Mutual Exclusion Problem

Question

Please take a look on the following pseudo-code:

boolean blocked[2];
int turn;
void P(int id) {
      while(true) {
             blocked[id] = true;
                 


        

Answer 1

Mutual Exclusion is in this exemple not guaranteed because of the following:

We begin with the following situation:

turn= 1;
blocked = {false, false};

The execution runs as follows:

P0: while (true) {
P0:   blocked[0] = true;
P0:   while (turn != 0) {
P0:     while (blocked[1]) {
P0:     }
P1: while (true) {
P1:   blocked[1] = true;
P1:   while (turn != 1) {
P1:   }
P1:   criticalSection(P1);
P0:     turn = 0;
P0:   while (turn != 0)
P0:   }
P0:   critcalSection(P0);