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POLinux TCP connect with Select() fails at testserver
 

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  1. POLinux TCP connect with Select() fails at testserver
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    <p>My problem is the following: I'm programming an Interface in Linux to control a GPIB Controller via Ethernet. To do so I open a TCP socket and just send the commands to the Controller. This is working fine so far. The problem I have occured at writing some kind of unit test for my Interface: To check I am using a tcp acceptor from boost lib in a seperate thread and just connect to it instead of the actual controller. This is working too, but only as long as the connect() call from the interface is blocking. However since I need a specified timeout for the connect() call I had to connect with the select() function:</p> <pre><code> // Open TCP Socket m_Socket = socket(PF_INET,SOCK_STREAM,0); if( m_Socket &lt; 0 ) { m_connectionStatus = STATUS_CLOSED; return ERR_NET_SOCKET; } struct sockaddr_in addr; inet_aton(m_Host.c_str(), &amp;addr.sin_addr); addr.sin_port = htons(m_Port); addr.sin_family = PF_INET; // Set timeout values for socket struct timeval timeouts; timeouts.tv_sec = SOCKET_TIMEOUT_SEC ; // const -&gt; 5 timeouts.tv_usec = SOCKET_TIMEOUT_USEC ; // const -&gt; 0 uint8_t optlen = sizeof(timeouts); if( setsockopt( m_Socket, SOL_SOCKET, SO_RCVTIMEO,&amp;timeouts,(socklen_t)optlen) &lt; 0 ) { m_connectionStatus = STATUS_CLOSED; return ERR_NET_SOCKET; } // Set the Socket to TCP Nodelay ( Send immediatly after a send / write command ) int flag_TCP_nodelay = 1; if ( (setsockopt( m_Socket, IPPROTO_TCP, TCP_NODELAY, (char *)&amp;flag_TCP_nodelay, sizeof(flag_TCP_nodelay))) &lt; 0) { m_connectionStatus = STATUS_CLOSED; return ERR_NET_SOCKET; } // Save Socket Flags int opts_blocking = fcntl(m_Socket, F_GETFL); if ( opts_blocking &lt; 0 ) { return ERR_NET_SOCKET; } int opts_noblocking = (opts_blocking | O_NONBLOCK); // Set Socket to Non-Blocking if (fcntl(m_Socket, F_SETFL, opts_noblocking)&lt;0) { return ERR_NET_SOCKET; } // Connect if ( connect(m_Socket, (struct sockaddr *)&amp;addr, sizeof(addr)) &lt; 0) { // EINPROGRESS always appears on Non Blocking connect if ( errno != EINPROGRESS ) { m_connectionStatus = STATUS_CLOSED; return ERR_NET_SOCKET; } // Create a set of sockets for select fd_set socks; FD_ZERO(&amp;socks); FD_SET(m_Socket,&amp;socks); // Wait for connection or timeout int fdcnt = select(m_Socket+1,NULL,&amp;socks,NULL,&amp;timeouts); if ( fdcnt &lt; 0 ) { return ERR_NET_SOCKET; } else if ( fdcnt == 0 ) { return ERR_TIMEOUT; } } //Set Socket to Blocking again if(fcntl(m_Socket,F_SETFL,opts_blocking)&lt;0) { return ERR_NET_SOCKET; } m_connectionStatus = STATUS_OPEN; return x2e::OK; </code></pre> <p>If I use this function I can still connect on the real controller and communicate with it. But if I use my testserver I just can't connect, select just leaves with a return value of 0. So now someone may say that my testserver just doesn't work....but If I use a blocking connect() call I can send to my testserver without any problems... Maybe someone has an idea what I could do...?</p>
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    1. COA return value of zero indicates a timeout. This may or may not be the issue, but you don't seem to be setting your timeouts struct within the posted excerpt. To quote the manual page "On Linux, select() modifies timeout to reflect the amount of time not slept...Consider timeout to be undefined after select() returns." which would cause problems if you call it again without resetting the value.
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      1. POLinux TCP connect with Select() fails at testserver
      1. USChris Stratton
    2. COSorry my fault , I forgot to add the definition of the timeouts struct to my code!!! Gonna fix that...but that also means that's not the problem :/ // So now the code contains the whole function which handles the connect
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      1. USToby
    3. COAre you aware that you are not closing the socket anywhere? You are not reusing it, calling connect several times with the same socket, do you?
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      1. USrodrigo
 

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