class Customer1 extends Thread{
    Storage storage;
    String name;
    int num;
    public Customer1(Storage storage,String name,int num){
        this.storage=storage;
        this.name=name;
        this.num=num;
    }
    public void consume(int num){
        storage.delete(num);
    }
    public void run(){
        consume(num);
    }
}

方法二：

使用lock

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

/**
 * Created by marsares on 15/7/7.
 */
public class ProducerAndCustomer2 {
    public static void main(String[]args){
        Storage2 storage=new Storage2();
        Producer2 p1=new Producer2(storage,"p1",10);
        Producer2 p2=new Producer2(storage,"p2",10);
        Producer2 p3=new Producer2(storage,"p3",10);
        Producer2 p4=new Producer2(storage,"p4",10);
        Producer2 p5=new Producer2(storage,"p5",10);
        Customer2 c1=new Customer2(storage,"c1",10);
        Customer2 c2=new Customer2(storage,"c2",10);
        p1.start();
        p2.start();
        p3.start();
        p4.start();
        p5.start();
        c1.start();
        c2.start();
    }
}
class Storage2{
    private static final int max=30;
    private int size=0;
    private int count=0;
    LinkedList<String> storage=new LinkedList<String>();
    private final Lock lock=new ReentrantLock();
    private final Condition full=lock.newCondition();
    private final Condition empty=lock.newCondition();
    public void add(int num){
        lock.lock();
        while(size+num>max){
            System.out.println(Thread.currentThread().getName()+"wait for customer");
            try{
                full.await();
            }catch(InterruptedException e){
                throw new RuntimeException(e);
            }
        }
        for(int i=0;i<num;i++){
            storage.add("apple" + count);
            count++;
            size++;
        }
        System.out.println(Thread.currentThread().getName()+" add "+num+" products,"+" size="+size);
        empty.signalAll();
        lock.unlock();
    }
    public void delete(int num){
        lock.lock();
        while(size-num<0){
            System.out.println(Thread.currentThread().getName()+"wait for producer");
            try{
                wait();
            }catch(InterruptedException e){
                throw new RuntimeException(e);
            }
        }
        for(int i=0;i<num;i++){
            storage.remove();
            size--;
        }
        System.out.println(Thread.currentThread().getName()+" delete "+num+" products,"+" size="+size);
        full.signalAll();
        lock.unlock();
    }
}
class Producer2 extends Thread{
    Storage2 storage;
    String name;
    int num;
    public Producer2(Storage2 storage,String name,int num){
        this.storage=storage;
        this.name=name;
        this.num=num;
    }
    public void produce(int num){
        storage.add(num);
    }
    public void run(){
        produce(num);
    }
}
class Customer2 extends Thread{
    Storage2 storage;
    String name;
    int num;
    public Customer2(Storage2 storage,String name,int num){
        this.storage=storage;
        this.name=name;
        this.num=num;
    }
    public void consume(int num){
        storage.delete(num);
    }
    public void run(){
        consume(num);
    }
}

方法三：

使用LinkedBlockingQueue

import java.util.concurrent.LinkedBlockingQueue;

/**
 * Created by marsares on 15/7/7.
 */
public class ProducerAndCustomer3 {
    public static void main(String[]args){
        Storage3 storage=new Storage3();
        Producer3 p1=new Producer3(storage,"p1",10);
        Producer3 p2=new Producer3(storage,"p2",10);
        Producer3 p3=new Producer3(storage,"p3",10);
        Producer3 p4=new Producer3(storage,"p4",10);
        Producer3 p5=new Producer3(storage,"p5",10);
        Customer3 c1=new Customer3(storage,"c1",10);
        Customer3 c2=new Customer3(storage,"c2",10);
        p1.start();
        p2.start();
        p3.start();
        p4.start();
        p5.start();
        c1.start();
        c2.start();
    }
}
class Storage3{
    private static final int max=30;
    private int size=0;
    private int count=0;
    LinkedBlockingQueue<String> storage=new LinkedBlockingQueue<String>(max);
    public void add(int num){
        for(int i=0;i<num;i++){
            try{
                storage.put("apple" + count);
                count++;
                size++;
            }catch(InterruptedException e){
                throw new RuntimeException(e);
            }
        }
        System.out.println(Thread.currentThread().getName() + " add " + num + " products," + " size=" + size);
    }
    public void delete(int num){
        for(int i=0;i<num;i++){
            try{
                storage.take();
                size--;
            }catch(InterruptedException e){
                throw new RuntimeException(e);
            }
        }
        System.out.println(Thread.currentThread().getName() + " delete " + num + " products," + " size=" + size);
    }
}
class Producer3 extends Thread{
    Storage3 storage;
    String name;
    int num;
    public Producer3(Storage3 storage,String name,int num){
        this.storage=storage;
        this.name=name;
        this.num=num;
    }
    public void produce(int num){
        storage.add(num);
    }
    public void run(){
        produce(num);
    }
}
class Customer3 extends Thread{
    Storage3 storage;
    String name;
    int num;
    public Customer3(Storage3 storage,String name,int num){
        this.storage=storage;
        this.name=name;
        this.num=num;
    }
    public void consume(int num){
        storage.delete(num);
    }
    public void run(){
        consume(num);
    }
}