關於epoll替代select作為高效能伺服器的事件通知機制的資料相當多，我就不在這裡班門弄斧了，有興趣的同學可以參考末尾的文獻連結。

這裡說明如下：

1.epoll是linux下高併發伺服器的完美方案，因為是基於事件觸發的，所以比select快的不只是一個數量級。

2.單執行緒epoll，觸發量可達到15000，參見文獻[4]

3.高效能server要使用非阻塞方式。

epoll伺服器端

//compile: g++ -g epoll_server.cpp -o epoll_server
//run: ./epoll_server
//
#include <sys/socket.h>
#include <sys/epoll.h>
#include <sys/sendfile.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <fcntl.h>
#include <errno.h>


#define MAX_EVENTS 10
#define LISTENQ 20
#define PORT 5000 //8080


//設定socket連線為非阻塞模式
void setnonblocking (int fd)
{
	int opts;

	opts = fcntl (fd, F_GETFL);
	if (opts < 0)
	{
		perror ("fcntl(F_GETFL)\n");
		exit (1);
	}
	opts = (opts | O_NONBLOCK);
	if (fcntl (fd, F_SETFL, opts) < 0)
	{
		perror ("fcntl(F_SETFL)\n");
		exit (1);
	}
}

int main ()
{
	struct epoll_event ev, events[MAX_EVENTS];
	int listenfd, connfd, nfds, epfd, sockfd, i, nread, n;
	struct sockaddr_in local, remote;
    socklen_t addrlen;
	char buf[BUFSIZ];

	//建立listen socket
	if ((listenfd = socket (AF_INET, SOCK_STREAM, 0)) < 0)
	{
		perror ("sockfd\n");
		exit (1);
	}
	setnonblocking (listenfd);
	bzero (&local, sizeof (local));
	local.sin_family = AF_INET;
	local.sin_addr.s_addr = htonl (INADDR_ANY);;
	local.sin_port = htons (PORT);
	if (bind (listenfd, (struct sockaddr *) &local, sizeof (local)) < 0)
	{
		perror ("bind\n");
		exit (1);
	}
	listen (listenfd, LISTENQ);

	epfd = epoll_create (MAX_EVENTS);
	if (epfd == -1)
	{
		perror ("epoll_create");
		exit (EXIT_FAILURE);
	}
	ev.events = EPOLLIN;
	ev.data.fd = listenfd;
	if (epoll_ctl (epfd, EPOLL_CTL_ADD, listenfd, &ev) == -1)
	{
		perror ("epoll_ctl: listen_sock");
		exit (EXIT_FAILURE);
	}

	for (;;)
	{
		nfds = epoll_wait (epfd, events, MAX_EVENTS, -1);
		if (nfds == -1)
		{
			perror ("epoll_wait error");
			exit (EXIT_FAILURE);
		}

		for (i = 0; i < nfds; ++i)
		{
			sockfd = events[i].data.fd;
			if (sockfd == listenfd)
			{
				while ((connfd = accept (listenfd, (struct sockaddr *) &remote, &addrlen)) > 0)
				{
                    char *ipaddr = inet_ntoa (remote.sin_addr);
                    printf("accept a connection from [%s]\n", ipaddr);
					setnonblocking (connfd);	//設定連線socket為非阻塞
					ev.events = EPOLLIN | EPOLLET;	//邊沿觸發要求套接字為非阻塞模式；水平觸發可以是阻塞或非阻塞模式
					ev.data.fd = connfd;
					if (epoll_ctl (epfd, EPOLL_CTL_ADD, connfd, &ev) == -1)
					{
						perror ("epoll_ctl: add");
						exit (EXIT_FAILURE);
					}
				}
				if (connfd == -1)
				{
					if (errno != EAGAIN && errno != ECONNABORTED && errno != EPROTO && errno != EINTR)
						perror ("accept");
				}
				continue;
			}
			if (events[i].events & EPOLLIN)
			{
				n = 0;
				while ((nread = read (sockfd, buf + n, BUFSIZ - 1)) > 0)
				{
					n += nread;
				}
				if (nread == -1 && errno != EAGAIN)
				{
					perror ("read error");
				}
                printf("recv from client data [%s]\n", buf);
				ev.data.fd = sockfd;
				ev.events = events[i].events | EPOLLOUT;
				if (epoll_ctl (epfd, EPOLL_CTL_MOD, sockfd, &ev) == -1)
				{
					perror ("epoll_ctl: mod");
				}
			}
			if (events[i].events & EPOLLOUT)
			{
				snprintf (buf, sizeof(buf), "HTTP/1.1 200 OK\r\nContent-Length: %d\r\n\r\nHello World", 11);
				int nwrite, data_size = strlen (buf);
				n = data_size;
				while (n > 0)
				{
					nwrite = write (sockfd, buf + data_size - n, n);
					if (nwrite < n)
					{
						if (nwrite == -1 && errno != EAGAIN)
						{
							perror ("write error");
						}
						break;
					}
					n -= nwrite;
				}
                printf("send to client data [%s]\n", buf);
				close (sockfd);
                events[i].data.fd = -1;
			}
		}
	}
	close (epfd);
	close (listenfd);
	return 0;
}
 

epoll客戶端

//compile: g++ -g epoll_client.cpp -o epoll_client
//run: ./epoll_client
//
#include <iostream>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>

using namespace std;

#define PORT 5000

int main(int argc, char* argv[])
{
    int sockfd, on = 1;
    char buffer[512] = {0};
    struct sockaddr_in servaddr;
    memset(&servaddr, 0, sizeof(servaddr));

    if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0){
        cout << "create socket fail" << endl;
        return -1;
    }
    cout << "succeed to create client socket fd " << sockfd  << endl;

    setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on));
    cout << "set socket reuse by etsockopt" << endl;

    servaddr.sin_port = htons((short)PORT);
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = inet_addr("127.0.0.1"); //此處更改epoll伺服器地址

    if(connect(sockfd, (struct sockaddr*)&servaddr, sizeof(servaddr)) < 0){
        cout << "connect error" << endl;
        return -1;
    }
    cout << "succeed to connect epoll server " << endl;

    char target[] = "The Author: 
 
[email protected]";
    memcpy(buffer, target, strlen(target));
    int wlen = send(sockfd, buffer, strlen(buffer), 0);
    if(wlen <= 0)
        cout << " send data to server fail " << strerror(errno) << endl;
    cout << "send data to server on success, data: [" << buffer << "]"<< endl;

    memset(buffer, 0, sizeof(buffer));
    int rlen = recv(sockfd, buffer, sizeof(buffer), 0);
    if(rlen <= 0)
        cout << " receive data from server fail " << strerror(errno) << endl;
    cout << "receive data from server on success, data: [" << buffer << "]" << endl;

    return 0;
}

大家可以在上述框架上進一步修改.下面是執行圖

下面的參考文獻按照我認為的優先順序遞減排列