简约而不简单epoll之EPOLLRDHUP

上一篇主要介绍EPOLLOUT，本篇介绍EPOLLRDHUP。在内核2.6.17（不含）以前版本，要想知道对端是否关闭socket，上层应用只能通过调用recv来进行判断，在2.6.17以后，这种场景上层只需要判断EPOLLRDHUP即可，无需在调用recv这个系统调用。

一、未使用EPOLLRDHUP

服务端代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <sys/epoll.h>


#define SERVPORT 9527
#define MAXBUF 1024*1024  //1MB
#define MAXFDS 5000
#define EVENTSIZE 100

int setnonblocking(int fd)
{
    int opts;
    if( (opts = fcntl(fd, F_GETFL, 0)) == -1)
    {
        perror("fcntl");
        return -1;
    }

    opts = opts | O_NONBLOCK;
    if( (opts = fcntl(fd, F_SETFL, opts)) == -1)
    {
        perror("fcntl");
        return -1;
    }

    return 0;
}

int main(void) {
    int len = 0, n = 0, once = 0;
    int  hasSend;
    char buf[MAXBUF] = {0};
    char sndMsg[MAXBUF] = {1};

    struct sockaddr_in servaddr;
    int sockfd, listenfd, epollfd, nfds;

    struct epoll_event ev;
    struct epoll_event events[EVENTSIZE];

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port = htons(SERVPORT);

    if( (epollfd = epoll_create(MAXFDS)) == -1) {
        perror("epoll");
        exit(1);
    }

    if( (listenfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
        perror("socket");
        exit(1);
    }

    if(setnonblocking(listenfd) == -1) {
        perror("setnonblocking");
        exit(1);
    }

    if(bind(listenfd, (struct sockaddr *)&servaddr, sizeof(servaddr)) == -1) {
        perror("bind");
        exit(1);
    }

    if(listen(listenfd, 10) == -1) {
        perror("listen");
        exit(1);
    }


    ev.events = EPOLLIN | EPOLLET;
    ev.data.fd = listenfd;
    if(epoll_ctl(epollfd, EPOLL_CTL_ADD, listenfd, &ev) == -1) {
        perror("epoll_ctl");
        exit(1);
    }

    for( ; ; ) {
        if( (nfds = epoll_wait(epollfd, events, EVENTSIZE, -1)) == -1) {
            perror("epoll_wait");
            exit(1);
        }

        for(n = 0; n < nfds; n++) {
            if(events[n].data.fd == listenfd) {
                while( (sockfd = accept(listenfd, (struct sockaddr *)NULL, NULL)) > 0) {
                    if(setnonblocking(sockfd) == -1) {
                        perror("setnonblocking");
                        exit(1);
                    }
                    ev.events = EPOLLIN | EPOLLOUT | EPOLLET;
                    ev.data.fd = sockfd;
                    if(epoll_ctl(epollfd, EPOLL_CTL_ADD, sockfd, &ev) == -1)
                    {
                        perror("epoll_ctl");
                        exit(1);
                    } else {
                        printf("new socketfd = %d register epoll success\n", sockfd);
                    }
                }
                continue;
            }
            printf("Events: 0x%x\n", events[n].events);
            if (events[n].events & EPOLLIN && events[n].events & EPOLLOUT) {
                printf(">> EPOLLIN And EPOLLOUTï¼Œ socketfd = %d\n", events[n].data.fd);
                len = recv(events[n].data.fd, buf, 1024, 0);
                if (len == 0) {
                    printf("Peer is closed, then we must close socket....\n");
                    close(events[n].data.fd);
                } else if (len == -1) {
                  printf("len = -1, errno=%d\n", len);
                  exit(-1);
                } else {
                  printf("len = %d\n", len);
                }
            }
            else if (events[n].events & EPOLLIN) {
                printf(">> Only EPOLLIN socketfd = %d\n", events[n].data.fd);
                len = recv(events[n].data.fd, buf, 1024, 0);
                if (len == 0) {
                    printf("Peer is closed, then we must close socket....\n");
                    close(events[n].data.fd);
                } else if (len == -1) {
                  printf("len = -1, errno=%d\n", len);
                } else {
                  printf("len = %d\n", len);
                }
            }
            else if (events[n].events & EPOLLOUT) {
                printf(">> Only EPOLLOUTï¼Œ socketfd = %d\n", events[n].data.fd);
            }
        }
    }
}

