概述:libevent 接口 evconnlistener_new_bind 的使用说明
libevent封装了监听套接字,将套接字和struct event
统一管理。
官方的解释是:
The evonnlistener mechanism gives you a way to listen for and accept incoming TCP connections
首先还是学习怎么去使用evconnlistener
(一)接口
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| struct evconnlistener *evconnlistener_new(struct event_base*base,evconnlistener_cb cb, void *ptr,unsigned flags ,int backlog,evutil_socket_t fd); struct evconnlistener*evconnlistener_new_bind(struct event_base*base,evconnlistener_cb cb, void *ptr,unsigned flags,int backlog,const struct sockaddr*sa,int socklen); void evconnlistener_free(struct evconnlistener*lev)
typedef void (*evconnlistener_cb)(struct evconnlistener *listener,evutil_socket_t sock, struct sockaddr*addr,int len,void *ptr);
int evconnlistener_disable(struct evconnlistener *lev); int evconnlistener_enable(struct evconnlistener *lev);
void evconnlistener_set_cb(struct evconnlistener*lev,evconnlistener_cb cb,void *arg)
evutil_socket_t evconnlistener_get_fd(struct evconnlistener *lev) struct event_base *evconnlistener_get_base(struct evconnlistener*lev)
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evconnlistener
是对 套接字和event
的封装,可以想见,在这些接口中,除了调用socket api
之外,还会关联套接子到event
上进而注册到event_base
上去
不过接口封装好了这些行为,只需要了解这些参数的含义即可。
base:即event_base
cb:当有新连接时调用的回调函数
ptr:callback的参数
flags:控制listner的行为
backlog:同 listen(2)中backlog的含义
fd:已经bind的fd,传入api让libevent做listen调用
(二)例子
使用evconnlistener
管理监听套接字构建一个简单的 echo server
代码也可参考gayhub
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| #include <event2/listener.h> #include <event2/bufferevent.h> #include <event2/buffer.h> #include <arpa/inet.h> #include <string.h> #include <stdlib.h> #include <stdio.h> #include <errno.h> #include <assert.h> static void echo_read_cb(struct bufferevent*bev,void*ctx) { struct evbuffer*input=bufferevent_get_input(bev); struct evbuffer*output=bufferevent_get_output(bev); evbuffer_add_buffer(output,input); } static void echo_event_cb(struct bufferevent*bev,short events,void*ctx) { if(events&BEV_EVENT_ERROR) perror("Error from bufferevent"); if(events&(BEV_EVENT_EOF|BEV_EVENT_ERROR)) { bufferevent_free(bev); } } static void accept_error_cb(struct evconnlistener*listener,void*ctx) { struct event_base*base=evconnlistener_get_base(listener); event_base_loopexit(base,NULL); } void accept_conn_cb(struct evconnlistener*listener,evutil_socket_t fd,struct sockaddr*address,int socklen,void*ctx) { struct event_base*base=evconnlistener_get_base(listener); struct bufferevent*bev = bufferevent_socket_new(base, fd, BEV_OPT_CLOSE_ON_FREE); bufferevent_setcb(bev,echo_read_cb,NULL,echo_event_cb,NULL); bufferevent_enable(bev,EV_READ|EV_WRITE); } int main(int argc,char**argv) { struct event_base *base; struct evconnlistener *listener; struct sockaddr_in sin; int port = 1025; base = event_base_new(); assert(base!=NULL); memset(&sin,0,sizeof(sin)); sin.sin_family=AF_INET; sin.sin_addr.s_addr=htonl(0); sin.sin_port=htons(port); listener=evconnlistener_new_bind(base, accept_conn_cb, NULL, LEV_OPT_CLOSE_ON_FREE|LEV_OPT_REUSEABLE, -1, (struct sockaddr*)&sin, sizeof(sin)); assert(listener!=NULL); evconnlistener_set_error_cb(listener,accept_error_cb); event_base_dispatch(base); return 0; }
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(三)源码
看看evconnlistenr做了哪些封装
3.1结构体
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| struct evconnlistener { const struct evconnlistener_ops *ops; void *lock; evconnlistener_cb cb; evconnlistener_errorcb errorcb; void *user_data; unsigned flags; short refcnt; unsigned enabled : 1; }; struct evconnlistener_event { struct evconnlistener base; struct event listener; };
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evconnlistener
结构体将一些基本的回调函数、用户数据等封装,然后evconnlistener_event
将这些东西和struct event
封装在一起
3.2创建一个evconnlistener
看一下初始化有哪些内容:
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| struct evconnlistener * evconnlistener_new(struct event_base *base, evconnlistener_cb cb, void *ptr, unsigned flags, int backlog, evutil_socket_t fd) { struct evconnlistener_event *lev; 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; lev->base.ops = &evconnlistener_event_ops; lev->base.cb = cb; lev->base.user_data = ptr; lev->base.flags = flags; lev->base.refcnt = 1; if (flags & LEV_OPT_THREADSAFE) { EVTHREAD_ALLOC_LOCK(lev->base.lock, EVTHREAD_LOCKTYPE_RECURSIVE); } event_assign(&lev->listener, base, fd, EV_READ|EV_PERSIST, listener_read_cb, lev); evconnlistener_enable(&lev->base); return &lev->base; }
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在另外一个接口evconnlistener_new_bind
中由于指定了套接字结构体,因此在底层还调用了bind
3.3 listener_read_cb
这个底层的回调函数先于用户回调函数调用,在这个回调中会调用用户回调,并且会将已连接的套接字作为参数传入用户回调,
这也正是evconnlistener
的精髓,无需要用户进行listen、bind、accept
等操作
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| static void listener_read_cb(evutil_socket_t fd, short what, void *p) { struct evconnlistener *lev = p; int err; evconnlistener_cb cb; evconnlistener_errorcb errorcb; void *user_data; LOCK(lev); while (1) { struct sockaddr_storage ss; socklen_t socklen = sizeof(ss); evutil_socket_t new_fd = accept(fd, (struct sockaddr*)&ss, &socklen); if (new_fd < 0) break; if (socklen == 0) {
evutil_closesocket(new_fd); continue; } if (!(lev->flags & LEV_OPT_LEAVE_SOCKETS_BLOCKING)) evutil_make_socket_nonblocking(new_fd); if (lev->cb == NULL) { UNLOCK(lev); return; } ++lev->refcnt; cb = lev->cb; user_data = lev->user_data; UNLOCK(lev); cb(lev, new_fd, (struct sockaddr*)&ss, (int)socklen, user_data); LOCK(lev); if (lev->refcnt == 1) { int freed = listener_decref_and_unlock(lev); EVUTIL_ASSERT(freed); return; } --lev->refcnt; } }
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(四)参考
1.libevent programming
2.libevent 深入浅出