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 1024
YuLibeventServer *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bufferevent
bufferevent *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 
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