The first known correct software solution to the critical-section problem for two processes was developed by Dekker. The two processes, P0 and P1, share the following variables:
boolean flag[2]; /* initially false */
int turn;
The structure of process Pi (i == 0 or 1) is shown in Figure 6.25; the other process is Pj (j == 1 or 0). Prove that the algorithm satisfies all three requirements for the critical-section problem.