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

def configure(self, n_jobs=1, parallel=None, **backend_args):

    n_jobs = self.effective_n_jobs(n_jobs)
    if (n_jobs == 1):
        raise FallbackToBackend(SequentialBackend())
    self.parallel = parallel
    self._pool = ThreadPool(n_jobs)
    return n_jobs
