>>>Then, since the runtimes themselves are not threadsafe, how can this work in a threadsafe manner?
>Either the calls have to be queued (which is not my idea of multithreading) or you have problems.
>
>That's not my understanding of how it works. If Mtdll uses STA then one block of memory can be shared between multiple simultaneous apartments that don't interfere with each other. It's not free-threaded, but it is thread-safe.

Hmm. So where am I wrong:
The VFP runtimes were not written as threadsafe DLLs.
Therefore the same instance cannot be safely accessed by more than one thread.
Therefore you must either queue the calls to the runtime or instantiate multiple instances.
If the former you gain no performance benifits. If the latter you eat RAM.