| /*! |
| |
| **A fast bump allocation arena for Rust.** |
| |
| [![](https://docs.rs/bumpalo/badge.svg)](https://docs.rs/bumpalo/) |
| [![](https://img.shields.io/crates/v/bumpalo.svg)](https://crates.io/crates/bumpalo) |
| [![](https://img.shields.io/crates/d/bumpalo.svg)](https://crates.io/crates/bumpalo) |
| [![Build Status](https://dev.azure.com/fitzgen/bumpalo/_apis/build/status/fitzgen.bumpalo?branchName=master)](https://dev.azure.com/fitzgen/bumpalo/_build/latest?definitionId=2&branchName=master) |
| |
| ![](https://github.com/fitzgen/bumpalo/raw/master/bumpalo.png) |
| |
| ## Bump Allocation |
| |
| Bump allocation is a fast, but limited approach to allocation. We have a chunk |
| of memory, and we maintain a pointer within that memory. Whenever we allocate an |
| object, we do a quick test that we have enough capacity left in our chunk to |
| allocate the object and then update the pointer by the object's size. *That's |
| it!* |
| |
| The disadvantage of bump allocation is that there is no general way to |
| deallocate individual objects or reclaim the memory region for a |
| no-longer-in-use object. |
| |
| These trade offs make bump allocation well-suited for *phase-oriented* |
| allocations. That is, a group of objects that will all be allocated during the |
| same program phase, used, and then can all be deallocated together as a group. |
| |
| ## Deallocation en Masse, but No `Drop` |
| |
| To deallocate all the objects in the arena at once, we can simply reset the bump |
| pointer back to the start of the arena's memory chunk. This makes mass |
| deallocation *extremely* fast, but allocated objects' `Drop` implementations are |
| not invoked. |
| |
| ## What happens when the memory chunk is full? |
| |
| This implementation will allocate a new memory chunk from the global allocator |
| and then start bump allocating into this new memory chunk. |
| |
| ## Example |
| |
| ``` |
| use bumpalo::Bump; |
| use std::u64; |
| |
| struct Doggo { |
| cuteness: u64, |
| age: u8, |
| scritches_required: bool, |
| } |
| |
| // Create a new arena to bump allocate into. |
| let bump = Bump::new(); |
| |
| // Allocate values into the arena. |
| let scooter = bump.alloc(Doggo { |
| cuteness: u64::max_value(), |
| age: 8, |
| scritches_required: true, |
| }); |
| |
| assert!(scooter.scritches_required); |
| ``` |
| |
| ## Collections |
| |
| When the `"collections"` cargo feature is enabled, a fork of some of the `std` |
| library's collections are available in the `collections` module. These |
| collection types are modified to allocate their space inside `bumpalo::Bump` |
| arenas. |
| |
| ```rust |
| # #[cfg(feature = "collections")] |
| # { |
| use bumpalo::{Bump, collections::Vec}; |
| |
| // Create a new bump arena. |
| let bump = Bump::new(); |
| |
| // Create a vector of integers whose storage is backed by the bump arena. The |
| // vector cannot outlive its backing arena, and this property is enforced with |
| // Rust's lifetime rules. |
| let mut v = Vec::new_in(&bump); |
| |
| // Push a bunch of integers onto `v`! |
| for i in 0..100 { |
| v.push(i); |
| } |
| # } |
| ``` |
| |
| Eventually [all `std` collection types will be parameterized by an |
| allocator](https://github.com/rust-lang/rust/issues/42774) and we can remove |
| this `collections` module and use the `std` versions. |
| |
| ## `#![no_std]` Support |
| |
| Bumpalo is a `no_std` crate. It depends only on the `alloc` and `core` crates. |
| |
| */ |
| |
| #![deny(missing_debug_implementations)] |
| #![deny(missing_docs)] |
| #![no_std] |
| |
| extern crate alloc as core_alloc; |
| |
| #[cfg(feature = "collections")] |
| pub mod collections; |
| |
| mod alloc; |
| |
| use core::cell::Cell; |
| use core::iter; |
| use core::marker::PhantomData; |
| use core::mem; |
| use core::ptr::{self, NonNull}; |
| use core::slice; |
| use core::str; |
| use core_alloc::alloc::{alloc, dealloc, Layout}; |
| |
| /// An arena to bump allocate into. |
| /// |
| /// ## No `Drop`s |
| /// |
| /// Objects that are bump-allocated will never have their `Drop` implementation |
