linux epoll example
2015-01-28
#include <netdb.h>
#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 <string.h>
#include <stdlib.h>
#include <errno.h>
/**
* 创建并绑定一个socket作为服务器。
*/
static int create_and_bind (char *port){
struct addrinfo hints;
struct addrinfo *result, *rp;
int s, sfd;
memset (&hints, 0, sizeof (struct addrinfo));
hints.ai_family = AF_UNSPEC; /* Return IPv4 and IPv6 choices */
hints.ai_socktype = SOCK_STREAM; /* 设置为STREAM模式，即TCP链接 */
hints.ai_flags = AI_PASSIVE; /* All interfaces */
s = getaddrinfo (NULL, port, &hints, &result);//获得本地主机的地址
if (s != 0){
fprintf (stderr, "getaddrinfo: %s\n", gai_strerror (s));
return -1;
}
for (rp = result; rp != NULL; rp = rp->ai_next){//本地主机地址可能有多个，任意绑定一个即可
sfd = socket (rp->ai_family, rp->ai_socktype, rp->ai_protocol); //创建socket
if (sfd == -1) {
continue;
}
s = bind (sfd, rp->ai_addr, rp->ai_addrlen); //并绑定socket
if (s == 0) {
/* 绑定成功 */
break;
}
close (sfd);
}
if (rp == NULL){
fprintf (stderr, "Could not bind\n");
return -1;
}
freeaddrinfo (result);
return sfd;
}
/**
* 设置socket为非阻塞模式。
* 先get flag，或上O_NONBLOCK 再set flag。
*/
static int make_socket_non_blocking (int sfd) {
int flags, s;
flags = fcntl (sfd, F_GETFL, 0);
if (flags == -1){
perror ("fcntl");
return -1;
}
flags |= O_NONBLOCK;
s = fcntl (sfd, F_SETFL, flags);
if (s == -1){
perror ("fcntl");
return -1;
}
return 0;
}
#define MAXEVENTS 64
/**
* 用法： ./epoll_test 8080
*/
int main (int argc, char *argv[]) {
int sfd, s;
int efd;
struct epoll_event event;
struct epoll_event *events;
if (argc != 2) {
fprintf (stderr, "Usage: %s [port]\n", argv[0]);
exit (EXIT_FAILURE);
}
sfd = create_and_bind (argv[1]); //sfd为绑定后等待连接接入的文件描述符
s = make_socket_non_blocking (sfd);
s = listen (sfd, SOMAXCONN);
efd = epoll_create1 (0);
event.data.fd = sfd;
event.events = EPOLLIN | EPOLLET;
s = epoll_ctl (efd, EPOLL_CTL_ADD, sfd, &event);
/* Buffer where events are returned，为events数组分配内存 */
events = (struct epoll_event*)calloc (MAXEVENTS, sizeof event);
/* The event loop 事件循环*/
while (1) {
int n, i;
n = epoll_wait (efd, events, MAXEVENTS, -1);
for (i = 0; i < n; i++) {
if ((events[i].events & EPOLLERR)
|| (events[i].events & EPOLLHUP)
|| (!(events[i].events & EPOLLIN))) {
/** 发生了错误或者被挂断，或者没有数据可读
* An error has occured on this fd,
* or the socket is not ready for reading (why were we notified then?)
*/
fprintf (stderr, "epoll error\n");
close (events[i].data.fd);
continue;
} else if (sfd == events[i].data.fd) {//新连接
/**
*sfd上有数据可读，则表示有新连接
* We have a notification on the listening socket,
* which means one or more incoming connections.
*/
printf("Incoming connection !\n");
while (1) {
struct sockaddr in_addr;
socklen_t in_len;
int infd;
char hbuf[NI_MAXHOST], sbuf[NI_MAXSERV];
in_len = sizeof in_addr;
infd = accept (sfd, &in_addr, &in_len); //读取到来的连接socket fd。
if (infd == -1) {
if ((errno == EAGAIN) || (errno == EWOULDBLOCK)) {
/**
* 已经读完了sfd上的所有数据（所有连接）。
* 最后一次读（非阻塞读）会返回EAGAIN（=EWOULDBLOCK）
* We have processed all incoming connections.
*/
break;
} else {
perror ("accept");
break;
}
}
s = getnameinfo (&in_addr, in_len, hbuf, sizeof hbuf,
sbuf, sizeof sbuf, NI_NUMERICHOST | NI_NUMERICSERV);
if (s == 0) {
printf("Accepted connection on descriptor %d (host=%s, port=%s)\n", infd, hbuf, sbuf);
}
s = make_socket_non_blocking (infd); //设置socket为非阻塞模式
event.data.fd = infd; //将data部分设置为fd
event.events = EPOLLIN | EPOLLET; //监听EPOLLIN事件，使用边缘触发模式
s = epoll_ctl (efd, EPOLL_CTL_ADD, infd, &event);
}
continue;
} else {//有客户端发来数据
/**
* 有客户端发来数据，因为处于ET模式，所以必须完全读取所有数据
* （要不然，剩下一部分数据后，就无法再收到内核通知了）。
*/
int done = 0;
while (1) {
ssize_t count;
char buf[512];
count = read (events[i].data.fd, buf, sizeof buf);
if (count == -1) {
if (errno != EAGAIN) { //如果errno=EAGAIN，表示我们已经读取了所有的数据
perror ("read");
done = 1;
}
break;
} else if (count == 0) { //读到文件尾（对端被关闭了）
/* End of file. The remote has closed the connection. */
done = 1;
break;
}
s = write (1, buf, count); /* 打印到屏幕 */
}
if (done) { //读完关闭（假设应用对每个连接只读取一次数据）
printf ("Closed connection on descriptor %d\n", events[i].data.fd);
/**
* Closing the descriptor will make epoll remove it
* from the set of descriptors which are monitored.
*/
close (events[i].data.fd);
}
}
}
}
free (events);//释放内存
close (sfd); //关闭sfd
return EXIT_SUCCESS;
}
