Silverlight DataAnnotations.Validator is not thread safe

 

I got this exception when using the Validator class with Silverlight. And yes, there is a property called ‘AProperty’ on the instance being validated :)

The type 'ClassWithValidatedProperty' does not contain a public property named 'AProperty'.
Parameter name: propertyName

at System.ComponentModel.DataAnnotations.ValidationAttributeStore.TypeStoreItem.GetPropertyStoreItem(String propertyName)
at System.ComponentModel.DataAnnotations.ValidationAttributeStore.GetPropertyType(ValidationContext validationContext)
at System.ComponentModel.DataAnnotations.Validator.ValidateProperty(Object value, ValidationContext validationContext)
at SilverlightValidationRepro.ClassWithValidatedProperty.set_AProperty(String value)
at SilverlightValidationRepro.ValidatorNotThreadSafeReproduction.<Should_be_able_to_validate_concurrently>b__1()

The exception occured only once in a while, so we suspected threading issues. However, the MSDN docs say that Any public static (Shared in Visual Basic) members of this type are thread safe. Then take a look at the following test. It reproduces with the exception above, effectively proving a concurrency bug.

Now take a look at the following screen shot from reflector. Can you spot the threading bug? Hint: the ‘return false’ should not happen in our case.

Oh, and the workaround is to not consider the Validator class thread safe. We dispatch the code to a single thread. Another workaround would be to ensure that the Validator is finished with its initialization phase before unleasing multiple threads on it.

Missing Mime Types option in IIS

I’ve been playing around with Silverlight 3 recently and until just now I’ve used the Visual Studio Development Server to run and debug the code. But when I changed to using IIS I got the following error when starting the application:

Error: Unhandled Error in Silverlight
Application Code: 2103
Category: InitializeError
Message: Invalid or malformed application: Check manifest

Google gave me several suggestions. One of them was to add the correct MIME types. However, the IIS Manager didn’t provide the “MIME Types” option to let me add them:

After feeling a bit puzzled I figured out that I could enable the “MIME Types” option by turning on “Static Content” in “Turn windows features on or off”:

The option appeared in the IIS Manager and it was allready configured with the needed MIME type for Silverlight apps. Problem solved.