[Opensim-dev] Using Socket polling for UDP receive handlers

[Dahlia Trimble]

Often processing incoming packets can require exclusive access to scene
data structures. I'd avoid using a threadpool task (FireAndForget) to
process a incoming packet to avoid potential lock contention and threadpool
task exhaustion.

On Thu, Apr 24, 2014 at 9:30 AM, matt lehmann <mlehmann8 at hotmail.com> wrote:

> Hello,
>
> The current implementation of UDP reception ( as of the latest release )
> is as follows.
>
> -- create an async read cycle on the socket, adding packets to a blocking
> queue
> -- create a smart thread which waits on the blocking queue, servicing new
> packets as the occur
>
> I propose a simpler solution, which will give more control over rate of
> reception, and also eliminate the need for two separate threads in
> reception.
>
> This solution involves polling the udp socket, from within the smart
> thread.
>
> The function IncomingPacketHandler, from within the LLUDPServer class
> changes to this:
>
> private void IncomingPacketHandler()
>  {
>
> ....
>              IncomingPacket incomingPacket = null;
>
>                     base.pollReceive();
>                     while(packetInbox.Count > 0)
>                     {
>                         incomingPacket = packetInbox.Dequeue();
>
>                         ProcessInPacket(incomingPacket);//,
> incomingPacket); Util.FireAndForget(ProcessInPacket, incomingPacket);
>
>                         if (UsePools)
>
> m_incomingPacketPool.ReturnObject(incomingPacket);
>                     }
>
> ....
> }
>
> packetInbox is now a standard .NET queue.
>
>
> The method, pollReceive on the base class looks like this:
>
>      public bool pollReceive()
>         {
>
>             if (m_udpSocket.Poll(100, SelectMode.SelectRead))
>             {
>
>                 UDPPacketBuffer buf = new UDPPacketBuffer();
>                 buf.DataLength = m_udpSocket.ReceiveFrom(buf.Data,
>                         0,
>                         UDPPacketBuffer.BUFFER_SIZE,
>                         SocketFlags.None,
>                         ref buf.RemoteEndPoint);
>                 PacketReceived(buf);
>                 return true;
>             }
>             return false;
>         }
>
>
> This setup should allow for better throughput, as there will be less
> context switching and reliance on the .NET threading runtime to service the
> async requests.  Also, it would now be possible to throttle incoming
> packets under heavy loads.
>
>
>
> * Matt Lehmann *
>
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>
>
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