Method connect_to_new_process

Lib/multiprocessing/forkserver.py:93–141

Request forkserver to create a child process. Returns a pair of fds (status_r, data_w). The calling process can read the child process's pid and (eventually) its returncode from status_r. The calling process should write to data_w the pickled preparation and process

(self, fds)

        return self._inherited_fds

    def connect_to_new_process(self, fds):
        '''Request forkserver to create a child process.

        Returns a pair of fds (status_r, data_w).  The calling process can read
        the child process's pid and (eventually) its returncode from status_r.
        The calling process should write to data_w the pickled preparation and
        process data.
        '''
        self.ensure_running()
        assert self._forkserver_authkey
        if len(fds) + 4 >= MAXFDS_TO_SEND:
            raise ValueError('too many fds')
        with socket.socket(socket.AF_UNIX) as client:
            client.connect(self._forkserver_address)
            parent_r, child_w = os.pipe()
            child_r, parent_w = os.pipe()
            allfds = [child_r, child_w, self._forkserver_alive_fd,
                      resource_tracker.getfd()]
            allfds += fds
            try:
                client.setblocking(True)
                wrapped_client = connection.Connection(client.fileno())
                # The other side of this exchange happens in the child as
                # implemented in main().
                try:
                    connection.answer_challenge(
                            wrapped_client, self._forkserver_authkey)
                    connection.deliver_challenge(
                            wrapped_client, self._forkserver_authkey)
                except (EOFError, ConnectionError, BrokenPipeError) as exc:
                    if (self._preload_modules and
                        self._preload_on_error == 'fail'):
                        exc.add_note(
                            "Forkserver process may have crashed during module "
                            "preloading. Check stderr."
                        )
                    raise
                finally:
                    wrapped_client._detach()
                    del wrapped_client
                reduction.sendfds(client, allfds)
                return parent_r, parent_w
            except:
                os.close(parent_r)
                os.close(parent_w)
                raise
            finally:
                os.close(child_r)
                os.close(child_w)

    def ensure_running(self):
        '''Make sure that a fork server is running.