Thread: If two sockets attempt to send and recv at the same time will program lock up?

  1. #1
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    If two sockets attempt to send and recv at the same time will program lock up?

    I have two sockets, which are running on my Linux board under localhost IPv6 (::1). I programmed the .so in C.

    If each socket is running in a separate loop and both sockets call the send() or the recv() socket function at the same time, will my program freeze because that is what is happening.

    I specified my sockets as non-blocking, but it still freezes.

    I tried running my code in one loop i.e. server send, client recv, client send, server recv, and that works. It only does not work if I run my code in parallel loops.

    Does anyone know why this might happen?

    Thanks.

  2. #2
    and the hat of int overfl Salem's Avatar
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    Without seeing the code, it would be wild speculation at best.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

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    Quote Originally Posted by Salem View Post
    Without seeing the code, it would be wild speculation at best.
    Do you want me to post the LabVIEW code (block diagram code) that calls my library, or just the C .so library?

    I don't want to post LabVIEW code, if it does not fit here.

    Thanks.
    Last edited by JHugh; 08-10-2017 at 06:29 AM.

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    It could be that I'm setting up a non-blocking socket wrong. Is this correct? I think I may be missing the argument in fcntl...

    I really need my company to buy me a good Linux C book... And, my terrible laptop won't let me cut and paste to this forum properly, so I have to reformat all my code...


    Code:
    if(fcntl(sockfd, F_SETFL, O_NONBLOCK) == -1) {
       *errnoOut = errno;
       return(-1);
    } else {
       printf("nonbloc val = %I", fcntl(sockfd, F_GETFL, O_NONBLOCK));
       *errnoOut = 0;
       return(sockfd);
    }

  5. #5
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    Nevermind, I solved it. I was passing sockfd instead of newsockfd to fcntrl().

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