forked from unom/punktfunk
enricobuehler
d2b6f5b65f
`unsafe impl Send`/`Sync` is the highest-risk unsafe category here and the one this program had never looked at: a wrong one is cross-thread UB that is invisible at every call site, with no `unsafe` block to catch a reviewer's eye. 49 of them (41 Send, 8 Sync). Two results. **`MappedView`'s `Sync` proof was factually wrong.** It read "only exposes accessors that are safe under concurrent use" — they are not. `read_u8`/`write_u8`/`read_u16` are plain unaligned accesses through `&self`, and `&MappedView` really is shared across threads: `ChannelState::data()` hands out `&'static MappedView`, and pf-xusb, pf-mouse and pf-gamepad all dispatch `WdfIoQueueDispatchParallel` with `NumberOfPresentedRequests = u32::MAX`. The struct's own doc had the right story — consistency is the channel protocol's job — but the `unsafe impl` stated a different, stronger claim, which is the one a reviewer checking that line would rely on. The impl is still sound, for a reason worth writing down: these bytes are mapped into ANOTHER PROCESS that writes them concurrently, so Rust-level exclusivity over them is unachievable no matter what this type does. Sync fields go through the atomic accessors; the plain ones cover only protocol-fenced bytes. The proof now says that, and states the rule it implies for accessors added later — plain path only for bytes the protocol already fences. **Four `Send` impls carried a one-line aside instead of a proof** — the pf-client-core decoders and `DrmFrameGuard`. All four are sound, and each now says why, including the two facts that make them work and were nowhere stated: libav permits a codec context to be used from a thread other than its creator provided use is serialised (`&mut self` is that serialisation), and D3D11's immediate context is thread-AGNOSTIC rather than thread-safe — it wants serialised use, not one fixed thread. Each also records that it is deliberately not `Sync`, which is the invariant a future `impl Sync` would silently break. Every one of the 49 now carries reasoning. Verified: Linux .21 fmt + both CI clippy steps rc=0; Windows .47 `-p pf-client-core` clippy `-D warnings` rc=0 (it compiles the `video_d3d11` proof the Linux run cannot see). The pf-umdf-util edit is comment-only — confirmed by diff, since that crate needs the WDK, which .47 does not have.