Because the Python interpreter embedded in Blender is still running, it still has the
core.pyd file open, and Windows ( ) doesn’t let you remove the file
A file with executable image sections mapped cannot be unlinked, even with POSIX semantics. (WINAPI
DeleteFileW uses POSIX delete semantics by default now in Windows 10, with supported filesystems such as NTFS.) The request is denied as
STATUS_CANNOT_DELETE, which maps to WINAPI
EACCES, and Python
That said, you are allowed to rename a loaded DLL to another directory in the same filesystem, which may allow the
unregister function to succeed.
My question is whether or not there is a way to tell the Python interpreter to close that
core.pyd file so that Windows will let you remove it.
AFAIK, the interpreter doesn’t implement detailed reference tracking to know whether it’s safe to unload an extension module. They’re loaded for the lifetime of the process.
Unix has the concept of unlinking files instead of deleting them outright so this problem thankfully doesn’t exist there.
Windows filesystems also support hard links. But Windows uses the term “delete” (e.g.
DeleteFileW) instead of “unlink” when deleting a link. Like Unix, a file is deleted from disk when its link count is 0. There are two fundamental differences compared to Unix.
- Windows filesystems implement a cooperative data access model, which requires all opens to agree to share read/execute, write/append, and delete/rename access. A link cannot be renamed or unlinked if existing opens do not share delete/rename access.
- Classically, Windows guarantees that a link will remain named in the filesystem as long as it’s referenced by an open File object. It can be renamed to another directory, but not removed entirely. This is implemented by making a ‘delete’ request just set a delete disposition on the underlying filesystem File Control Block (FCB). This disposition is executed once the last File object reference is cleaned up. Until then, a ‘deleted’ link remains linked in the directory and cannot be opened again for any access.
Windows 10 supports unlinking with POSIX semantics. This still requires shared delete/rename access, but the target file in this case gets immediately unlinked from the directory. Interestingly, NTFS still keeps the file linked in the filesystem, but renames it according to its file ID in an inaccessible system directory. For example:
>>> f = tempfile.NamedTemporaryFile()
>>> h = msvcrt.get_osfhandle(f.fileno())
>>> print(GetFinalPathNameByHandle(h, 0))
This behavior isn’t specified, so other filesystems that implement POSIX delete semantics may have undefined behavior (e.g. fail the request) if
FileNameInfo is called on an existing handle for a file that was deleted POSIX style.