簡約而不簡單epoll之EPOLLRDHUP

上一篇主要介紹EPOLLOUT，本篇介紹EPOLLRDHUP。在內核2.6.17（不含）以前版本，要想知道對端是否關閉socket，上層應用只能通過調用recv來進行判斷，在2.6.17以後，這種場景上層只需要判斷EPOLLRDHUP即可，無需在調用recv這個系統調用。

一、未使用EPOLLRDHUP

服務端代碼：

#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);
            }
        }
    }
}

客戶端代碼：


#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;//只註冊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) {//因爲發生了EPOLLIN事件，所以調用recv函數，但是卻返回是0，所以可以認爲是對端關閉了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);
            }
        }
    }
}

輸出數據：

結論：

服務端需要通過調用recv函數且返回爲0進行判斷，當返回值爲0說明對端已經關閉了socket，此時我們直接調用close關閉本端的socket即可。

二、使用EPOLLRDHUP

2.1、client直接close

服務端代碼：


#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);
                    }
                    // 註冊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;
                }
                //正常讀
                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);
            }
        }
    }
}

客戶端代碼：

#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); //設置成非阻塞
    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;
}

輸出數據：

結論：

1）客戶端直接調用close，會觸犯EPOLLRDHUP事件

2）通過EPOLLRDHUP屬性，來判斷是否對端已經關閉，這樣可以減少一次系統調用。在2.6.17的內核版本之前，只能再通過調用一次recv函數來判斷

2.2、tcp的半關閉shutdown

我們通過shutdown系統調用，來實現tcp的半關閉，通過man shutdown可知，函數支持的參數SHUT_RD、SHUT_WR、SHUT_RDWR。例如：

shutdown(s, SHUT_RD)：client關閉本端讀，實際上是通知server不要在發送數據給我了（client），但是client仍然可以發送數據給server，server接收到該消息後會將server自己的發送緩衝區數據直接丟棄。

shutdown(s, SHUT_WR)：client關閉本端寫，實際上是通知對方server以後不會有新數據來了，但是對方server仍然可以發送數據給client，如果server在epoll事件模型中註冊了EPOLLRDHUP，那麼epoll_wait會返回EPOLLRDHUP。

close函數等價於shutdown(s, SHUT_RDWR)， close屬於優雅關閉，shutdown(s, SHUT_RDWR)屬於暴力關閉。

2.2.1、shutdown(s, SHUT_RD)場景

服務端代碼：


#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);
                    }
                    // 註冊EPOLLRDHUP
                    ev.events = EPOLLIN | EPOLLRDHUP | EPOLLOUT | EPOLLET;
                    ev.data.fd = sockfd;
                    int nSendBuf = 4096; //上層應用設置成4096 但是底層內核實際是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;
                }
                //正常讀
                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) {// 說明發送成功
                        hasSend += len;
                        once = 0;
                        printf("Send ok， length = %d.\n", len);
                    } else if (len == -1) {
                        if (errno == EAGAIN) {//說明發送緩衝區已經滿
                            printf(" EPOLLOUT ==》 Socket SndBuf is fulled. \n");
                            once = 1;
                            break;
                        }
                    } else {//出現錯誤
                        perror(" EPOLLOUT ==》 Send failed.\n");
                        exit(-1);
                    }
                }
            }
        }
    }
}

客戶端代碼：

#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秒保證
    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;
}

輸出數據：

備註：通常直接調用close不會出發EPOLLERR和EPOLLMSG，猜測是因爲client調用shutdown導致的。

2.2.2、shutdown(s, SHUT_WR)

服務端代碼：


#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);
                    }
                    // 註冊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);
            }
        }
    }
}

客戶端代碼：

#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秒保證
    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;
}

輸出數據：

總結：當客戶端調用shutdown write，服務端由於註冊是EPOLLRDHUP，所以可以認爲客戶端數據已經發送完不會再有新的數據到來，但是爲了保證本端（服務端）的數據能夠發出，所有還是需要嘗試發送（畢竟客戶端沒有關閉READ）。但是當客戶端調用close方法後，服務端不會出發任何事件，這一點也需要考慮當中。可以參考Nginx實現方式，通過一個pending_eof變量來控制，盡最大可能將數據發送出去。

三、總結

本篇把EPOLLRDHUP相關場景通過代碼形式進行總結，希望起到拋磚引玉的作用。

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