Best way to poll sockets?

This is a discussion on Best way to poll sockets? within the Networking/Device Communication forums, part of the General Programming Boards category; I'm making a server emulator for an old mmo and would like to know the best way to poll sockets. ...

  1. #1
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    Best way to poll sockets?

    I'm making a server emulator for an old mmo and would like to know the best way to poll sockets. At the moment i've got a class called SoxPoller that uses select. The code below is the class:
    Code:
        SoxPoller::SoxPoller()
        {
            FD_ZERO(&readSet);
            FD_ZERO(&writeSet);
            FD_ZERO(&errorSet);
            range = 0;
            options = 0;
        }
    
        void SoxPoller::AddSocket(const Socket& s, int options)
        {
            unsigned int socketId = s.GetSocket();
            this->options |= options;
    
            if(options & POLL_READ)
                FD_SET(socketId, &readSet);
    
            if(options & POLL_WRITE)
                FD_SET(socketId, &writeSet);
    
            if(options & POLL_ERROR)
                FD_SET(socketId, &errorSet);
    
            if(socketId > range)
                range = socketId;
        }
    
        bool SoxPoller::IsSet(const Socket& s, int option)
        {
            unsigned int socketId = s.GetSocket();
            if(option == POLL_READ)
                return FD_ISSET(socketId, &readSet);
    
            if(option == POLL_WRITE)
                return FD_ISSET(socketId, &writeSet);
    
            if(option == POLL_ERROR)
                return FD_ISSET(socketId, &errorSet);
    
            return false;
        }
    
        int SoxPoller::Poll(int timeOut)
        {
            struct timeval timev;
            timev.tv_sec = 0;
            timev.tv_usec = timeOut;
    
            return select(range + 1, &readSet, &writeSet, &errorSet, (timeOut >= 0 ? &timev : NULL));
        }
    But i've read select can only do like 64 sockets at a time. Linux has a method called "poll" but it's not available on windows. I know windows has "async" sockets that uses events but i want the server to be cross platform. What's the best way i can poll these sockets?

  2. #2
    Carnivore ('-'v) Hunter2's Avatar
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    I doubt you'll find an effective method that works on both platforms. You'll also have the same limitation with any method that uses Events, since WaitForMultipleObjects() etc. has an upper limit of 63 or 64 handles. On the Windows side of things, you could try asynchronous sockets using the message queue (that seems to be how most people use them), or Overlapped completion routines, or else IOCP (IO completion ports).

    I've heard that IOCP is the most scalable/efficient for large-scale servers (I don't have any benchmarks or proof), but in general you may find IOCP and completion routines to be harder to write code for, since they notify you when an operation is *done*, as opposed to when an operation is *ready*. On the flip side, they don't require a message queue, making them more flexible from the standpoint of multithreading.
    Just Google It. √

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  3. #3
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    I've decided all i'm going to do is add this warning at runtime:

    Code:
            if(FD_SETSIZE < maxPlayers)
            {
                log << LogHeader() << "WARNING: FD_SETSIZE " << FD_SETSIZE << " is smaller than the maximum players. "
                    "The maximum players has been changed to " << FD_SETSIZE << ". If you want more players, you need to "
                    "recompile the server with a larger FD_SETSIZE value.\n";
                maxPlayers = FD_SETSIZE;
            }
    Last edited by 39ster; 07-19-2008 at 11:22 PM.

  4. #4
    Malum in se abachler's Avatar
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    There are two primary methods for handlign multiple socket connections. Thread per client, or polling. Polling is by far the fastest, although most difficult to impliment. Rather than use WaitForMultipleObjects, use WaitForSingleObject() with a timeout of zero. The return value will tell you whether it returned due to timeout, or from being signlaled. You can then queue that socket for service by your worker threads.
    Until you can build a working general purpose reprogrammable computer out of basic components from radio shack, you are not fit to call yourself a programmer in my presence. This is cwhizard, signing off.

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