linux socket的IO多路复用简单例子（四）

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本文介绍如何使用epoll函数实现高效的socket编程。通过创建epoll实例并管理多个文件描述符，实现实时监控和处理客户端连接及数据收发。文章详细展示了epoll在服务器端的具体实现过程。

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使用epoll函数编写socket。

原理：使用一个文件描述符来管理多个描述符。epoll只拷贝一次描述符到内核态，当监控的事件发生时，通过函数回调将fd加入到一个就绪表中。接着，检测某个fd是否在就绪表中，存在的话进行对应的读写操作。epoll引入了一个事件结构体。每一个文件描述符对应一个事件结构体。结构体包含文件描述符，需要监控的事件。

server端：

#include <iostream>
#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <sys/shm.h>
#include <sys/epoll.h>
#include <vector>
using namespace std;


int main()
{
	int server_fd = socket(AF_INET, SOCK_STREAM, 0);
	if (server_fd == -1)
	{
		perror("create server fd error");
		return 0;
	}
	struct sockaddr_in serverAttr;
	serverAttr.sin_family = AF_INET;
	serverAttr.sin_port = htons(5875);
	serverAttr.sin_addr.s_addr = htonl(INADDR_ANY);

	if (bind(server_fd, (struct sockaddr*)&serverAttr, sizeof(serverAttr)) == -1)
	{
		perror("bind error");
		return 0;
	}
	if (listen(server_fd, 10))
	{
		perror("listen error");
		return 0;
	}
	/*
	Creates an epoll instance.  Returns an fd for the new instance.
	The "size" parameter is a hint specifying the number of file
	descriptors to be associated with the new instance.  The fd
	returned by epoll_create() should be closed with close().
	int epoll_create (int __size) __THROW;
	*/
	//创建一个总的文件描述符
	int epollFd = epoll_create(1024);
	//创建服务器fd所对应的事件结构体
	struct epoll_event event;
	event.events = EPOLLIN;
	event.data.fd = server_fd;

	/*
	 Manipulate an epoll instance "epfd". Returns 0 in case of success,
	 -1 in case of error ( the "errno" variable will contain the
	 specific error code ) The "op" parameter is one of the EPOLL_CTL_*
	 constants defined above. The "fd" parameter is the target of the
	 operation. The "event" parameter describes which events the caller
	 is interested in and any associated user data.
	int epoll_ctl (int __epfd, int __op, int __fd,
		      struct epoll_event *__event) __THROW;
	*/
	//将服务器fd和事件结构体增加到总的fd中
	epoll_ctl(epollFd, EPOLL_CTL_ADD, server_fd, &event);
	//用来保存系统监控发生后，已经改变的fd事件
	struct epoll_event evs[1024];
	while (1)
	{
		/* Wait for events on an epoll instance "epfd". Returns the number of
   		triggered events returned in "events" buffer. Or -1 in case of
   		error with the "errno" variable set to the specific error code. The
   		"events" parameter is a buffer that will contain triggered
   		events. The "maxevents" is the maximum number of events to be
   		returned ( usually size of "events" ). The "timeout" parameter
   		specifies the maximum wait time in milliseconds (-1 == infinite).
	    int epoll_wait (int __epfd, struct epoll_event *__events,
		       int __maxevents, int __timeout);
		 */
		//ret表示发生改变的事件数量
		int ret = epoll_wait(epollFd, evs, 100, -1);
		for (int i = 0; i < ret; i++)
		{
			int fd = evs[i].data.fd;
			//表示接受到新的请求
			if ((fd == server_fd) && (evs[i].events & EPOLLIN))
			{
				struct sockaddr_in clAttr;
				socklen_t len = sizeof(clAttr);
				int clFd = accept(server_fd, (struct sockaddr*)&clAttr, &len);
				if (clFd == -1)
				{
					perror("accept error");
					continue;
				}
				cout << "accept client :" << inet_ntoa(clAttr.sin_addr) << ":" << clAttr.sin_port << endl;
				//将新的客户端fd和对应的事件添加到总的fd中
				struct epoll_event e;
				e.events = EPOLLIN;
				e.data.fd = clFd;
				epoll_ctl(epollFd, EPOLL_CTL_ADD, clFd, &e);
				continue;
			}
			//表示这个fd接受到客户端发送的消息
			if (evs[i].events & EPOLLIN)
			{
				char buf[1024] = {0};
				int nread = read(evs[i].data.fd, buf, 1024);
				if (nread == -1)
				{
					perror("read error");
					close(fd);
					epoll_ctl(epollFd, EPOLL_CTL_DEL, evs[i].data.fd, &evs[i]);
					continue;
				}
				if (nread == 0)
				{
					perror("server close");
					close(fd);
					epoll_ctl(epollFd, EPOLL_CTL_DEL, evs[i].data.fd, &evs[i]);
					continue;
				}
				cout << "read msg is " << buf << endl;
				evs[i].events = EPOLLOUT;
				epoll_ctl(epollFd, EPOLL_CTL_MOD, evs[i].data.fd, &evs[i]);
				continue;
			}
			//返回信息给对应的客户端
			if (evs[i].events & EPOLLOUT)
			{
				string wrtBuf = "hello,clients[i]ient " + to_string(i);
				int nwrite = write(evs[i].data.fd, wrtBuf.c_str(), 1024);
				if (nwrite == -1)
				{
					perror("write error");
					close(evs[i].data.fd);
					epoll_ctl(epollFd, EPOLL_CTL_DEL, evs[i].data.fd, &evs[i]);
					continue;
				}
				evs[i].events = EPOLLIN;
				epoll_ctl(epollFd, EPOLL_CTL_MOD, evs[i].data.fd, &evs[i]);
			}
		}

	}
	return 0;
}

参考：

http://www.cnblogs.com/Anker/p/3263780.html