/*
   Other examples of threads and synchronization:

   The basic bounded buffer (producer-consumer) problem:
*/

class boundedbuffer
{
    private int[] buffer;  // circular queue
    private int front, end, size, max;
    public boundedbuffer(int m) 
    {
	max = m;  size = front = end = 0;
	buffer = new int[m];
    }

    public synchronized int read() throws Exception
    {
	while (size<1) wait(); // wait 'til there's stuff to read
	                       // why "while" and not just "if"?
	// at this point, thread has been "notified", or woken up
	int answer = buffer[front];
	front = (front + 1) % max;
	size--;
	if (size==max-1) notifyAll(); // there's now space for new write
	return answer;
	// do we need to wake anyone up at this point?
    }


    public synchronized void write(int x) throws Exception
    {
	while (size==max) wait();
	buffer[end] = x;
	end = (end+1) % max;
	size++;
	if (size==1) notifyAll(); // there's now something to read
    }
} // boundedbuffer

/*
   note that if "notify" is called, only one thread is awoke - it can be
   a reader or a writer thread.  
*/


class reader implements Runnable
{
   boundedbuffer bb;
    reader(boundedbuffer x) { bb = x; }
    public void run()
    {
     try {
	for (int i=0;i<1000;i++)
	    {
		System.out.println("reader has read "+bb.read());
	    }
      } catch (Exception e) {System.out.println(e); System.exit(1);}
    } // run
}


class writer implements Runnable
{
    boundedbuffer bb;
    writer(boundedbuffer x) { bb = x; }
    public void run()
    {
     try {
	for (int i=0;i<1000;i++)
	    {
		bb.write(i);
		System.out.println("writer has written "+i);
	    }
      } catch (Exception e) {System.out.println(e); System.exit(1);}
    } // run
}


public class notes213
{
   public static void main(String[] args)
    {
     try {
	boundedbuffer bb = new boundedbuffer(20);
	Thread freddy = new Thread(new reader(bb));
	Thread jason = new Thread(new writer(bb));
	freddy.start();
	jason.start();
	freddy.join();
	jason.join();
     } catch (Exception e) {System.exit(1);}
	System.exit(0);
    }
}