/* Code of Figure 14.8, pages 645-646 from
   Kenneth C. Louden, Programming Languages
   Principles and Practice 2nd Edition
   Copyright (C) Brooks-Cole/ITP, 2003
*/

class Buffer {
    private final char[] buf;
    private int start = -1;
    private int end = -1;
    private int size = 0;
    private Semaphore nonFull, nonEmpty, mutEx;

    public Buffer(int length) {
        buf = new char[length];
        nonFull = new Semaphore(length);
        nonEmpty = new Semaphore(0);
        mutEx = new Semaphore(1);
    }

    public boolean more()
    { return size > 0; }

    public void put(char ch)
    { try {
        nonFull.delay();
        mutEx.delay();
        end = (end+1) % buf.length;
        buf[end] = ch;
        size++;
        mutEx.signal();
        nonEmpty.signal();
      }
      catch (InterruptedException e)
      { Thread.currentThread().interrupt(); }
    }

    public char get()
    { try {
        nonEmpty.delay();
        mutEx.delay();
        start = (start+1) % buf.length;
        char ch = buf[start];
        size--;
        mutEx.signal();
        nonFull.signal();
        return ch;
      }
      catch (InterruptedException e)
      { Thread.currentThread().interrupt(); }
      return 0;
    }
}