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/* * Copyright (C) 2021 taylor.fish <contact@taylor.fish> * * This file is part of fixed-bump. * * fixed-bump is free software: you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation, either version 3 of the License, or * (at your option) any later version. * * fixed-bump is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with fixed-bump. If not, see <https://www.gnu.org/licenses/>. */ use super::inner::BumpInner; use alloc::alloc::Layout; #[cfg(feature = "allocator_api")] use alloc::alloc::{AllocError, Allocator}; use core::cell::UnsafeCell; use core::ptr::NonNull; /// A bump allocator that allocates memory in non-amortized O(1) (constant) /// time. /// /// The allocator internally uses fixed-size chunks of memory. The size and /// alignment of each chunk of memory is determined by the type parameters /// `Size` and `Align`: the size is [`mem::size_of::<Size>()`][size_of] and the /// alignment is [`mem::align_of::<Align>()`][align_of]. The default value of /// `Align` is `Size`, so you can specify both the size and alignment with a /// single type parameter. /// /// A common use of this type, and the most space-efficient way to use it, is /// to allocate many values of the same type (or at least the same size and /// alignment). In this case, it may be convenient to specify the chunk size /// using an array type: to use properly aligned chunks large enough to /// allocate `n` values of type `T`, pass `[T; n]` as the `Size` parameter, /// which will also be the `Align` parameter by default. /// /// [size_of]: core::mem::size_of /// [align_of]: core::mem::align_of pub struct Bump<Size, Align = Size>(UnsafeCell<BumpInner<Size, Align>>); impl<Size, Align> Bump<Size, Align> { /// Creates a new [`Bump`]. pub fn new() -> Self { Self(UnsafeCell::new(BumpInner::new())) } /// Tries to allocate memory with a size and alignment matching `layout`. /// /// Returns a pointer to the memory on success, or [`None`] on failure. /// The memory is valid until the [`Bump`] is dropped. Note that the /// returned memory could be larger than [`layout.size()`]. /// /// This method is similar to [`Allocator::allocate`], except it returns an /// [`Option`] instead of a [`Result`]. /// /// Allocation is guaranteed to succeed, assuming the global allocator /// succeeds, if [`layout.size()`] is less than or equal to /// [`mem::size_of::<Size>()`][size_of] and [`layout.align()`] is less than /// or equal to [`mem::align_of::<Align>()`][align_of]. /// /// Allocation may fail, but is not guaranteed to fail, if /// [`layout.align()`] is greater than /// [`mem::align_of::<Align>()`][align_of]. Allocation *is* guaranteed to /// fail if [`layout.size()`] is greater than /// [`mem::size_of::<Size>()`][size_of]. /// /// [`layout.size()`]: Layout::size /// [`layout.align()`]: Layout::align /// [size_of]: core::mem::size_of /// [align_of]: core::mem::align_of /// [`Allocator::allocate`]: alloc::alloc::Allocator::allocate pub fn allocate(&self, layout: Layout) -> Option<NonNull<[u8]>> { // SAFETY: `BumpInner::alloc` does not run any code that could possibly // call any methods of `Self`, which ensures that we do not borrow the // data in the `UnsafeCell` multiple times concurrently. unsafe { &mut *self.0.get() }.allocate(layout) } /// Allocates a value of type `T`. /// /// The memory is initialized with `value` and a reference to the value is /// returned. Note that the value's destructor will not be called /// automatically. /// /// # Panics /// /// Panics if [`Self::allocate`] is not able to allocate memory matching /// [`Layout::new::<T>()`](Layout::new). See [`Self::allocate`] for /// details regarding the circumstances in which allocation can fail. /// /// For a non-panicking equivalent, see [`Self::try_alloc_value`]. #[allow(clippy::mut_from_ref)] pub fn alloc_value<T>(&self, value: T) -> &mut T { self.try_alloc_value(value).ok().expect("allocation failed") } #[allow(clippy::doc_markdown)] /// Tries to allocate a value of type `T`. /// /// If the allocation succeeds, the memory is initialized with `value` and /// a reference to the value is returned. Note that the value's destructor /// will not be called automatically. /// /// Allocation succeeds if and only if [`Self::allocate`] is able to /// allocate memory matching [`Layout::new::<T>()`]. See [`Self::allocate`] /// for details regarding the circumstances in which allocation can fail. /// /// # Errors /// /// If allocation fails, <code>[Err]\(value)</code> is returned. #[allow(clippy::mut_from_ref)] pub fn try_alloc_value<T>(&self, value: T) -> Result<&mut T, T> { let memory = if let Some(memory) = self.allocate(Layout::new::<T>()) { memory.cast::<T>() } else { return Err(value); }; // SAFETY: `Self::allocate`, when not returning `None`, is guaranteed // to return valid memory that matches the provided layout. Thus, we // can store a value of type `T` in it. unsafe { memory.as_ptr().write(value); } // SAFETY: We just initialized `memory` with `value`. Ok(unsafe { &mut *memory.as_ptr() }) } } impl<Size, Align> Default for Bump<Size, Align> { fn default() -> Self { Self::new() } } // SAFETY: `Bump::allocate` (when not returning `None`) returns pointers to // valid memory that matches the provided `Layout`. // // `&Bump` is a normal reference type, so clones of `&Bump` will behave like // the same allocator, and moving a `&Bump` will not invalidate any returned // memory. #[cfg(feature = "allocator_api")] unsafe impl<Size, Align> Allocator for &Bump<Size, Align> { fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> { (*self).allocate(layout).ok_or(AllocError) } unsafe fn deallocate(&self, _ptr: NonNull<u8>, _layout: Layout) { // No-op: `Bump` deallocates all its memory when dropped. } }