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Editorial Team
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Asked: 2026-05-13T23:29:28+00:00

Here is the situation: Silverlight 3 Application hits an asp.net hosted WCF service to

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Here is the situation:

Silverlight 3 Application hits an asp.net hosted WCF service to get a list of items to display in a grid. Once the list is brought down to the client it is cached in IsolatedStorage. This is done by using the DataContractSerializer to serialize all of these objects to a stream which is then zipped and then encrypted. When the application is relaunched, it first loads from the cache (reversing the process above) and the deserializes the objects using the DataContractSerializer.ReadObject() method. All of this was working wonderfully under all scenarios until recently with the entire “load from cache” path (decrypt/unzip/deserialize) taking hundreds of milliseconds at most.

On some development machines but not all (all machines Windows 7) the deserialize process – that is the call to ReadObject(stream) takes several minutes an seems to lock up the entire machine BUT ONLY WHEN RUNNING IN THE DEBUGGER in VS2008. Running the Debug configuration code outside the debugger has no problem.

One thing that seems to look suspicious is that when you turn on stop on Exceptions, you can see that the ReadObject() throws many, many System.FormatException’s indicating that a number was not in the correct format. When I turn off “Just My Code” thousands of these get dumped to the screen. None go unhandled. These occur both on the read back from the cache AND on a deserialization at the conclusion of a web service call to get the data from the WCF Service. HOWEVER, these same exceptions occur on my laptop development machine that does not experience the slowness at all. And FWIW, my laptop is really old and my desktop is a 4 core, 6GB RAM beast.

Again, no problems unless running under the debugger in VS2008. Anyone else seem this? Any thoughts?

Here is the bug report link: https://connect.microsoft.com/VisualStudio/feedback/details/539609/very-slow-performance-deserializing-using-datacontractserializer-in-a-silverlight-application-only-in-debugger

EDIT: I now know where the FormatExceptions are coming from. It seems that they are “by design” – they occur when when I have doubles being serialized that are double.NaN so that that xml looks like NaN…It seems that the DCS tries to parse the value as a number, that fails with an exception and then it looks for “NaN” et. al. and handles them. My problem is not that this does not work…it does…it is just that it completely cripples the debugger. Does anyone know how to configure the debugger/vs2008sp1 to handle this more efficiently.

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  1. Editorial Team

    Ok – I figured out the root issue. It was what I alluded to in the EDIT to the main question. The problem was that in the xml, it was correctly serializing doubles that had a value of double.NaN. I was using these values to indicate “na” for when the denominator was 0D. Example: ROE (Return on Equity = Net Income / Average Equity) when Average Equity is 0D would be serialized as:

    <ROE>NaN</ROE>

    When the DCS tried to de-serialize it, evidently it first tries to read the number and then catches the exception when that fails and then handles the NaN. The problem is that this seems to generate a lot of overhead when in DEBUG mode.

    Solution: I changed the property to double? and set it to null instead of NaN. Everything now happens instantly in DEBUG mode now. Thanks to all for your help.

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