Unloading COM dlls, help needed

[Thomas Heller]

Sorry for the somewhat offtopic question, but I know here is an
interested and competent audience available to answer questions.

Background:

I'm implementing a COM server framework in pure Python (TM) on base of
the ctypes module.

Everything works very nice - I have a Shell Extension which extends
the Explorer context menu for .py files, it lets you run tools like
PyChecker and reindent.  I have also started some ActiveX controls
which can be shown in several containers, IE among them (not all
possible interfaces are implemented, but it is already very
interesting).

Everything - except the dlls (_ctypes.pyd, together with python22.dll
and others) are never unloaded from the process.  This makes
development very slow, I have to restart Explorer each time I want to
change the source files.

I think I got everything correct, COM reference counting seems OK,
DllCanUnloadNow returns correct values, all I can think of.

A control implemented in ATL, IIRC, behaves different.

Reading through the MSDN docs shows that it may take 10 minutes after
the call to CoFreeUnusedLibraries() before the dlls are actually
unloaded, I've even waited longer, but nothing happpens.

This leads me to my question: Are there any other things that may
prevent dlls from being unloaded by COM?

My understanding is that each DLL mapped into a process has an
internal reference count, and the DLL is unloaded when this reaches
zero.  Since Python itself calls LoadLibrary on the _ctypes.pyd (which
is the COM dll), can it be that this circular reference between the
dlls prevent unloading?  Oh, btw: is there *any* way to get this
refcount?

Or could it simply be that unmatched CoInitialize/CoUninitialize calls
are responsible?

Note that I've read the pycom-dev archives the reason why Mark's
PythonCOM is never unloaded - it returns S_FALSE from
DllCanUnloadNow() because Python can never be shutdown safely in a
running process, but I want to try it anyway.

Any help appreciated,

Thomas