libevent代码阅读（8）——“hello-world.c”之 创建监听器

创建完成event_base之后，调用evconnlistener_new_bind函数来创建监听器：

// 创建一个监听器struct evconnlistener *evconnlistener_new_bind(struct event_base *base, // 监听器所属的event_base对象evconnlistener_cb cb, // 新连接到来的时候的回调函数void *ptr, // 回调函数的参数unsigned flags, // 一些标识int backlog, // 监听队列的长度，如果小于0，那么队列长度是128const struct sockaddr *sa,// 监听的地址int socklen)// 地址长度{struct evconnlistener *listener;// 监听套接字evutil_socket_t fd;int on = 1;int family = sa ? sa->sa_family : AF_UNSPEC;if (backlog == 0)return NULL;// 创建一个套接字fd = socket(family, SOCK_STREAM, 0);if (fd == -1)return NULL;// 设置套接字为非阻塞if (evutil_make_socket_nonblocking(fd) < 0) {evutil_closesocket(fd);return NULL;}if (flags & LEV_OPT_CLOSE_ON_EXEC) {// 设置套接字在调用exec的时候关闭if (evutil_make_socket_closeonexec(fd) < 0) {evutil_closesocket(fd);return NULL;}}// 设置套接字选项（保活）if (setsockopt(fd, SOL_SOCKET, SO_KEEPALIVE, (void*)&on, sizeof(on))<0) {evutil_closesocket(fd);return NULL;}if (flags & LEV_OPT_REUSEABLE) {// 设置套接字地址可复用if (evutil_make_listen_socket_reuseable(fd) < 0) {evutil_closesocket(fd);return NULL;}}// 套接字绑定if (sa) {if (bind(fd, sa, socklen)<0) {evutil_closesocket(fd);return NULL;}}// 利用刚刚创建的套接字新建一个监听器listener = evconnlistener_new(base, cb, ptr, flags, backlog, fd);if (!listener) {evutil_closesocket(fd);return NULL;}return listener;}

evconnlistener_new_bind内部调用了evconnlistener_new，定义如下：

/* * 监听器的进一步构造 */struct evconnlistener *evconnlistener_new(struct event_base *base,    evconnlistener_cb cb, void *ptr, unsigned flags, int backlog,    evutil_socket_t fd){// 监听事件struct evconnlistener_event *lev;#ifdef WIN32if (base && event_base_get_iocp(base)) {const struct win32_extension_fns *ext =event_get_win32_extension_fns();if (ext->AcceptEx && ext->GetAcceptExSockaddrs)return evconnlistener_new_async(base, cb, ptr, flags,backlog, fd);}#endif// 监听if (backlog > 0) {if (listen(fd, backlog) < 0)return NULL;} else if (backlog < 0) {if (listen(fd, 128) < 0)return NULL;}lev = mm_calloc(1, sizeof(struct evconnlistener_event));if (!lev)return NULL;// 监听器字段的初始化// 监听器内部的一些操作（如启用、禁用、销毁等）lev->base.ops = &evconnlistener_event_ops;// 监听回调函数lev->base.cb = cb;lev->base.user_data = ptr;lev->base.flags = flags;lev->base.refcnt = 1;// 是否为线程安全，如果是那么就需要分配一个锁if (flags & LEV_OPT_THREADSAFE) {EVTHREAD_ALLOC_LOCK(lev->base.lock, EVTHREAD_LOCKTYPE_RECURSIVE);}// 事件处理的一些赋值操作// 该事件处理处理EV_READ事件（即接受连接）// 处理的回调函数是用户传递进来的listener_read_cbevent_assign(&lev->listener, base, fd, EV_READ|EV_PERSIST,    listener_read_cb, lev);// 启动监听evconnlistener_enable(&lev->base);return &lev->base;}