How to organize the interaction of C# (Unity) with a C++ library in the case when you need to save state on the C++ side?

Question

C++ / C#

I'm trying to solve a problem in which I need to call a function from C ++ from Unity code that uses the dl i b library for tracking a face in a picture (the case itself - the unit sends a frame from the webcam to c ++ and tracking information comes back)
From the c ++ side, when the function is called, a the predictor object which processes the frame and the problem is exactly in this object.
The predictor object is created for a long time, and if such an object is created every time the function is called, there will be too much delay.
I would like the object to be created once, after which it is stored in memory until the end of the program execution on the unit.
I still do not even understand which direction to dig in order to solve this problem