arc.rs

  1// SPDX-License-Identifier: GPL-2.0
  2
  3use super::HasHrTimer;
  4use super::HrTimer;
  5use super::HrTimerCallback;
  6use super::HrTimerCallbackContext;
  7use super::HrTimerHandle;
  8use super::HrTimerMode;
  9use super::HrTimerPointer;
 10use super::RawHrTimerCallback;
 11use crate::sync::Arc;
 12use crate::sync::ArcBorrow;
 13
 14/// A handle for an `Arc<HasHrTimer<T>>` returned by a call to
 15/// [`HrTimerPointer::start`].
 16pub struct ArcHrTimerHandle<T>
 17where
 18    T: HasHrTimer<T>,
 19{
 20    pub(crate) inner: Arc<T>,
 21}
 22
 23// SAFETY: We implement drop below, and we cancel the timer in the drop
 24// implementation.
 25unsafe impl<T> HrTimerHandle for ArcHrTimerHandle<T>
 26where
 27    T: HasHrTimer<T>,
 28{
 29    fn cancel(&mut self) -> bool {
 30        let self_ptr = Arc::as_ptr(&self.inner);
 31
 32        // SAFETY: As we obtained `self_ptr` from a valid reference above, it
 33        // must point to a valid `T`.
 34        let timer_ptr = unsafe { <T as HasHrTimer<T>>::raw_get_timer(self_ptr) };
 35
 36        // SAFETY: As `timer_ptr` points into `T` and `T` is valid, `timer_ptr`
 37        // must point to a valid `HrTimer` instance.
 38        unsafe { HrTimer::<T>::raw_cancel(timer_ptr) }
 39    }
 40}
 41
 42impl<T> Drop for ArcHrTimerHandle<T>
 43where
 44    T: HasHrTimer<T>,
 45{
 46    fn drop(&mut self) {
 47        self.cancel();
 48    }
 49}
 50
 51impl<T> HrTimerPointer for Arc<T>
 52where
 53    T: 'static,
 54    T: Send + Sync,
 55    T: HasHrTimer<T>,
 56    T: for<'a> HrTimerCallback<Pointer<'a> = Self>,
 57{
 58    type TimerMode = <T as HasHrTimer<T>>::TimerMode;
 59    type TimerHandle = ArcHrTimerHandle<T>;
 60
 61    fn start(
 62        self,
 63        expires: <<T as HasHrTimer<T>>::TimerMode as HrTimerMode>::Expires,
 64    ) -> ArcHrTimerHandle<T> {
 65        // SAFETY:
 66        //  - We keep `self` alive by wrapping it in a handle below.
 67        //  - Since we generate the pointer passed to `start` from a valid
 68        //    reference, it is a valid pointer.
 69        unsafe { T::start(Arc::as_ptr(&self), expires) };
 70        ArcHrTimerHandle { inner: self }
 71    }
 72}
 73
 74impl<T> RawHrTimerCallback for Arc<T>
 75where
 76    T: 'static,
 77    T: HasHrTimer<T>,
 78    T: for<'a> HrTimerCallback<Pointer<'a> = Self>,
 79{
 80    type CallbackTarget<'a> = ArcBorrow<'a, T>;
 81
 82    unsafe extern "C" fn run(ptr: *mut bindings::hrtimer) -> bindings::hrtimer_restart {
 83        // `HrTimer` is `repr(C)`
 84        let timer_ptr = ptr.cast::<super::HrTimer<T>>();
 85
 86        // SAFETY: By C API contract `ptr` is the pointer we passed when
 87        // queuing the timer, so it is a `HrTimer<T>` embedded in a `T`.
 88        let data_ptr = unsafe { T::timer_container_of(timer_ptr) };
 89
 90        // SAFETY:
 91        //  - `data_ptr` is derived form the pointer to the `T` that was used to
 92        //    queue the timer.
 93        //  - As per the safety requirements of the trait `HrTimerHandle`, the
 94        //    `ArcHrTimerHandle` associated with this timer is guaranteed to
 95        //    be alive until this method returns. That handle borrows the `T`
 96        //    behind `data_ptr` thus guaranteeing the validity of
 97        //    the `ArcBorrow` created below.
 98        //  - We own one refcount in the `ArcTimerHandle` associated with this
 99        //    timer, so it is not possible to get a `UniqueArc` to this
100        //    allocation from other `Arc` clones.
101        let receiver = unsafe { ArcBorrow::from_raw(data_ptr) };
102
103        // SAFETY:
104        // - By C API contract `timer_ptr` is the pointer that we passed when queuing the timer, so
105        //   it is a valid pointer to a `HrTimer<T>` embedded in a `T`.
106        // - We are within `RawHrTimerCallback::run`
107        let context = unsafe { HrTimerCallbackContext::from_raw(timer_ptr) };
108
109        T::run(receiver, context).into_c()
110    }
111}