Question 10103 –

A concurrent system consists of 3 processes using a shared resource R in a non-preemptible and mutually exclusive manner. The processes have unique priorities in the range 1…..3, 3 being the highest priority. It is required to synchronize the processes such that the resource is always allocated to the highest priority requester. The pseudo code for the system is as follows.

Shared Data 
mutex:semaphore = 1:/* initialized to 1*/
process[3]:semaphore = 0; /*all initialized to 0 */
R_requested [3]:boolean = false; /*all initialized to false */
busy: boolean = false; /*initialized to false */
Code for processes
begin process
my-priority:integer;
my-priority:=____; /*in the range 1...3*/
repeat
    request_R(my-priority);
    P (proceed [my-priority]);
    {use shared resource R}
    release_R (my-priority);
forever
end process;
Procedures
procedure request_R(priority);
P(mutex);
if busy = true then
    R_requested [priority]:=true;
else
 begin
    V(proceed [priority]);
    busy:=true;
 end
V(mutex); 

Give the pseudo code for the procedure release_R.

Correct Answer: A