商业网站模板,新网站怎么做seo,淄博网站制作,鲜花网站设计论文文章目录 前言libevent-API调用的基本流程给事件提供缓冲区 前言
本文是libevent的入门文档。本文不涉及#xff0c;这个库在某些方面的具体使用。
本文内容来自A tiny introduction to asynchronous IO。通过这篇链接#xff0c;我们可以了解libevent的基本使用。在开始之… 文章目录 前言libevent-API调用的基本流程给事件提供缓冲区 前言
本文是libevent的入门文档。本文不涉及这个库在某些方面的具体使用。
本文内容来自A tiny introduction to asynchronous IO。通过这篇链接我们可以了解libevent的基本使用。在开始之前我们需要一些前置准备
TCP客户端和服务端之间的同步通信chapter05_TCP客户_服务器示例IO复用-select的使用unix网络编程-select函数如果知道这两个就更好了epoll实现Reactor模式、使用asio实现一个单线程异步的socket服务程序
注释libevent-文档、libevent-API libevent-API调用的基本流程
在使用API之前我们需要了解这三部分
event_baseevent_base是一个事件处理的基础结构它提供了事件循环的基本框架。可以认为它是对select、epoll等函数的封装以提供跨平台的支持。eventevent是一个表示某种事件(套接字的读写事件,定时器事件等)的结构体或对象。它保存了事件触发时回调函数的指针供event_base调用。事件能被触发的前提时事件被注册到event_base中参与循环检查。event loop运行event_base,直到没有任何注册事件。
总的来说创建event对象后需要将其添加到一个event_base实例中以便在事件发生时被正确处理。event_base提供了方法来添加、删除和处理事件。当事件发生时event_base负责调用与之相关联的回调函数。下面时一个简单的伪代码示例
// 创建 event_base 实例
struct event_base *base event_base_new();// 创建一个读事件
struct event *ev event_new(base, fd, EV_READ | EV_PERSIST, callback, arg);// 将事件添加到事件循环中
event_add(ev, NULL);// 开始事件循环
event_base_dispatch(base);具体的API接口使用见官方文档。
下面我们来看一个提供ROT13功能的服务端程序。
// come from: https://libevent.org/libevent-book/01_intro.html/* For sockaddr_in */
#include netinet/in.h
/* For socket functions */
#include sys/socket.h
/* For fcntl */
#include fcntl.h#include event2/event.h#include assert.h
#include errno.h
#include stdio.h
#include stdlib.h
#include string.h
#include unistd.h#define MAX_LINE 16384void do_read(evutil_socket_t fd, short events, void *arg);
void do_write(evutil_socket_t fd, short events, void *arg);char rot13_char(char c) {/* We dont want to use isalpha here; setting the locale would change* which characters are considered alphabetical. */if ((c a c m) || (c A c M))return c 13;else if ((c n c z) || (c N c Z))return c - 13;elsereturn c;
}struct fd_state {char buffer[MAX_LINE];size_t buffer_used;size_t n_written;size_t write_upto;struct event *read_event;struct event *write_event;
};struct fd_state *alloc_fd_state(struct event_base *base, evutil_socket_t fd) {struct fd_state *state malloc(sizeof(struct fd_state));if (!state)return NULL;state-read_event event_new(base, fd, EV_READ | EV_PERSIST, do_read, state);if (!state-read_event) {free(state);return NULL;}state-write_event event_new(base, fd, EV_WRITE | EV_PERSIST, do_write, state);if (!state-write_event) {event_free(state-read_event);free(state);return NULL;}state-buffer_used state-n_written state-write_upto 0;assert(state-write_event);return state;
}void free_fd_state(struct fd_state *state) {event_free(state-read_event);event_free(state-write_event);free(state);
}void do_read(evutil_socket_t fd, short events, void *arg) {struct fd_state *state arg;char buf[1024];int i;ssize_t result;while (1) {assert(state-write_event);result recv(fd, buf, sizeof(buf), 0);if (result 0)break;for (i 0; i result; i) {if (state-buffer_used sizeof(state-buffer))state-buffer[state-buffer_used] rot13_char(buf[i]);if (buf[i] \n) {assert(state-write_event);event_add(state-write_event, NULL);state-write_upto state-buffer_used;}}}if (result 0) {free_fd_state(state);} else if (result 0) {if (errno EAGAIN) // XXXX use evutil macroreturn;perror(recv);free_fd_state(state);}
