CODEWITHSUNDEEP
silverlightwcf
mr_dunski
mr_dunski

Reputation: 451

Is PollingDuplex right for Silverlight client notification?

I'm trying to figure out if PollingDuplex is the right way to go for my problem.

Here is my scenario: 1. 3rd party application sends a UDP packet with a client's IP address to a server app. 2. The server app needs to the notify the specified client and send along some data.

The client is a Silverlight application.

I've been looking at some guides and sample code (http://petermcg.wordpress.com/2008/09/03/silverlight-polling-duplex-part-1-architecture/) but I don't understand how clients are identified on the server using PollingDuplex. I understand that the clients register with the server and continually poll for messages. How would I make sure that only the right clients get the message designated for that client? In other words, the messages on the server should not be broadcasted to all polling clients but only sent to one specific client.

Any help is much appreciated.

Upvotes: 0

Views: 633

Answers (2)

Ken Smith
Ken Smith

Reputation: 20445

Whether you're using Net.TCP or HttpDuplexBinding, clients can be identified using OperationContext.Current.Channel.SessionId. And more specifically, you can grab the actual channel that WCF uses to talk to them using OperationContext.Current.GetCallbackChannel<IMyCustomServiceInterface>(). You can store those in memory, perhaps associated with some other identifier passed up from the client, and when you need to communicate with the client in question (e.g., to pass them the data from the UDP packet), you call the appropriate method on that specific stored channel; and the client will get notified.

I should note that while I don't particularly recommend HttpDuplexBinding, apart from its quirks and stability and performance issues, it should work for what you're doing, and in exactly the same way as Net.TCP. Although the clients technically do "poll" the server, that's hidden from you. All you know on the server is that you're calling a method on a particular channel. The underlying binding code takes care of making sure that the right client gets notified.

Upvotes: 1

Jeff
Jeff

Reputation: 36573

Polling duplex is actually an entirely client side implementation that exists only for Silverlight (there's no regular .NET framework version of it, except a project on Codeplex Microsoft's own internal consulting services developed for a high profile client of theirs). There's nothing at all special about it on the server side.

It's not really meant to be used in production by Microsoft's own admission (we have a Microsoft contact at our company who admitted this to us candidly). It's not very robust or well implemented and can/will DoS your server under any kind of volume: http://forums.silverlight.net/p/89970/239380.aspx

You're better off rolling your own client side polling mechanism - or (better and more scalable) using TCP with session in Silverlight 4, which provides true duplex support (because the connection is not stateless and thus supports true push notifications): http://www.silverlightshow.net/items/WCF-NET.TCP-Protocol-in-Silverlight-4.aspx.

Upvotes: 0

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