为什么在这种情况下read()块？(linux epoll)

在级别触发模式下,我认为包括Ctrl-D在内的每个新输入事件都会导致epoll_wait返回.它工作正常.但是当我输入像aaa这样的东西时,按下Ctrl-D,读取块.当我键入Ctrl-D时,它不会.

你能解释一下会发生什么吗？

我应该在epoll_wait完成并根据fd准备好时读取所有数据吗？

谢谢！

#include <sys/epoll.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>

int main(int argc,const char *argv[]) {
    // create event
    struct epoll_event stdin_ev,events[10];

    // set event
    stdin_ev.events = EPOLLIN;
    stdin_ev.data.fd = STDIN_FILENO;

    // create epoll
    int epfd = epoll_create(1),i,rcnt;
    char c;

    // set monitoring STDIN_FILENO 
    epoll_ctl(epfd,EPOLL_CTL_ADD,STDIN_FILENO,&stdin_ev);

    while(1) {
        int ret = epoll_wait(epfd,events,1,1000);

        // timeout or failed
        if(ret == 0) {
            fprintf(stdout,"timeoutn");
            continue;
        } else if (ret < 0) {
            perror("ret<0");
            exit(EXIT_FAILURE);
        }

        // readable
        fprintf(stdout,"%d event(s) happened...n",ret);
        for(i=0; i < ret; i++) {
            if(events[i].data.fd == STDIN_FILENO &&
               events[i].events&EPOLLIN) {
                // read a char
                rcnt = read(STDIN_FILENO,&c,1); 
                // if read 0 char,EOF?
                if(rcnt != 1) {
                    fprintf(stdout,"read %d byten",rcnt);
                    continue;
                }
                // else print ascii
                fprintf(stdout,"ascii code: %dn",c);
            }
        } 
    }
    close(epfd);
    return 0;
}

输入：aaa Ctrl-D,结果：

timeout
aaa // <-- `aaa`+`Ctrl-D`
1 event(s) happened...
ascii code: 97
1 event(s) happened...
ascii code: 97
1 event(s) happened...
ascii code: 97
1 event(s) happened...
^C // <-- read block here,`Ctrl-C` to kill

然后我尝试将STDIN_FILENO设置为非阻塞,我发现虽然read()返回-1,但epoll_wait仍然告诉我有一个可读的事件.但是如果我只输入Ctrl-D,则read()返回0.

#include <sys/epoll.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>

int set_nonblock(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;
}

int main(int argc,rcnt;
    char c;

    // set nonblocking
    if(set_nonblock(STDIN_FILENO) != 0) {
        exit(EXIT_FAILURE);
    };

    // set monitoring STDIN_FILENO 
    epoll_ctl(epfd,ret);
        for(i=0;i < ret;i++) {
            if(events[i].data.fd == STDIN_FILENO &&
               events[i].events&EPOLLIN) {
                // read a char
                rcnt = read(STDIN_FILENO,c);
            }
        } 
    }
    close(epfd);
    return 0;
}

结果：

timeout
1 event(s) happened... // <-- `Ctrl-D`
read 0 byte // <-- read() -> 0
timeout
timeout
aaa // `aaa`+`Ctrl-D`
1 event(s) happened...
ascii code: 97
1 event(s) happened...
ascii code: 97
1 event(s) happened...
ascii code: 97
read -1 byte // `EPOLLIN` still happens.
timeout
^C