Rework loading vxlapi DLLs #1937
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…_directory() are searched In Python 3.8, DLL loading changed, and the recommended way to add arbitrary directories to the search locations is with os.add_dll_directory(), see https://docs.python.org/3/library/os.html#os.add_dll_directory can/interfaces/vector/xldriver.py used ctypes.util.find_library() to first get a path to the vxlapi/vxlapi64 for the DLLs; if a path was found, the DLL was loaded with ctypes.windll.LoadLibrary(<DLL path>), if not, a FileNotFoundError exception was manually raised. find_library() only searches paths in os.environ['PATH'], which does not include directories added with os.add_dll_directory(), so find_library() fails if the vxlapi DLLs are located in an arbitrary (non-standard) directory, whether or not the directory was first added with add_dll_directory(). LoadLibrary() raises a FileNotFoundError if the DLL cannot be located, and it will look in the standard locations and arbitrary locations added with add_dll_directory(). So, rather than trying to find the DLL first with find_library(), simply wrap the LoadLibrary() call in a try/except block and raise any exceptions. This has two benefits: first, it allows the vxlapi DLLs to be located in an arbitrary directory that can be added in an end-user script with os.add_dll_directory(); second, it catches other exceptions raised by LoadLibrary().
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In Python 3.8, DLL loading changed, and the recommended way to add arbitrary directories to DLL search locations is with os.add_dll_directory(), see https://docs.python.org/3/library/os.html#os.add_dll_directory
can/interfaces/vector/xldriver.py used ctypes.util.find_library() to first get a path to the vxlapi/vxlapi64 for the DLLs; if a path was found, the DLL was loaded with ctypes.windll.LoadLibrary(), if not, a FileNotFoundError exception was manually raised.
find_library() only searches paths in os.environ['PATH'], which does not include directories added with os.add_dll_directory(), so find_library() fails if the vxlapi DLLs are located in an arbitrary (non-standard) directory, whether or not the directory was first added with add_dll_directory().
LoadLibrary() raises a FileNotFoundError if the DLL cannot be located, and it will look in the standard locations and arbitrary locations added with add_dll_directory(). So, rather than trying to find the DLL first with find_library(), simply wrap the LoadLibrary() call in a try/except block and raise any exceptions.
This has two benefits: first, it allows the vxlapi DLLs to be located in an arbitrary directory that can be added in an end-user script with os.add_dll_directory(); second, it catches other exceptions raised by LoadLibrary().
I don't know how this might affect legacy applications or if other interface drivers in the repository have the same problem with find_library(), nor am I sure how to test this beyond my local system, but I am happy to help if anyone can offer guidance.