题记
windows平台下对于服务器高并发的网络模型选型中，使用libevent是个不错的选择。 本文的背景基于：国内博客对于libevent大多介绍linux实现，大多是c语言的实现，Windows平台下C++相对较少或者较旧。 本文针对libevent从服务端、客户端两个角度实现了封装类，真正做到，我们在使用封装类时候，只需要关注业务逻辑的处理，不需要关注socket的通信的细节。
1. Libevent介绍
[维基百科]libevent是一个异步事件处理软件函式库，以BSD许可证发布。libevent提供了一组应用程序编程接口（API），让程序员可以设定某些事件发生时所执行的回调函数，也就是说，libevent可以用来取代网络服务器所使用的事件循环检查框架。由于可以省去对网络的处理，且拥有不错的效能，有些软件使用libevent作为网络底层的函式库，如：memcached、Tor。
[libevent官网介绍] libevent API提供了一种机制，用于在文件描述符上发生特定事件或达到超时后执行回调函数。此外，libevent还支持基于信号或常规超时的回调。 libevent旨在替换在事件驱动的网络服务器中的事件循环机制。应用程序只需要调用event_dispatch()接口，然后动态添加或删除事件，而不必更改事件循环。 目前，libevent支持 /dev/poll, kqueue, event ports, POSIX select, Windows select(), poll 和 epoll。 其内在的事件机制是完全独立于外在的事件API ，并且libevent的简单更新可以提供新的功能，而无需重新设计应用程序。因此: 1）Libevent允许便携式应用程序开发，并提供操作系统上可用的最可扩展的事件通知机制。 2）Libevent也可以用于多线程应用程序，通过隔离每个event_base，以便只有一个线程访问它，或通过锁定访问单个共享的event_base。 Libevent可以在Linux，* BSD，Mac OS X，Solaris，Windows等上编译。 3）Libevent还为缓冲网络IO提供了复杂的框架，支持套接字，过滤器，速率限制，SSL，零拷贝文件传输和IOCP。 4）Libevent包括对几个有用的协议的支持，包括DNS，HTTP和最小的RPC框架。
以下关于阻塞、非阻塞，同步、异步，大牛陈硕的经典回复。 在处理 IO 的时候，阻塞和非阻塞都是同步 IO。 只有使用了特殊的 API 才是异步 IO。
2.为什么要使用封装好的网络库？
[陈硕]网络编程是什么？是熟练使用Sockets API吗？说实话，在实际项目里我只用过两次Sockets API，其他时候都是使用封装好的网络库。 使用封装好的网络库如libevent， muduo网络库 目的之一就是想让日常的网络编程从Sockets API的琐碎细节中解脱出来，让程序员专注于业务逻辑，把时间用在刀刃上。 程序员的主要工作是在事件处理函数中实现业务逻辑，而不是和Sockets API较劲。 陈硕认为网络编程也可以分为三个层次： 1). 读过教程和文档 2). 熟悉本系统TCP/IP协议栈的脾气 3). 自己写过一个简单的TCP/IP stack
陈硕认为TCP网络编程有三个例子最值得学习研究，分别是echo、chat、proxy，都是长连接协议。 Echo的作用：熟悉服务端被动接受新连接、收发数据、被动处理连接断开。每个连接是独立服务的，连接之间没有关联。在消息内容方面Echo有一些变种：比如做成一问一答的方式，收到的请求和发送响应的内容不一样，这时候要考虑打包与拆包格式的设计，进一步还可以写简单的HTTP服务。
3.Libevent通信核心
服务端核心步骤简化如下：
步骤1：设置sockfd为nonblocking;步骤2：使用bufferevent_socket_new创建一个struct bufferevent *bev，关联该sockfd,托管给event_base;步骤3：使用bufferevent_setcb(bev, read_cb, write_cb, error_cb, (void *)arg)将EV_READ/EV_WRITE对应的函数；步骤4：使用bufferevent_enable(bev, EV_READ|EV_WRITE|EV_PERSIST)来启动read/write事件；
其中，在read_cb里面从input读取数据，处理完毕后塞到output中，会自动写入到sockfd; 在write_cb里面（对于一个echo server来说，read_cb足够了） 在error_cb里面处理遇到的错误。使用bufferevent_set_timeout(bev, struct timeval *READ, struct timeval *WRITE)来设置读写超时，在error_cb里面也可以处理超时。 可以使用bev中libevent的API提取出event_base，sockfd，input/output等相关数据。 客户端的操作步骤详见代码，提炼即可。
4.C++封装的libevent Echo类
分为：服务端YuLibeventServer类和客户端YuLibeventClient类。
//服务端核心代码如下参考地址：
