The Application static members are supposed to be thread safe:
The public static (Shared in Visual
Basic) members of this type are thread
safe. In addition, the FindResource
and TryFindResource methods and the
Properties and Resources properties
are thread safe.1
How much can we trust that statement in a multithreaded environment when calling static member methods of System.Windows.Application?
Update:
It’s all in reference to this question: Threading errors with Application.LoadComponent (key already exists)
I never thought I’d see a real bug in the library, but this must be the day for me… that question seems to show a genuine bug. Usually it’s "user error," but this doesn’t seem to be the case.
This is the general pattern of the .Net framework and associated libraries. Static / Shared members are assumed to be thread safe unless otherwise marked. If you find a member that is not thread safe and is not marked as such in the documentation it is a bug (in either the documentation or implementation).
Therefore I think it’s safe to rely on them being thread safe.