Comments on Tomek on Software: Pub/sub sample using HTTP polling duplex WCF chann...

I got this working, seems I had a mixup between SL...

2011-12-18T02:32:15.382-08:00

I got this working, seems I had a mixup between SL 4 and SL 5 assemblies. Everything now works as expected. ;) I still get a Visual Studio error when I try to update the service reference however, about pollingDuplex (the name i gave my registration of the pollingDuplexHttpBindingElement in the Extensions section of the server web.config) not being a recognized element. I have to remove the entire system.serviceModel tag from the clientConfig before it will update the service reference successfully, and then put it back. Any idea why this happens?

Hi Tomasz I have a working service and client app...

2011-12-17T02:18:33.175-08:00

Hi Tomasz

I have a working service and client application implementing Polling Duplex targeting the Silverlight 4 runtime and it works brilliantly. I'm now trying to implement the same technique in a SL 5 application and my client throws an exception when trying to instantiate the service reference client object; "the given key was not present in the dictionary". In my SL4 app I declare the client endpoint config in the ServiceReference.ClientConfig file so that I could modify timeout settings. When I do the same in the SL5 app, it complains about not being able to load ServiceModel.PollingDuplex.dll. I presume the "key not present" exception is because the client doesnt know about the pollingDuplex element in the client config file? What has changed in how PollingDuplex works in SL5 that would stop it behaving as it did in 4? I've looked at all the runtime versions of the ServiceModel, ServiceModel.PollingDuplex and SeviceModel.Extensions dll versions between the SL4 and SL5 runtime and they're the same, so it should be exactly the same code running. Its very perplexing. Do you have any thoughts? Help would be appreciated :)

Hello Tomasz, I am facing a scenario where Client...

2011-11-02T01:20:24.948-07:00

Hello Tomasz,

I am facing a scenario where Client Channel is getting faulted at random intervals. At this point if try to run the service in browser it gives me the error "The contract name 'MyApp.Interfaces.IPubSub' could not be found". I am using fully qualified name of interface in web.config file. I have to either add back the reference to System.ServiceModel.PollingDuplex dll or restart World Wide Web Publishing Service. I have been unable to find any solution to this for some time now. Could you please explain the cause and suggest a solution ? Thanks.

Omer

Hi Tomasz, I have done so much research on this n...

2011-06-13T12:52:20.915-07:00

Hi Tomasz,

I have done so much research on this now that I am bleary eyed and getting frustrated. I am simply trying to get Http Polling Duplex working within a .net framework 4 wcf service for use with a Silverlight 4 client.

I have followed several instructions including this one ( http://msdn.microsoft.com/en-us/library/cc645027(VS.95).aspx ) and several others. I have verified that I am referencing the correct version of the System.ServiceModel.PollingDuplex DLL. I really don't know what else I can do at this point.

I have received the "Contract requires Duplex" and the "pollingDuplex not valid" errors at different times. Is there any way you could post a Pub/Sub sample that works in .net framework 4/Silverlight 4?

Thanks!

~Matt

Hie tomasaz janczuk, The remote server returned ...

2011-05-06T02:11:48.735-07:00

Hie tomasaz janczuk,

The remote server returned an error NotFound

i dont knw what m i doing wrong..

whenever i try pollingduplex i got this error on each and every application
even this one which u provide above.

i have all the solution which is given for this type of error above but nothing works please help me out

Hello! I still can't fix the .dll problem. Whe...

2011-04-10T05:39:35.321-07:00

Hello! I still can't fix the .dll problem. Where is located the right file that should be added to the refference?

Hi Tomaz, First many thanks for you. Please I hav...

2010-12-06T08:03:55.330-08:00

Hi Tomaz, First many thanks for you.

Please I have a question, when I set duplexMode="MultipleMessagePerRole" and serverPoll="00:01:00" for testing purpose I got the clinet channel Faulted event fired when the serverPoll timeout reached. When I dont set duplexMode,however, the channel Faulted event does not fire. Please could you explain for me this issue! And also "Sorry for that" could you explain what do we mean by Polling either server or client. I've read many msdn articles related to it and to the timeouts but am not feeling myself really understand it.

Thanks in advance, and I really appreciate your hard work...

Sumeet, there is a number of quotas that may affec...

2010-11-24T16:12:53.965-08:00

Sumeet, there is a number of quotas that may affect this behavior. What is the size of the message you are sending? Are any exceptions thrown? Does Fiddler2 provide any insight into whether the message is leaving the server or not?

