Originally from:

  Implementing Semaphores in the Shell
  10/6/2004 By Ed Schaefer and John Spurgeon for UNIX Review

  Summary:
  The authors present a Korn shell implementation of a counting
  semaphore.


The link to the artilce (and in theory the source code) I found for it
at:

  http://unix.ittoolbox.com/documents/implementing-semaphores-in-the-shell-15726

is dead.

In this directory you will find:

  semaphore.tar - the original downloadable source code
  semaphore.patch - my patch to fix a logic bug and make it run on modern ksh's
  README - this file

Enjoy.