#include "YuLibeventServer.h"/***@author: laoyang360**@date: 20161211**@brief: The server of SimLibeventClient*/static int s_iBlockSize = 10;#define MAX_LINE 1024YuLibeventServer *YuLibeventServer::pThis = NULL;YuLibeventServer::YuLibeventServer(){pThis = this; //将this指针赋给pThis，使得回调函数能通过pThis指针访问本对象m_pBase = NULL;m_pListener = NULL;m_pEvstop = NULL;}YuLibeventServer::~YuLibeventServer(){}/***@author: laoyang360**@date: 20161211**@param: evutil_socket_t fd**@brief: 设置非阻塞，禁止Nagle算法。*/void YuLibeventServer::set_tcp_no_delay(evutil_socket_t fd){int iOne = 1;setsockopt(fd, IPPROTO_TCP, TCP_NODELAY, (const char*)&iOne, sizeof iOne);}/***@author: laoyang360**@date: 20161211**@param: evutil_socket_t fd**@brief: 等待接受客户端连接处理accept、一个新客户端连接上服务器了*/void YuLibeventServer::accept_conn_cb(evconnlistener *listener, evutil_socket_t fd,struct sockaddr *sock, int socklen, void *arg){printf("We got a new connection! Set up a bufferevent for it. accept a client %d\n", fd);event_base *base = evconnlistener_get_base(listener);//为这个客户端分配一个buffereventbufferevent *bev = bufferevent_socket_new(base, fd, BEV_OPT_CLOSE_ON_FREE);set_tcp_no_delay(fd);bufferevent_setcb(bev, echo_read_cb, NULL, echo_event_cb, NULL);bufferevent_enable(bev, EV_READ | EV_WRITE);}/***@author: laoyang360**@date: 20161211**@param: bufferevent *bev, void *arg**@brief: echo_read_cb回调接口*/void YuLibeventServer::echo_read_cb(bufferevent *bev, void *arg){char msg[MAX_LINE + 1] = {0};int iLen = 0;evutil_socket_t fd = bufferevent_getfd(bev);while (iLen = bufferevent_read(bev, msg, sizeof(msg)-1 ), iLen > 0){msg[iLen] = '\0';printf("fd=%u, read len = %d\t read msg: %s\n", fd, iLen, msg);int iRst = bufferevent_write(bev, msg, iLen);if (-1 == iRst){printf("[socket_write_cb]:error occur!\n");}}/*char reply[] = "[server: i'm server, send 1111]";printf("writecb: len = %d\n", 1 + strlen(reply));int iRst = bufferevent_write(bev, reply, 1 + strlen(reply));if (-1 == iRst){printf("[socket_write_cb]:error occur!\n");}*//*This callback is invoked when there is data to read on bev *///struct evbuffer *input = bufferevent_get_input(bev);//struct evbuffer *output = bufferevent_get_output(bev);/*把input buffer中的所有数据 拷贝到 output buffer*///evbuffer_add_buffer(output, input);}/***@author: laoyang360**@date: 20161211**@param: bufferevent *bev, void *arg**@brief: socket_write_cb回调接口，暂时未使用*/void YuLibeventServer::socket_write_cb(bufferevent *bev, void *arg){/*char reply[] = "[server: i'm server, send 1111]";printf("writecb: len = %d\n", 1 + strlen(reply));int iRst = bufferevent_write(bev, reply, 1 + strlen(reply));if (-1 == iRst){printf("[socket_write_cb]:error occur!\n");}*/}/***@author: laoyang360**@date: 20161211**@param: bufferevent *bev, short events, void *arg**@brief: echo_event_cb事件处理或异常处理*/void YuLibeventServer::echo_event_cb(bufferevent *bev, short events, void *arg){struct evbuffer *output = bufferevent_get_output(bev);size_t remain = evbuffer_get_length(output);if (events & BEV_EVENT_TIMEOUT){printf("Timed out\n"); //if bufferevent_set_timeouts() called.