Comments on Tomek on Software: Scale-out of Silverlight HTTP polling duplex WCF s...

Hi , I took the sample and did many modification ...

2011-08-23T08:45:28.349-07:00

Hi ,

I took the sample and did many modification to accomodate my need. However, I am trying to design it so that once the duplex service receives the new session request I'm getting the object like
IClientPushNotification callback =OperationContext.Current.GetCallbackChannel and trying to pass the callback object to another service through a service call. Problem is siince my IClientPushNotification is already a sevice contract, I can't make it again a DataContract to pass over the wcf channel to the other serice. I tried KnownType, [System.ServiceModel.ServiceKnownTypeAttribute(typeof(IClientPushNotification))] like these, but none of them works. I know its a different issue not directly related to the topic here , but thought someone could help.

Anyone has any idea, how to dear with this kinda situation?

Thanks for your efforts. It's too bad this w...

2011-07-01T15:19:42.221-07:00

Thanks for your efforts.

It's too bad this whole continuous data delivery paradigm is so hard to implement. Push still has no quality solution I'm afraid. Your code does help though. SL4/5 hasn't come up with an industry solution to this yet?

Code confusion: your use of the "Microsoft.???" naming convention continuously forces me to stop and ask "is this a Microsoft supplied library/code/example/etc.?" I suggest you use verbiage that identifies your code more clearly.

For instance : "Microsoft.ServiceModel.PollingDuplex", did Microsoft provide this? Is this namespace to be found within some Microsoft assembly? Convolutes the issue I believe.

Lastly, Ten. Regardless of how I configure any polling duplex silverlight client or the web.config for the service all I can manage is 10 simultaneous client connections. Tried this on 3 different web servers (iis6,7,vsserver). Any clues as to how to fix this. (did all the service behavior gymnastics with session max and such.)

Thanks.

Couldnt agree more with that, very attractive arti...

2011-04-10T09:54:32.752-07:00

Couldnt agree more with that, very attractive article

clomid

Anonymous, it is public domain, do whatever you de...

2010-11-09T09:27:42.736-08:00

Anonymous, it is public domain, do whatever you desire with the code (but don't hold me accountable for losses etc. etc.)

are there any license restrictions for the code in...

2010-11-09T08:51:02.879-08:00

are there any license restrictions for the code in Microsoft.ServiceModel.PollingDuplex.Scalable.dll included in the sample download?

Pacome, you may also want to check out http://la...

2010-10-12T09:44:23.783-07:00

Pacome,

you may also want to check out http://laharsub.codeplex.com, an open source project addressing similar scenario as Silverlight's polling duplex. It offers a .NET backend you can deploy anywhere you can run .NET (including Azure), and a selection of clients (Silverlight, .NET, and jQuery). I have not tried recompiling the client for WP7, but given it is only using generic HTTP features, I don't suppose this would be a problem. Also check out the performance measurements for Laharsub - it performs better than polling duplex in Silverlight.

Thanks for your reply Tomasz, it's more clear ...

2010-10-12T05:14:40.999-07:00

Thanks for your reply Tomasz, it's more clear for me.

About Windows Phone 7 notifications, I already read a lot of mail threads about it, and to be honest, it seems the only existing way is to use Azure (marketing boys won the war ?)...

In order to use Silverlight notifications inside video games, several ways exists and the best one is to use low level sockets. It's not implemented in WP7 for the moment, that's why I was looking for another flexible solution, and yours seemed to be the good one.

Thanks again for your help.

Pacome, in general you can generate client proxy...

2010-10-11T09:51:20.156-07:00

Pacome,

in general you can generate client proxy for a WCF service using either the Add Service Reference feature in Visual Studio, or the slsvcutil.exe tool that ships with Silverlight 4 SDK. In the context of the scale-out method describe above, the only way to generate a client proxy automatically is to do so _before_ refactoring the service implementation to allow scale-out (i.e. when the service is still in the duplex form and exposed over HTTP long polling binding.

We have not performed any validation of the polling duplex protocol with Windows Phone 7, so I cannot confirm one way or the other if it works on the Phone platform. However, given that battery power is an important constraint on the mobile devices, I would recommend looking at the notification APIs specifically targetting the mobile platform (http://msdn.microsoft.com/en-us/library/ff402537(v=VS.92).aspx) instead of polling duplex.

Hello, first, thanks a lot for both PollingDuplei...

2010-10-10T03:01:40.322-07:00

Hello,

first, thanks a lot for both PollingDupleix samples, they're very useful.

Two quick questions :
- How do you generate the *good* reference.cs without VS2010 automation ? You write it manually ?
- I noticed PollingDupleix is not supported on WindowsPhone7, but I noticed that this "scalable" example seems to be compatible, can you confirm ?

Thanks again.

Jurassic, Silverlight 4 does not add any new scale...

2010-07-26T12:08:15.339-07:00

Jurassic, Silverlight 4 does not add any new scale-out specific features and the mechanism described in this article is still applicable. If scale-out of HTTP long polling is of particular interest to you, please check out the http://laharsub.codeplex.com open source project which experiments with this technology.

Hi Thomasz, Thanks for the excellent article. I cr...

2010-07-26T12:04:55.945-07:00

Hi Thomasz,
Thanks for the excellent article. I created a chat application using your sample code. Now that Silverlight 4 is out do i still have to use this approach to build a scale-out app or can i use the out of box Silverlight 4 Http Polling Duplex?

Hi Tomasz, I had developed an application with he...

