[IronPython] ctypes.py from FePy

Curt Hagenlocher curt at hagenlocher.org
Mon Apr 7 20:21:02 PDT 2008


On Mon, Apr 7, 2008 at 9:54 AM, Michael Foord <fuzzyman at voidspace.org.uk> wrote:
>
> I've been trying to use ctypes.py from FePy for dynamic platform invoke.
> Unfortunately it doesn't appear to work...

The main problem appears to be that MethodTarget.CanOptimize in
IronPython 1.1.1 assumes that the method will have a DeclaringType --
but a dynamically generated method isn't necessarily attached to a
type.  As such, it doesn't appear that this version of ctypes.py could
have ever worked with IronPython 1.1.1.

I haven't checked earlier versions of IronPython 1.

By changing MethodTarget.CanOptimize in the IronPython source so that
it returns false when mi.DeclaringType == null, I was able to make
ctypes.py work.

> Unfortunately 'WDLL' doesn't exist in ctypes. If I replace it with
> 'CDLL' it blows up with the following error:

Presumably, the difference between WDLL and CDLL was that the latter
uses a calling convention of CallingConvention.Cdecl while the former
would have used CallingConvention.Winapi.  This is a pretty important
difference!

In general, I think that there's some really nice code in ctypes.py,
but like all invocations of pInvoke, you definitely can't use it
blindly.  Your PostMessage would probably break on a 64-bit OS even if
it weren't for the issues of the calling convention and the problem in
MethodTarget.CanOptimize -- because in the proper definition of
PostMessage, the second and third parameters are IntPtr, but ctypes.py
would treat them as "int32"

--
Curt Hagenlocher
curt at hagenlocher.org


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