Fix external DLL loading on wheels

packaging/wheel/relocate.py

@@ -259,6 +259,12 @@ def relocate_elf_library(patchelf, output_dir, output_library, binary):
 
 
 def relocate_dll_library(dumpbin, output_dir, output_library, binary):
+    """
+    Relocate a DLL/PE shared library to be packaged on a wheel.
+
+    Given a shared library, find the transitive closure of its dependencies,
+    rename and copy them into the wheel.
+    """
     print('Relocating {0}'.format(binary))
     binary_path = osp.join(output_library, binary)
 

torchvision/extension.py

@@ -12,6 +12,29 @@ def _register_extensions():
 
     # load the custom_op_library and register the custom ops
     lib_dir = os.path.dirname(__file__)
+    if os.name == 'nt':
+        # Register the main torchvision library location on the default DLL path
+        import ctypes
+        import sys
+
+        kernel32 = ctypes.WinDLL('kernel32.dll', use_last_error=True)
+        with_load_library_flags = hasattr(kernel32, 'AddDllDirectory')
+        prev_error_mode = kernel32.SetErrorMode(0x0001)
+
+        if with_load_library_flags:
+            kernel32.AddDllDirectory.restype = ctypes.c_void_p
+
+        if sys.version_info >= (3, 8):
+            os.add_dll_directory(lib_dir)
+        elif with_load_library_flags:
+            res = kernel32.AddDllDirectory(lib_dir)
+            if res is None:
+                err = ctypes.WinError(ctypes.get_last_error())
+                err.strerror += f' Error adding "{lib_dir}" to the DLL directories.'
+                raise err
+
+        kernel32.SetErrorMode(prev_error_mode)
+
     loader_details = (
         importlib.machinery.ExtensionFileLoader,
         importlib.machinery.EXTENSION_SUFFIXES

torchvision/io/_video_opt.py

@@ -13,7 +13,7 @@
 _HAS_VIDEO_OPT = False
 
 try:
-    lib_dir = os.path.join(os.path.dirname(__file__), "..")
+    lib_dir = os.path.abspath(os.path.join(os.path.dirname(__file__), ".."))
 
     loader_details = (
         importlib.machinery.ExtensionFileLoader,
@@ -22,6 +22,29 @@
 
     extfinder = importlib.machinery.FileFinder(lib_dir, loader_details)
     ext_specs = extfinder.find_spec("video_reader")
+
+    if os.name == 'nt':
+        # Load the video_reader extension using LoadLibraryExW
+        import ctypes
+        import sys
+
+        kernel32 = ctypes.WinDLL('kernel32.dll', use_last_error=True)
+        with_load_library_flags = hasattr(kernel32, 'AddDllDirectory')
+        prev_error_mode = kernel32.SetErrorMode(0x0001)
+
+        if with_load_library_flags:
+            kernel32.LoadLibraryExW.restype = ctypes.c_void_p
+
+        if ext_specs is not None:
+            res = kernel32.LoadLibraryExW(ext_specs.origin, None, 0x00001100)
+            if res is None:
+                err = ctypes.WinError(ctypes.get_last_error())
+                err.strerror += (f' Error loading "{ext_specs.origin}" or any or '
+                                 'its dependencies.')
+                raise err
+
+        kernel32.SetErrorMode(prev_error_mode)
+
     if ext_specs is not None:
         torch.ops.load_library(ext_specs.origin)
         _HAS_VIDEO_OPT = True

torchvision/io/image.py

@@ -7,7 +7,7 @@
 _HAS_IMAGE_OPT = False
 
 try:
-    lib_dir = osp.join(osp.dirname(__file__), "..")
+    lib_dir = osp.abspath(osp.join(osp.dirname(__file__), ".."))
 
     loader_details = (
         importlib.machinery.ExtensionFileLoader,
@@ -16,6 +16,30 @@
 
     extfinder = importlib.machinery.FileFinder(lib_dir, loader_details)  # type: ignore[arg-type]
     ext_specs = extfinder.find_spec("image")
+
+    if os.name == 'nt':
+        # Load the image extension using LoadLibraryExW
+        import ctypes
+        import sys
+
+        kernel32 = ctypes.WinDLL('kernel32.dll', use_last_error=True)
+        with_load_library_flags = hasattr(kernel32, 'AddDllDirectory')
+        prev_error_mode = kernel32.SetErrorMode(0x0001)
+
+        kernel32.LoadLibraryW.restype = ctypes.c_void_p
+        if with_load_library_flags:
+            kernel32.LoadLibraryExW.restype = ctypes.c_void_p
+
+        if ext_specs is not None:
+            res = kernel32.LoadLibraryExW(ext_specs.origin, None, 0x00001100)
+            if res is None:
+                err = ctypes.WinError(ctypes.get_last_error())
+                err.strerror += (f' Error loading "{ext_specs.origin}" or any or '
+                                 'its dependencies.')
+                raise err
+
+        kernel32.SetErrorMode(prev_error_mode)
+
     if ext_specs is not None:
         torch.ops.load_library(ext_specs.origin)
         _HAS_IMAGE_OPT = True