Hi Tomasz thanks for answering previous posts that...

2010-11-21T22:00:30.201-08:00

Hi Tomasz thanks for answering previous posts that helped a lot....

One more concern we have now when we send large amount of data to the silverlight client it is not able to receive..it goes to faulted state...can u please suggest the cause of it and how we can resolve it...
thanks

Bogdan, unfortunately there is no .NET client impl...

2010-11-19T09:18:07.854-08:00

Bogdan, unfortunately there is no .NET client implementation of the HTTP polling duplex protocol from Silverlight, so you cannot call into a polling duplex service from a WPF application. You may want to check out http://laharsub.codeplex.com, an open source message server that is based on http polling duplex and comes with a .NET client (as well as Silverlight and jQuery).

Hi! Can I use this duplex for a WPF client applica...

2010-11-19T07:25:59.518-08:00

Hi! Can I use this duplex for a WPF client application? What about a xbap WPF application? Thanks! Bogdan I.

It was noted in an earlier comment, that clients t...

2010-11-10T08:15:59.423-08:00

It was noted in an earlier comment, that clients that are shutdown, are not "unsubscribed" on the server. the Original poster hinted at a solution but didn't offer one. I can't seem to find a place to discover that the subscribing client is no longer there. I would have expected some sort of exception on executing the callback.

Kristian Let me make sure I understand your scena...

2010-11-03T23:43:38.165-07:00

Kristian

Let me make sure I understand your scenario: a WPF client is sending messages to the server using net.tcp binding. The server is forwarding these message to multiple Silverlight 4 clients using the HTTP polling duplex binding. Is that correct?

One possible reason for the system to "disconnect" clients is that a networking component decides to terminate inactive TCP connections. This theory seems to be supported by the fact that the system under some load is stable. Two great tools that help to understand what is going on at the protocol layer are Fiddler2 (http://www.fiddler2.com/fiddler2/) and NetMon (http://www.microsoft.com/downloads/en/details.aspx?FamilyID=983b941d-06cb-4658-b7f6-3088333d062f&displaylang=en).

HTTP polling duplex protocol has a number of timeouts that may affect the behavior you are seeing. A comprehensive documentation of those is at http://blogs.msdn.com/b/silverlightws/archive/2010/07/16/pollingduplex-multiple-mode-timeouts-demystified.aspx.

Lastly, the messaging pattern in your application indeed resembles a publish\subscribe flow. One technology that can be helpful in addressing the needs of your application is http://laharsub.codeplex.com. Laharsub is a pub\sub messaging server based on HTTP long polling. It comes with Silverlight, .NET, and jQuery clients.

An update to my previous post: To achieve so many...

2010-11-03T10:56:39.846-07:00

An update to my previous post:

To achieve so many clients we had to start multiple instances of internet explorer on each computer (around 5). It seems that this can be the cause of the problem because when I tried on only one computer with multiple instances it seems to be a breakpoint at around 5 instances before clients starts to disconnect and reconnect.

Do you have any clue why multiple instances of the application on one computer can cause the system to behave like this?

Thanks for help!

/Kristian

Hi Tomasz, Thanks for nice articles about the Sil...

2010-11-03T08:14:26.953-07:00

Hi Tomasz,

Thanks for nice articles about the Silverlight polling duplex.

We're developing a platform were we're using pollingDuplex a lot for sending different commands (strings) from a WPF-desktop client over Net.TCP binding to Silverlight 4 clients.

I guess that makes the service a pub/sub service. We've implemented many of your suggestions in this article and also in your article that talks about performance in polling duplex.

We also have reconnecting logic in the clients and the clients ping the service every 15 seconds to tell the service that the client is still alive. If the ping does not succeed the client reconnects.

A major problem we're facing now is that when we connect many clients everything becomes very unstable. When more than 400 clients (approx) are connected clients begins disconnect and reconnect randomly.

Also, the Net.Tcp connection for the desktop client becomes very unstable and faults a lot.

When observing the CPU load on the server it looks good so I does not think that is the problem. The problems are actually only present when nothing is sent from the publishing client.

However, if commands are sent from the desktop client to the service (and published to the SL-clients) at a higher frequency (about once every 5 seconds) the clients doesn't disconnect but instead seems to stay connected (even if there are more than 400 connected).

Can you draw any conclusions out of this? Can it be some timeouts that are configured in the wrong way?

Any ideas?

The service log file doesn't provide much information.

Help will be much appreciated!

/Kristian

Sumeet, yes, in Fiddler you should be able to see ...