客户端代码：


#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <sys/epoll.h>


#define SERVPORT 9527
#define MAXBUF 1024*1024  //1MB
#define MAXFDS 5000
#define EVENTSIZE 100

int setnonblocking(int fd)
{
    int opts;
    if( (opts = fcntl(fd, F_GETFL, 0)) == -1)
    {
        perror("fcntl");
        return -1;
    }

    opts = opts | O_NONBLOCK;
    if( (opts = fcntl(fd, F_SETFL, opts)) == -1)
    {
        perror("fcntl");
        return -1;
    }

    return 0;
}

int main(void) {
    int len = 0, n = 0, once = 0;
    int  hasSend;
    char buf[MAXBUF] = {0};
    char sndMsg[MAXBUF] = {1};

    struct sockaddr_in servaddr;
    int sockfd, listenfd, epollfd, nfds;

    struct epoll_event ev;
    struct epoll_event events[EVENTSIZE];

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port = htons(SERVPORT);

    if( (epollfd = epoll_create(MAXFDS)) == -1) {
        perror("epoll");
        exit(1);
    }

    if( (listenfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
        perror("socket");
        exit(1);
    }

    if(setnonblocking(listenfd) == -1) {
        perror("setnonblocking");
        exit(1);
    }

    if(bind(listenfd, (struct sockaddr *)&servaddr, sizeof(servaddr)) == -1) {
        perror("bind");
        exit(1);
    }

    if(listen(listenfd, 10) == -1) {
        perror("listen");
        exit(1);
    }


    ev.events = EPOLLIN | EPOLLET;
    ev.data.fd = listenfd;
    if(epoll_ctl(epollfd, EPOLL_CTL_ADD, listenfd, &ev) == -1) {
        perror("epoll_ctl");
        exit(1);
    }

    for( ; ; ) {
        if( (nfds = epoll_wait(epollfd, events, EVENTSIZE, -1)) == -1) {
            perror("epoll_wait");
            exit(1);
        }

        for(n = 0; n < nfds; n++) {
            if(events[n].data.fd == listenfd) {
                while( (sockfd = accept(listenfd, (struct sockaddr *)NULL, NULL)) > 0) {
                    if(setnonblocking(sockfd) == -1) {
                        perror("setnonblocking");
                        exit(1);
                    }
                    ev.events = EPOLLIN | EPOLLET;//只注册EPOLLIN
                    ev.data.fd = sockfd;
                    if(epoll_ctl(epollfd, EPOLL_CTL_ADD, sockfd, &ev) == -1)
                    {
                        perror("epoll_ctl");
                        exit(1);
                    } else {
                        printf("new socketfd = %d register epoll success\n", sockfd);
                    }
                }
                continue;
            }
            printf("Events: 0x%x\n", events[n].events);
            if (events[n].events & EPOLLIN) {
                printf(">>Only EPOLLIN socketfd = %d\n", events[n].data.fd);
                len = recv(events[n].data.fd, buf, 1024, 0);
                if (len == 0) {//因为发生了EPOLLIN事件，所以调用recv函数，但是却返回是0，所以可以认为是对端关闭了socket
                    printf("Peer is closed, then we must close socket....\n");
                    close(events[n].data.fd);
                } else if (len == -1) {
                  printf("len = -1, errno=%d\n", len);
                  exit(-1);
                } else {
                  printf("len = %d, data = %s\n", len, buf);
                }
            }
            if (events[n].events & EPOLLOUT) {
                printf(">> Only EPOLLOUT socketfd = %d\n", events[n].data.fd);
            }
        }
    }
}

