官网:https://libevent.org/
使用文档:https://www.monkey.org/~provos/libevent/doxygen-2.0.1/index.html
libevent和libiop,redis等一样都是采用事件回调机制,这种模式被称作Reactor模式。Reactor模式:https://www.jianshu.com/p/458e4b276607
#include
#include
#include
内部使用select、epoll、kqueue等系统调用管理事件机制。
编译库代码,编译脚本会判断OS支持哪种类型的事件机制(select、epoll或kqueue),然后条件编译相应代码,供上层使用的接口仍然是保持统一的。
libevent支持用户使用三种类型的事件,分别是网络IO、定时器、信号三种。定时器的数据结构使用最小堆(Min Heap),以提高效率。网络IO和信号的数据结构采用了双向链表(TAILQ)。在实现上主要有3种链表:EVLIST_INSERTED, EVLIST_ACTIVE, EVLIST_TIMEOUT,一个ev在这3种链表之间被插入或删除,处于EVLIST_ACTIVE链表中的ev最后将会被调度执行。
初始化libevent库:
调用event_base_new,初始化struct event_base对象。
event_base_new里做了如下工作:
1、 申请内存
2、 初始化定时器堆和事件队列
3、 为event_base对象选择底层事件函数封装对象。根据编译选项,初始化eventops全局对象。该对象存放指向底层select/pool/epoll等功能的封装函数。
4、 初始化活动队列。
初始化struct event结构。可以用event_add把该事件结构增加到事件循环,用event_del从事件循环中删除。支持的事件类型可以是下面组合:
EV_TIMEOUT:超时;
EV_READ:只要网络缓冲中还有数据,回调函数就会被触发;
EV_WRITE:只要塞给网络缓冲的数据被写完,回调函数就会被触发;
EV_SIGNAL:POSIX信号量;
EV_PERSIST:不指定这个属性,回调函数被触发后事件会被删除;
EV_ET:Edge-Trigger边缘触发
1、 把参数中指定初始化的事件对象的ev_base指向全局的current_base。
2、 赋值回调函数、描述符、监视事件等变量。
修改structevent事件结构所属的event_base为指定的event_base。Libevnet内置一个全局的event_base结构。多个线程应用中,如果多个线程都需要一个libevent事件循环,需要调用event_base_set修改事件结构基于的event_base。
增加事件到事件监控中。
1、 对于读、写、信号事件,调用封装的add函数,调用底层select/pool/epoll相关函数,增加到操作系统事件监控里。对于epoll,调用的是epoll_add函数。Epoll_add函数调用epoll_ctl添加事件监控,libevent使用水平触发方式。把监听时间加入到event_base的事件队列中。
2、 对应定时器事件,加入到event_base的定时器最小堆里。
3、 对信号事件,调用evsignal_add,加入事件处理队列中。
事件循环。调用底层的select、poll或epoll等,如监听事件发生,调用事件结构中指定的回调函数。
1、 计算最近的超时时间:定时器最小堆按照超时时间排序,取最小的超时时间;如已有活动事件或指定不阻塞,超时时间为0。
2、 调用dispatch。对epoll,对应epoll_dispatch函数。该函数调用epoll_wait监控指定事件。
3、 把到了超时时间的时间加入到活动事件队列。从超时时间最小堆中依次取最小超时时间和当前时间比较,对小于/等于当前时间的事件,加入到活动事件队列。
4、 循环调用活动事件队列中所有事件的回调函数。
struct eventop {
constchar *name;
void*(*init)(struct event_base *);
int(*add)(void *, struct event *);
int(*del)(void*, struct event *);
int(*dispatch)(struct event_base *, void *, struct timeval *);
void(*dealloc)(struct event_base *, void *);
/*set if we need to reinitialize the event base */
intneed_reinit;
};
struct event_base {
conststruct eventop *evsel; //指向编译时选择的一个select/pool/epoll/kqueue接口封装对象。
void*evbase;
intevent_count; /* counts numberof total events */
intevent_count_active; /* counts number ofactive events */
intevent_gotterm; /* Set to terminateloop */
intevent_break; /* Set toterminate loop immediately */
/*active event management */
structevent_list **activequeues; //活动事件队列
intnactivequeues;
/*signal handling info */
structevsignal_info sig;
structevent_list eventqueue; //监听事件队列
structtimeval event_tv;
structmin_heap timeheap; //定时器时间堆
structtimeval tv_cache;
};
struct event {
TAILQ_ENTRY(event) ev_next;
TAILQ_ENTRY(event) ev_active_next;
TAILQ_ENTRY(event) ev_signal_next;
unsignedint min_heap_idx; /* for managingtimeouts */
structevent_base *ev_base; //事件输入的evnet_base
intev_fd;
shortev_events;
shortev_ncalls;
short*ev_pncalls; /* Allows deletes incallback */
structtimeval ev_timeout;
intev_pri; /* smaller numbers arehigher priority */
void(*ev_callback)(int, short, void *arg); //回调函数
void*ev_arg;
intev_res; /* result passed toevent callback */
intev_flags;
};
server端代码:
/**
You need libevent2 to compile this piece of code
