UtilBox(ub)基础组件 -- epoll_server网络事件模型

        今天事情比较少，突然在在网上看到了一篇关于网络同步异步IO的帖子，正好想起了前几天分析过的Redis的代码。Redis的代码很精练也很轻巧，基本没有第三方以来的库(最新版本中加入了jemalloc，但已集成在了redis的src里，所以依旧可以直接make)，并实现一套轻量型的非阻塞半异步框架-aeEvent(很少有大型互联网后台应用采用全异步框架，一是逻辑和IO都是异步的这样即时性较低，二是编程难度较高)！

        完整的分析过了redis的aeEvent，也对比了一下memcached用的libevent。感觉却是比libevent轻量些，两者在linux下都是用epoll实现(定时器的实现细节略有不同，libevent是用最小堆管理，aeEvent是链表，后期redis可能改进)。大体思想基本类似，由于redis是单线程模型，据作者说是考虑到线程锁的问题。两者暂时没有做过效率对比，之后有机会可以跑些数据。

        看了redis之后，自己也做了一个微型的基于epoll的event_server模型，可以应用在一些自己环境之中，同样采用单线程infinite_loop的方式，通过epoll_ctl注册和删除需要关注的file descript (fd) ，然后通过epoll_wait来循环等待IO事件，触发记录在该fd上的write或者read回调函数(通过附加结构体实现)。

/*
* =====================================================================================
*
*       Filename:  epoll_server.c
*
*    Description:  A example for Linux epoll
*
*        Version:  1.0
*        Created:  03/28/2012 03:40:37 PM
*       Revision:  none
*       Compiler:  gcc
*
*         Author:  Michael LiuXin,
*   Organization:
*
* =====================================================================================
*/
#include <sys/socket.h>
#include <sys/epoll.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <errno.h>
#include <stdlib.h>
#include <assert.h>
#include <netinet/tcp.h>

#include <string.h>
#include <strings.h>

#define MAX_EVENTS 500
#define EPOLL_WAIT_TIMEOUT 1000

#define EVENT_READABLE 1
#define EVENT_WRITEABLE 2

struct event_server;

// 回调在fd上的write和read的callback函数指针
typedef void (*event_handler)(struct event_server*,int);

// 每个fd一个的event结构
struct event_t
{
unsigned char mask;	// 标志WRITE和READ的掩码
event_handler read;
event_handler write;
void* data;
};

/**
* Event server structure , maintain a core Events
*/
struct event_server
{
int epfd;		// epoll_create的fd
int is_blocking;		// 设置非阻塞
struct epoll_event events[MAX_EVENTS];		// 数组实现某个fd的结构的索引，也可以用Hash
struct event_t events_set[MAX_EVENTS];
unsigned long loops;
};

// 创建一个event_server
struct event_server* create_server()
{
struct event_server *server = (struct event_server*)malloc(sizeof(*server));
memset(server,0,sizeof(*server));
// just a hint for kernel
server->epfd = epoll_create(1024);
if (-1 != server->epfd) {
printf("ok=create_server\n");
return server;
} else {
printf("err=create_server\n");
return NULL;
}
}

// 反注册一个fd的event
int unregister_server_event(struct event_server* server, int fd, int type)
{
struct epoll_event ev;
ev.data.fd = fd;
ev.events = server->events_set[fd].mask;

if (type & EVENT_WRITEABLE)
ev.events &= ~EPOLLOUT ;
if (type & EVENT_READABLE)
ev.events &= ~EPOLLIN;

// if there is no event then delelte , otherwise modify
int op = ev.events ? EPOLL_CTL_MOD : EPOLL_CTL_DEL ;
// to listen the fd
if (-1 == epoll_ctl(server->epfd,op,fd,&ev)) {
printf("err=epoll_ctl_del\n");
return -1;
} else {
// record the read/write callback-function
// use it at epoll_wait call
server->events_set[fd].read = (type&EVENT_READABLE)?NULL:server->events_set[fd].read;
server->events_set[fd].write = (type&EVENT_WRITEABLE)?NULL:server->events_set[fd].write;
server->events_set[fd].mask = ev.events;
//printf("ok=epoll_ctl_%s\n",op==EPOLL_CTL_MOD?"mod":"del");
return 0;
}
}

// 注册一个fd的event
int register_server_event(struct event_server* server, int fd, int type, event_handler fun)
{
assert(fd);
assert(type);
assert(fun);

struct epoll_event ev = {0};
ev.data.fd = fd;
ev.events |= server->events_set[fd].mask;
if (type & EVENT_WRITEABLE)
ev.events |= EPOLLOUT ;
if (type & EVENT_READABLE)
ev.events |= EPOLLIN;

// to listen the fd MOD or ADD
int op = server->events_set[fd].mask ? EPOLL_CTL_MOD : EPOLL_CTL_ADD;
if (-1 == epoll_ctl(server->epfd,op,fd,&ev)) {
printf("err=epoll_ctl_%s\n",server->events_set[fd].mask?"mod":"add");
return -1;
} else {
// record the read/write callback-function
// use it at epoll_wait call
//printf("ok=epoll_ctl_%s\n",server->events_set[fd].mask?"mod":"add");
type&EVENT_READABLE ? server->events_set[fd].read=fun : 0;
type&EVENT_WRITEABLE ? server->events_set[fd].write=fun : 0;
server->events_set[fd].mask = ev.events;

return 0;
}
}

// 阻塞非阻塞，基本的网络模型为防止read阻塞都采用nonblocking
void set_server_nonblocking(struct event_server* server)
{
server->is_blocking = 0;
}

void set_server_blocking(struct event_server* server)
{
server->is_blocking = 1;
}

