前言
Libevent 是一个用C语言编写的、轻量级的开源高性能事件通知库，主要有以下几个亮点：事件驱动（ event-driven），高性能;轻量级，专注于网络，不如 ACE 那么臃肿庞大；源代码相当精炼、易读；跨平台，支持 Windows、 Linux、 *BSD 和 Mac Os；支持多种 I/O 多路复用技术， epoll、 poll、 dev/poll、 select 和 kqueue 等；支持 I/O，定时器和信号等事件；注册事件优先级。Libevent 已经被广泛的应用，作为底层的网络库；比如 memcached、 Vomit、 Nylon、 Netchat等
Libevent下载和安装
1. 下载
官方网站：http://libevent.org/，目前最新版是2.1
下载压缩包名为 libevent-2.1.11-stable.tar.gz
2. 解压
tar -zxvf libevent-2.1.11-stable.tar.gz 3. 配置安装路径
cd libevent-2.1.11-stable
./configure也可以指定后缀，比如路径为./configure -prefix=/usr
4. 编译安装
make
make install5. 测试是否已安装
ls -al /usr/local/lib | grep libevent6. 使用样例程序进行测试
cd sample/此目录下，有很多样例，可以进行测试，也可以进行学习
使用Libevent编写简单的程序和编译
使用libevent库开发的程序，默认编译需要加入-levent
问题：如果在编译或运行时候发现出现：error while loading shared libraries: libevent-2.1.so.7: cannot open shared object file: No such file or directory
则需要查看libevent-2.1.so.7是否存在，需要先安装mlocate
locate libevent-2.1.so.7结果： 系统已经安装了该模块，在路径 /usr/local/lib/
映射libevent-2.1.so.7到lib64下即可
ln -s /usr/local/lib/libevent-2.1.so.7 /usr/lib64/libevent-2.1.so.7然后就可以正常的运行了
Libevent程序实例
初等
客户端代码
#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<errno.h>
#include<unistd.h>
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<event.h>
#include<event2/util.h>
int tcp_connect_server(const char* server_ip, int port);
void cmd_msg_cb(int fd, short events, void* arg);
void socket_read_cb(int fd, short events, void *arg);
int main(int argc, char** argv)
{
if( argc < 3 )
{
printf("please input 2 parameter\n");
return -1;
}
//两个参数依次是服务器端的IP地址、端口号
int sockfd = tcp_connect_server(argv[1], atoi(argv[2]));
if( sockfd == -1)
{
perror("tcp_connect error ");
return -1;
}
printf("connect to server successful\n");
struct event_base* base = event_base_new();
struct event *ev_sockfd = event_new(base, sockfd,
EV_READ | EV_PERSIST,
socket_read_cb, NULL);
event_add(ev_sockfd, NULL);
//监听终端输入事件
struct event* ev_cmd = event_new(base, STDIN_FILENO,
EV_READ | EV_PERSIST, cmd_msg_cb,
(void*)&sockfd);
event_add(ev_cmd, NULL);
event_base_dispatch(base);
printf("finished \n");
return 0;
}
void cmd_msg_cb(int fd, short events, void* arg)
{
char msg[1024];
int ret = read(fd, msg, sizeof(msg));
if( ret <= 0 )
{
perror("read fail ");
exit(1);
}
int sockfd = *((int*)arg);
//把终端的消息发送给服务器端
//为了简单起见，不考虑写一半数据的情况
write(sockfd, msg, ret);
}
void socket_read_cb(int fd, short events, void *arg)
{
char msg[1024];
//为了简单起见，不考虑读一半数据的情况
int len = read(fd, msg, sizeof(msg)-1);
if( len <= 0 )
{
perror("read fail ");
exit(1);
}
msg[len] = '\0';
printf("recv %s from server\n", msg);
}
typedef struct sockaddr SA;
int tcp_connect_server(const char* server_ip, int port)
{
int sockfd, status, save_errno;
struct sockaddr_in server_addr;
memset(&server_addr, 0, sizeof(server_addr) );
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(port);
status = inet_aton(server_ip, &server_addr.sin_addr);
if( status == 0 ) //the server_ip is not valid value
{
errno = EINVAL;
return -1;
}
sockfd = ::socket(PF_INET, SOCK_STREAM, 0);
if( sockfd == -1 )
return sockfd;
status = ::connect(sockfd, (SA*)&server_addr, sizeof(server_addr) );
if( status == -1 )
{
save_errno = errno;
::close(sockfd);
errno = save_errno; //the close may be error
return -1;
}
evutil_make_socket_nonblocking(sockfd);
return sockfd;
}服务器代码
#include<stdio.h>
#include<string.h>
#include<errno.h>
#include<unistd.h>
#include<event.h>
void accept_cb(int fd, short events, void* arg);
void socket_read_cb(int fd, short events, void *arg);
int tcp_server_init(int port, int listen_num);
int main(int argc, char** argv)
{
int listener = tcp_server_init(9999, 10);
if( listener == -1 )
{