输出数据：

结论：

服务端需要通过调用recv函数且返回为0进行判断，当返回值为0说明对端已经关闭了socket，此时我们直接调用close关闭本端的socket即可。

二、使用EPOLLRDHUP

2.1、client直接close

服务端代码：


#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <sys/epoll.h>


#define SERVPORT 9527
#define MAXBUF 1024*1024  //1MB
#define MAXFDS 5000
#define EVENTSIZE 100

int setnonblocking(int fd)
{
    int opts;
    if( (opts = fcntl(fd, F_GETFL, 0)) == -1)
    {
        perror("fcntl");
        return -1;
    }

    opts = opts | O_NONBLOCK;
    if( (opts = fcntl(fd, F_SETFL, opts)) == -1)
    {
        perror("fcntl");
        return -1;
    }

    return 0;
}

int main(void) {
    int len = 0, n = 0, once = 0;
    int  hasSend;
    char buf[MAXBUF] = {0};
    char sndMsg[MAXBUF] = {1};

    struct sockaddr_in servaddr;
    int sockfd, listenfd, epollfd, nfds;

    struct epoll_event ev;
    struct epoll_event events[EVENTSIZE];

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port = htons(SERVPORT);

    if( (epollfd = epoll_create(MAXFDS)) == -1) {
        perror("epoll");
        exit(1);
    }

    if( (listenfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
        perror("socket");
        exit(1);
    }

    if(setnonblocking(listenfd) == -1) {
        perror("setnonblocking");
        exit(1);
    }

    if(bind(listenfd, (struct sockaddr *)&servaddr, sizeof(servaddr)) == -1) {
        perror("bind");
        exit(1);
    }

    if(listen(listenfd, 10) == -1) {
        perror("listen");
        exit(1);
    }


    ev.events = EPOLLIN | EPOLLET;
    ev.data.fd = listenfd;
    if(epoll_ctl(epollfd, EPOLL_CTL_ADD, listenfd, &ev) == -1) {
        perror("epoll_ctl");
        exit(1);
    }

    for( ; ; ) {
        if( (nfds = epoll_wait(epollfd, events, EVENTSIZE, -1)) == -1) {
            perror("epoll_wait");
            exit(1);
        }

        for(n = 0; n < nfds; n++) {
            if(events[n].data.fd == listenfd) {
                while( (sockfd = accept(listenfd, (struct sockaddr *)NULL, NULL)) > 0) {
                    if(setnonblocking(sockfd) == -1) {
                        perror("setnonblocking");
                        exit(1);
                    }
                    // 注册EPOLLRDHUP
                    ev.events = EPOLLIN | EPOLLRDHUP | EPOLLET;
                    ev.data.fd = sockfd;
                    if(epoll_ctl(epollfd, EPOLL_CTL_ADD, sockfd, &ev) == -1)
                    {
                        perror("epoll_ctl");
                        exit(1);
                    } else {
                        printf("new socketfd = %d register epoll success\n", sockfd);
                    }
                }
                continue;
            }
            printf("Events: 0x%x\n", events[n].events);
            if (events[n].events & EPOLLIN) {
                if (events[n].events & EPOLLRDHUP) {
                    printf("Peer close socket, close socket now....\n");
                    close(events[n].data.fd);
                    continue;
                }
                //正常读
                len = recv(events[n].data.fd, buf, 1024, 0);
                if (len == 0) {
                    printf("Peer is closed, then we must close socket....\n");
                    close(events[n].data.fd);
                } else if (len == -1) {
                  printf("len = -1, errno=%d\n", len);
                  exit(-1);
                } else {
                  printf("len = %d, data = %s\n", len, buf);
                }
            }
            if (events[n].events & EPOLLOUT) {
                printf(">> Only EPOLLOUT， socketfd = %d\n", events[n].data.fd);
            }
        }
    }
}

客户端代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <sys/epoll.h>

#define SERVPORT 9527
#define MAXBUF 4096

int setnonblocking(int fd)
{
    int opts;
    if( (opts = fcntl(fd, F_GETFL, 0)) == -1)
    {
        perror("fcntl");
        return -1;
    }

    opts = opts | O_NONBLOCK;
    if( (opts = fcntl(fd, F_SETFL, opts)) == -1)
    {
        perror("fcntl");
        return -1;
    }

    return 0;
}

int main(void)
{
    char buf[MAXBUF];
    struct sockaddr_in servaddr;
    int fd;
    int n, len;

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
    servaddr.sin_port = htons(SERVPORT);

    if ((fd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
    {
        perror("socket");
        exit(1);
    }

    if (connect(fd, (struct sockaddr *)&servaddr, sizeof(servaddr)) == -1)
    {
        perror("connect");
        exit(1);
    }
    setnonblocking(fd); //设置成非阻塞
    printf("Connection ok, send data after sleep 10s\n");
    sleep(10); //睡眠10秒
    send(fd, "hello world", sizeof("hello world") - 1, 0);
    printf("Send ok, client will be closed after sleep 10s\n");
    sleep(10); //睡眠10秒
    printf("close\n");
    close(fd);
    return 0;
}

