Memory issue in C#, normal use if dll is called by .Net app but astronomical if dll called from legacy app

I have created dll in C# 3.5 which does some memory intensive matrix calculations where matrices get created and disposed a lot. Everything works fine if dll is called from .Net app but if it is called from C++ created app memory usage just climbs until the functi开发者_运维知识库on that uses matrices is done. I guess there is a problem with a automatic garbage collection.

Most probably you are not 'Release'ing the references to the .Net object wrappers from your unmanaged app. The GC cannot collect that memory unless all references (including external ones) are released.

Expanding on logicnp's answer.

The CLR can only garbage collect memory that is allocated and owned by managed code. It has no view or understanding of unmanaged memory. In the case of C++ calling a .Net DLL via COM interop you have a mix of managed and unmanaged memory. Additionally you have C++ objects which are keeping managed objects alive (via COM pointers and CCW's).

The CLR will free up the managed objects properly but only when no references to them exist anymore. When C++ accesses a managed object it creates a CCW under the hood which is kept alive by the native C++ COM interface pointer. Until the ref count on that pointer reaches 0 via calls to Release and Add it will keep the CCW alive and hence the underlying managed object.

Try wrapping all of the places in C++ where you access your managed object with a CComPtr and seeing if this takes care of your problem.