_parallel_backends.py 文件源码

def effective_n_jobs(self, n_jobs):
        """Determine the number of jobs which are going to run in parallel.

        This also checks if we are attempting to create a nested parallel
        loop.
        """
        if mp is None:
            return 1

        if mp.current_process().daemon:
            # Daemonic processes cannot have children
            if n_jobs != 1:
                warnings.warn(
                    'Multiprocessing-backed parallel loops cannot be nested,'
                    ' setting n_jobs=1',
                    stacklevel=3)
            return 1

        if not isinstance(threading.current_thread(), threading._MainThread):
            # Prevent posix fork inside in non-main posix threads
            warnings.warn(
                'Multiprocessing-backed parallel loops cannot be nested'
                ' below threads, setting n_jobs=1',
                stacklevel=3)
            return 1

        return super(MultiprocessingBackend, self).effective_n_jobs(n_jobs)