'Write the C source code.  It is produced in \'self.sourcefilename\',
which can be tweaked beforehand.'

def write_source(self, file=None):

    with self.ffi._lock:
        if (self._has_source and (file is None)):
            raise ffiplatform.VerificationError('source    code    already    written')
        self._write_source(file)
