import java.util.concurrent.Semaphore;

public class Reader extends Thread 
{
	private static volatile int readers = 0;
	private static final Semaphore mutex = new Semaphore(1);

	public void run()
	{
		try 
		{
			Reader.mutex.acquire();
			Reader.readers++;
			if (Reader.readers == 1) 
			{
				Writer.writer.acquire();
			}
			Reader.mutex.release();
			//read
			Reader.mutex.acquire();
			Reader.readers--;
			if (Reader.readers == 0)
			{
				Writer.writer.release();
			}
			Reader.mutex.release();
		} 
		catch (InterruptedException e) 
		{
			e.printStackTrace();
		}
	}
}