}else if (events & BEV_EVENT_EOF){printf("connection closed, remain %d\n", remain);}else if (events & BEV_EVENT_ERROR){printf("some other error, remain %d\n", remain);}//这将自动close套接字和free读写缓冲区bufferevent_free(bev);}/***@author: laoyang360**@date: 20161211**@param: bufferevent *bev, short events, void *arg**@brief: signal_cb停止信号处理*/void YuLibeventServer::signal_cb(evutil_socket_t sig, short events, void *arg){struct event_base *base = (event_base *)arg;printf("exception: interrupt, stop now!\n");event_base_loopexit(base, NULL);}/***@author: laoyang360**@date: 20161211**@param: int port, 传入端口。**@brief: libevent，socket初始化等*/void YuLibeventServer::init(int port){WSADATA wsaData;DWORD Ret;if ((Ret = WSAStartup(MAKEWORD(2, 2), &wsaData)) != 0){printf("WSAStartup failed with error %d\n", Ret);exit(1);}m_pBase = event_base_new();if (NULL == m_pBase){printf("couldn't open event base!\n");exit(1);}m_pEvstop = evsignal_new(m_pBase, SIGINT, signal_cb, m_pBase);evsignal_add(m_pEvstop, NULL);struct sockaddr_in sin;memset(&sin, 0, sizeof(struct sockaddr_in));sin.sin_family = AF_INET;sin.sin_port = htons(port);m_pListener = evconnlistener_new_bind(m_pBase, accept_conn_cb, NULL,LEV_OPT_REUSEABLE|LEV_OPT_CLOSE_ON_FREE,-1, (struct sockaddr*)&sin,sizeof(struct sockaddr_in));if (NULL == m_pListener){printf("couldn't create listener!\n");exit(1);}}/***@author: laoyang360**@date: 20161211**@param: 无**@brief: 启动，循环执行*/void YuLibeventServer::start(){event_base_dispatch(m_pBase);}/***@author: laoyang360**@date: 20161211**@param: 无**@brief: 停止*/void YuLibeventServer::stop(){if (NULL != m_pListener){evconnlistener_free(m_pListener);}if (NULL != m_pEvstop){event_free(m_pEvstop);}if (NULL != m_pBase){event_base_free(m_pBase);}}//客户端核心代码参考地址：
#include "yuLibEventClient.h"/***@author: laoyang360**@date: 20161211**@brief: The client of SimLibeventClient*/YuLibeventClient *YuLibeventClient::pThis = NULL;const static char* s_serverIpAddr = "127.0.0.1";const static int s_iBlockSize = 10;const static long s_iTimeOut = 10; //超时时间const static int s_iSessionCnt = 10;int YuLibeventClient::m_siLtotal_bytes_read = 0;int YuLibeventClient::m_siLtotal_messages_read = 0;YuLibeventClient::YuLibeventClient(){pThis = this; //将this指针赋给pThis，使得回调函数能通过pThis指针访问本对象m_pBase = NULL;m_pListener = NULL;m_pszMsg = NULL;m_evtimeout = NULL;m_bevs = NULL;}YuLibeventClient::~YuLibeventClient(){}/***@author: laoyang360**@date: 20161211**@param: evutil_socket_t fd**@brief: 设置非阻塞，禁止Nagle算法。*/void YuLibeventClient::set_tcp_no_delay(evutil_socket_t fd){int iOne = 1;setsockopt(fd, IPPROTO_TCP, TCP_NODELAY, (const char*)&iOne, sizeof iOne);}/***@author: laoyang360**@date: 20161211**@param: evutil_socket_t fd, short events, void *arg**@brief: 超时回调函数。