Consider a system consisting of processes P1 , P2 , ..., Pn , each of which has a unique priority number. Write a monitor that allocates three identical printers to these processes, using the priority numbers for deciding the order of allocation.

See explaination

Explanation:

The code

type printer = monitor

var P: array[0…2] of boolean;

X: condition;

procedure acquire (id: integer, printer-id: integer);

begin

if P[0] and P[1] and P[2] then X.wait(id)

if not P[0] then printer-id := 0;

else if not P[1] then printer-id := 1;

else printer-id := 2;

P[printer-id]:=true;

end;

procedure release (printer-id: integer)

begin

P[printer-id]:=false;

X.signal;

end;

begin

P[0] := P[1] := P[2] := false;

end ;

Note:

Monitors are implemented by using queues to keep track of the processes attempting to become active int he monitor. To be active, a monitor must obtain a lock to allow it to execute the monitor code. Processes that are blocked are put in a queue of processes waiting for an unblocking event to occur.