输出数据：

结论：

1）客户端直接调用close，会触犯EPOLLRDHUP事件

2）通过EPOLLRDHUP属性，来判断是否对端已经关闭，这样可以减少一次系统调用。在2.6.17的内核版本之前，只能再通过调用一次recv函数来判断

2.2、tcp的半关闭shutdown

我们通过shutdown系统调用，来实现tcp的半关闭，通过man shutdown可知，函数支持的参数SHUT_RD、SHUT_WR、SHUT_RDWR。例如：

shutdown(s, SHUT_RD)：client关闭本端读，实际上是通知server不要在发送数据给我了（client），但是client仍然可以发送数据给server，server接收到该消息后会将server自己的发送缓冲区数据直接丢弃。

shutdown(s, SHUT_WR)：client关闭本端写，实际上是通知对方server以后不会有新数据来了，但是对方server仍然可以发送数据给client，如果server在epoll事件模型中注册了EPOLLRDHUP，那么epoll_wait会返回EPOLLRDHUP。

close函数等价于shutdown(s, SHUT_RDWR)， close属于优雅关闭，shutdown(s, SHUT_RDWR)属于暴力关闭。

2.2.1、shutdown(s, SHUT_RD)场景

服务端代码：


#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <sys/epoll.h>


#define SERVPORT 9527
#define MAXBUF 1024*1024  //1MB
#define MAXFDS 5000
#define EVENTSIZE 100

int setnonblocking(int fd)
{
    int opts;
    if( (opts = fcntl(fd, F_GETFL, 0)) == -1)
    {
        perror("fcntl");
        return -1;
    }

    opts = opts | O_NONBLOCK;
    if( (opts = fcntl(fd, F_SETFL, opts)) == -1)
    {
        perror("fcntl");
        return -1;
    }

    return 0;
}

int main(void) {
    int len = 0, n = 0, once = 0;
    int  hasSend;
    char buf[MAXBUF] = {0};
    char sndMsg[MAXBUF] = {1};

    struct sockaddr_in servaddr;
    int sockfd, listenfd, epollfd, nfds;

    struct epoll_event ev;
    struct epoll_event events[EVENTSIZE];

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port = htons(SERVPORT);

    if( (epollfd = epoll_create(MAXFDS)) == -1) {
        perror("epoll");
        exit(1);
    }

    if( (listenfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
        perror("socket");
        exit(1);
    }

    if(setnonblocking(listenfd) == -1) {
        perror("setnonblocking");
        exit(1);
    }

    if(bind(listenfd, (struct sockaddr *)&servaddr, sizeof(servaddr)) == -1) {
        perror("bind");
        exit(1);
    }

    if(listen(listenfd, 10) == -1) {
        perror("listen");
        exit(1);
    }


    ev.events = EPOLLIN | EPOLLET;
    ev.data.fd = listenfd;
    if(epoll_ctl(epollfd, EPOLL_CTL_ADD, listenfd, &ev) == -1) {
        perror("epoll_ctl");
        exit(1);
    }

    for( ; ; ) {
        if( (nfds = epoll_wait(epollfd, events, EVENTSIZE, -1)) == -1) {
            perror("epoll_wait");
            exit(1);
        }

