From 77ecaed6f2204284869c5ab30f3c97292a0904de Mon Sep 17 00:00:00 2001
From: neworderofjamie <neworderofjamie@gmail.com>
Date: Fri, 24 Mar 2023 12:16:45 +0000
Subject: [PATCH] On Windows, call ``os.add_dll_directory`` before trying to
 load CUDA backend

---
 pygenn/genn_model.py | 40 ++++++++++++++++++++++++----------------
 1 file changed, 24 insertions(+), 16 deletions(-)

diff --git a/pygenn/genn_model.py b/pygenn/genn_model.py
index 6d1bd84f2f..d50792f3e8 100644
--- a/pygenn/genn_model.py
+++ b/pygenn/genn_model.py
@@ -47,6 +47,7 @@
 from psutil import cpu_count
 from setuptools import msvc
 from subprocess import check_call  # to call make
+import sys
 from textwrap import dedent
 from warnings import warn
 
@@ -71,22 +72,6 @@
                           CurrentSource, CustomUpdate)
 from .model_preprocessor import prepare_snippet
 
-# Loop through backends in preferential order
-backend_modules = OrderedDict()
-for b in ["CUDA", "SingleThreadedCPU", "OpenCL"]:
-    # Try and import
-    try:
-        m = import_module(".genn_wrapper." + b + "Backend", "pygenn")
-    # Ignore failed imports - likely due to non-supported backends
-    except ImportError as ex:
-        pass
-    # Raise any other errors
-    except:
-        raise
-    # Otherwise add to (ordered) dictionary
-    else:
-        backend_modules[b] = m
-
 # If we're on windows
 if system() == "Windows":
     # Get environment and cache in class, convertings
@@ -105,6 +90,29 @@
     # **NOTE** shutil.which would be nicer, but isn't in Python < 3.3
     _msbuild = find_executable("msbuild",  _msvc_env["PATH"])
 
+    # If Python version is newer than 3.8 and CUDA path is in environment
+    if sys.version_info >= (3, 8) and "CUDA_PATH" in environ:
+        # Add CUDA bin directory to DLL search directories
+        from os import add_dll_directory
+        add_dll_directory(path.join(environ["CUDA_PATH"], "bin"))
+
+
+# Loop through backends in preferential order
+backend_modules = OrderedDict()
+for b in ["CUDA", "SingleThreadedCPU", "OpenCL"]:
+    # Try and import
+    try:
+        m = import_module(".genn_wrapper." + b + "Backend", "pygenn")
+    # Ignore failed imports - likely due to non-supported backends
+    except ImportError as ex:
+        pass
+    # Raise any other errors
+    except:
+        raise
+    # Otherwise add to (ordered) dictionary
+    else:
+        backend_modules[b] = m
+
 GeNNType = namedtuple("GeNNType", ["np_dtype", "assign_ext_ptr_array", "assign_ext_ptr_single"])
 
 class GeNNModel(object):