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78 lines
2.7 KiB
Rust
78 lines
2.7 KiB
Rust
// SPDX-License-Identifier: MIT OR Apache-2.0
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//
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// Copyright (c) 2020-2022 Andre Richter <andre.o.richter@gmail.com>
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//! Synchronization primitives.
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//!
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//! # Resources
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//!
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//! - <https://doc.rust-lang.org/book/ch16-04-extensible-concurrency-sync-and-send.html>
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//! - <https://stackoverflow.com/questions/59428096/understanding-the-send-trait>
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//! - <https://doc.rust-lang.org/std/cell/index.html>
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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 wrapped within
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/// the Mutex for the duration of the provided closure.
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pub trait Mutex {
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/// The type of the data that is wrapped by this mutex.
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type Data;
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/// Locks the mutex and grants the closure temporary mutable access to the wrapped data.
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fn lock<'a, R>(&'a self, f: impl FnOnce(&'a mut 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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/// 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 single-threaded, aka only running on a single core with interrupts disabled.
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pub struct NullLock<T>
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where
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T: ?Sized,
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{
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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> Send for NullLock<T> where T: ?Sized + Send {}
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unsafe impl<T> Sync for NullLock<T> where T: ?Sized + Send {}
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impl<T> NullLock<T> {
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/// Create an instance.
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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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impl<T> interface::Mutex for NullLock<T> {
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type Data = T;
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fn lock<'a, R>(&'a self, f: impl FnOnce(&'a 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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f(data)
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}
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}
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