Marshal.DestroyStructure vs Marshal.FreeHGlobal in .Net

Question

I have a managed .Net class that creates unmanaged resources that I need to ensure are cleaned up properly.

I have a sequential struct:

[StructLayout(LayoutKind.Sequential)]
struct FooBar { ... }

Then in the constructor I have:

// Allocate the memory
var fb = new FooBar(...);
int length = Marshal.SizeOf(typeof(FooBar));
this.pointer = Marshal.AllocHGlobal(length);
Marshal.StructureToPtr(fb, this.pointer, false);

// Then I use this.pointer in extern calls

Then in my ~Finaliser/Dispose methods do I use Marshal.DestroyStructure or Marshal.FreeHGlobal or both (and if so in what order) to endure I don't leak the memory?

Bonus questions:

• Does my IDisposable class need to inherit CriticalFinalizerObject to ensure that the cleanup is always called?
• Is there a Microsoft.Win32.SafeHandles class I could use here to wrap the dangerous unmanaged memory?

Answer 1

Both. The Marshal.DestroyStructure will free the "content" of the FooBar, while Marshal.FreeHGlobal will free the "container". Clearly first you free the content, then the container. So first Marshal.DestroyStructure then Marshal.FreeHGlobal.

I don't think CriticalFinalizerObject is in any way related to marshaling struct, and a struct can't inherit from anything, so the response is no to the first question.