The live test showed a read during a background refresh taking 2.2 s instead
of 0.07 s: the walk held the GIL for about 2 s in the server. py-spy split
that walk into two halves: Path.relative_to per file in folder_sets, and
Path.stat + Path.is_symlink + Path joins per file in the scan.
- _walk_media visits folders in os.walk's order with os.scandir entries:
the file type comes from the listing (no lstat per file) and the mtime
from entry.stat (one call, none on Windows). _iter_media_files is now a
thin wrapper, so its other caller is unchanged.
- folder_sets slices the path strings (in the path flavour's separator)
instead of calling relative_to, falling back to it for a path that does
not start with the root string.
On the maintainer's 19,935-file output folder: scan 0.386 s -> 0.112 s,
folder sets 0.452 s -> 0.007 s, both results identical to the previous code.
A reference copy of the os.walk version checks order, filters, the depth
cap, symlinks and the file cap.
Vito Sansevero
168af0d868