perror(" tcp_server_init error ");
return -1;
}
struct event_base* base = event_base_new();
//添加监听客户端请求连接事件
struct event* ev_listen = event_new(base, listener, EV_READ | EV_PERSIST,
accept_cb, base);
event_add(ev_listen, NULL);
event_base_dispatch(base);
return 0;
}
void accept_cb(int fd, short events, void* arg)
{
evutil_socket_t sockfd;
struct sockaddr_in client;
socklen_t len = sizeof(client);
sockfd = ::accept(fd, (struct sockaddr*)&client, &len );
evutil_make_socket_nonblocking(sockfd);
printf("accept a client %d\n", sockfd);
struct event_base* base = (event_base*)arg;
//仅仅是为了动态创建一个event结构体
struct event *ev = event_new(NULL, -1, 0, NULL, NULL);
//将动态创建的结构体作为event的回调参数
event_assign(ev, base, sockfd, EV_READ | EV_PERSIST,
socket_read_cb, (void*)ev);
event_add(ev, NULL);
}
void socket_read_cb(int fd, short events, void *arg)
{
char msg[4096];
struct event *ev = (struct event*)arg;
int len = read(fd, msg, sizeof(msg) - 1);
if( len <= 0 )
{
printf("some error happen when read\n");
event_free(ev);
close(fd);
return ;
}
msg[len] = '\0';
printf("recv the client msg: %s", msg);
char reply_msg[4096] = "I have recvieced the msg: ";
strcat(reply_msg + strlen(reply_msg), msg);
write(fd, reply_msg, strlen(reply_msg) );
}
typedef struct sockaddr SA;
int tcp_server_init(int port, int listen_num)
{
int errno_save;
evutil_socket_t listener;
listener = ::socket(AF_INET, SOCK_STREAM, 0);
if( listener == -1 )
return -1;
//允许多次绑定同一个地址。要用在socket和bind之间
evutil_make_listen_socket_reuseable(listener);
struct sockaddr_in sin;
sin.sin_family = AF_INET;
sin.sin_addr.s_addr = 0;
sin.sin_port = htons(port);
if( ::bind(listener, (SA*)&sin, sizeof(sin)) < 0 )
goto error;
if( ::listen(listener, listen_num) < 0)
goto error;
//跨平台统一接口，将套接字设置为非阻塞状态
evutil_make_socket_nonblocking(listener);
return listener;
error:
errno_save = errno;
evutil_closesocket(listener);
errno = errno_save;
return -1;
}中等
客户端代码
#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<errno.h>
#include<unistd.h>
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<event.h>
#include<event2/bufferevent.h>
#include<event2/buffer.h>
#include<event2/util.h>
int tcp_connect_server(const char* server_ip, int port);
void cmd_msg_cb(int fd, short events, void* arg);
void server_msg_cb(struct bufferevent* bev, void* arg);
void event_cb(struct bufferevent *bev, short event, void *arg);
int main(int argc, char** argv)
{
if( argc < 3 )
{
printf("please input 2 parameter\n");
return -1;
}
//两个参数依次是服务器端的IP地址、端口号
int sockfd = tcp_connect_server(argv[1], atoi(argv[2]));
if( sockfd == -1)
{
perror("tcp_connect error ");
return -1;
}
printf("connect to server successful\n");
struct event_base* base = event_base_new();
struct bufferevent* bev = bufferevent_socket_new(base, sockfd,
BEV_OPT_CLOSE_ON_FREE);
//监听终端输入事件
struct event* ev_cmd = event_new(base, STDIN_FILENO,
EV_READ | EV_PERSIST, cmd_msg_cb,
(void*)bev);
event_add(ev_cmd, NULL);
//当socket关闭时会用到回调参数
bufferevent_setcb(bev, server_msg_cb, NULL, event_cb, (void*)ev_cmd);
bufferevent_enable(bev, EV_READ | EV_PERSIST);
event_base_dispatch(base);
printf("finished \n");
return 0;
}
void cmd_msg_cb(int fd, short events, void* arg)
{
char msg[1024];
int ret = read(fd, msg, sizeof(msg));
if( ret < 0 )
{
perror("read fail ");
exit(1);
}
struct bufferevent* bev = (struct bufferevent*)arg;
//把终端的消息发送给服务器端
bufferevent_write(bev, msg, ret);
}
void server_msg_cb(struct bufferevent* bev, void* arg)
{
char msg[1024];
size_t len = bufferevent_read(bev, msg, sizeof(msg));
msg[len] = '\0';
printf("recv %s from server\n", msg);
}
void event_cb(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");
