incorrect use of WinDLL

[carandraug]

We use ctypes.WinDLL to load all shared libraries in Windows but that's wrong. We should be using ctypes.CDLL even on Windows for some libraries.

We have been using WinDLL under the incorrect assumption that's what one needs to do in Windows. However, the choice is not about the underlying OS, it's about the calling convention used by the functions. We should be using WinDLL to access functions that use the stdcall calling convention and CDLL to access functions that use the standard C calling convention (called cdecl on Windows).

If I understood this correctly, we need to check the header files and see if in Windows the functions are defined with __stdcall (may happen indirectly such as when the WINAPI macro is used). If not, then we should be using CDLL even on windows. It seems that using the wrong one will not immediately lead to issues but may lead to weird unpredictably issues later.

I've checked the header files and seems we need to change for Alpao and BMC mirrors, for Hamamatsu cameras, and for Linkam stages:

device (module)	checked header	needs fix
alpao mirrors (microscope/_wrappers/asdk.py)	yes	probably
BMC mirrors (microscope/_wrappers/BMC.py)	yes	probably
hamamatsu cameras (microscope/_wrappers/dcamapi4.py)	yes	probably
mirao mirrors (microscope/_wrappers/mirao52e.py)	yes	no (MIRAOCALL expands to __stdcall)
pvcam cameras (microscope/cameras/pvcam.py)	yes	no (PV_DECL expands to __stdcall on Windows)
andor SOLIS (microscope/cameras/atmcd.py)	yes	maybe (uses WINAPI on one version but nothing on other)
andor SDK3 cameras (microscope/cameras/_SDK3.py)	yes	no (AT_EXP_CONV expands to WINAPI)
linkam stage (microscope/stages/linkam.py)	yes	probably

However, I no longer have access to any of these. Could someone who does have access test it?

[dstoychev]

Tested the ALPAO mirror wrapper. Replacing WinDLL with CDLL on line 29 works fine!

microscope/microscope/_wrappers/asdk.py

Line 29 in 55138bf

SDK = ctypes.WinDLL("ASDK")

[carandraug]

Thank you for testing Danny. I've pushed e837dfc. I've also asked @thomasmfish by email whether he could check the Linkam stage.

[iandobbie]

Tom Fish says that Diamond is using CDLL for the linkam stage there and it works for them.