Re: [PATCH 2/6] rust: hrtimer: Add HrTimerCallbackContext and ::forward()

Lyude Paul
2025-04-11T20:48:55Z

On Thu, 2025-04-10 at 08:21 +0200, Andreas Hindborg wrote:
> "Lyude Paul" <lyude@redhat.com> writes:
>
>
> We should not be able to obtain a unique reference/pointer when the
> timer is armed. In this case the timer handle will somehow own the
> timer, either directly, by refcount, or by reference.
>
> At any rate, you can add this to the current series, or you can submit
> it later as a separate series. I don't think we need to stall the
> current series till we figure this out. But it is good to keep it in mind.

Gotcha. JFYI - I was about to just leave a note instead of implementing this
until I realized that actually this is a lot simpler to implement then I
realized. It turns out I actually don't think we need to check if the timer is
running or even cancel it before forwarding. For tbox and pin_mut, both
require that we sacrifice the type in question in order to schedule the timer.
This actually means that if we add a context-less forward to hrtimer there
would be exactly three places forward could be called:

* Outside of the timer callback context. So we have both uniqueness and a
confirmation the timer can't be running, since otherwise we wouldn't have
access to the type anymore since it would be consumed (we do have the timer
handle of course, but I -think- that should be fine so long as the only
thing the timer handle can be used for is stopping the timer).
* Inside the timer callback context through HrTimerCallbackContext of course
* Inside the timer callback context through direct access to the HrTimer<T>,
which pretty much means it's identical to using HrTimerCallbackContext in
this case.

So - I think this should be good :). I will include it in the next patch
series and we can figure out what to do, I'm still open to dropping it and
leaving it for later if we decide it's going to be too much work for the time
being.
>
>
> Best regards,
> Andreas Hindborg
>
>
>

--
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