*/void YuLibeventClient::timeoutcb(evutil_socket_t fd, short events, void *arg){struct event_base *base = (event_base*)arg;printf("timeout...\n");event_base_loopexit(base, NULL);}/***@author: laoyang360**@date: 20161211**@param: int fd, short events, void* arg**@brief: 暂时未使用*/void YuLibeventClient::cmd_msg_cb(int fd, short events, void* arg){printf("server_msg_cb ing....\n");struct bufferevent* bev = (struct bufferevent*)arg;char msg[1024] = "testlaoyang20161210";int iLen = 1 + strlen(msg);/*int iLen = bufferevent_read(bev, msg, sizeof(msg));if (0 == iLen){printf("recv message empty.\n");exit(1);}*///把终端的消息发送给服务器端bufferevent_write(bev, msg, iLen);}/***@author: laoyang360**@date: 20161211**@param: struct bufferevent* bev, void* arg**@brief: writecb回调函数，暂时未使用*/void YuLibeventClient::writecb(struct bufferevent* bev, void* arg){/*printf("send_server_cb running....\n");char szSendMsg[1024] = "[writecb: i'am client]";int iLen = 1 + strlen(szSendMsg);printf("iLen = %d\n", iLen);//把终端的消息发送给服务器端bufferevent_write(bev, szSendMsg, iLen);*/}/***@author: laoyang360**@date: 20161211**@param: struct bufferevent* bev, void* arg**@brief: readcb回调函数，接收处理回调接口。*/void YuLibeventClient::readcb(struct bufferevent* bev, void* arg){char szRecvMsg[1024] = {0};int len = bufferevent_read(bev, szRecvMsg, sizeof(szRecvMsg));szRecvMsg[len] = '\0';printf("recv from server: cnt = %d, len = %d, msg = %s\n", m_siLtotal_messages_read, len, szRecvMsg);++m_siLtotal_messages_read;m_siLtotal_bytes_read += len;//把终端的消息发送给服务器端bufferevent_write(bev, szRecvMsg, len);//以下是chenshuo的使用方法/*This callback is invoked when there is data to read on bev @by chenshuo below *///struct evbuffer *input = bufferevent_get_input(bev);//struct evbuffer *output = bufferevent_get_output(bev);//++m_siLtotal_messages_read;//m_siLtotal_bytes_read += evbuffer_get_length(input);//evbuffer_add_buffer(output, input);}/***@author: laoyang360**@date: 20161211**@param: struct bufferevent *bev, short event, void *arg**@brief: eventcb回调函数，事件或出错处理回调接口。*/void YuLibeventClient::eventcb(struct bufferevent *bev, short event, void *arg){if (event & BEV_EVENT_EOF){printf("connection closed\n");}else if (event & BEV_EVENT_ERROR){printf("some other error\n");}else if( event & BEV_EVENT_CONNECTED){printf("the client has connected to server\n");evutil_socket_t fd = bufferevent_getfd(bev);set_tcp_no_delay(fd);}}/***@author: laoyang360**@date: 20161211**@param: int iPort, 传入端口。