docs: def _exclusive_lock(path):
      """A simple wrapper for fcntl exclusive lock."""
      _create_file_dirs(path)
      fd = os.open(path, os.O_WRONLY | os.O_CREAT, 0o600)
  
      try:
          retries_left = _LOCK_RETRIES
          success = False
  
          while retries_left > 0:
              # try to acquire the lock in a loop
              # because gevent doesn't treat flock as IO,
              # so waiting here without yielding would get the worker killed
              try:
                  fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
                  success = True
                  break
              except IOError as e:
                  if e.errno in [errno.EAGAIN, errno.EWOULDBLOCK]:
                      # This yields execution to other green threads.
                      gevent.sleep(_LOCK_SLEEP_TIME_S)
                      retries_left -= 1
                  else:
                      raise
  
          if success:
              yield
          else:
              raise ConcurrentModificationError(path)
      finally:
          if success:
              fcntl.flock(fd, fcntl.LOCK_UN)
          os.close(fd)