I've had an issue with two requests accessing the frDocument document (especially when either loading the image from memory or during the process command) at the same time. I put a mutex in my application before pretty much touching anything in regards to the FREngine and it works fine but it is slow.
Is there any example Objective C code that shows how to have multiple threads interacting with the frDocument object? The two samples provided don't seem to be designed to support multiple simultaneous requests.
 I switched to using the engine object instead of the frDocument object and it explicitly states only a single engine object can be loaded per process. If that is the case, how does FREngine handle threading?