epoll()是Linux特有的I/O复用函数，它的实现与使用上和select()、poll()、有很大差异。
epoll()用一组函数来完成任务，而不是单个函数；其次，epoll()把文件描述放到内核事件表中，只需一个额外的文件描述符，来标识内核中唯一的这个事件表。
需要使用的API：
int epoll_create(int size);
int epoll_ctl(int epfd, int op, int fd, struct epoll_event *event);需要使用的结构体信息：
typedef union epoll_data {
void *ptr;
int fd; //一般情况下，都用的是这个文件描述符
uint32_t u32;
uint64_t u64;
} epoll_data_t;
struct epoll_event {
uint32_t events; /* Epoll events */
epoll_data_t data; /* User data variable */
};int epoll_wait(int epfd, struct epoll_event *events, int maxevents, int timeout);关键：对epoll_wait()函数的核心理解
- 返回值：事件表中就绪客户端的个数；
- 参数events：将事件表中的就绪客户端的信息放到了events数组中。
就是创建一个内核事件表，存放所监听客户端的套接字和当前的事件，在利用epoll_wait()函数查找就绪的套接字，最后经过增加、删除、修改利用epoll_ctl()函数进行；当然了，这其中还有一批搭配使用的宏；
#include<unistd.h>
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<sys/socket.h>
#include<arpa/inet.h>
#include<netinet/in.h>
#include<assert.h>
#include<sys/select.h>
#define SERVER_IP "127.0.0.1"
#define SERVER_PORT 8787
#define LISTEN_QUEUE 5
#define SIZE 10
#define BUFFER_SIZE 256
#include<poll.h>
#define OPEN_MAX 1000
#include<sys/epoll.h>
#define FDSIZE 1000
#define EPOLLEVENTS 100#include"../utili.h"
static int socket_bind(const char *ip, int port){
int listenfd = socket(AF_INET, SOCK_STREAM, 0);
struct sockaddr_in addrSer;
addrSer.sin_family = AF_INET;
//addrSer.sin_addr.s_addr = inet_addr(ip);
inet_pton(AF_INET, ip, &addrSer.sin_addr);
addrSer.sin_port = htons(port);
bind(listenfd, (struct sockaddr*)&addrSer, sizeof(struct sockaddr));
return listenfd;
}
static void add_event(int epollfd, int fd, int state){
struct epoll_event ev;
ev.events = state;
ev.data.fd = fd;
epoll_ctl(epollfd, EPOLL_CTL_ADD, fd, &ev);
}
static void delete_event(int epollfd, int fd, int state){
struct epoll_event ev;
ev.events = state;
ev.data.fd = fd;
epoll_ctl(epollfd, EPOLL_CTL_DEL, fd, &ev);
}
static void modify_event(int epollfd, int fd, int state){
struct epoll_event ev;
ev.events = state;
ev.data.fd = fd;
epoll_ctl(epollfd, EPOLL_CTL_MOD, fd, &ev);
}
static void handle_accept(int epollfd, int listenfd){
int clifd;
struct sockaddr_in addrCli;
socklen_t len = sizeof(struct sockaddr);
clifd = accept(listenfd, (struct sockaddr*)&addrCli, &len);
if(clifd != -1){
add_event(epollfd, clifd, EPOLLIN);
}
}
static void do_read(int epollfd, int fd, char *buf){
int nread = read(fd, buf, BUFFER_SIZE);
if(nread == -1){
close(fd);
delete_event(epollfd, fd, EPOLLIN);
}else{
printf("read msg:>%s\n",buf);
modify_event(epollfd, fd, EPOLLOUT);
}
}
static void do_write(int epollfd, int fd, char *buf){
int nwrite = write(fd, buf, strlen(buf)+1);
if(nwrite == -1){
close(fd);
delete_event(epollfd, fd, EPOLLOUT);
} else{
modify_event(epollfd, fd , EPOLLIN);
}
memset(buf, 0, BUFFER_SIZE);
}
static void handle_events(int epollfd, struct epoll_event *events, int num,
int listenfd, char *buf){
int i;
int fd;
for(i=0; i<num; ++i){
fd = events[i].data.fd;
