Dijkstra posed each of the following solutions as a potential software solution to the critical section problem and then explained why they failed [Dijkstra, 1968]. Provide your explanation about why they failed.

a. proc(int i) {

while (TRUE) {

compute;

while (turn != i);

critical_section;

turn = (i+1) mod 2;

}

}

shared int turn;

turn = 1;

fork(proc, 1, 0);

fork(proc, 1, 1);

b. proc(int i) {

while (TRUE) {

compute;

while (flag[(i+1) mod 2]);

flag[i] = TRUE;

critical_section;

flag[i] = FALSE;

}

}

shared boolean flag[2];

flag[0] = flag[1] = FALSE;

fork(proc, 1, 0);

fork(proc, 1, 1);

c. proc(int i) {

while (TRUE) {

compute;

flag[i] = TRUE;

while (flag[(i+1) mod 2]);

critical_section;

flag[i] = FALSE;

}

}

shared boolean flag[2];

flag[0] = flag[1] = FALSE;

fork(proc, 1, 0);

fork(proc, 1, 1);