tree bff9e203e01731dd6caa0b8d3ee8488e237790a1
parent cb1b906e444a790e51af3089506c105177b31e22
author Boqun Feng <boqun.feng@gmail.com> 1750265373 -0700
committer Boqun Feng <boqun.feng@gmail.com> 1752125601 -0700

WIP: rust: sync: atomic: Add Atomic<*mut T>

Add atomic support for raw pointer values, similar to `isize` and
`usize`, the representation type is selected based on CONFIG_64BIT.

`*mut T` is not `Send`, however `Atomic<*mut T>` definitely needs to be
a `Sync`, and that's the whole point of atomics: being able to have
multiple shared references in different threads so that they can sync
with each other. As a result, a pointer value will be transferred from
one thread to another via `Atomic<*mut T>`:

	<thread 1>		<thread 2>
	x.store(p1, Relaxed);
				let p = x.load(p1, Relaxed);

This means a raw pointer value (`*mut T`) needs to be able to transfer
across thread boundaries, which is essentially `Send`.

To reflect this in the type system, and based on the fact that pointer
values can be transferred safely (only using them to dereference is
unsafe), as suggested by Alice, extend the `AllowAtomic` trait to
include a customized `Send` semantics, that is: `impl AllowAtomic` has
to be safe to be transferred across thread boundaries.

Suggested-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>