| # Bit-Slice Thread Safety |
| |
| This allows bit-slice references to be moved across thread boundaries only when |
| the underlying `T` element can tolerate concurrency. |
| |
| All `BitSlice` references, shared or exclusive, are only threadsafe if the `T` |
| element type is `Send`, because any given bit-slice reference may only have |
| partial control of a memory element that is also being shared by a bit-slice |
| reference on another thread. As such, this is never implemented for `Cell<U>`, |
| but always implemented for `AtomicU` and `U` for a given unsigned integer type |
| `U`. |
| |
| Atomic integers safely handle concurrent writes, cells do not allow concurrency |
| at all, so the only missing piece is `&mut BitSlice<_, U: Unsigned>`. This is |
| handled by the aliasing system that the mutable splitters employ: a mutable |
| reference to an unsynchronized bit-slice can only cross threads when no other |
| handle is able to exist to the elements it governs. Splitting a mutable |
| bit-slice causes the split halves to change over to either atomics or cells, so |
| concurrency is either safe or impossible. |