//这将自动close套接字和free读写缓冲区
bufferevent_free(bev);
struct event *ev = (struct event*)arg;
//因为socket已经没有，所以这个event也没有存在的必要了
event_free(ev);
}
typedef struct sockaddr SA;
int tcp_connect_server(const char* server_ip, int port)
{
int sockfd, status, save_errno;
struct sockaddr_in server_addr;
memset(&server_addr, 0, sizeof(server_addr) );
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(port);
status = inet_aton(server_ip, &server_addr.sin_addr);
if( status == 0 ) //the server_ip is not valid value
{
errno = EINVAL;
return -1;
}
sockfd = ::socket(PF_INET, SOCK_STREAM, 0);
if( sockfd == -1 )
return sockfd;
status = ::connect(sockfd, (SA*)&server_addr, sizeof(server_addr) );
if( status == -1 )
{
save_errno = errno;
::close(sockfd);
errno = save_errno; //the close may be error
return -1;
}
evutil_make_socket_nonblocking(sockfd);
return sockfd;
}服务器代码
#include<stdio.h>
#include<string.h>
#include<errno.h>
#include<event.h>
#include<event2/bufferevent.h>
void accept_cb(int fd, short events, void* arg);
void socket_read_cb(bufferevent* bev, void* arg);
void event_cb(struct bufferevent *bev, short event, void *arg);
int tcp_server_init(int port, int listen_num);
int main(int argc, char** argv)
{
int listener = tcp_server_init(9999, 10);
if( listener == -1 )
{
perror(" tcp_server_init error ");
return -1;
}
struct event_base* base = event_base_new();
//添加监听客户端请求连接事件
struct event* ev_listen = event_new(base, listener, EV_READ | EV_PERSIST,
accept_cb, base);
event_add(ev_listen, NULL);
event_base_dispatch(base);
event_base_free(base);
return 0;
}
void accept_cb(int fd, short events, void* arg)
{
evutil_socket_t sockfd;
struct sockaddr_in client;
socklen_t len = sizeof(client);
sockfd = ::accept(fd, (struct sockaddr*)&client, &len );
evutil_make_socket_nonblocking(sockfd);
printf("accept a client %d\n", sockfd);
struct event_base* base = (event_base*)arg;
bufferevent* bev = bufferevent_socket_new(base, sockfd, BEV_OPT_CLOSE_ON_FREE);
bufferevent_setcb(bev, socket_read_cb, NULL, event_cb, arg);
bufferevent_enable(bev, EV_READ | EV_PERSIST);
}
void socket_read_cb(bufferevent* bev, void* arg)
{
char msg[4096];
size_t len = bufferevent_read(bev, msg, sizeof(msg));
msg[len] = '\0';
printf("recv the client msg: %s", msg);
char reply_msg[4096] = "I have recvieced the msg: ";
strcat(reply_msg + strlen(reply_msg), msg);
bufferevent_write(bev, reply_msg, strlen(reply_msg));
}
void event_cb(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");
//这将自动close套接字和free读写缓冲区
bufferevent_free(bev);
}
typedef struct sockaddr SA;
int tcp_server_init(int port, int listen_num)
{
int errno_save;
evutil_socket_t listener;
listener = ::socket(AF_INET, SOCK_STREAM, 0);
if( listener == -1 )
return -1;
//允许多次绑定同一个地址。要用在socket和bind之间
evutil_make_listen_socket_reuseable(listener);
struct sockaddr_in sin;
sin.sin_family = AF_INET;
sin.sin_addr.s_addr = 0;
sin.sin_port = htons(port);
if( ::bind(listener, (SA*)&sin, sizeof(sin)) < 0 )
goto error;
if( ::listen(listener, listen_num) < 0)
goto error;
//跨平台统一接口，将套接字设置为非阻塞状态
evutil_make_socket_nonblocking(listener);
return listener;
error:
errno_save = errno;
evutil_closesocket(listener);
errno = errno_save;
return -1;
}高等
客户端代码
#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<errno.h>
#include<unistd.h>
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<event.h>
#include<event2/bufferevent.h>
#include<event2/buffer.h>
#include<event2/util.h>
int tcp_connect_server(const char* server_ip, int port);
void cmd_msg_cb(int fd, short events, void* arg);
void server_msg_cb(struct bufferevent* bev, void* arg);
