#ifdef HAVE_EVENT_PORTS extern const struct eventop evportops; #endif #ifdef HAVE_SELECT extern const struct eventop selectops; #endif #ifdef HAVE_POLL extern const struct eventop pollops; #endif #ifdef HAVE_EPOLL extern const struct eventop epollops; #endif #ifdef HAVE_WORKING_KQUEUE extern const struct eventop kqops; #endif #ifdef HAVE_DEVPOLL extern const struct eventop devpollops; #endif #ifdef WIN32 extern const struct eventop win32ops; #endif /* In order of preference */ static const struct eventop *eventops[] = { #ifdef HAVE_EVENT_PORTS &evportops, #endif #ifdef HAVE_WORKING_KQUEUE &kqops, #endif #ifdef HAVE_EPOLL &epollops, #endif #ifdef HAVE_DEVPOLL &devpollops, #endif #ifdef HAVE_POLL &pollops, #endif #ifdef HAVE_SELECT &selectops, #endif #ifdef WIN32 &win32ops, #endif NULL };

按照上面的顺序，取第一个os支持的接口,如下初始化的过程：

 struct event_base * event_base_new(void) { ... base->evbase = NULL; for (i = 0; eventops[i] && !base->evbase; i++) { base->evsel = eventops[i]; base->evbase = base->evsel->init(base); } if (base->evbase == NULL) event_errx(1, "%s: no event mechanism available", __func__); ... }

下面是epoll的eventop封装

epoll.c const struct eventop epollops = { "epoll", epoll_init, epoll_add, epoll_del, epoll_dispatch, epoll_dealloc, 1 /* need reinit */ };