procedure main()
  ...
  // Stops all threads, but the first one that passess it passess the rest
  shared turnstile := create_semaphore(0)
  ...
end procedure

procedure secondary()
  while true do
    Statement A
    ...
    // Use turnstile
    wait(turnstile)
    signal(turnstile)
    ...
    // Statement B can be only executed until all threads have run Statement A
    Statement B
  end while
end procedure