Dijkstra posed each of the following solutions as a potential software solution

Question

Dijkstra posed each of the following solutions as a potential software solution o the critical section problem and then explained why they failed. Provide your explanation about why they filed.

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)

Explanation / Answer

Not sure with (1) any help please comment

2)

If one process does "flag[i] = TRUE", then gets interrupted immediately afterwards and the other one does the same thing, then both of them will block at "while(flag[(i+1) mod 2]", violating Starvation.

3)
"while(flag[(i+1)mod2])", gets interrupted immediately afterwards, then the other process does the same thing, then they both go on to do “flag[i]=TRUE” and enter their critical sections at the same time, violating Mutual Exclusion.

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