[Mono-devel-list] UDP 40%+ loss

marcusmonaghan at f2s.com marcusmonaghan at f2s.com
Mon Apr 4 12:03:52 EDT 2005

Thanks for the reply Jason.

I didn't post code initially as I was just seeing if there was a "ah yes, we
know about that one" answer.

So as there doesn't seem to be that, here is the code snippets. I have exluded
obtaining settings:

C code:
        while (TRUE) /* receive (and pass on) loop */
            /* Now clear buffers ready for next iteration */
            memset(buffer, '\0', BUFLEN);
            memset(outbuf, '\0', BUFLEN);

            /* Let select know which file descriptor we want to wait on */
            FD_SET(multicast_socket, &read_set);
            /* If we are not using a file then add the tcp socket to the set */
            if (message_file <= FAILURE) FD_SET(tcp_socket, &read_set);

            /* Select needs to know the maximum file descriptor to look for. We
could specify FS_SETSIZE which is defined as 256 but
               this would meen the kernal would be checking for extra file
descriptors that did not exist. */
            if (multicast_socket > tcp_socket || message_file >= VALID)
                max_fd = multicast_socket + 1;
                max_fd = tcp_socket + 1;

            /* Now select and wait for a signal */
            now_msg(0, "Waiting on select ...\n", errno);
            selected_fd = select(max_fd, &read_set, NULL, NULL, NULL);
            now_msg(1, "After select ...\n", errno);

            /* We have a connection so reset the connection_try indicator */

            if (selected_fd == FAILURE)
                now_msg_err(0, errno, "Error on select");
            if (selected_fd == TIMEOUT)
                /* Currently this isn't supported so shouldn't be called yet */
                now_msg(0, "Select timed out ... POLL");

                /* Need to clear here as we are resetting at the top of the loop
                FD_CLR(multicast_socket, &read_set);
                FD_CLR(tcp_socket, &read_set);

            if ((message_file <= FAILURE) && FD_ISSET(tcp_socket, &read_set))   
    /* Data available on tcp socket, only if not using a file */

.. Doesn't fire!!!

            }   /* End of data available on TCP socket */

            if (FD_ISSET(multicast_socket, &read_set))  /* Data available on udp
socket */
                bytes_received=recvfrom(multicast_socket, buffer, BUFLEN, 0,
NULL, NULL); /* get one message at a time (as it is UDP) */
                    now_msg_err(0, errno, "Error receiving multicast messages");
                /* Let the user know what we have received (remove a linefeed if
one is already there due to testing) */
                if (buffer[bytes_received - 1] == '\n')
                    now_msg(5, "removing LF from input\n");
                    buffer[--bytes_received] = 0;
                now_msg(0, "<<<[%d][%s]\n", bytes_received, buffer);
                if (add_ascii_header == TRUE)
.. No longer used
                    sprintf(outbuf, "\"%s\"\n", buffer);
                bytes_to_send = strlen(outbuf);

                /* Depending on whether or not a file has been specified send to
to a tcp server or write it to a file */
                if (message_file >= VALID) /* File provided */
                    now_msg(5, "Writing to file [%d]\n", bytes_to_send);
                    bytes_sent=write(message_file, outbuf, bytes_to_send);
                    now_msg(5, "Writing to socket [%d]\n", bytes_to_send);
                    bytes_sent=send(tcp_socket, outbuf, bytes_to_send, 0 );	/*
write the message - 0 = no options */

                outbuf[bytes_to_send] = 0; /* for the record, remove the \n, but
retain real length for checking purposes */
                now_msg(0, ">>>[%d][%s]\n", bytes_sent, outbuf);
            }   /* End of data available on udp socket */
        } /* listener failed */

c# Code

	public class MulticastClient
		#region Member Variables
		private string _multicastAddress = string.Empty;
		private int _multicastPort = 0;
		#endregion Member Variables

		#region Variables
		private int messageCount = 0;
		private IPAddress multicastAddress;
		private Socket multicastSocket;
		#endregion Variables

		#region Constructors
		public MulticastClient(string MulticastGroup, int MulticastPort)
			new MulticastClient(MulticastGroup, MulticastPort, true);

		public MulticastClient(string MulticastGroup, int MulticastPort, bool
			_multicastAddress = MulticastGroup;
			_multicastPort = MulticastPort;

			// Do we want to start?
			if (StartImmediately) { StartListening(); }

		#endregion Constructors

		#region Properties
		public string HostAddress
				return _multicastAddress;
				// TODO: Only allow the setting of the property if the client is not active

				if (value != _multicastAddress)
					_multicastAddress = value;

		public int Port
				return _multicastPort;
				// TODO: Only allow the setting of the property if the client is not active
				_multicastPort = value;

		#region Methods

		private void ConfigureMulticastSocket()
			// Assign the local address automatically
			EndPoint localEndPoint;
			MulticastOption multicastOption;
			IPAddress localIPAddress = IPAddress.Any;	// TODO: Possibly need to change
this to be specific

			// Configure the multicast address object
			multicastAddress = IPAddress.Parse(_multicastAddress);

