select & pselect
#include <sys/select.h>
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>
void FD_CLR(int fd, fd_set *set);
int FD_ISSET(int fd, fd_set *set);
void FD_SET(int fd, fd_set *set);
void FD_ZERO(fd_set *set);
int select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);
监控fd状态（timeout 是到期前剩余时间）
int pselect(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, const struct timespec *timeout, const sigset_t *sigmask);
除了监测fd状态，pselect精度更准，且监测signal(另外pselect的timeout参数是const的)
monitor multiple file descriptors, waiting until one or more of the file descriptors become “ready” for some class of I/O operation
poll & ppoll
#include <poll.h>
int poll(struct pollfd *fds, nfds_t nfds, int timeout);
fds: 监听事件的item数组
nfds: 数组成员数
timeout: 超时时间(unit:milliseconds, -1 mean infinite, 0 mean immediately)
return: success: > 0 带有revents事件的数组个数; = 0 time out 或者没有fd 事件
error: -1, errno is set
int ppoll(struct pollfd *fds, nfds_t nfds, const struct timespec *timeout_ts, const sigset_t *sigmask);
fds: 监听事件的item数组
nfds: 数组成员数
timeout_ts: 超时时间(unit:seconds+nanoseconds, -1:indefinitely, 0:immediately)
sigmask: 监测的signal (遇到这些signal，ppoll也会返回) (NULL:indefinitely)
return: success: > 0 带有revents事件的数组个数; = 0 time out 或者没有fd 事件
error: -1, errno is set
performs a similar task to select(2): it waits for one of a set of file descriptors to become ready to perform I/O.
结构体
struct pollfd {
int fd; /* in, file descriptor */
short events; /* in, requested events 请求需要监测的事件类型 */
short revents; /* out, returned events 发生的事件类型 */
};
The bits that may be set/returned in events and revents are defined in <poll.h>:
POLLIN 可读
POLLPRI 紧急数据可读
POLLOUT 可读(不会block)
POLLRDHUP 对端关闭, 本段hangup, 只针对stream socket fd
POLLERR 错误状态 (output only，即只会出现在revents中)
POLLHUP Hang up (output only，即只会出现在revents中)
POLLNVAL 无效请求 (output only，即只会出现在revents中)
epoll
The epoll API performs a similar task to poll(2): monitoring multiple file descriptors to see if I/O is possible on any of them.
The epoll API can be used either as an edge-triggered or a level-triggered interface and scales well to large numbers of watched file descriptors.
模式 and
LT(Level-triggered) 一般
ET(edge-triggered) 事件发生时就触发
epoll_create
creates an epoll instance and returns a file descriptor referring to that instance, The more recent epoll_create1 extends the functionality.
#include <sys/epoll.h>
int epoll_create(int size);
int epoll_create1(int flags);
epoll_ctl
register particular file descriptors interested.
#include <sys/epoll.h>
int epoll_ctl(int epfd, int op, int fd, struct epoll_event *event);
epfd: return by epoll_create
op:
EPOLL_CTL_ADD Register the target file descriptor fd on the epoll instance
EPOLL_CTL_MOD Change the event event associated with the target file descriptor fd.
EPOLL_CTL_DEL Remove (deregister) the target file descriptor fd from the epoll
fd: 需要监听的描述符fd
event：需要监听的指定fd上的事件
typedef union epoll_data {
void *ptr;
int fd;
uint32_t u32;
uint64_t u64;
} epoll_data_t;
struct epoll_event {
uint32_t events; // EPOLLIN EPOLLOUT EPOLLRDHUP EPOLLPRI EPOLLERR
EPOLLHUP EPOLLET EPOLLONESHOT
epoll_data_t data; // User data variable
};
return:
success 0
error -1 errno
epoll_wait
waits for I/O events, blocking the calling thread if no events are currently available.
#include <sys/epoll.h>
int epoll_wait(int epfd, struct epoll_event *events, int maxevents, int timeout);
int epoll_pwait(int epfd, struct epoll_event *events, int maxevents, int timeout, const sigset_t *sigmask);
epfd: return by epoll_create
events：out, 监听到的事件数组
maxevents: in, 需要监听到事件个数，>0
timeout: time out值， (-1 mean infinite, 0 mean immediately)
sigmask: 监测的signal
return: the number of file descriptors ready for the requested I/O.
