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53 lines
1.8 KiB
Rust
53 lines
1.8 KiB
Rust
// SPDX-License-Identifier: MIT OR Apache-2.0
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//
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// Copyright (c) 2018-2019 Andre Richter <andre.o.richter@gmail.com>
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//! Synchronization primitives.
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use crate::interface;
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use core::cell::UnsafeCell;
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//--------------------------------------------------------------------------------------------------
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// Arch-public
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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 to the
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/// 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 single-threaded, aka only running on a single core with interrupts disabled.
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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 NullLock<T: ?Sized> {
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data: UnsafeCell<T>,
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}
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unsafe impl<T: ?Sized + Send> Send for NullLock<T> {}
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unsafe impl<T: ?Sized + Send> Sync for NullLock<T> {}
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impl<T> NullLock<T> {
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pub const fn new(data: T) -> NullLock<T> {
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NullLock {
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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 implementations
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//--------------------------------------------------------------------------------------------------
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impl<T> interface::sync::Mutex for &NullLock<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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f(unsafe { &mut *self.data.get() })
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}
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}
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