foil on monitor solution to Exercise 12-9 sleeping barber problem

barbershop: monitor

waiting : integer := 0; % customers waiting to be cut

customers : condition :=0; % for the barber to wait for a customer

barber : condition := 0; % for a customer to wait for the barber

procedure seek-customer( ) % called by the barber

begin if waiting=0 then WAIT (customers); % sleeps if there are none

waiting := waiting-1; % one less customer waiting

SIGNAL (barber); % frees a waiting customer

end seek-customer ;

procedure get-haircut( ) % called by a customer

begin if waiting < chairs % is there a free chair to sit and wait?

% if there are no free chairs just go away

then { waiting := waiting+1; % one more customer waiting

SIGNAL (customers) % in case the barber is asleep

WAIT (barber); % wait for your turn with the barber

}

end get-haircut;

end barbershop;