线程间通信-生产者消费者

喜欢ヅ旅行 2022-06-16 02:06 169阅读 0赞

对于多个生产者和消费者：

1.不要用if ，而要定义while判断标记，使得被唤醒的线程再一次判断标记；

2.需要使用notifyAll唤醒对方线程。因为之用notify，容易出现只唤醒本方线程的情况，导致程序中的所有线程都等待。

但使用notifyAll不仅仅会唤醒对方线程，也会唤醒本方线程，这种解决方案并不是很好。

package com.javase.thread;
    
    public class ProducerConsumer {
    	
    	public static void main(String[] args){
    		Resources res = new Resources();
    		Thread t1 = new Thread(new Producer(res));
    		Thread t2 = new Thread(new Producer(res));
    		Thread t3 = new Thread(new Consumer(res));
    		Thread t4 = new Thread(new Consumer(res));
    		t1.start();
    		t2.start();
    		t3.start();
    		t4.start();
    	}
    	
    }
    
    
    class Resources{
    	private String name;
    	private int count=0;
    	boolean flag = false;
    	public synchronized void set(String name){
    		while(flag){
    			try {
    				wait();
    			} catch (InterruptedException e) {
    				e.printStackTrace();
    			}
    		}
    		this.name=name;
    		System.out.println("***生产者："+name+(++count));
    		flag=true;
    		notifyAll();
    		
    	}
    	
    	public synchronized void print(){
    		while(!flag){
    			try {
    				wait();
    			} catch (InterruptedException e) {
    				e.printStackTrace();
    			}
    		}
    		System.out.println("消费者："+this.name+count);
    		flag=false;
    		notifyAll();
    		
    	}
    }
    
    class Producer implements Runnable{
    	private Resources res ;
    	public Producer(Resources res){
    		this.res=res;
    	}
    	public void run(){
    		while(true)
    			res.set("Product");
    	}
    }
    
    class Consumer implements Runnable{
    	private Resources res ;
    	public Consumer(Resources res){
    		this.res=res;
    	}
    	public void run(){
    		while(true)
    			res.print();
    	}
    }

JDK1.5 中提供了多线程升级解决方案。将同步Synchronized替换成现实Lock操作。将Object中的wait，notify , notifyAll 替换成Condition对象。该对象可以通过Lock锁进行获取。下面代码实现了本方只唤醒对方的操作。

package com.javase.thread;
    
    import java.util.concurrent.locks.Condition;
    import java.util.concurrent.locks.Lock;
    import java.util.concurrent.locks.ReentrantLock;
    
    public class ProducerConsumer {
    	
    	public static void main(String[] args){
    		Resources res = new Resources();
    		Thread t1 = new Thread(new Producer(res));
    		Thread t2 = new Thread(new Producer(res));
    		Thread t3 = new Thread(new Consumer(res));
    		Thread t4 = new Thread(new Consumer(res));
    		t1.start();
    		t2.start();
    		t3.start();
    		t4.start();
    	}
    	
    }
    
    
    class Resources{
    	private Lock resLock = new ReentrantLock();
    	private Condition condition_pro = resLock.newCondition();
    	private Condition condition_con = resLock.newCondition();
    	private String name;
    	private int count=0;
    	boolean flag = false;
    	public void set(String name){
    		resLock.lock();
    		try{
    			while(flag){
    				try {
    					condition_pro.await();
    				} catch (InterruptedException e) {
    					e.printStackTrace();
    				}
    			}
    			this.name=name;
    			System.out.println(Thread.currentThread().getName()+"--生产者："+name+(++count));
    			flag=true;
    			condition_con.signal();
    		}finally{
    			resLock.unlock();
    		}
    		
    	}
    	
    	public void print(){
    		resLock.lock();
    		try{
    			while(!flag){
    				try {
    					condition_con.await();
    				} catch (InterruptedException e) {
    					e.printStackTrace();
    				}
    			}
    			System.out.println(Thread.currentThread().getName()+"--消费者："+this.name+count);
    			flag=false;
    			condition_pro.signal();
    		}finally{
    			resLock.unlock();
    		}
    		
    		
    	}
    }
    
    class Producer implements Runnable{
    	private Resources res ;
    	public Producer(Resources res){
    		this.res=res;
    	}
    	public void run(){
    		while(true)
    			res.set("Product");
    	}
    }
    
    class Consumer implements Runnable{
    	private Resources res ;
    	public Consumer(Resources res){
    		this.res=res;
    	}
    	public void run(){
    		while(true)
    			res.print();
    	}
    }