}void do_write(evutil_socket_t fd, short events, void *arg) {struct fd_state *state arg;while (state-n_written state-write_upto) {ssize_t result send(fd, state-buffer state-n_written,state-write_upto - state-n_written, 0);if (result 0) {if (errno EAGAIN) // XXX use evutil macroreturn;free_fd_state(state);return;}assert(result ! 0);state-n_written result;}if (state-n_written state-buffer_used)state-n_written state-write_upto state-buffer_used 0;event_del(state-write_event);
}void do_accept(evutil_socket_t listener, short event, void *arg) {struct event_base *base arg;struct sockaddr_storage ss;socklen_t slen sizeof(ss);int fd accept(listener, (struct sockaddr *)ss, slen);if (fd 0) { // XXXX eagain??perror(accept);} else if (fd FD_SETSIZE) {close(fd); // XXX replace all closes with EVUTIL_CLOSESOCKET */} else {struct fd_state *state;evutil_make_socket_nonblocking(fd);state alloc_fd_state(base, fd);assert(state); /*XXX err*/assert(state-write_event);event_add(state-read_event, NULL);}
}void run(void) {evutil_socket_t listener;struct sockaddr_in sin;struct event_base *base;struct event *listener_event;base event_base_new();if (!base)return; /*XXXerr*/sin.sin_family AF_INET;sin.sin_addr.s_addr 0;sin.sin_port htons(40713);listener socket(AF_INET, SOCK_STREAM, 0);evutil_make_socket_nonblocking(listener);// not work in windows systemevutil_make_listen_socket_reuseable(listener);if (bind(listener, (struct sockaddr *)sin, sizeof(sin)) 0) {perror(bind);return;}if (listen(listener, 16) 0) {perror(listen);return;}listener_event event_new(base, listener, EV_READ | EV_PERSIST, do_accept, (void *)base);/*XXX check it */event_add(listener_event, NULL);event_base_dispatch(base);
}int main(int c, char **v) {setvbuf(stdout, NULL, _IONBF, 0);run();return 0;
}给事件提供缓冲区
上面的代码中我们需要为每个连接显示的分配堆栈作为缓冲区这是麻烦的。
网络异步编程的通常模式是
当连接可读时将数据读取到缓冲区然后处理。将处理结果写入输出缓冲区然后将连接设置为可写。尽可能多地写入数据。写完之后关闭连接的可写。(因为套接字的输出缓冲区不满的时候总是可写的。)
Libevent 提供了一个 它的通用机制Bufferevents。它包含一个底层传输(如套接字)、读缓冲区和写缓冲区缓冲。从底层IO中读取数据到用户层的缓冲区然后触发读取回调将需要发送的数据放入用户层的缓冲区中libevent会将数据发送出去。每个Bufferevents都有下面四个watermarks
Read low-water mark: 当输入缓冲区存储的数据比当前设置的低水位多则调用读取回调。Read high-water mark当输入缓冲区的数据达到当前的高水位缓冲区不再从底层IO去获取更多数据。等待回调函数消耗些数据缓冲区才有空间继续存放从IO获取来数据。Write low-water mark当输出缓冲区存储的数据比当前设置的低水位多则调用写回调。Write high-water mark可以暂时不管。具体见官方文档。
下面使用bufferevent重写上一节的代码
/* For sockaddr_in */
#include netinet/in.h
/* For socket functions */
#include sys/socket.h
/* For fcntl */
#include fcntl.h#include event2/buffer.h
#include event2/bufferevent.h
#include event2/event.h#include assert.h
#include errno.h
#include stdio.h
#include stdlib.h
#include string.h
#include unistd.h#define MAX_LINE 16384void do_read(evutil_socket_t fd, short events, void *arg);
