thumbs

File thumbnails the way the freedesktop desktops make them. A thumbnail lives in the shared cache ($XDG_CACHE_HOME/thumbnails, the Thumbnail Managing Standard), so one made by another file manager shows at once, and the reverse. A missing one is made by a thumbnailer installed on the system (a .thumbnailer entry, the contract GNOME, COSMIC and glycin share). It runs as a plain argv in its own process group under a timeout, and its output is checked before it is cached. Thumbnailers reach every format the system knows, and keep decoders MixOS cannot ship under its licences (FFmpeg-backed video, for one) in their own process.

The crate is headless: no toolkit, no pixels. Showing a cached thumbnail is toolkit::thumbnail's part.

• Pool<K> makes thumbnails off the caller's thread. Each Request has a lane (a new request replaces the one waiting in its lane) and a Ticket (a shared generation counter: bump it when the view moves on, and its requests are dropped or their runs killed). Replies go to the callback given to Pool::new, which also names the app the cache is written as.
• generate::Generator makes one thumbnail. Everything that touches the file before its thumbnailer runs happens on a probe thread under a deadline, so a hung filesystem strands a thread, never a worker.
• mounts refuses network, FUSE and automounted files from the mount table before anything touches them.
• cache, png and registry are the cache, the few PNG facts it needs, and the installed thumbnailers.

Users: DOpus (the Properties preview). Build and test with cargo test -p thumbs.

The source is libs/thumbs.

Known limits

• Output is checked structurally, never decoded (no decoders here), so a well-formed PNG with corrupt image data is cached as ready. The display side shows the type icon for it until the file changes.
• There is no way to withdraw one lane's waiting request short of making its ticket stale. A folder view that scrolls will want one; it can be added without changing what exists.
• The PNG and mountinfo parsers have unit tests but no fuzz targets yet.