EVBACKEND_PORT
if (EV_USE_PORT ) flags |= EVBACKEND_PORT;
int flags = EVBACKEND_EPOLL | EVBACKEND_KQUEUE | EVBACKEND_PORT;
if (!backend && (flags & EVBACKEND_PORT )) backend = port_init (EV_A_ flags);
if (backend == EVBACKEND_PORT ) port_destroy (EV_A);
if (backend == EVBACKEND_PORT ) port_fork (EV_A);