Is there a reason this has not landed? The patch works perfectly for me, except for one issue:

    @@ -268,6 +275,9 @@
             if self.undef:
                 self.undef = self.undef.split(',')
     
    +        if self.parallel:
    +            self.parallel = int(self.parallel)
    +
             if self.swig_opts is None:
                 self.swig_opts = []
             else:

If self.parallel is True, this will set self.parallel to 1, causing it to use one worker instead of n (where n is the number of processors).

An updated patch is attached.