[PATCH v10 1/8] rust: types: add `NotThreadSafe`

[Serge E. Hallyn]

On Wed, Sep 25, 2024 at 01:06:10PM +0200, Alice Ryhl wrote:
> On Tue, Sep 24, 2024 at 9:45 PM Serge E. Hallyn <serge at hallyn.com> wrote:
> >
> > On Sun, Sep 15, 2024 at 02:31:27PM +0000, Alice Ryhl wrote:
> > > This introduces a new marker type for types that shouldn't be thread
> > > safe. By adding a field of this type to a struct, it becomes non-Send
> > > and non-Sync, which means that it cannot be accessed in any way from
> > > threads other than the one it was created on.
> > >
> > > This is useful for APIs that require globals such as `current` to remain
> > > constant while the value exists.
> > >
> > > We update two existing users in the Kernel to use this helper:
> > >
> > >  * `Task::current()` - moving the return type of this value to a
> > >    different thread would not be safe as you can no longer be guaranteed
> > >    that the `current` pointer remains valid.
> > >  * Lock guards. Mutexes and spinlocks should be unlocked on the same
> > >    thread as where they were locked, so we enforce this using the Send
> > >    trait.
> >
> > Hi,
> >
> > this sounds useful, however from kernel side when I think thread-safe,
> > I think must not be used across a sleep.  Would something like ThreadLocked
> > or LockedToThread make sense?
> 
> Hmm, those names seem pretty similar to the current name to me?

Seems very different to me:

If @foo is not threadsafe, it may be global or be usable by many
threads, but must be locked to one thread during access.

What you're describing here is (iiuc) that @foo must only be used
by one particular thread.

-serge