docs: def pipe_cloexec():
      """Create a pipe with FDs set CLOEXEC."""
      # Pipes' FDs are set CLOEXEC by default because we don't want them
      # to be inherited by other subprocesses: the CLOEXEC flag is removed
      # from the child's FDs by _dup2(), between fork() and exec().
      # This is not atomic: we would need the pipe2() syscall for that.
      r, w = os.pipe()
      _set_cloexec_flag(r)
      _set_cloexec_flag(w)
      return r, w