Java中的生產者消費者問題（多線程間同步通信）

JDK1.5之前的版本

<strong><span style="font-size:18px;">class ProducerConsumerDemo 
{
	public static void main(String[] args) 
	{
		Resource r = new Resource();

		Producer pro = new Producer(r);
		Consumer con = new Consumer(r);

		Thread t1 = new Thread(pro);
		Thread t2 = new Thread(pro);
		Thread t3 = new Thread(con);
		Thread t4 = new Thread(con);

		t1.start();
		t2.start();
		t3.start();
		t4.start();

	}
}

/*
對於多個生產者和消費者。
爲什麼要定義while判斷標記。
原因：讓被喚醒的線程再一次判斷標記。


爲什麼定義notifyAll，
因爲需要喚醒對方線程。
因爲只用notify，容易出現只喚醒本方線程的情況。導致程序中的所有線程都等待。

*/


class Resource
{
	private String name;
	private int count = 1;
	private boolean flag = false;
			//  t1    t2
	public synchronized void set(String name)
	{
		while(flag)
			try{this.wait();}catch(Exception e){}//t1(放棄資格)  t2(獲取資格)
		this.name = name+"--"+count++;

		System.out.println(Thread.currentThread().getName()+"...生產者.."+this.name);
		flag = true;
		this.notifyAll();
	}


	//  t3   t4  
	public synchronized void out()
	{
		while(!flag)
			try{wait();}catch(Exception e){}//t3(放棄資格) t4(放棄資格)
		System.out.println(Thread.currentThread().getName()+"...消費者........."+this.name);
		flag = false;
		this.notifyAll();
	}
}

class Producer implements Runnable
{
	private Resource res;

	Producer(Resource res)
	{
		this.res = res;
	}
	public void run()
	{
		while(true)
		{
			res.set("+商品+");
		}
	}
}

class Consumer implements Runnable
{
	private Resource res;

	Consumer(Resource res)
	{
		this.res = res;
	}
	public void run()
	{
		while(true)
		{
			res.out();
		}
	}
}
</span></strong>

JDK1.5以後版本

<strong><span style="font-size:18px;">import java.util.concurrent.locks.*;

class ProducerConsumerDemo2 
{
	public static void main(String[] args) 
	{
		Resource r = new Resource();

		Producer pro = new Producer(r);
		Consumer con = new Consumer(r);

		Thread t1 = new Thread(pro);
		Thread t2 = new Thread(pro);
		Thread t3 = new Thread(con);
		Thread t4 = new Thread(con);

		t1.start();
		t2.start();
		t3.start();
		t4.start();

	}
}

/*
JDK1.5 中提供了多線程升級解決方案。
將同步Synchronized替換成現實Lock操作。
將Object中的wait，notify notifyAll，替換了Condition對象。
該對象可以Lock鎖 進行獲取。
該示例中，實現了本方只喚醒對方操作。

Lock:替代了Synchronized
	lock 
	unlock
	newCondition()

Condition：替代了Object wait notify notifyAll
	await();
	signal();
	signalAll();
*/
class Resource
{
	private String name;
	private int count = 1;
	private boolean flag = false;
			//  t1    t2
	private Lock lock = new ReentrantLock();

	private Condition condition_pro = lock.newCondition();
	private Condition condition_con = lock.newCondition();



	public  void set(String name)throws InterruptedException
	{
		lock.lock();
		try
		{
			while(flag)
				condition_pro.await();//t1,t2
			this.name = name+"--"+count++;

			System.out.println(Thread.currentThread().getName()+"...生產者.."+this.name);
			flag = true;
			condition_con.signal();
		}
		finally
		{
			lock.unlock();//釋放鎖的動作一定要執行。
		}
	}


	//  t3   t4  
	public  void out()throws InterruptedException
	{
		lock.lock();
		try
		{
			while(!flag)
				condition_con.await();
			System.out.println(Thread.currentThread().getName()+"...消費者........."+this.name);
			flag = false;
			condition_pro.signal();
		}
		finally
		{
			lock.unlock();
		}
		
	}
}

class Producer implements Runnable
{
	private Resource res;

	Producer(Resource res)
	{
		this.res = res;
	}
	public void run()
	{
		while(true)
		{
			try
			{
				res.set("+商品+");
			}
			catch (InterruptedException e)
			{
			}
			
		}
	}
}

class Consumer implements Runnable
{
	private Resource res;

	Consumer(Resource res)
	{
		this.res = res;
	}
	public void run()
	{
		while(true)
		{
			try
			{
				res.out();
			}
			catch (InterruptedException e)
			{
			}
		}
	}
}
</span></strong>