if((fd==listenfd) && (events[i].events&EPOLLIN)) //根据其结果分别进入三种状态
handle_accept(epollfd, listenfd); //申请与服务器连接
else if(events[i].events & EPOLLIN)
do_read(epollfd, fd, buf); //只读
else if(events[i].events & EPOLLOUT)
do_write(epollfd, fd, buf); //只写
}
}
static void do_epoll(int listenfd){
int ret;
char buffer[BUFFER_SIZE];
struct epoll_event events[EPOLLEVENTS];
int epollfd = epoll_create(FDSIZE);
add_event(epollfd, listenfd, EPOLLIN);
for(;;){
//select poll
ret = epoll_wait(epollfd, events, EPOLLEVENTS, -1);
handle_events(epollfd, events, ret, listenfd, buffer);
}
close(epollfd);
}
int main(void){
int listenfd;
listenfd = socket_bind(SERVER_IP, SERVER_PORT);
listen(listenfd, LISTEN_QUEUE);
do_epoll(listenfd);
return 0;
}#include"../utili.h"
static void add_event(int epollfd, int fd, int state){
struct epoll_event ev;
ev.events = state;
ev.data.fd = fd;
epoll_ctl(epollfd, EPOLL_CTL_ADD, fd, &ev);
}
static void delete_event(int epollfd, int fd, int state){
struct epoll_event ev;
ev.events = state;
ev.data.fd = fd;
epoll_ctl(epollfd, EPOLL_CTL_DEL, fd, &ev);
}
static void modify_event(int epollfd, int fd, int state){
struct epoll_event ev;
ev.events = state;
ev.data.fd = fd;
epoll_ctl(epollfd, EPOLL_CTL_MOD, fd, &ev);
}
static void do_read(int epollfd, int fd, int sockfd, char *buf){
int nread = read(fd, buf, BUFFER_SIZE);
if(nread == -1) {
close(fd);
delete_event(epollfd, fd, EPOLLIN);
}else{
if(fd == STDIN_FILENO)
add_event(epollfd, fd, EPOLLIN);
else{
delete_event(epollfd, fd, EPOLLIN);
add_event(epollfd, STDOUT_FILENO, EPOLLOUT);
}
}
printf("Ser :>%s", buf);
}
static void do_write(int epollfd, int fd, int sockfd, char *buf){
int nwrite = write(fd, buf, strlen(buf)+1);
if(nwrite == -1){
perror("write");
close(fd);
}else{
if(fd == STDOUT_FILENO){
delete_event(epollfd, fd, EPOLLOUT);
}else{
modify_event(epollfd, fd, EPOLLIN);
}
}
memset(buf, 0, BUFFER_SIZE);
}
static void handle_events(int epollfd, struct epoll_event *events, int num,
int sockfd, char *buf){
int i;
int fd;
for(i=0; i<num; ++i){
fd = events[i].data.fd;
if(events[i].events & EPOLLIN)
do_read(epollfd, fd, sockfd, buf);
else if(events[i].events, fd, sockfd, buf)
do_write(epollfd, fd, sockfd, buf);
}
}
static void handle_connection(int sockfd){
struct epoll_event events[EPOLLEVENTS];
int epollfd = epoll_create(FDSIZE);
add_event(epollfd, STDIN_FILENO, EPOLLIN);
int ret;
char buffer[BUFFER_SIZE];
for(;;){
ret = epoll_wait(epollfd, events, EPOLLEVENTS, -1);
handle_events(epollfd, events, ret, sockfd, buffer);
}
close(epollfd);
}
int main(void){
int sockfd = socket(AF_INET, SOCK_STREAM, 0);
struct sockaddr_in addrSer;
addrSer.sin_family = AF_INET;
addrSer.sin_port = htons(SERVER_PORT);
addrSer.sin_addr.s_addr = inet_addr(SERVER_IP);
connect(sockfd, (struct sockaddr*)&addrSer, sizeof(struct sockaddr));
handle_connection(sockfd);
close(sockfd);
return 0;
}服务器端就是等待客户端的使用；
客户端1
客户端2
利用epoll()函数，不用轮询每个套接字，效率更高效一些；