根据我的研究，您可以将 epoll 文件描述符添加到 poll、select 或另一个 epoll 中，如果事件可用，它将返回 POLLIN。根据 epoll(7)：
Q3 Is the epoll file descriptor itself poll/epoll/selectable?
A3 Yes. If an epoll file descriptor has events waiting, then it will
indicate as being readable.
这在我的测试中有效。但是，我现在正尝试将 O_ASYNC 应用于我的 epoll fd，以便在事件准备好时引发 SIGIO：
//Epoll setup code - trySc runs perror on the string and exits if the function returns -1
int epollFd = epoll_create1(EPOLL_CLOEXEC);
trySc(epollFd, "epoll_create1");
trySc(fcntl(epollFd, F_SETOWN, getpid()), "fcntl F_SETOWN");
trySc(fcntl(epollFd, F_SETSIG, SIGIO), "fcntl F_SETSIG");
int oldFlags = fcntl(epollFd, F_GETFL, 0);
trySc(oldFlags, "fcntl F_GETFL");
trySc(fcntl(epollFd, F_SETFL, oldFlags | O_ASYNC), "fcntl F_SETFL");
//Set up SIGIO and get a socket fd, you don't need to see this
//All my handler does is exit - it's a definite method of knowing SIGIO was raised
struct epoll_event event = {
.events = EPOLLIN | EPOLLET,
.data.fd = socketFd
};
trySc(epoll_ctl(epollFd, EPOLL_CTL_ADD, socketFd, &event), "epoll_ctl");
//Then connect
while(1){
struct pollfd pfd = {
.fd = epollFd,
.events = POLLIN
};
//This blocks until I write something to the socket. Then it enters an infinite loop.
printf("Returning to main(), poll = %d\n", poll(&pfd, 1, -1));
}
当我这样做时，它不会为 epoll 中的新事件引发 SIGIO。poll 表示 epollFd 中有准备好的事件，但它应该首先引发 SIGIO（它只是检查事件是否在 epollFd 中并退出）。我知道我可以将 O_ASYNC 应用于套接字（我也尝试过），但我希望在我的事件中包含数据。Epoll 让我这样做。
这是我的完整代码：
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/epoll.h>
#include <fcntl.h>
#include <netdb.h>
#include <poll.h>
#include <signal.h>
#include <errno.h>
void handleSIGIO(int, siginfo_t *, void *);
const struct sigaction saSIGIO = {
.sa_sigaction = handleSIGIO,
.sa_flags = SA_SIGINFO
};
const struct addrinfo hints = {
.ai_flags = AI_PASSIVE,
.ai_family = AF_INET,
.ai_socktype = SOCK_STREAM
};
void trySc(int err, const char *msg){
if(err != -1) return;
perror(msg);
exit(errno);
}
int main(){
signal(SIGPIPE, SIG_IGN);
trySc(sigaction(SIGIO, &saSIGIO, NULL), "sigaction");
int epollFd = epoll_create1(EPOLL_CLOEXEC);
trySc(epollFd, "epoll_create1");
trySc(fcntl(epollFd, F_SETOWN, getpid()), "fcntl F_SETOWN");
trySc(fcntl(epollFd, F_SETSIG, SIGIO), "fcntl F_SETSIG");
int oldFlags = fcntl(epollFd, F_GETFL, 0);
trySc(oldFlags, "fcntl F_GETFL");
trySc(fcntl(epollFd, F_SETFL, oldFlags | O_ASYNC), "fcntl F_SETFL");
int socketFd = socket(AF_INET, SOCK_STREAM, 0);
trySc(socketFd, "socket");
struct addrinfo *servinfo;
trySc(getaddrinfo("127.0.0.1", "5000", &hints, &servinfo),
"getaddrinfo");
struct epoll_event event = {
.events = EPOLLIN | EPOLLET,
.data.fd = socketFd
};
trySc(epoll_ctl(epollFd, EPOLL_CTL_ADD, socketFd, &event), "epoll_ctl");
trySc(connect(socketFd, servinfo->ai_addr, servinfo->ai_addrlen),
"connect");
printf("Connected\n");
while(1){
struct pollfd pfd = {
.fd = epollFd,
.events = POLLIN
};
printf("Returning to main(), poll = %d\n", poll(&pfd, 1, -1));
}
}
void handleSIGIO(int sn, siginfo_t *info, void *ctx){
printf("SIGIO called\n");
struct epoll_event event;
if(epoll_wait(info->si_fd, &event, 1, 0) != 1){
printf("Warning: no event available\n");
return;
}
printf("Event raised for fd %d\n", event.data.fd);
exit(0);
}
编辑：根据这个网站，我想做的应该是：
Note that an epoll set descriptor can be used much like a regular file
descriptor. That is, it can be made to generate SIGIO (or another signal)
when input (i.e. events) is available on it; likewise it can be used with
poll() and can even be stored inside another epoll set.