eonix/crates/eonix_sync/src/spin/guard.rs

use super::{Relax, Spin, SpinRelax};
use crate::{marker::NotSend, ForceUnlockableGuard, UnlockableGuard, UnlockedGuard};
use core::{
    marker::PhantomData,
    mem::ManuallyDrop,
    ops::{Deref, DerefMut},
};

pub struct SpinGuard<'a, T, R = SpinRelax>
where
    T: ?Sized,
{
    pub(super) lock: &'a Spin<T, R>,
    pub(super) value: &'a mut T,
    /// We don't want this to be `Send` because we don't want to allow the guard to be
    /// transferred to another thread since we have disabled the preemption on the local cpu.
    pub(super) _not_send: PhantomData<NotSend>,
}

pub struct SpinIrqGuard<'a, T, R = SpinRelax>
where
    T: ?Sized,
{
    pub(super) lock: &'a Spin<T, R>,
    pub(super) value: &'a mut T,
    pub(super) irq_state: ManuallyDrop<arch::IrqState>,
    /// We don't want this to be `Send` because we don't want to allow the guard to be
    /// transferred to another thread since we have disabled the preemption and saved
    /// IRQ states on the local cpu.
    pub(super) _not_send: PhantomData<NotSend>,
}

pub struct UnlockedSpinGuard<'a, T, R>(&'a Spin<T, R>)
where
    T: ?Sized;

pub struct UnlockedSpinIrqGuard<'a, T, R>
where
    T: ?Sized,
{
    lock: &'a Spin<T, R>,
    irq_state: arch::IrqState,
}

// SAFETY: As long as the value protected by the lock is able to be shared between threads,
//         we can access the guard from multiple threads.
unsafe impl<T, R> Sync for SpinGuard<'_, T, R> where T: ?Sized + Sync {}

// SAFETY: As long as the value protected by the lock is able to be shared between threads,
//         we can access the guard from multiple threads.
unsafe impl<T, R> Sync for SpinIrqGuard<'_, T, R> where T: ?Sized + Sync {}

impl<T, R> Drop for SpinGuard<'_, T, R>
where
    T: ?Sized,
{
    fn drop(&mut self) {
        unsafe {
            // SAFETY: We are dropping the guard, so we are not holding the lock anymore.
            self.lock.do_unlock();
        }
    }
}

impl<T, R> Drop for SpinIrqGuard<'_, T, R>
where
    T: ?Sized,
{
    fn drop(&mut self) {
        unsafe {
            // SAFETY: We are dropping the guard, so we are not holding the lock anymore.
            self.lock.do_unlock();

            // SAFETY: We are dropping the guard, so we are never going to access the value.
            ManuallyDrop::take(&mut self.irq_state).restore();
        }
    }
}

impl<T, R> Deref for SpinGuard<'_, T, R>
where
    T: ?Sized,
{
    type Target = T;

    fn deref(&self) -> &Self::Target {
        // SAFETY: We are holding the lock, so we can safely access the value.
        self.value
    }
}

impl<T, R> DerefMut for SpinGuard<'_, T, R>
where
    T: ?Sized,
{
    fn deref_mut(&mut self) -> &mut Self::Target {
        // SAFETY: We are holding the lock, so we can safely access the value.
        self.value
    }
}

impl<T, U, R> AsRef<U> for SpinGuard<'_, T, R>
where
    T: ?Sized,
    U: ?Sized,
    <Self as Deref>::Target: AsRef<U>,
{
    fn as_ref(&self) -> &U {
        self.deref().as_ref()
    }
}

impl<T, U, R> AsMut<U> for SpinGuard<'_, T, R>
where
    T: ?Sized,
    U: ?Sized,
    <Self as Deref>::Target: AsMut<U>,
{
    fn as_mut(&mut self) -> &mut U {
        self.deref_mut().as_mut()
    }
}

impl<T, R> Deref for SpinIrqGuard<'_, T, R>
where
    T: ?Sized,
{
    type Target = T;