**@brief: libevent，socket初始化等*/void YuLibeventClient::init(int iPort){WSADATA wsaData;DWORD Ret;if ((Ret = WSAStartup(MAKEWORD(2, 2), &wsaData)) != 0){printf("WSAStartup failed with error %d\n", Ret);exit(1);}m_timeout.tv_sec = s_iTimeOut; //60s超时m_timeout.tv_usec = 0;m_pszMsg = (char*)malloc(1 + s_iBlockSize);memset(m_pszMsg, 0, s_iBlockSize);for (int i = 0; i < s_iBlockSize; ++i){m_pszMsg[i] = 't'; /*i%128;*/}m_pszMsg[s_iBlockSize] = '\0';//printf("m_pszMsg = %s\n", m_pszMsg);m_pBase = event_base_new();if (!m_pBase){printf("Couldn't open event base!\n");exit(1);}//设定超时m_evtimeout = evtimer_new(m_pBase, timeoutcb, m_pBase);evtimer_add(m_evtimeout, &m_timeout);struct sockaddr_in server_addr;memset(&server_addr, 0, sizeof(server_addr) );server_addr.sin_family = AF_INET;server_addr.sin_port = htons(iPort);server_addr.sin_addr.s_addr = inet_addr(s_serverIpAddr);m_bevs = (bufferevent**)malloc(s_iSessionCnt * sizeof(struct bufferevent *));for (int i=0; i < s_iSessionCnt; ++i){struct bufferevent* bev = bufferevent_socket_new(m_pBase, -1, BEV_OPT_CLOSE_ON_FREE);bufferevent_setcb(bev, readcb, NULL, eventcb, NULL);bufferevent_enable(bev, EV_READ | EV_WRITE);evbuffer_add(bufferevent_get_output(bev), m_pszMsg, s_iBlockSize);if (bufferevent_socket_connect(bev, (struct sockaddr *)&server_addr,sizeof(server_addr)) < 0){printf("Error starting connection!\n");bufferevent_free(bev);exit(1);}m_bevs[i] = bev;}}/***@author: laoyang360**@date: 20161211**@param: 无**@brief: 启动，循环执行*/void YuLibeventClient::start(){event_base_dispatch(m_pBase);}/***@author: laoyang360**@date: 20161211**@param: 无**@brief: 停止，内存等释放&结果统计*/void YuLibeventClient::stop(){//evconnlistener_free(m_pListener);if (NULL != m_pBase){event_base_free(m_pBase);}for (int i = 0; i < s_iSessionCnt; ++i){if (NULL != m_bevs[i]){bufferevent_free(m_bevs[i]);}}if (NULL != m_bevs){free(m_bevs);}if (NULL != m_pszMsg){free(m_pszMsg);}printf("%d total bytes read\n", m_siLtotal_bytes_read);printf("%d total messages read\n", m_siLtotal_messages_read);printf("%.3f average messages size read\n", (double)m_siLtotal_bytes_read/m_siLtotal_messages_read);printf("%.3f MiB/s throughtput\n", (double)m_siLtotal_bytes_read/(m_timeout.tv_sec * 1024 * 1024));}4.测试效果如下
5.源码包下载
http://download.csdn.net/detail/wojiushiwo987/9708418
后记： 项目中用到了libevent，但我自己一直没有总结这块，从去年开始到现在这个想法持续了一年，总算了了心愿。 代码对大牛陈硕的C的测试代码进行了C++的封装、测试、验证。向大牛的钻研精神和毅力学习和致敬！
参考： http://blog.csdn.net/solstice/article/details/6527585 https://github.com/chenshuo/recipes/tree/master/pingpong/libevent http://blog.csdn.net/funkri/article/details/9352955 http://blog.csdn.net/laoyang360/article/details/8675922
2016年12月11日 22:16 思于宾馆
作者：铭毅天下 转载请标明出处，原文地址： http://blog.csdn.net/laoyang360/article/details/53576132 如果感觉本文对您有帮助，请点击‘顶’支持一下，您的支持是我坚持写作最大的动力，谢谢！
如果你曾歌颂黎明，那么也请你拥抱黑夜
