Make add_dll_directory(), load_dependencies() side-effects more deterministic. (#855)

Author: rwgk

cuda_pathfinder/cuda/pathfinder/_dynamic_libs/load_dl_linux.py

@@ -127,21 +127,7 @@ def get_candidate_sonames(libname: str) -> list[str]:
     return candidate_sonames
 
 
-def check_if_already_loaded_from_elsewhere(libname: str) -> Optional[LoadedDL]:
-    """Check if the library is already loaded in the process.
-
-    Args:
-        libname: The name of the library to check
-
-    Returns:
-        A LoadedDL object if the library is already loaded, None otherwise
-
-    Example:
-        >>> loaded = check_if_already_loaded_from_elsewhere("cudart")
-        >>> if loaded is not None:
-        ...     print(f"Library already loaded from {loaded.abs_path}")
-    """
-
+def check_if_already_loaded_from_elsewhere(libname: str, _have_abs_path: bool) -> Optional[LoadedDL]:
     for soname in get_candidate_sonames(libname):
         try:
             handle = ctypes.CDLL(soname, mode=os.RTLD_NOLOAD)

cuda_pathfinder/cuda/pathfinder/_dynamic_libs/load_dl_windows.py

@@ -100,25 +100,16 @@ def abs_path_for_dynamic_library(libname: str, handle: ctypes.wintypes.HMODULE)
     return buffer.value
 
 
-def check_if_already_loaded_from_elsewhere(libname: str) -> Optional[LoadedDL]:
-    """Check if the library is already loaded in the process.
-
-    Args:
-        libname: The name of the library to check
-
-    Returns:
-        A LoadedDL object if the library is already loaded, None otherwise
-
-    Example:
-        >>> loaded = check_if_already_loaded_from_elsewhere("cudart")
-        >>> if loaded is not None:
-        ...     print(f"Library already loaded from {loaded.abs_path}")
-    """
-
+def check_if_already_loaded_from_elsewhere(libname: str, have_abs_path: bool) -> Optional[LoadedDL]:
     for dll_name in SUPPORTED_WINDOWS_DLLS.get(libname, ()):
         handle = kernel32.GetModuleHandleW(dll_name)
         if handle:
             abs_path = abs_path_for_dynamic_library(libname, handle)
+            if have_abs_path and libname in LIBNAMES_REQUIRING_OS_ADD_DLL_DIRECTORY:
+                # This is a side-effect if the pathfinder loads the library via
+                # load_with_abs_path(). To make the side-effect more deterministic,
+                # activate it even if the library was already loaded from elsewhere.
+                add_dll_directory(abs_path)
             return LoadedDL(abs_path, True, ctypes_handle_to_unsigned_int(handle))
     return None
 

cuda_pathfinder/cuda/pathfinder/_dynamic_libs/load_nvidia_dynamic_lib.py

@@ -24,26 +24,29 @@
 
 
 def _load_lib_no_cache(libname: str) -> LoadedDL:
-    # Check whether the library is already loaded into the current process by
-    # some other component. This check uses OS-level mechanisms (e.g.,
-    # dlopen on Linux, GetModuleHandle on Windows).
-    loaded = check_if_already_loaded_from_elsewhere(libname)
-    if loaded is not None:
-        return loaded
+    found = _FindNvidiaDynamicLib(libname)
+    have_abs_path = found.abs_path is not None
+
+    # If the library was already loaded by someone else, reproduce any OS-specific
+    # side-effects we would have applied on a direct absolute-path load (e.g.,
+    # AddDllDirectory on Windows for libs that require it).
+    loaded = check_if_already_loaded_from_elsewhere(libname, have_abs_path)
 
-    # Load dependencies first
+    # Load dependencies regardless of who loaded the primary lib first.
+    # Doing this *after* the side-effect ensures dependencies resolve consistently
+    # relative to the actually loaded location.
     load_dependencies(libname, load_nvidia_dynamic_lib)
 
-    # Find the library path
-    found = _FindNvidiaDynamicLib(libname)
-    if found.abs_path is None:
+    if loaded is not None:
+        return loaded
+
+    if not have_abs_path:
         loaded = load_with_system_search(libname)
         if loaded is not None:
             return loaded
         found.retry_with_cuda_home_priority_last()
         found.raise_if_abs_path_is_None()
 
-    # Load the library from the found path
     assert found.abs_path is not None  # for mypy
     return load_with_abs_path(libname, found.abs_path)
 

cuda_pathfinder/cuda/pathfinder/_version.py

@@ -1,4 +1,4 @@
 # SPDX-FileCopyrightText: Copyright (c) 2025 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
 # SPDX-License-Identifier: Apache-2.0
 
-__version__ = "1.1.1a1"
+__version__ = "1.1.1a2"