Here is a solution to the Barber's Chair problem.

Constants:
   N = number of waiting chairs in the shop.

Semaphores (and initial values):
   chair = 1;		/* is the chair free */
   barber = 0;		/* number of waiting customers - between 0 and N 
				this is used to wake up the barber if need be
			*/
   mutex = 1;		/* mutual exclusion over the counter */
   customer = 0;	/* is the customer's hair cut done */
	  
Variables 
   count;		/* number of waiting customers */

Barber:
   while (1) {
       P(barber);	/* sleep waiting for customer */
       P(mutex);	/* CS for count */
       count -= 1;
       V(mutex);	/* count updated */

       /* cut hair - could be short busy wait until customer is seated.
		but we know the customer will be seated soon so this is OK 
       */

       V(customer);	/* hair cut is done, the customer can get up */
   }

Customer:
   while (1) {
       P(mutex);
       if (count < N) {
	   V(barber);	/* wakeup barber or indicate we are waiting */
	   count += 1;	/* add to total waiting */
	   V(mutex);	/* we are done updating count */

	   P(chair);	/* wait for the chair to be free */

	   /* sit down in the barber's chair */

	   P(customer);	/* wait until the barber indicates our hair is done */

	   /* stand up and get out of chair */

	   V(chair);	/* indicate that we are out of the chair */
       } else {
	   V(mutex);	/* too many people waiting - leave the shop */
       }

       /* grow hair */
   }