RTM implementation of Thread.GetData/Thread.SetData has several scalability issues
caused by global locks being taken. The appdomain-global lock
taken in LocalDataStore.SetData is one of them. There is another global lock taken in ThreadNative::GetDomainLocalStore that is even worse since it is
static Object foo;
[ThreadStatic] variables do not suffer from the contention
issues. Moreover [ThreadStatic] variables are several times faster compared to Thread.GetData/Thread.SetData.