Santa-elf IPC problem:

Use semaphores to coordinates three  types of processes in the problem
described here. Santa  Claus sleeps in his shop at  the North pole and
can only be  awakened by either (1) all nine  reindeer being back from
their  vacation, or  (2) by  some of  the elves  having  difficulty in
making  toys.   Elves  can wake  Santa  up  when  three of  them  have
problems. When three elves are having their problems solved, any other
elves  wishing  to  visit Santa  must  wait  for  the three  elves  to
return. ``Three elves waiting''  has higher priority than all reindeer
getting back. That is because without any toys Santa cannot go on h is
gift-giving spree.  All the elves' difficulty should  be solved before
Santa leaves.  Solve this problem using semaphores.