附（epoll 使用示例）
功能: 使用epoll 实现tcp server
#include <iostream>
#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>
using namespace std;
#define MAXLINE 5
#define OPEN_MAX 100
#define LISTENQ 20
#define SERV_PORT 5000
#define INFTIM 1000
void setnonblocking(int sock)
{
int opts;
opts=fcntl(sock,F_GETFL);
if(opts<0)
{
perror("fcntl(sock,GETFL)");
exit(1);
}
opts = opts|O_NONBLOCK;
if(fcntl(sock,F_SETFL,opts)<0)
{
perror("fcntl(sock,SETFL,opts)");
exit(1);
}
}
int main(int argc, char* argv[])
{
int i, maxi, listenfd, connfd, sockfd, epfd, nfds, portnumber;
ssize_t n;
char line[MAXLINE];
socklen_t clilen;
if (2 == argc ) {
if( (portnumber = atoi(argv[1])) < 0 ) {
fprintf(stderr,"Usage:%s portnumber/a/n", argv[0]);
return 1;
}
}
else {
fprintf(stderr,"Usage:%s portnumber/a/n",argv[0]);
return 1;
}
//声明epoll_event结构体的变量,ev用于注册事件,数组用于回传要处理的事件
struct epoll_event ev, events[20];
epfd = epoll_create(256); //生成用于处理accept的epoll专用的文件描述符
if (epollfd == -1) {
perror("epoll_create");
exit(EXIT_FAILURE);
}
// set up server listen socket
listenfd = socket(AF_INET, SOCK_STREAM, 0);
//setnonblocking(listenfd); //把socket设置为非阻塞方式
ev.events=EPOLLIN | EPOLLET; //设置要处理的事件类型及事件触发模式
ev.data.fd=listenfd; //设置与要处理的事件相关的文件描述符
//注册epoll事件
if (epoll_ctl(epfd, EPOLL_CTL_ADD, listenfd, &ev) == -1) {
perror("epoll_ctl: listen_sock");
exit(EXIT_FAILURE);
}
// bind server listen socket
struct sockaddr_in serveraddr;
bzero(&serveraddr, sizeof(serveraddr));
serveraddr.sin_family = AF_INET;
char *local_addr="127.0.0.1";
inet_aton(local_addr, &(serveraddr.sin_addr));
serveraddr.sin_port = htons(portnumber);
bind(listenfd, (sockaddr *)&serveraddr, sizeof(serveraddr));
listen(listenfd, LISTENQ);
maxi = 0;
struct sockaddr_in clientaddr;
for ( ; ; ) {
nfds = epoll_wait(epfd,events,20,500); //等待epoll事件的发生
//处理所发生的所有事件
for(i=0; i<nfds; ++i)
{
if(events[i].data.fd==listenfd)//如果新监测到一个SOCKET用户连接到了绑定的SOCKET端口，建立新的连接。
{
connfd = accept(listenfd,(sockaddr *)&clientaddr, &clilen);
if(connfd<0){
perror("connfd<0");
exit(1);
}
//setnonblocking(connfd);
char *str = inet_ntoa(clientaddr.sin_addr);
cout << "accapt a connection from " << str << endl;
//设置用于读操作的文件描述符
ev.data.fd=connfd;
//设置用于注测的读操作事件
ev.events=EPOLLIN|EPOLLET;
//ev.events=EPOLLIN;
//注册ev
epoll_ctl(epfd,EPOLL_CTL_ADD,connfd,&ev);
}
else if(events[i].events&EPOLLIN)//如果是已经连接的用户，并且收到数据，那么进行读入。
{
cout << "EPOLLIN" << endl;
if ( (sockfd = events[i].data.fd) < 0)
continue;
if ( (n = read(sockfd, line, MAXLINE)) < 0) {
if (errno == ECONNRESET) {
close(sockfd);
events[i].data.fd = -1;
} else
std::cout<<"readline error"<<std::endl;
} else if (n == 0) {
close(sockfd);
events[i].data.fd = -1;
}
line[n] = '/0';
cout << "read " << line << endl;
//设置用于写操作的文件描述符
ev.data.fd=sockfd;
//设置用于注测的写操作事件
ev.events=EPOLLOUT|EPOLLET;
//修改sockfd上要处理的事件为EPOLLOUT
//epoll_ctl(epfd,EPOLL_CTL_MOD,sockfd,&ev);
}
else if(events[i].events&EPOLLOUT) // 如果有数据发送
{
sockfd = events[i].data.fd;
write(sockfd, line, n);
//设置用于读操作的文件描述符
ev.data.fd=sockfd;
//设置用于注测的读操作事件
ev.events=EPOLLIN|EPOLLET;
//修改sockfd上要处理的事件为EPOLIN
epoll_ctl(epfd,EPOLL_CTL_MOD,sockfd,&ev);
}
}
}
return 0;
}