__init__.py 文件源码

def parallel_scan(self, num_cursors, **kwargs):
        """Scan this entire collection in parallel.

        Returns a list of up to ``num_cursors`` cursors that can be iterated
        concurrently. As long as the collection is not modified during
        scanning, each document appears once in one of the cursors' result
        sets.

        For example, to process each document in a collection using some
        function ``process_document()``::

            @gen.coroutine
            def process_cursor(cursor):
                while (yield cursor.fetch_next):
                    process_document(document)

            # Get up to 4 cursors.
            cursors = yield collection.parallel_scan(4)
            yield [process_cursor(cursor) for cursor in cursors]

            # All documents have now been processed.

        If ``process_document()`` is a coroutine, do
        ``yield process_document(document)``.

        With :class:`MotorReplicaSetClient`, pass `read_preference` of
        :attr:`~pymongo.read_preference.ReadPreference.SECONDARY_PREFERRED`
        to scan a secondary.

        :Parameters:
          - `num_cursors`: the number of cursors to return

        .. note:: Requires server version **>= 2.5.5**.
        """
        command_cursors = yield self.__parallel_scan(num_cursors, **kwargs)
        motor_command_cursors = [
            MotorCommandCursor(cursor, self)
            for cursor in command_cursors]

        raise gen.Return(motor_command_cursors)