LabVIEW spawning new threads with every call to DLL via CLN, but same DLL works fine being called from CVI

[acerenzio]

This is repost from a topic I posted yesterday in the LabVIEW board.

The short version is:

• I have a 3rd party C++ dll that I call to capture pixel data from a camera
• When I run the "GrabFrames" function in a loop in a CVI .exe I can do it indefinitely with no issue
• If I call that exact same function from LabVIEW, after about 50 loops LabVIEW will crash. This exact behavior can be replicated in TestStand
• When in LabVIEW or TestStand, each call to the functions spawns ~5 new threads (found by watching the Windows Resource Monitor while stepping through code)

I fully believe the DLL is to blame, but I'm trying to figure out what about the CVI environment or act of building as an .exe prevents this thread creation phenomenon. Any insight would be greatly appreciated.

Full text from original post in LabVIEW board:

I have been hunting down an issue with a call library node (CLN) for several weeks now and I'm hoping someone can offer some guidance. I have a 3rd party c++ DLL we'll call "Camera.dll". It has two functions that I'm using:

1. Configure 

2. GrabFrameAverage

What I want to do is call the GrabFrameAverage function in a loop in LabVIEW. The function basically just returns pixel data from a camera. I can return data fine for about 50 loops and then LabVIEW will freeze and crash. After many days of troubleshooting I've been able to identify that with each call to this function I see ~5-8 new threads spawn when I watch the Windows Resource Monitor. The crash seems to happen when the thread count hits around 600.

As one troubleshooting step, I tried to see if I could call the function from TestStand. When I do I get the same behavior where it will work fine for several loops and then crash, all while increasing thread count. 

I was ready to fully blame the DLL (and haven't ruled that out yet), but when I run this same test in CVI I can run it indefinitely and I see no new threads spawn which has me questioning if the DLL is really to blame.

Some additional troubleshooting info that has all led to the same results:

1. In LabVIEW
   1. Tried slowing the loop down by manually stepping through
   2. Changing thread from to "any" instead of UI (then returned to UI thread for all additional attempts)
   3. Tried both calling conventions (the import wizard defaults to C)
   4. Wrote a CVI wrapper around the 3rd party DLL and called the wrapper from LabVIEW
   5. Instead of initializing a new array each loop I have tried doing an initialization outside the loop and then making the array into a local variable that I can pass in and and then use as the output. The thought here was that maybe somehow the threads were related to creating 'new' arrays each time.
2. In TestStand
   1. Slowed loop down
   2. Changed adapter settings between CVI and C/C++
   3. Called DLL directly and using CVI wrapper

• Is there any way that I could be messing up a the CLN and that be what's causing the threads?
• Is there a way to manually close out the threads? 
• Could it be related to the way I'm creating the Array Data Pointers?
• Do I need to "free" the Array Data Pointers somehow?

I'm kind of at a loss at the moment so any help or guidance would be appreciated.

This is all using TS/LV/CVI 2019.