WCF based full duplex service issue

Discussion in 'ASP .Net Web Services' started by Nadeem Ashraf, Nov 3, 2009.

  1. Hi,

    We are working on a Silverlight 3 based tool that we call "Live Presenter".
    Briefly speaking, the purpose of this tool is to provide an environment
    where a teacher/presentation host can push himself live to other users (with
    the help of a camera and a software tool like Expression Encoder; for
    example). Apart from the live video, a presenter can also push selected
    multimedia content from his library including video, audio, image, text and
    form etc. which may serve as a subject reference material during
    presentation. The attendees/students on the other hand can also connect
    through the same tool and watch the presentation live, as it is being
    conducted by the presenter.

    In order to push the messages from the client to the server and then pass
    those messages around to various different connected clients, we are using
    WCF full duplex messaging service. So for example, when a presenter tries to
    push a video content to clients, a message is sent to the messaging service
    which then sends the same message to each of the connected clients of that
    specific session. On receiving the message, source of a medialement based
    control is set to the url passed in the message.

    We have used the following URLs for reference in building this service:

    http://weblogs.asp.net/dwahlin/arch...ht-client-with-wcf-duplex-service-part-i.aspx
    http://weblogs.asp.net/dwahlin/arch...client-with-a-wcf-duplex-service-part-ii.aspx

    Having said above, we are running into two very critical issues pertaining
    to this service that is hindering any serious progress since the last one
    week.

    1) The messages are getting lost somewhere in the transit when we try to run
    this tool with even 3-4 members in a session.
    2) The messages are getting significantly delayed in reaching the
    destination

    It is worthwhile to mention that we are using the same service for passing
    around two different categories of messages. one category is our
    command/control messages to push the content around (from presenter's
    perspective) and other category is chat messages.

    Since the Service has to maintain the state of the connected clients, it is
    a singleton service (InstanceContextMode is single). We have tried to set
    ConcurrenyMode to multiple without any luck. We even tried to break the
    Service into two different services each serving different category of
    messages but that didn't solve our problem either.

    Today, we tried to follow a different approach and created a simple Socket
    based chat Service (for processing chat messages only). This looked to be
    fine until 2-3 clients connected with the Server and they started sending
    and receiving messages rapidly. At one point the server failed with the
    following exception:

    Socket Error
    System.InvalidOperationException: An asynchronous socket operation is
    already in progress using this SocketAsyncEventArgs instance.

    Client Code
    args = new SocketAsyncEventArgs();
    args.UserToken = socket;
    args.RemoteEndPoint = endPoint;
    args.SetBuffer(message, 0, message.Length);
    socket.SendAsync(args);

    Just like previous case, we have no clue as to what is wrong here and how
    can this problem be resolved. Can somebody please help or guide us in an
    appropriate manner.

    Thanks.
    Nadeem Ashraf, Nov 3, 2009
    #1
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