Critical Section Problem: Algorithm 3

Peterson's algorithm is a correct solution to the critical section problem and it is simpler than Dekker's algorithm. It requires both an array of boolean values and an integer variable:

var	flag: array [0..1] of boolean;
	turn: 0..1;

The array elements are initialized to false and turn is either 0 or 1.

repeat

        flag[i] := true;
        turn := j;
        while (flag[j] and turn = j) do no-op;

                critical section

        flag[i] := false;

                remainder section

until false;

This algorithm guarantees the mutual exclusion, progress, and fairness requirements.