Shared variables:

freeChairs = n;
BarberBusy = false;
customerShaved = true;
CriticalSectionFree = 1 /* the semaphore */

Process Customer {
    Acquire (CriticalSectionFree);
    if (freeChairs == 0) {
       Release (CriticalSectionFree);
       exit; /* Customer leaves shop */
    }

    freeChairs --; /* Customer sits  down */
    Release (CriticalSectionFree);
    wakeup_Barber;
    Acquire (CriticalSectionFree);
    while (BarberBusy) {
        Release (CriticalSectionFree);
	sleep; /* Barber busy - wait until free */
        Acquire (CriticalSectionFree);
    }
    BarberBusy = true; /* now our turn to be served */
    customerShaved = false;
    Release (CriticalSectionFree);
    /* now get shaved */
    Acquire (CriticalSectionFree);
    customerShaved = true; /* necessary for synchronisation: customer
                              now finished */
    Release (CriticalSectionFree);
    exit;
}

Process Barber {
   while (1) {
      Acquire (CriticalSectionFree);
      while (freeChairs == n) {
          Release (CriticalSectionFree);
      	  sleep; /* nothing to do: no customers in shop */
          Acquire (CriticalSectionFree);
      }
      freeChairs ++;
      Release (CriticalSectionFree);
      /* shave */

      Acquire (CriticalSectionFree);
      while (!customerShaved) {
         Release (CriticalSectionFree);
   	 sleep; /* wait for customer to finish */
         Acquire (CriticalSectionFree);
      }
      BarberBusy = false;
      Release (CriticalSectionFree);
      wakeup_Customers;
   }
}