Question 5 (20 marks): Consider the mutual exclusion protocol for two processes shown below:

//Shared variables

boolean c1 = false, c2 = false;

int turn = 1;

Process P1: Process P2:

init1; init2;

while(true){ while(true){

//entry protocol //entry protocol

turn = 2; c1 = true; turn = 1; c2 = true;

while(c2 && turn ==2){ } while(c1 && turn == 1) { }

crit1; crit2;

//exit protocol //exit protocol

c1 = false; c2 = false;

rem1; rem2;

} }

where init1 and init2 are non-critical initialisations, crit1 and crit2 are critical sections and

rem1 and rem2 are non-critical remainders of the programs.

Q5.a) Does the protocol satisfy the properties of mutual exclusion, absence of deadlock, absence of unnecessary delay and eventual entry? Please give your judgement and explanation for each property.

(16 marks)

Q5.b) If not, give an example trace that results in the property being violated and fix the algorithm using only standard C-like instructions as in the original algorithm so that it satisfies all the properties.

(4 marks)