2010-07-14T03:23:11.775-07:00

Hi Tomasz,

I had developed an application with help of your articals. But I am not getting large data. A table having 10 columns ( 256 char ) and 10000 rows.

Can you suggest changes required for that??

Bernd, the Add Server Reference (and Update Servic...

2010-07-05T13:59:21.890-07:00

Bernd, the Add Server Reference (and Update Service Reference) functionality of Visual Studio will not generate the correct Silverlight proxy after the service has been refactored to allow load balancing - see the second comment to this post for a more detailed explanation.

Hi Bernd, this is exactly what we do. The main adv...

2010-07-01T06:24:19.185-07:00

Hi Bernd,
this is exactly what we do. The main advantage of this solution is, as you described, the full control and less magic behind the scenes. Furthermore we can use REST-based communication. I'm also very interested in potential disadvantages.
Cheers
Alex

Hi Gurus ;) I spent some days now following Tomas...

2010-06-30T16:32:44.849-07:00

Hi Gurus ;)

I spent some days now following Tomasz samples and all the related blogs of mostly frustrated people trying to create a reliable Load-Balance capable real-time update using PollingDuplex.

My question here is : WHY Polling Duplex ?

In most cases your RIA Website works like that:
1. Navigate to a page.
2. The page loads some data from a WebService and displays it.
3. When there is a relevant update of the data on the server, it should immediately reflected on the client.

OK, step 3 needs some magic - but not necessarily PollingDuplex.

I would suggest to create your own "real-time updating WebService". This will keep you in full control and with RIA its unbelievably easy to create even a load-balance capable solution.

So what I do is:
1. My page requests the data to be displayed from a WebService.
2. Then it calls another WebService which checks the scalable storage for changes.
2.1. This call is async - so the client can go on even if the service will not come back immediately.
2.2.a. When the WebService detects a relevant change it returns this change.
2.2.b. When the WebService cant detect a relevant change within 30seconds, it returns an empty result.
2.3. When the WebService returns a result or empty, the client updates its data and calls the WebService again.
2.4. When the Client doesnt need more "real-time updates" it cancels the WebService and goes on with whatever next.

So you see, this is a kind of self made "long time polling" which is load-balance capable and keeps you in full control as far as you are in control of your WebServices.

Now I need the Gurus telling me what are the disadvantages of this solution compared to the PollingDuplexScalable Tomasz suggested.

Cheers

Bernd

Hi Tomasz Do you have a fixed sample of your Poll...

2010-06-29T20:03:46.189-07:00

Hi Tomasz

Do you have a fixed sample of your PollingDuplexSampleScalable ?

The one which can be downloaded here is broken. When you update the Service on the Client the NotifyReceived is undefined. I guess something is just confused/unfinished in your sample code.

Cheers

Bernd

Thanks for the heads-up. I realize it's not ea...

2010-06-25T06:58:34.157-07:00

Thanks for the heads-up. I realize it's not easy, that's why I asked the expert first ;)

Good luck. I look forward to the article.

Cheers!

Tim, it is not easy to change the framing or encod...

2010-06-24T18:05:46.676-07:00

Tim, it is not easy to change the framing or encoding in the polling duplex binding that shipped in Silverlight. Coincidentally, I am currently prototyping a REST-based pub\sub protocol which has the full content type support of HTTP (including JSON). I plan to blog it in about 2 weeks.

Thanks for some really great posts! How would yo...

2010-06-24T16:37:51.078-07:00

Thanks for some really great posts!

How would you modify your "scaled-out" version to use JSON encoding instead of SOAP? I'm putting together a web service that will service iPhone applications, and JSON-over-HTTP looks like the best approach for that platform.

Thanks in advance!

I'm having trouble with this. Everything work...

2010-06-16T12:43:48.852-07:00

I'm having trouble with this. Everything works fine except

e.request.GetBody().Content

My client does not see NotificationData.

Hey Tomasz, thanks for the great info here. I want...

2010-01-30T14:51:04.878-08:00

Hey Tomasz, thanks for the great info here. I want to address Andy's issue for proxy generation for the duplex service.

The problem usually arises in WCF when an Interface inherits from another Interface. In this case: IPubSub inherits form IPollingDuplex, which is then implemented in the PubSubService class.

To fix the auto proxy gen, remove the IPollingDuplex inheritance to IPubSub and then move it to PubSubService class instead, like this:

public class PubSubService : IPubSub, IPollingDuplex { .... }

This should solve the problem.

Cheers!

Nasir Aziz

Andy said...
Hi Tomasz

This looks a great solution. The only issue I see is that if you change the contract so for instance add a method to IPubSub it's not possible to re-generate the client proxy through visual studio as it doesn't generate the DuplexContract client side. Is there anyway to get around this issue that you know of?

Thanks

September 20, 2009 1:32 PM

I've seen the same as 3axap - it's very st...

2010-01-15T00:54:13.858-08:00

I've seen the same as 3axap - it's very strange that Silverlight just stops sending requests. Could it be anything to do with the silverlight plugin being suspended if the browser is not the active application???

*big responses

2009-11-27T02:28:25.960-08:00

*big responses

I can't understand, why, but In some time silv...

2009-11-27T02:27:26.283-08:00

I can't understand, why, but In some time silverlight stops sending requests to server. Maybe it is because server sends big requests, something like 30Kb. The connection lives for just 4-5 minutes, sometimes more, and then it dies. Could you please explain this?

I was considering writing something close to this ...

2009-11-11T18:08:23.234-08:00

I was considering writing something close to this solution, but I have to say you've done an excellent job thinking this through and explaining it.. Well Done!