Linux下Libevent安装和简单实用

Posted 2020-11-24 WindSun

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 install

5. 测试是否已安装

ls -al /usr/local/lib | grep libevent

6. 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
");
        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
");
    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 
");
    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] = '';
    printf("recv %s from server
", 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
", 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
");
        event_free(ev);
        close(fd);
        return ;
    }
    msg[len] = '';
    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
");
        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
");
    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 
");
    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] = '';
    printf("recv %s from server
", msg);
}

void event_cb(struct bufferevent *bev, short event, void *arg)
{
    if (event & BEV_EVENT_EOF)
        printf("connection closed
");
    else if (event & BEV_EVENT_ERROR)
        printf("some other error
");
    //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
", 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] = '';
    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
");
    else if (event & BEV_EVENT_ERROR)
        printf("some other error
");
    //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
");
        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 
");
    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] = '';
    printf("recv %s from server
", msg);
}

void event_cb(struct bufferevent *bev, short event, void *arg)
{
    if (event & BEV_EVENT_EOF)
        printf("connection closed
");
    else if (event & BEV_EVENT_ERROR)
        printf("some other error
");
    else if( event & BEV_EVENT_CONNECTED)
    {
        printf("the client has connected to server
");
        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
", 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] = '';  
    printf("server read the data %s
", 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
");  
    else if (events & BEV_EVENT_ERROR)  
        printf("some other error
");  
    //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