Please see: http://libevent.org/
Or you can simply run this command to install on Mac: brew install libevent
Cmd to compile this piece of code: g++ LibeventQuickStartServer.c -o LibeventQuickStartServer /usr/local/lib/libevent.a
**/
#include
#include
#include
#include
#include
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 const *argv[])
{
/* code */
int listener = tcp_server_init(9999, 10);
if (listener == -1)
{
perror("tcp_server_init error");
return -1;
}
struct event_base* base = event_base_new();
// 监听客户端请求链接事件
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;
//动态创建一个event结构体,并将其作为回调参数传递给
struct event* ev = event_new(NULL, -1, 0, NULL, NULL);
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\n", msg);
char reply_msg[4096] = "I have received 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;
}
client端代码
/**
You need libevent2 to compile this piece of code
Please see: http://libevent.org/
Or you can simply run this command to install on Mac: brew install libevent
Cmd to compile this piece of code: g++ LibeventQuickStartClient.c -o LibeventQuickStartClient /usr/local/lib/libevent.a
**/
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
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;
}
设置scokfd为nonblocking;
使用bufferevent_socket_new创建一个struct bufferevent* bev,关联上面的sockfd,并托管给event_base;
使用bufferevent_setcb(bev, read_cb, write_cb, error_cb, (void*)arg);
使用buffevent_enable(bev, EV_READ|EV_WRITE|EV_PERSIST)来启动read/write事件
server端代码
#include
#include
#include
#include
#include
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 const *argv[])
{
/* code */
int listener = tcp_server_init(9999, 10);
if (listener == -1)
{
perror("tcp_server_init error");
return -1;
}
struct event_base* base = event_base_new();
// 监听客户端请求链接事件
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;
//动态创建一个event结构体,并将其作为回调参数传递给
struct event* ev = event_new(NULL, -1, 0, NULL, NULL);
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\n", msg);
char reply_msg[4096] = "I have received 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;
}
client端代码
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
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, //#include 系统级的API,是一个文件句柄
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); //将其设置为非阻塞式IO
return sockfd;
}
server端(编译有错误)
#include
#include
#include
#include
#include
#include
#include
#include
#include
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);
}
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
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);
}
代码中新出现的函数:
evutil_make_socket_nonblocking //跨平台统一接口,将套接字设置为非阻塞状态
evutil_socket_t 结构体
evutil_make_listen_socket_reuseable//在socket和listen之间调用,允许多次绑定同一个地址
evutil_closesocket
event_new //动态创建一个event结构体
event_assign//将动态创建的结构体作为event的回调参数
event_free
bufferevent 结构体
bufferevent_socket_new
bufferevent_write
bufferevent_setcb//当socket关闭时会用到回调参数
bufferevent_enable//设置属性
bufferevent_read
bufferevent_free
参考文章:
http://blog.csdn.net/luotuo44/article/details/39670221
https://blog.csdn.net/luotuo44/category_2435521.html
https://blog.csdn.net/windeal3203/category_6489079.html