void event_cb(struct bufferevent *bev, short event, void *arg);
int main(int argc, char** argv)
{
if( argc < 3 )
{
//两个参数依次是服务器端的IP地址、端口号
printf("please input 2 parameter\n");
return -1;
}
struct event_base *base = event_base_new();
struct bufferevent* bev = bufferevent_socket_new(base, -1,
BEV_OPT_CLOSE_ON_FREE);
//监听终端输入事件
struct event* ev_cmd = event_new(base, STDIN_FILENO,
EV_READ | EV_PERSIST,
cmd_msg_cb, (void*)bev);
event_add(ev_cmd, NULL);
struct sockaddr_in server_addr;
memset(&server_addr, 0, sizeof(server_addr) );
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(atoi(argv[2]));
inet_aton(argv[1], &server_addr.sin_addr);
bufferevent_socket_connect(bev, (struct sockaddr *)&server_addr,
sizeof(server_addr));
bufferevent_setcb(bev, server_msg_cb, NULL, event_cb, (void*)ev_cmd);
bufferevent_enable(bev, EV_READ | EV_PERSIST);
event_base_dispatch(base);
printf("finished \n");
return 0;
}
void cmd_msg_cb(int fd, short events, void* arg)
{
char msg[1024];
int ret = read(fd, msg, sizeof(msg));
if( ret < 0 )
{
perror("read fail ");
exit(1);
}
struct bufferevent* bev = (struct bufferevent*)arg;
//把终端的消息发送给服务器端
bufferevent_write(bev, msg, ret);
}
void server_msg_cb(struct bufferevent* bev, void* arg)
{
char msg[1024];
size_t len = bufferevent_read(bev, msg, sizeof(msg));
msg[len] = '\0';
printf("recv %s from server\n", msg);
}
void event_cb(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");
return ;
}
//这将自动close套接字和free读写缓冲区
bufferevent_free(bev);
struct event *ev = (struct event*)arg;
event_free(ev);
}服务器代码
#include<netinet/in.h>
#include<sys/socket.h>
#include<unistd.h>
#include<stdio.h>
#include<string.h>
#include<event.h>
#include<listener.h>
#include<bufferevent.h>
#include<thread.h>
void listener_cb(evconnlistener *listener, evutil_socket_t fd,
struct sockaddr *sock, int socklen, void *arg);
void socket_read_cb(bufferevent *bev, void *arg);
void socket_event_cb(bufferevent *bev, short events, void *arg);
int main()
{
//evthread_use_pthreads();//enable threads
struct sockaddr_in sin;
memset(&sin, 0, sizeof(struct sockaddr_in));
sin.sin_family = AF_INET;
sin.sin_port = htons(9999);
event_base *base = event_base_new();
evconnlistener *listener
= evconnlistener_new_bind(base, listener_cb, base,
LEV_OPT_REUSEABLE|LEV_OPT_CLOSE_ON_FREE,
10, (struct sockaddr*)&sin,
sizeof(struct sockaddr_in));
event_base_dispatch(base);
evconnlistener_free(listener);
event_base_free(base);
return 0;
}
//一个新客户端连接上服务器了
//当此函数被调用时，libevent已经帮我们accept了这个客户端。该客户端的
//文件描述符为fd
void listener_cb(evconnlistener *listener, evutil_socket_t fd,
struct sockaddr *sock, int socklen, void *arg)
{
printf("accept a client %d\n", fd);
event_base *base = (event_base*)arg;
//为这个客户端分配一个bufferevent
bufferevent *bev = bufferevent_socket_new(base, fd,
BEV_OPT_CLOSE_ON_FREE);
bufferevent_setcb(bev, socket_read_cb, NULL, socket_event_cb, NULL);
bufferevent_enable(bev, EV_READ | EV_PERSIST);
}
void socket_read_cb(bufferevent *bev, void *arg)
{
char msg[4096];
size_t len = bufferevent_read(bev, msg, sizeof(msg)-1 );
msg[len] = '\0';
printf("server read the data %s\n", msg);
char reply[] = "I has read your data";
bufferevent_write(bev, reply, strlen(reply) );
}
void socket_event_cb(bufferevent *bev, short events, void *arg)
{
if (events & BEV_EVENT_EOF)
printf("connection closed\n");
else if (events & BEV_EVENT_ERROR)
printf("some other error\n");
//这将自动close套接字和free读写缓冲区
bufferevent_free(bev);
} 关于libevent编程时的一些疑问可以阅读《libevent编程疑难解答》。假如读者还想了解libevent的具体实现，可以阅读《libevent源码分析》系统文章。
更多文章参考：
http://blog.csdn.net/luotuo44/article/details/39547391
https:/blog.csdn.net/luotuo44/article/category/2435521