'Build a process or thread pool and return the number of workers'

def _initialize_backend(self):

    try:
        n_jobs = self._backend.configure(n_jobs=self.n_jobs, parallel=self, **self._backend_args)
        if ((self.timeout is not None) and (not self._backend.supports_timeout)):
            warnings.warn("The    backend    class    {!r}    does    not    support    timeout.    You    have    set    'timeout={}'    in    Parallel    but    the    'timeout'    parameter    will    not    be    used.".format(self._backend.__class__.__name__, self.timeout))
    except FallbackToBackend as e:
        self._backend = e.backend
        n_jobs = self._initialize_backend()
    return n_jobs
