Why does LabView crash when unloading my DLL (reentrant calls)?

Question

I have written a DLL in Borland Delphi using multiple threads that exports several functions (stdcall). I am using LabVIEW 6i on a WinXP machine.  All functions in the DLL work as expected and return correct values. Everything works fine if I set all Call Library Function Nodes to 'UI-Thread', but as soon as I set one Function Node to 'Reentrant', LabView crashes when I close the VI after it has been executed. I assume the error is caused by the DLL unloading mechanism of LabView. Other C++/Delphi programs using the DLL reentrantly work fine, this only occurs in LabView. In which thread does LabView call FreeLibrary/DLL_PROCESS_DETACH? Has anyone experienced similar problems?

Answer 1

I have never run into this situation myself, but I do know that calling a multi-threaded DLL or CIN from LabVIEW does depend upon the following criteria:
If your CIN/DLL doesn't have any global data storage (global variables, files on disk, etc.), AND it doesn't access any hardware (register-level programming) AND it doesn't call any functions/DLLs/Drivers that are thread-unsafe.
OR
Your CIN/DLL protects (with semaphores or mutex's) access to those global resources.
OR
Your DLL is only called from one, non-reentrant VI
OR
Your CIN is only called from one, non-reentrant VI AND you don't access any global resources from CINInit, CINAbort, CINDispose, etc. procedures.
Hopefully this information can help you out in some way.
J.R. Allen