多生产者多消费者问题

/**
 * 多生产者 多消费者问题
 * 
 * 该代码存在死锁问题
 * 因为有可能唤醒本方 
 * @author 黄二狗
 *
 */

public class Test {
     public static void main(String[] args) {
        Resource r = new Resource();
        Producer producer = new Producer(r);
        Consumer consumer = new Consumer(r);
        Thread t0 = new Thread(producer);
        Thread t1 = new Thread(producer);
        Thread t2 = new Thread(consumer);
        Thread t3 = new Thread(consumer);
        t0.start();
        t1.start();
        t2.start();
        t3.start();
    }
}

class Resource {
    private String name;
    private int count;
    private boolean flag;
    
    public synchronized void set(String name) throws InterruptedException {
        while(flag) 
            this.wait();  // t0 t1 
        this.name = name + count;
        count++;     
        System.out.println(Thread.currentThread().getName() + "....生产者..." + this.name);
        flag = true;
        this.notify();
    }
    
    public synchronized void out() throws InterruptedException {
        while(!flag)    //t2 t3
            this.wait();  
        System.out.println(Thread.currentThread().getName() + "....消费者..." + this.name);
        flag = false;
        this.notify();
    }
}

class Producer implements Runnable {
     private Resource r;
     public Producer(Resource r) {
         this.r = r;
     }
    @Override
    public void run() {
       while(true) {
           try {
            r.set("烤鸭");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
       }    
    }
}

class Consumer implements Runnable {
     private Resource r;
     public Consumer(Resource r) {
         this.r = r;
     }
    @Override
    public void run() {
        try {
            while(true) {
              r.out();
            }
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

 

改进方法:将notify()换成notifyAll(),这样的话就不会产生死锁了.

 

package test;

/**
 * 多生产者 多消费者问题
 * 
 * 该代码存在死锁问题
 * 因为有可能唤醒本方 
 * @author 黄二狗
 *
 */

public class Test {
     public static void main(String[] args) {
		Resource r = new Resource();
		Producer producer = new Producer(r);
		Consumer consumer = new Consumer(r);
		Thread t0 = new Thread(producer);
		Thread t1 = new Thread(producer);
		Thread t2 = new Thread(consumer);
		Thread t3 = new Thread(consumer);
		t0.start();
		t1.start();
		t2.start();
		t3.start();
	}
}

class Resource {
	private String name;
	private int count;
	private boolean flag;
	
	public synchronized void set(String name) throws InterruptedException {
		while(flag) 
			this.wait();  // t0 t1 
		this.name = name + count;
		count++;     
		System.out.println(Thread.currentThread().getName() + "....生产者..." + this.name);
		flag = true;
		this.notifyAll();
	}
	
	public synchronized void out() throws InterruptedException {
		while(!flag)    //t2 t3
			this.wait();  
		System.out.println(Thread.currentThread().getName() + "....消费者..." + this.name);
		flag = false;
		this.notifyAll();
	}
}

class Producer implements Runnable {
	 private Resource r;
	 public Producer(Resource r) {
		 this.r = r;
	 }
	@Override
	public void run() {
	   while(true) {
		   try {
			r.set("烤鸭");
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	   }	
	}
}

class Consumer implements Runnable {
	 private Resource r;
	 public Consumer(Resource r) {
		 this.r = r;
	 }
	@Override
	public void run() {
		try {
			while(true) {
			  r.out();
			}
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
}

　　

 

package test;

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

/**
 * 使用Lock和Condition解决唤醒的低效率问题
 *
 */

public class Test {
     public static void main(String[] args) {
		Resource r = new Resource();
		Producer producer = new Producer(r);
		Consumer consumer = new Consumer(r);
		Thread t0 = new Thread(producer);
		Thread t1 = new Thread(producer);
		Thread t2 = new Thread(consumer);
		Thread t3 = new Thread(consumer);
		t0.start();
		t1.start();
		t2.start();
		t3.start();
	}
}

class Resource {
	private String name;
	private int count;
	private boolean flag;
	private Lock lock = new ReentrantLock();
	private Condition producer_condition = lock.newCondition();
	private Condition consumer_condition = lock.newCondition();
	
	
	public void set(String name) throws InterruptedException {
		lock.lock();
		while(flag) 
			producer_condition.await();
		this.name = name + count;
		count++;     
		System.out.println(Thread.currentThread().getName() + "....生产者..." + this.name);
		flag = true;
		consumer_condition.signal();
		lock.unlock();
	}
	
	public void out() throws InterruptedException {
		
		lock.lock();
		while(!flag)     
		    consumer_condition.await();
		System.out.println(Thread.currentThread().getName() + "....消费者..." + this.name);
		flag = false;
		producer_condition.signal();
		lock.unlock();
	}
}

class Producer implements Runnable {
	 private Resource r;
	 public Producer(Resource r) {
		 this.r = r;
	 }
	@Override
	public void run() {
	   while(true) {
		   try {
			r.set("烤鸭");
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	   }	
	}
}

class Consumer implements Runnable {
	 private Resource r;
	 public Consumer(Resource r) {
		 this.r = r;
	 }
	@Override
	public void run() {
		try {
			while(true) {
			  r.out();
			}
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
}

　　

package test;

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

/**
 * 真实场景下的多生产者多消费者模型
 * @author 黄二狗
 *
 */
public class BoundeBuffer {
    final Lock lock = new ReentrantLock();
    final Condition notFull = lock.newCondition();
    final Condition notEmpty = lock.newCondition();
    
    final Object [] items = new Object[100];
    int putPosition = 0;
    int takePosition = 0;
    int count = 0;
    
    public void put(Object obj) throws InterruptedException {
       lock.lock();
       while(items.length == count) {
           notFull.await();
       }
       items[putPosition] = obj;
       putPosition = putPosition + 1;
       if(putPosition == items.length)
           putPosition = 0;
       count = count + 1;
       notEmpty.signal();
       lock.unlock();
    }
   
    public Object take() throws InterruptedException {
        
     lock.lock();
     try {
     while(count == 0) {
         notEmpty.wait();
     }
     Object x = items[takePosition];
     takePosition = takePosition + 1;
     if(takePosition == items.length) {
         takePosition ++;
     }
     count = count - 1;
     notFull.signal();
     return x ;
     } 
     finally {
         lock.unlock();    
    }
     
    }
    public static void main(String[] args) {
       
    }
}