void do_write(evutil_socket_t fd, short events, void *arg);int print_output(struct bufferevent *bev) {struct evbuffer *output bufferevent_get_output(bev);size_t len evbuffer_get_length(output);char buff[len 1];int size evbuffer_copyout(output, buff, len);if (size 0) {printf(read fail\n);return -1;}buff[size] \0;printf(Output Buffer Contents: %s\n, buff);return 0;
}char rot13_char(char c) {/* We dont want to use isalpha here; setting the locale would change* which characters are considered alphabetical. */if ((c a c m) || (c A c M))return c 13;else if ((c n c z) || (c N c Z))return c - 13;elsereturn c;
}void readcb(struct bufferevent *bev, void *ctx) {struct evbuffer *input, *output;char *line;size_t n;int i;input bufferevent_get_input(bev);output bufferevent_get_output(bev);while ((line evbuffer_readln(input, n, EVBUFFER_EOL_LF))) {for (i 0; i n; i)line[i] rot13_char(line[i]);evbuffer_add(output, line, n);evbuffer_add(output, \n, 1);free(line);}if (evbuffer_get_length(input) MAX_LINE) {/* Too long; just process what there is and go on so that the buffer* doesnt grow infinitely long. */char buf[1024];while (evbuffer_get_length(input)) {int n evbuffer_remove(input, buf, sizeof(buf));for (i 0; i n; i)buf[i] rot13_char(buf[i]);evbuffer_add(output, buf, n);}evbuffer_add(output, \n, 1);}
}void errorcb(struct bufferevent *bev, short error, void *ctx) {if (error BEV_EVENT_EOF) {/* connection has been closed, do any clean up here *//* ... */} else if (error BEV_EVENT_ERROR) {/* check errno to see what error occurred *//* ... */} else if (error BEV_EVENT_TIMEOUT) {/* must be a timeout event handle, handle it *//* ... */}bufferevent_free(bev);
}void do_accept(evutil_socket_t listener, short event, void *arg) {struct event_base *base arg;struct sockaddr_storage ss;socklen_t slen sizeof(ss);int fd accept(listener, (struct sockaddr *)ss, slen);if (fd 0) {perror(accept);} else if (fd FD_SETSIZE) {close(fd);} else {struct bufferevent *bev;evutil_make_socket_nonblocking(fd);bev bufferevent_socket_new(base, fd, BEV_OPT_CLOSE_ON_FREE);bufferevent_setcb(bev, readcb, NULL, errorcb, NULL);bufferevent_setwatermark(bev, EV_READ, 0, MAX_LINE);bufferevent_enable(bev, EV_READ | EV_WRITE);}
}void run(void) {evutil_socket_t listener;struct sockaddr_in sin;struct event_base *base;struct event *listener_event;base event_base_new();if (!base)return; /*XXXerr*/sin.sin_family AF_INET;sin.sin_addr.s_addr 0;sin.sin_port htons(40713);listener socket(AF_INET, SOCK_STREAM, 0);evutil_make_socket_nonblocking(listener);#ifndef WIN32{int one 1;setsockopt(listener, SOL_SOCKET, SO_REUSEADDR, one, sizeof(one));}
#endifif (bind(listener, (struct sockaddr *)sin, sizeof(sin)) 0) {perror(bind);return;}if (listen(listener, 16) 0) {perror(listen);return;}listener_event event_new(base, listener, EV_READ | EV_PERSIST, do_accept, (void *)base);/*XXX check it */event_add(listener_event, NULL);event_base_dispatch(base);
}int main(int c, char **v) {setvbuf(stdout, NULL, _IONBF, 0);run();return 0;
}
