zoukankan      html  css  js  c++  java
  • poll() can't detect event when socket is closed locally?

    from https://stackoverflow.com/questions/5039608/poll-cant-detect-event-when-socket-is-closed-locally

    I'm working on a project that will port a TCP/IP client program onto an embedded ARM-Linux controller board. The client program was originally written in epoll(). However, the target platform is quite old; the only kernel available is 2.4.x, and epoll() is not supported. So I decided to rewrite the I/O loop in poll().

    But when I'm testing code, I found that poll() does not act as I expected : it won't return when a TCP/IP client socket is closed locally, by another thread. I've wrote a very simple codes to do some test:

    #include <stdio.h>
    #include <stdlib.h>
    #include <sys/socket.h>
    #include <netinet/in.h>
    #include <arpa/inet.h>
    #include <fcntl.h>
    #include <pthread.h>
    #include <poll.h>
    
    struct pollfd   fdList[1];
    
    void *thread_runner(void *arg)
    {
        sleep(10);
        close(fdList[0].fd);
        printf("socket closed
    ");
        pthread_exit(NULL);
    }
    
    int main(void)
    {
        struct  sockaddr_in hostAddr;
        int sockFD;
        char buf[32];
        pthread_t handle;
    
        sockFD = socket(AF_INET, SOCK_STREAM, 0);
        fcntl(sockFD,F_SETFL,O_NONBLOCK|fcntl(sockFD,F_GETFL,0));
    
        inet_aton("127.0.0.1",&(hostAddr.sin_addr));
        hostAddr.sin_family = AF_INET;
        hostAddr.sin_port  = htons(12345);
        connect(sockFD,(struct sockaddr *)&hostAddr,sizeof(struct sockaddr));
    
        fdList[0].fd = sockFD;
        fdList[0].events = POLLOUT;
    
        pthread_create(&handle,NULL,thread_runner,NULL);
    
        while(1) {
            if(poll(fdList,1,-1) < 1) {
                continue;
            }
            if(fdList[0].revents & POLLNVAL ) {
                printf("POLLNVAL
    ");
                exit(-1);
            }
            if(fdList[0].revents & POLLOUT) {
                printf("connected
    ");
                fdList[0].events = POLLIN;
            }
            if(fdList[0].revents & POLLHUP ) {
                printf("closed by peer
    ");
                close(fdList[0].fd);
                exit(-1);
            }
            if(fdList[0].revents & POLLIN) {
                if( read(fdList[0].fd, buf, sizeof(buf)) < 0) {
                    printf("closed by peer
    ");
                    close(fdList[0].fd);
                    exit(-1);
                }
            }
        }
        return 0;
    }
    

     

    In this code I first create a TCP client socket, set to non-blocking mode, add to poll(), and close() the socket in another thread. And the result is: "POLLNVAL" is never printed while the socket is closed.

    Is that an expected behavior of poll() ? Will it help if I choose select() instead of poll() ?

    Answer:

    Yes, this is expected behavior. You solve this by using shutdown() on the socket instead of close().

    See e.g. http://www.faqs.org/faqs/unix-faq/socket/ section 2.6

    EDIT: The reason this is expected is that poll() and select() reacts to events happening on one of their fd's. close() removes the fd, it does not exist at all anymore, and thus it can't have any events associated with it.

    It worked. poll() will return with POLLHUP event

     

  • 相关阅读:
    C++调用WebService
    vs2005 环境的字体和颜色的设置
    自娱自乐~经典24点游戏
    再探利用C++的STL和堆栈编程思想实现数学四则运算计算结果
    如何在Linux中关闭apache服务(转)
    ios推送:本地通知UILocalNotification
    ASIHTTPRequest的使用(转)
    实战新浪微博、腾讯微博的分享功能(转)
    UIImagePickerController拍照与摄像(转)
    iOS通过http post上传图片 (转)
  • 原文地址:https://www.cnblogs.com/kex1n/p/7375572.html
Copyright © 2011-2022 走看看