[fbsync] Fix windows python 3.8 required dlls not found (#6715)

Summary:
* Fix windows python 3.8

* Update torchvision/extension.py

* Update torchvision/extension.py

Reviewed By: NicolasHug

Differential Revision: D40427461

fbshipit-source-id: 8aeb7eba3dd573b2d700680276cf947d724a1d35

Co-authored-by: Vasilis Vryniotis <[email protected]>
Co-authored-by: Vasilis Vryniotis <[email protected]>

Author: 2 people

torchvision/extension.py

@@ -16,6 +16,18 @@ def _has_ops():
 
 
 try:
+    # On Windows Python-3.8.x has `os.add_dll_directory` call,
+    # which is called to configure dll search path.
+    # To find cuda related dlls we need to make sure the
+    # conda environment/bin path is configured Please take a look:
+    # https://stackoverflow.com/questions/59330863/cant-import-dll-module-in-python
+    if os.name == "nt" and sys.version_info >= (3, 8) and sys.version_info < (3, 9):
+        env_path = os.environ["PATH"]
+        path_arr = env_path.split(";")
+        for path in path_arr:
+            if os.path.exists(path):
+                os.add_dll_directory(path)  # type: ignore[attr-defined]
+
     lib_path = _get_extension_path("_C")
     torch.ops.load_library(lib_path)
     _HAS_OPS = True