        for(n = 0; n < nfds; n++) {
            if(events[n].data.fd == listenfd) {
                while( (sockfd = accept(listenfd, (struct sockaddr *)NULL, NULL)) > 0) {
                    if(setnonblocking(sockfd) == -1) {
                        perror("setnonblocking");
                        exit(1);
                    }
                    // 注册EPOLLRDHUP
                    ev.events = EPOLLIN | EPOLLRDHUP | EPOLLOUT | EPOLLET;
                    ev.data.fd = sockfd;
                    int nSendBuf = 4096; //上层应用设置成4096 但是底层内核实际是4096*2 = 8192
                    socklen_t opt_len = sizeof(int);
                    int ret = setsockopt(sockfd, SOL_SOCKET, SO_SNDBUF, &nSendBuf, sizeof(int));
                    if (ret == -1) {
                        perror("setsockopt");
                    }
                    if(epoll_ctl(epollfd, EPOLL_CTL_ADD, sockfd, &ev) == -1)
                    {
                        perror("epoll_ctl");
                        exit(1);
                    } else {
                        printf("new socketfd = %d register epoll success\n", sockfd);
                    }
                }
                continue;
            }
            printf("Events: 0x%x\n", events[n].events);
            if (events[n].events & EPOLLIN) {
                if (events[n].events & EPOLLRDHUP) {
                    printf("Peer close socket, close socket now....\n");
                    close(events[n].data.fd);
                    continue;
                }
                //正常读
                len = recv(events[n].data.fd, buf, 1024, 0);
                if (len == 0) {
                    printf("Peer is closed, then we must close socket....\n");
                    close(events[n].data.fd);
                } else if (len == -1) {
                  printf("len = -1, errno=%d\n", len);
                  exit(-1);
                } else {
                  printf("len = %d, data = %s\n", len, buf);
                }
            }
            if (events[n].events & EPOLLOUT) {
                printf(">> EPOLLOUT， socketfd = %d\n", events[n].data.fd);
                if (once) {
                    printf("SndBuf can be written, but peer has SHUTDOWN RD\n");
                }
                while (!once) {
                    len = send(events[n].data.fd, sndMsg + hasSend, MAXBUF-hasSend, 0);
                    if (len > 0) {// 说明发送成功
                        hasSend += len;
                        once = 0;
                        printf("Send ok， length = %d.\n", len);
                    } else if (len == -1) {
                        if (errno == EAGAIN) {//说明发送缓冲区已经满
                            printf(" EPOLLOUT ==》 Socket SndBuf is fulled. \n");
                            once = 1;
                            break;
                        }
                    } else {//出现错误
                        perror(" EPOLLOUT ==》 Send failed.\n");
                        exit(-1);
                    }
                }
            }
        }
    }
}

客户端代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <sys/epoll.h>

#define SERVPORT 9527
#define MAXBUF 4096

int main(void)
{
    char buf[MAXBUF];
    struct sockaddr_in servaddr;
    int fd;
    int n, len;

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
    servaddr.sin_port = htons(SERVPORT);

    if ((fd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
    {
        perror("socket");
        exit(1);
    }
    int nSendBuf = 3072;
    socklen_t opt_len = sizeof(int);
    int ret = setsockopt(fd, SOL_SOCKET, SO_RCVBUF, &nSendBuf, sizeof(int));
    if (ret == -1) {
        perror("setsockopt");
    }
    if (connect(fd, (struct sockaddr *)&servaddr, sizeof(servaddr)) == -1)
    {
        perror("connect");
        exit(1);
    }

    printf("Connection ok, socket will be shutdown after sleep 30s\n");
    sleep(30); //睡眠10秒保证
    printf("shutdown read\n");
    shutdown(fd, SHUT_RD);
    sleep(10);

    send(fd, "I close RD, But i can write.", sizeof("I close RD, But i can write.") - 1, 0);
    printf("close\n");
    close(fd);
    return 0;
}

输出数据：

备注：通常直接调用close不会出发EPOLLERR和EPOLLMSG，猜测是因为client调用shutdown导致的。

2.2.2、shutdown(s, SHUT_WR)

服务端代码：


#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <sys/epoll.h>


#define SERVPORT 9527
#define MAXBUF 1024*1024  //1MB
#define MAXFDS 5000
#define EVENTSIZE 100

int setnonblocking(int fd)
{
    int opts;
    if( (opts = fcntl(fd, F_GETFL, 0)) == -1)
    {
        perror("fcntl");
        return -1;
    }

    opts = opts | O_NONBLOCK;
    if( (opts = fcntl(fd, F_SETFL, opts)) == -1)
    {
        perror("fcntl");
        return -1;
    }

    return 0;
}

int main(void) {
    int len = 0, n = 0, once = 0;
    int  hasSend;
    char buf[MAXBUF] = {0};
    char sndMsg[MAXBUF] = {1};

    struct sockaddr_in servaddr;
    int sockfd, listenfd, epollfd, nfds;

    struct epoll_event ev;
    struct epoll_event events[EVENTSIZE];

