move the initialization of _nworkers from __init__() to start_workers() in MPEventLoopRunner
move the initialization of _nworkers from __init__() to start_workers() in MPEventLoopRunner

alphatwirl/alphatwirl,TaiSakuma/AlphaTwirl,TaiSakuma/AlphaTwirl,alphatwirl/alphatwirl,alphatwirl/alphatwirl,alphatwirl/alphatwirl