Monitor implementation of the Sleeping-Barber Problem:

type sleeping_barber = monitor

    var number_of_customer: integer;

    var x_barber: condition;

    var x_customer: condition;

    procedure entry get_customer()

        begin

            if (number_of_customer = 0)

              x_barber.wait; /* the barber has to wait for customers */

            number_of_customers := number_of_customers - 1;

            x_customer.signal; /* inform the customer that the barber is ready */

        end

    procedure entry haircut()

        begin

            number_of_customer := number_of_customer + 1;

            x_barber.signal; /* inform the barber that a customer is in */

            x_customer.wait; /* wait for the barber */

            do_haircut();

        end

    begin /*initialization*/

        number_of_customer = 0;

    end

 end /* monitor */

sb: monitor sleeping_barber;

Barber code:

while (true)

  begin

    sb.get_customer();

    cut_hair();

  end;

customer code:

   hair_cut();