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port = htons(SERVPORT);

    if( (epollfd = epoll_create(MAXFDS)) == -1) {
        perror("epoll");
        exit(1);
    }

    if( (listenfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
        perror("socket");
        exit(1);
    }

    if(setnonblocking(listenfd) == -1) {
        perror("setnonblocking");
        exit(1);
    }

    if(bind(listenfd, (struct sockaddr *)&servaddr, sizeof(servaddr)) == -1) {
        perror("bind");
        exit(1);
    }

    if(listen(listenfd, 10) == -1) {
        perror("listen");
        exit(1);
    }


    ev.events = EPOLLIN | EPOLLET;
    ev.data.fd = listenfd;
    if(epoll_ctl(epollfd, EPOLL_CTL_ADD, listenfd, &ev) == -1) {
        perror("epoll_ctl");
        exit(1);
    }

    for( ; ; ) {
        if( (nfds = epoll_wait(epollfd, events, EVENTSIZE, -1)) == -1) {
            perror("epoll_wait");
            exit(1);
        }

        for(n = 0; n < nfds; n++) {
            if(events[n].data.fd == listenfd) {
                while( (sockfd = accept(listenfd, (struct sockaddr *)NULL, NULL)) > 0) {
                    if(setnonblocking(sockfd) == -1) {
                        perror("setnonblocking");
                        exit(1);
                    }
                    // 注册EPOLLRDHUP
                    ev.events = EPOLLIN | EPOLLRDHUP | EPOLLOUT | EPOLLET;
                    ev.data.fd = sockfd;
                    if(epoll_ctl(epollfd, EPOLL_CTL_ADD, sockfd, &ev) == -1)
                    {
                        perror("epoll_ctl");
                        exit(1);
                    } else {
                        printf("new socketfd = %d register epoll success\n", sockfd);
                    }
                }
                continue;
            }
            printf("Events: 0x%x\n", events[n].events);
            if (events[n].events & EPOLLIN) {
                if (events[n].events & EPOLLRDHUP) {
                    if (!once) {
                        printf("Peer shutdown WRITE, close socket now....\n");
                        send(events[n].data.fd, "Hello client, you are shutdown-write",
                             sizeof("Hello client, you are shutdown-write") - 1, 0);
                        once = 1;
                    } else {
                        printf("Peer shutdown WRITE, close socket now....\n");
                        close(events[n].data.fd);
                    }
                    continue;
                }
            }
            if (events[n].events & EPOLLOUT) {
                printf(">>First EPOLLOUT， socketfd = %d\n", events[n].data.fd);
            }
        }
    }
}

客户端代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <sys/epoll.h>

#define SERVPORT 9527
#define MAXBUF 4096

int main(void)
{
    char buf[MAXBUF];
    struct sockaddr_in servaddr;
    int fd;
    int n, len;

    bzero(&servaddr, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
    servaddr.sin_port = htons(SERVPORT);

    if ((fd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
    {
        perror("socket");
        exit(1);
    }

    if (connect(fd, (struct sockaddr *)&servaddr, sizeof(servaddr)) == -1)
    {
        perror("connect");
        exit(1);
    }

    printf("Connection ok, socket will be shutdown after sleep 10s\n");
    sleep(10); //睡眠10秒保证
    printf("shutdown write\n");
    shutdown(fd, SHUT_WR);
    recv(fd, buf, MAXBUF, 0);
    printf("recv:%s\n", buf);
    sleep(30);
    printf("close\n");
    close(fd);
    return 0;
}

输出数据：

总结：当客户端调用shutdown write，服务端由于注册是EPOLLRDHUP，所以可以认为客户端数据已经发送完不会再有新的数据到来，但是为了保证本端（服务端）的数据能够发出，所有还是需要尝试发送（毕竟客户端没有关闭READ）。但是当客户端调用close方法后，服务端不会出发任何事件，这一点也需要考虑当中。可以参考Nginx实现方式，通过一个pending_eof变量来控制，尽最大可能将数据发送出去。

三、总结

本篇把EPOLLRDHUP相关场景通过代码形式进行总结，希望起到抛砖引玉的作用。

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https://yachay.unat.edu.pe/blog/index.php?comment_area=format_blog&comment_component=blog&comment_co

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