Critical Section Problem: Dekker's Algorithm

Dekker's algorithm was the first provably-correct solution to the critical section problem. It requires both an array of boolean values and an integer variable:

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

repeat

        flag[i] := true;
        while flag[j] do
                if turn = j then
                begin
                        flag[i] := false;
                        while turn = j do no-op;
                        flag[i] := true;
                end;

                critical section

        turn := j;
        flag[i] := false;

                remainder section

until false;