			// Create the socket object
			// TODO: Make sure the socket is not already active
			multicastSocket = new Socket(AddressFamily.InterNetwork,
				SocketType.Dgram, ProtocolType.Udp);

			// Now create an end point for this end. Local IP address with the multicast
			localEndPoint = (EndPoint)new IPEndPoint(localIPAddress, _multicastPort);

			// Bind the socket object to the end point

			// Now set the multicast options
			multicastOption = new MulticastOption(multicastAddress, localIPAddress);


		private void StartListening()
			bool complete = false;		// Flag to indicate completion of processing loop
			IPEndPoint groupEndPoint;	// The end point to the group
			EndPoint remoteEndPoint;	// The other end of the socket
			byte[] recievedBytes = new byte[10000];	// Bytes to receive
			int recievedByteCount = 0;	// Number of bytes recieved

			// Configure the socket and start listening

			// Configure the end point for the group
			groupEndPoint = new IPEndPoint(multicastAddress, _multicastPort);

			// Configure the other end point or where we want to retrieve data from.
			// For this example we are going to accept data from anywhere, but
			// we should be able to specify where we want to receive data from.
			// Port 0 is given to allow the framework/OS to decide what is used.
			remoteEndPoint = (EndPoint) new IPEndPoint(IPAddress.Any, 0);

			// Wait for data
			// TODO: This should be asynchronous
					Console.WriteLine("Waiting for multicast messages ...");

					// Wait for some data
					recievedByteCount = multicastSocket.ReceiveFrom(recievedBytes, ref

					// Show we have got something
					Console.WriteLine("Received {2}: {0} from {1}",
						Encoding.ASCII.GetString(recievedBytes, 0, recievedByteCount),
			catch(Exception e)


		#endregion Methods


As you can see the c# code is no where near complete compared to the C code. It
has less processing, but still manages to miss the messages. The only thing I
can think of is to remove the Console.Writelines and log the messages to a log
file. Just incase this is actually causing the issue (overhead of writing out
to the console is more than writing to a file perhaps).


Quoting Jason Starin | Giant Head <jasonstarin at giant-head.com>:

>  Hi Marcus,
>   First off, without code, I feel like I'm going into this question blind,
> but I do have a similar example that I did find a solution for.
> I had a web service that was capturing web requests from several different
> forms, it then incremented a database, and then sent confirmation mails as
> well as lead emails to different targets, based upon the web data.  I had
> all exceptions mailed to me, and it allowed me a little time to figure out
> about how to configure my application to work well with xsp.
> Here's the general idea:
> 1.  I made receipt of requests a top priority process, running on a separate
> service, so that I always received requests.  I had those requests write to
> a common xml file that was hosted in memory.  Whenever my requests exceeded
> 1000 or so a minute, the service would crash if I was trying to write a file
> to disk, so instead, I had a single write at the end of each minute as part
> of a separate thread.
> 2.  Database updates seem to be slow using the ByteFX and the MySql.Data
> ADO.net connections.  I built a timer that updated with the common XML file
> every 4 minutes.  That reduced the total number of database requests to a
> manageable number that gave them plenty of time to finish (all of my
> requests seem to take between 9 and 15 seconds to run almost regardless of
> their size).
> 3.  Because mail services (I'm using sendmail on RedHat Fedora Core 2, but I
> also tested SMTP on a Win2k3 with Mono box) seemed to flake out on repeated
> connections, I batched emails, and sent them in groups, every ten minutes.
> If I allowed each process to send an email message, immediately, my dual
> processor server seemed to choke on all of the connections, and eventually
> XSP would crash and take apache with it.  On Windows, I'd have a great big
> collection of emails bogged down in my logs, needing to be resent.
> Frankly, I don't think these are bugs, but more along the lines of
> enviornmental constraints, that you can adapt to if you map out the process
> and look for where things are flaking out.  Perhaps establish a separate log
> file to watch each step through your process, and save at the end of your
> test?
> Send code if you get a chance, I'm interested to see where I can help, and
> have you thought about testing your C# app on a windows machine?
> Interesting problem,
> Jason
>  From: mono-devel-list-admin at lists.ximian.com
> [mailto:mono-devel-list-admin at lists.ximian.com] On Behalf Of
> marcusmonaghan at f2s.com
> Sent: Monday, April 04, 2005 10:37 AM
> To: Mono Help
> Subject: [Mono-devel-list] UDP 40%+ loss
> All,
> I am trying to re-creating a C program in C# mono (as there are more C#
> developers in our company now) and it seems it's not behaving in the
> expected
> way.
> The program is very simple. It listens on a multicast group, receives data
> and
> writes it to a file. The problem is that I'm seeing roughly 40%+ missed
> messages when compared to the C program. I ran the C# and C program on the
> same
> box. On another box I send out 100 messages in 10 second bursts. The C
> program
> receives all of them whereas the C# program only receive 60 on the first
> burst
> 50 on the second 55 on the third and so on.
> I then (just for a laugh) unthrottled the sending program. It sent 51,000
> messages, all of which where received by the C program. The c# program
> recorded
> 7152.
> Anyone got any ideas? Possibly a bug?
> Regards,
> Marcus
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