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48 lines
1.4 KiB
Rust
48 lines
1.4 KiB
Rust
5 years ago
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// SPDX-License-Identifier: MIT
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//
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// Copyright (c) 2018-2019 Andre Richter <andre.o.richter@gmail.com>
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5 years ago
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//! Synchronization primitives.
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5 years ago
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use crate::interface;
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use core::cell::UnsafeCell;
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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
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/// concurrent access to the contained data. This part is preserved for later
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/// 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
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/// the kernel is executing single-threaded, aka only running on a single core
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/// 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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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
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// ensures that this mutable reference will ever only be given out once
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// 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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