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151 lines
5.0 KiB
Rust
151 lines
5.0 KiB
Rust
// SPDX-License-Identifier: MIT OR Apache-2.0
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//
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// Copyright (c) 2020 Andre Richter <andre.o.richter@gmail.com>
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//! Synchronization primitives.
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use core::cell::UnsafeCell;
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//--------------------------------------------------------------------------------------------------
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// Public Definitions
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//--------------------------------------------------------------------------------------------------
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/// Synchronization interfaces.
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pub mod interface {
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/// Any object implementing this trait guarantees exclusive access to the data contained within
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/// the Mutex for the duration of the provided closure.
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///
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/// The trait follows the [Rust embedded WG's
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/// proposal](https://github.com/korken89/wg/blob/master/rfcs/0377-mutex-trait.md) and therefore
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/// provides some goodness such as [deadlock
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/// prevention](https://github.com/korken89/wg/blob/master/rfcs/0377-mutex-trait.md#design-decisions-and-compatibility).
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///
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/// # Example
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///
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/// Since the lock function takes an `&mut self` to enable deadlock-prevention, the trait is
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/// best implemented **for a reference to a container struct**, and has a usage pattern that
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/// might feel strange at first:
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///
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/// ```
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/// static MUT: Mutex<RefCell<i32>> = Mutex::new(RefCell::new(0));
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///
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/// fn foo() {
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/// let mut r = &MUT; // Note that r is mutable
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/// r.lock(|data| *data += 1);
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/// }
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/// ```
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pub trait Mutex {
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/// The type of encapsulated data.
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type Data;
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/// Creates a critical section and grants temporary mutable access to the encapsulated data.
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fn lock<R>(&mut self, f: impl FnOnce(&mut Self::Data) -> R) -> R;
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}
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/// A reader-writer exclusion type.
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///
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/// The implementing object allows either a number of readers or at most one writer at any point
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/// in time.
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pub trait ReadWriteEx {
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/// The type of encapsulated data.
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type Data;
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/// Grants temporary mutable access to the encapsulated data.
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fn write<R>(&mut self, f: impl FnOnce(&mut Self::Data) -> R) -> R;
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/// Grants temporary immutable access to the encapsulated data.
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fn read<R>(&mut self, f: impl FnOnce(&Self::Data) -> R) -> R;
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}
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}
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/// A pseudo-lock for teaching purposes.
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///
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/// Used to introduce [interior mutability].
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///
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/// In contrast to a real Mutex implementation, does not protect against concurrent access from
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/// other cores to the contained data. This part is preserved for later lessons.
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///
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/// The lock will only be used as long as it is safe to do so, i.e. as long as the kernel is
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/// executing on a single core.
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///
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/// [interior mutability]: https://doc.rust-lang.org/std/cell/index.html
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pub struct IRQSafeNullLock<T: ?Sized> {
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data: UnsafeCell<T>,
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}
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/// A pseudo-lock that is RW during the single-core kernel init phase and RO afterwards.
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///
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/// Intended to encapsulate data that is populated during kernel init when no concurrency exists.
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pub struct InitStateLock<T: ?Sized> {
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data: UnsafeCell<T>,
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}
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//--------------------------------------------------------------------------------------------------
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// Public Code
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//--------------------------------------------------------------------------------------------------
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unsafe impl<T: ?Sized> Sync for IRQSafeNullLock<T> {}
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impl<T> IRQSafeNullLock<T> {
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/// Wraps `data` into a new `IRQSafeNullLock`.
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pub const fn new(data: T) -> Self {
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Self {
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data: UnsafeCell::new(data),
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}
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}
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}
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unsafe impl<T: ?Sized> Sync for InitStateLock<T> {}
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impl<T> InitStateLock<T> {
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pub const fn new(data: T) -> Self {
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Self {
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data: UnsafeCell::new(data),
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}
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}
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}
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//------------------------------------------------------------------------------
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// OS Interface Code
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//------------------------------------------------------------------------------
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use crate::{exception, state};
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impl<T> interface::Mutex for &IRQSafeNullLock<T> {
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type Data = T;
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fn lock<R>(&mut self, f: impl FnOnce(&mut Self::Data) -> R) -> R {
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// In a real lock, there would be code encapsulating this line that ensures that this
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// mutable reference will ever only be given out once at a time.
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let data = unsafe { &mut *self.data.get() };
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// Execute the closure while IRQs are masked.
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exception::asynchronous::exec_with_irq_masked(|| f(data))
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}
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}
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impl<T> interface::ReadWriteEx for &InitStateLock<T> {
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type Data = T;
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fn write<R>(&mut self, f: impl FnOnce(&mut Self::Data) -> R) -> R {
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assert!(
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state::state_manager().state() == state::State::Init,
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"InitStateLock::write called after kernel init phase"
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);
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assert!(
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!exception::asynchronous::is_local_irq_masked(),
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"InitStateLock::write called with IRQs unmasked"
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);
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let data = unsafe { &mut *self.data.get() };
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f(data)
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}
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fn read<R>(&mut self, f: impl FnOnce(&Self::Data) -> R) -> R {
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let data = unsafe { &*self.data.get() };
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f(data)
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}
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}
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