I have a unmanaged DLL that exposes a function that takes a pointer to a data structure. I have C# code that creates the data structure and calls the dll function without any problem. At the point of the function call to the dll the pointer is correct.
My problem is that the DLL keeps the pointer to the structure and uses the data structure pointer at a later point in time. When the DLL comes to use the pointer it has become invalid (I assume the .net runtime has moved the memory somewhere else).
What are the possible solutions to this problem?
The possible solutions I can think of are:
- Fix the memory location of the data structure somehow? I don’t know how you would do this in C# or even if you can.
- Allocate memory manually so that I have control over it e.g. using Marshal.AllocHGlobal
- Change the DLL function contract to copy the structure data (this is what I’m currently doing as a short term change, but I don’t want to change the dll at all if I can help it as it’s not my code to begin with).
Are there any other better solutions?
You can allocate the structure using AllocHGlobal, which puts it in unmanaged memory, where the GC won’t move it around or release it. You could also use a helper class like this to have the GC pin the memory, so it won’t be moved or released until un-pinned.