// infinite loop 事件循环，线程在此循环
void run(struct event_server* server)
{
// do an infinite loop for epoll_wait
while(1) {
//printf("before_epoll_wait\n");
int n = epoll_wait(server->epfd,server->events,MAX_EVENTS,EPOLL_WAIT_TIMEOUT);
//printf("after_epoll_wait\n");

if (0 == n) {
//printf("Waiting<%lu>...\n",server->loops++);
continue;
}

//printf("for_each<%d>\n",n);
for (int i=0; i!=n; i++) {
assert(server->events[i].data.fd);
assert(server->events_set[server->events[i].data.fd].mask);
if ((server->events[i].events & EPOLLIN) && server->events_set[server->events[i].data.fd].read) {
server->events_set[server->events[i].data.fd].read(server,server->events[i].data.fd);
continue;
}
if ((server->events[i].events & EPOLLOUT) && server->events_set[server->events[i].data.fd].write) {
server->events_set[server->events[i].data.fd].write(server,server->events[i].data.fd);
continue;
}
}
}
}

// write事件回调函数
void tcp_write(struct event_server* server, int clientfd)
{
int length = strlen("received");
while(1) {
int n = write(clientfd,"received",length);
if (-1==n && errno==EAGAIN)
break;
length -= n;
//printf("ok=write_client<%d>\n",n);
if (length <= 0)
break;
}
unregister_server_event(server,clientfd,EVENT_WRITEABLE);
}

// read事件回调函数
void tcp_read(struct event_server* server, int clientfd)
{
/**
* this method is called by epoll_wait callback if there has
* something to read in buffer
*/
char buf[1024] = {0};
int ret = -1;
while(1) {
ret=read(clientfd,buf,1024);
if (0 == ret) {
unregister_server_event(server,clientfd,EVENT_READABLE|EVENT_WRITEABLE);
close(clientfd);
printf("ok=client_quit\n");
break;
}
if (-1==ret && errno==EAGAIN)
break;
//printf("ok=read_from_%d<%d>:\"%s\"\n",clientfd,ret,buf);
//register_server_event(server,clientfd,EVENT_WRITEABLE,tcp_write);
}
}

// server的socket fd的回调函数。只负责accept并注册
void tcp_accept(struct event_server* server, int server_socket)
{
// the server must be accepted
int cfd = accept(server_socket,NULL,NULL);

if (cfd) {

int flag = fcntl(cfd,F_GETFL,0);
// nonblocking
flag |= O_NONBLOCK;
if (-1 == fcntl(cfd,F_SETFL,flag))
printf("err=set_nonblocking\n");
// no delay (without nagle)
int nodelay = 1;
if (-1 == setsockopt(cfd,IPPROTO_TCP,TCP_NODELAY,&nodelay,sizeof(nodelay)))
printf("err=set_tcp_no_delay\n");

// add the client_fd to epoll loop
register_server_event(server,cfd,EVENT_READABLE,tcp_read);
} else {
printf("err=accept_socket\n");
}

}

// drive function
#define ut_main main
int ut_main()
{
// setup a socket
int server_socket = socket(AF_INET,SOCK_STREAM,0);
if (-1 == server_socket) {
printf("err=create_socket\n");
return -1;
}
else
printf("ok=create_socket\n");
struct sockaddr_in server_addr;
bzero(&server_addr,sizeof(server_addr));
server_addr.sin_family = AF_INET;
server_addr.sin_addr.s_addr = htons(INADDR_ANY);
server_addr.sin_port = htons(9898);

int flag=1,len=sizeof(flag);
// we can reuse the port
setsockopt(server_socket,SOL_SOCKET,SO_REUSEADDR,&flag,len);
if (-1 == setsockopt(server_socket,IPPROTO_TCP,TCP_NODELAY,&flag,sizeof(flag)))
printf("err=set_tcp_no_delay\n");

// bind ip/port
if (-1 == bind(server_socket,(struct sockaddr*)&server_addr,sizeof(server_addr))) {
printf("err=bind_socket\n");return -1; }
else
printf("ok=bind_socket\n");
if (-1 == listen(server_socket,1024)) {
printf("err=listen_socket\n");return -1; }
else
printf("ok=listen_socket\n");

// create a epoll server handle
struct event_server* server = create_server();
set_server_nonblocking(server);
// firstly listen the server's socket with ACCEPT
register_server_event(server,server_socket,EVENT_READABLE,tcp_accept);

// do event loop
run(server);

return 0;
}

        有些细节没特别关注，例如Linger之类的问题(readv/writev)暂时不care，后续继续完善。单线程下压力QPS可以打到5万(blocksize很小只是一个字符串，会对数据包的使用率造成和并发造成一定影响)。还没试过多线程(可以一个线程包一个server，或者由server来托管线程)。只是简单做了一个epoll多路复用的引子，基本“画出”了网络框架的影子，其实不管是redis、libevent还是apache、nginx都是以此位基点进行扩展，在上面做线程、并发控制、进程池(apache的prefork)等。