Question

以下面的代码片段为例，创建套接字，监听和接受新套接字工作正常。非阻塞模式也在工作，但是pselect（甚至用select替换）不能识别FDset上准备好的任何IO请求。所以返回值始终为0（超时）。

我想知道在进入pselect（）之前是否需要进一步设置其他内容以便识别IO活动。

.....
 // Create the socket
        *m_pSockFD = socket(AF_INET, SOCK_STREAM, 0);
        if( *this->m_pSockFD == -1 ){
            throw ....
        }

        // Set the socket address information
        m_pSockAddr->sin_family = AF_INET;
        m_pSockAddr->sin_port =  htons( 6001 );
        m_pSockAddr->sin_addr.s_addr = INADDR_ANY;

        if( bind(*m_pSockFD, (struct sockaddr *) m_pSockAddr, sizeof(*m_pSockAddr) ) != 0 ){
                .....
        }

        // Listen on this socket using a block queue of 5 - default Block Size
        if( listen( *m_pSockFD, 5) != 0 )
                ........


        // change function control to non blocking file descritor for I/O operations
        long fcntlArg;
        if( (fcntlArg = fcntl( *m_pSockFD, F_GETFL, NULL ) ) < 0 ){
               ...........
        }

        fcntlArg |= O_NONBLOCK;
        if( fcntl( *m_pSockFD, F_SETFL, fcntlArg ) <0 ){
              ...........
        }

        //.........

        int newFD = -1;
        socklen_t salen = sizeof(*m_pSockAddr);


        // loop selecting for a I/O operation ready on the file descriptor then go into accept mode
        struct timespec timeOut;
        timeOut.tv_sec = 1;
        timeOut.tv_nsec = 0;

        fd_set fdset;
        FD_SET( *this->m_pSockFD, &fdset );

        while( !m_bShutDownFinished ){

            // TODO pselect is not registering the activity on the socket
            if( pselect( *this->m_pSockFD, &fdset, NULL , NULL , &timeOut,  NULL ) > 0 ){
                cout << "hello client" << endl;
                break;
            }

            // re-initialize the time struct
            timeOut.tv_sec = 1;
            timeOut.tv_nsec = 0;
        }


        // application is shutting down do not try to accept a new socket
        if( m_bShutDownFinished ) return -1;

        newFD = accept(*m_pSockFD, (struct sockaddr *) m_pSockAddr, &salen);
        if( newFD > -1 ){
            ................
        }

        return newFD;

Answer 1

在每次调用select()之前，您必须重新初始化fdset参数。

readfds，writefds和exceptfds中的每一个都是输入/输出参数。返回时，它们被修改为只有fds，它们分别是可读，可写或具有某种特殊条件的。

for (;;) {
    fd_set rfds;
    FD_ZERO(&rfds);
    FD_SET(sock, &rfds);
    /* code to set up timeout omitted */
    n = select(sock + 1, &rfds, 0, 0, &timeout);
    /* check n, and if sock is present in rfds */
}

您编写代码的方式，只有在第一次调用pselect()期间到达时才会检测到传入连接。另外，鉴于您未使用sigmask的{{1}}参数，您也可以致电pselect()。

Answer 2

pselect的第一个参数应该是*this->m_pSockFD + 1，不应该吗？

pselect（）无法识别具有任何IO活动的套接字

2 个答案: