63 lines
2.3 KiB
Rust
63 lines
2.3 KiB
Rust
/*
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* MIT License
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*
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* Copyright (c) 2019 Andre Richter <andre.o.richter@gmail.com>
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in all
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* copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*/
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use core::cell::UnsafeCell;
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pub struct NullLock<T> {
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data: UnsafeCell<T>,
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}
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// Since we are instantiating this struct as a static variable, which could
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// potentially be shared between different threads, we need to tell the compiler
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// that sharing of this struct is safe by marking it with the Sync trait.
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//
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// At this point in time, we can do so without worrying, because the kernel
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// anyways runs on a single core and interrupts are disabled. In short, multiple
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// threads don't exist yet in our code.
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//
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// Literature:
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// https://doc.rust-lang.org/beta/nomicon/send-and-sync.html
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// https://doc.rust-lang.org/book/ch16-04-extensible-concurrency-sync-and-send.html
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unsafe impl<T> 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> NullLock<T> {
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pub fn lock<F, R>(&self, f: F) -> R
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where
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F: FnOnce(&mut T) -> R,
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{
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// In a real lock, there would be code around this line that ensures
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// that this mutable reference will ever only be given out to one thread
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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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