code: def _write_pidfile(self):
          
          flags = os.O_CREAT | os.O_RDWR
          try:
              # Some systems don't have os.O_EXLOCK
              flags = flags | os.O_EXLOCK
          except AttributeError:
              pass
          self._pid_fd = os.open(self.pidfile, flags, 0o666 & ~self.umask)
          os.write(self._pid_fd, str(os.getpid()).encode('utf-8'))
docs: Create, write to, and lock the PID file.