import java.util.Random;

public class ReadWriteConcurrent {
	
	public static void main(String[] args) {

		Database d = new Database();

		Reader r1 = new Reader(d);
		Reader r2 = new Reader(d);
		Reader r3 = new Reader(d);
		Reader r4 = new Reader(d);
		Reader r5 = new Reader(d);


		Writer w1 = new Writer(d,1);
		Writer w2 = new Writer(d,10);
		Writer w3 = new Writer(d,100);
		Writer w4 = new Writer(d,1000);
		Writer w5 = new Writer(d,10000);
		
		w1.start();
		w2.start();
		r1.start();
		r2.start();
		r3.start();
		r4.start();
		r5.start();
		w3.start();
		w4.start();
		w5.start();

	}
}

class Database {
	int data = 0;
	int r = 0;   // # active readers
	int w = 0;   // # active writers (0 or 1)
	int ww = 0;  // # waiting writers
	int wr = 0;  // # waiting readers
	

	public synchronized void request_read() {
		while (w == 1 || ww > 0)
			try { wr++;  wait();  wr--; }   
		    catch (Exception e) {
		}
		r++;
	}

	public synchronized void done_read() {
		r--;
		notifyAll();
	}

	public synchronized void request_write() {
		// wait if writer is active or there are waiting writers
 		while (w == 1 || ww > 0) {
			try {
				 ww++;  wait();  ww--;
			} catch (Exception e) {}
 		}
		w = 1;
	}

	public synchronized void done_write() {
		w = 0;
		notifyAll();
	} 

	int read() {
		return data;
	}

	void write(int x) {
		data = data + x;
	}
}

class Reader extends Thread {
	Database d;

	public Reader(Database d) {
		this.d = d;
	}

	public void run() {

		for (int i = 0; i < 5; i++){		
			d.request_read();
			System.out.println(d.read());
			d.done_read();
			
		}
	}
}

class Writer extends Thread {
	Database d;
	int x;

	public Writer(Database d, int x) {
		this.d = d;
		this.x = x;
	}

	public void run() {
		for (int i = 0; i < 5; i++) {			
			d.request_write();
			d.write(x);
			try { Thread.sleep(150); }
			catch (Exception e) {}
			d.done_write();
		}
	}
}