2010-10-25T09:49:48.710-07:00

Sumeet, yes, in Fiddler you should be able to see the multiplexing in action: each HTTP long poll contains two pieces of information: the client ID that uniquely identifies an instance of a Silverlight application, and a session ID that uniquely identifies an instance of a client proxy within this application. Every message in the HTTP long poll response targets a specific session ID. You can read more about the protocol itself at http://tomasz.janczuk.org/2009/09/scale-out-of-silverlight-http-polling.html.

You should not worry about this mechanism working correctly our of the box, unless we have not done our job right testing it. If you find an issue, please let me know.

Mahdi, WebSockets is an upcoming protocol standard...

2010-10-25T09:44:27.015-07:00

Mahdi, WebSockets is an upcoming protocol standard for duplex communication on the web, and it is going to be far superior to any http long polling solution, including HTTP Polling Duplex in Silverlight. Check out http://tomasz.janczuk.org/2010/07/silverlight-html5-websocket-client-with.html for more information.

Note that as of today WebSocket implementation is not available in .NET Framework or Silverlight.

All Flash based solutions I have seen are using one form or another of HTTP long polling, but I would not be surprised to see a websocket implementation as well at this point.

There is more to a chat application than just a duplex messaging capability either websockets or http long polling protocols provide. You need to organize your message flow such that messages are exchnaged between clients, not just between the server and a client. Chat applications I have seen typically use a publish\subscribe message exchange pattern (that utilizes a duplex messaging protocol underneath for low notification delivery latency). One pub\sub solution suitable for implementing chat with Silverlight clients (or JavaScript clients) is at http://laharsub.codeplex.com. Check it out.

Thanks for quick response... If my understanding ...

2010-10-24T23:51:27.855-07:00

Thanks for quick response...

If my understanding is correct this is expected what we could see in Fiddler..the multiplexing of the messages.it gets de-multiplexed and sent to the respective clients ..regardless of the the request URL.

we need not worry about it..correct?

Hi Tomasz, What's the difference between HTML...

2010-10-24T13:25:11.389-07:00

Hi Tomasz,

What's the difference between HTML5 WebSockect API
and WCF Polling Duplex?

For creating a chat application which is better?
As you say, in a HTTP long polling, the server may be faulted, is this right for WCF polling duplex with net.TCP binding and HTML5 WebSocket API?

I saw flash chat rooms work well in duplex communication what api uses for flash duplex communication's?

Finally, if you want to create a real web chat, Which would you use(in Silverlight)?

thanks

Sumeet, even if you have several client proxies ca...

2010-10-22T10:04:06.653-07:00

Sumeet, even if you have several client proxies calling several services using the HTTP polling duplex protocol, you shoudl only ever see up to one outstanding HTTP long poll request. Regardless what the request URL of the HTTP long poll is, we multiplex notifications sent from any of the backend services onto the poll response. The notifications should be correctly dispatched to appropriate proxy instances on the client side. This mechanism is meant to minimize the TCP connection use in a browser enviroment, since browsers impose a quota on the maximum number of concurrent HTTP requests to a single backend server.

Hi Tomasz, thanks for such nice explanation... ...

2010-10-21T23:07:59.712-07:00

Hi Tomasz,

thanks for such nice explanation...

we are using pubsub implementation and we have 3 different pubsubs services hosted in iis7 under same application pool..

we are facing some problem with it..actually when we see the data in client side with fiddler...we could see the messages are mixed for the services...one service data is coming from other service...

for example alarm service is sending data for trend service...which is not expected..even we do have different class objects for different services

can u please suggest what could be the reason for it..

Thanks.

Tomasz I learn more with your great and quick resp...

2010-10-13T23:20:21.142-07:00

Tomasz I learn more with your great and quick responses, Articles and video.

Very Thanks

Mahdi, creating a new polling duplex proxy instanc...

2010-10-13T15:41:10.304-07:00

Mahdi, creating a new polling duplex proxy instance on the client will result in a new sessionId.

OK-and if I create a new instance I have a new ses...

2010-10-13T14:22:50.856-07:00

OK-and if I create a new instance I have a new sessionId,yes?
finally I haven't problem with changing sessionId because I used user names for identify and can change the sessionId property of my clients in the server with a special userName after I create a new instance of my proxy.

Thanks a lot Tomasz

Tomasz, Thank you for the quick responses and...

2010-10-13T13:32:56.408-07:00

Tomasz,
Thank you for the quick responses and great info.
James