    fn deref(&self) -> &Self::Target {
        // SAFETY: We are holding the lock, so we can safely access the value.
        self.value
    }
}

impl<T, R> DerefMut for SpinIrqGuard<'_, T, R>
where
    T: ?Sized,
{
    fn deref_mut(&mut self) -> &mut Self::Target {
        // SAFETY: We are holding the lock, so we can safely access the value.
        self.value
    }
}

impl<T, U, R> AsRef<U> for SpinIrqGuard<'_, T, R>
where
    T: ?Sized,
    U: ?Sized,
    <Self as Deref>::Target: AsRef<U>,
{
    fn as_ref(&self) -> &U {
        self.deref().as_ref()
    }
}

impl<T, U, R> AsMut<U> for SpinIrqGuard<'_, T, R>
where
    T: ?Sized,
    U: ?Sized,
    <Self as Deref>::Target: AsMut<U>,
{
    fn as_mut(&mut self) -> &mut U {
        self.deref_mut().as_mut()
    }
}

impl<'a, T, R> UnlockableGuard for SpinGuard<'a, T, R>
where
    T: ?Sized,
    R: Relax,
{
    type Unlocked = UnlockedSpinGuard<'a, T, R>;

    fn unlock(self) -> Self::Unlocked {
        let me = ManuallyDrop::new(self);
        unsafe {
            // SAFETY: No access is possible after unlocking.
            me.lock.do_unlock();
        }

        UnlockedSpinGuard(me.lock)
    }
}

impl<'a, T, R> UnlockableGuard for SpinIrqGuard<'a, T, R>
where
    T: ?Sized,
    R: Relax,
{
    type Unlocked = UnlockedSpinIrqGuard<'a, T, R>;

    fn unlock(self) -> Self::Unlocked {
        let mut me = ManuallyDrop::new(self);
        unsafe {
            // SAFETY: No access is possible after unlocking.
            me.lock.do_unlock();
        }

        UnlockedSpinIrqGuard {
            lock: me.lock,
            // SAFETY: `me` is going to be dropped so never used again.
            irq_state: unsafe { ManuallyDrop::take(&mut me.irq_state) },
        }
    }
}

// SAFETY: The guard is stateless so no more process needed.
unsafe impl<'a, T, R> UnlockedGuard for UnlockedSpinGuard<'a, T, R>
where
    T: ?Sized,
    R: Relax,
{
    type Guard = SpinGuard<'a, T, R>;

    fn relock(self) -> Self::Guard {
        let Self(lock) = self;
        lock.lock()
    }
}

// SAFETY: The guard is stateless so no more process needed.
unsafe impl<'a, T, R> UnlockedGuard for UnlockedSpinIrqGuard<'a, T, R>
where
    T: ?Sized,
    R: Relax,
{
    type Guard = SpinIrqGuard<'a, T, R>;

    fn relock(self) -> Self::Guard {
        let mut guard = self.lock.lock_irq();

        guard.irq_state = ManuallyDrop::new(self.irq_state);
        guard
    }
}

impl<'a, T, R> ForceUnlockableGuard for SpinGuard<'a, T, R>
where
    T: ?Sized,
    R: Relax,
{
    unsafe fn force_unlock(&mut self) {
        unsafe {
            // SAFETY: The caller assures that the value is no longer accessed.
            self.lock.do_unlock();
        }
    }

    unsafe fn force_relock(&mut self) {
        self.lock.do_lock();
    }
}

impl<'a, T, R> ForceUnlockableGuard for SpinIrqGuard<'a, T, R>
where
    T: ?Sized,
    R: Relax,
{
    unsafe fn force_unlock(&mut self) {
        unsafe {
            // SAFETY: The caller assures that the value is no longer accessed.
            self.lock.do_unlock();
        }

        // IRQ state is not restored.
    }

    unsafe fn force_relock(&mut self) {
        self.lock.do_lock();
    }
}