Two processes are trying to enter their critical sections, executing the same program:

while true do begin
  b[i] := true;
  while not(turn=i) do begin
    while b[j] do begin
      skip; // do nothing
    turn := i;
  // beginning critical region
  b[i] := false;

The constant i identifies the process executing the code (i.e., has the value 1 or 2), and j is the identifier of the other process. b is an array with indices 1 and 2. Moreover let turn be either 1 or 2 initially.