| /// called — unless you do it manually yourself. This makes it relatively |
| /// easy to leak memory or other resources. |
| /// |
| /// If you have a type which internally manages |
| /// |
| /// * an allocation from the global heap (e.g. `Vec<T>`), |
| /// * open file descriptors (e.g. `std::fs::File`), or |
| /// * any other resource that must be cleaned up (e.g. an `mmap`) |
| /// |
| /// and relies on its `Drop` implementation to clean up the internal resource, |
| /// then if you allocate that type with a `Bump`, you need to find a new way to |
| /// clean up after it yourself. |
| /// |
| /// Potential solutions are |
| /// |
| /// * calling [`drop_in_place`][drop_in_place] or using |
| /// [`std::mem::ManuallyDrop`][manuallydrop] to manually drop these types, |
| /// * using `bumpalo::collections::Vec` instead of `std::vec::Vec`, or |
| /// * simply avoiding allocating these problematic types within a `Bump`. |
| /// |
| /// Note that not calling `Drop` is memory safe! Destructors are never |
| /// guaranteed to run in Rust, you can't rely on them for enforcing memory |
| /// safety. |
| /// |
| /// [drop_in_place]: https://doc.rust-lang.org/stable/std/ptr/fn.drop_in_place.html |
| /// [manuallydrop]: https://doc.rust-lang.org/stable/std/mem/struct.ManuallyDrop.html |
| /// |
| /// ## Example |
| /// |
| /// ``` |
| /// use bumpalo::Bump; |
| /// |
| /// // Create a new bump arena. |
| /// let bump = Bump::new(); |
| /// |
| /// // Allocate values into the arena. |
| /// let forty_two = bump.alloc(42); |
| /// assert_eq!(*forty_two, 42); |
| /// |
| /// // Mutable references are returned from allocation. |
| /// let mut s = bump.alloc("bumpalo"); |
| /// *s = "the bump allocator; and also is a buffalo"; |
| /// ``` |
| #[derive(Debug)] |
| pub struct Bump { |
| // The current chunk we are bump allocating within. |
| current_chunk_footer: Cell<NonNull<ChunkFooter>>, |
| } |
| |
| #[repr(C)] |
| #[derive(Debug)] |
| struct ChunkFooter { |
| // Pointer to the start of this chunk allocation. This footer is always at |
| // the end of the chunk. |
| data: NonNull<u8>, |
| |
| // The layout of this chunk's allocation. |
| layout: Layout, |
| |
| // Link to the previous chunk, if any. |
| prev: Cell<Option<NonNull<ChunkFooter>>>, |
| |
| // Bump allocation finger that is always in the range `self.data..=self`. |
| ptr: Cell<NonNull<u8>>, |
| } |
| |
| impl Default for Bump { |
| fn default() -> Bump { |
| Bump::new() |
| } |
| } |
| |
| impl Drop for Bump { |
| fn drop(&mut self) { |
| unsafe { |
| dealloc_chunk_list(Some(self.current_chunk_footer.get())); |
| } |
| } |
| } |
| |
| #[inline] |
| unsafe fn dealloc_chunk_list(mut footer: Option<NonNull<ChunkFooter>>) { |
| while let Some(f) = footer { |
| footer = f.as_ref().prev.get(); |
| dealloc(f.as_ref().data.as_ptr(), f.as_ref().layout); |
| } |
| } |
| |
| // `Bump`s are safe to send between threads because nothing aliases its owned |
| // chunks until you start allocating from it. But by the time you allocate from |
| // it, the returned references to allocations borrow the `Bump` and therefore |
| // prevent sending the `Bump` across threads until the borrows end. |
| unsafe impl Send for Bump {} |
| |
| #[inline] |
| pub(crate) fn round_up_to(n: usize, divisor: usize) -> Option<usize> { |
| debug_assert!(divisor > 0); |
| debug_assert!(divisor.is_power_of_two()); |
| Some(n.checked_add(divisor - 1)? & !(divisor - 1)) |
| } |
| |
| // After this point, we try to hit page boundaries instead of powers of 2 |
| const PAGE_STRATEGY_CUTOFF: usize = 0x1000; |
| |
| // We only support alignments of up to 16 bytes for iter_allocated_chunks. |
| const SUPPORTED_ITER_ALIGNMENT: usize = 16; |
| const CHUNK_ALIGN: usize = SUPPORTED_ITER_ALIGNMENT; |
| const FOOTER_SIZE: usize = mem::size_of::<ChunkFooter>(); |
| |
| // Assert that ChunkFooter is at most the supported alignment. This will give a compile time error if it is not the case |
| const _FOOTER_ALIGN_ASSERTION: bool = mem::align_of::<ChunkFooter>() <= CHUNK_ALIGN; |
| const _: [(); _FOOTER_ALIGN_ASSERTION as usize] = [()]; |
| |
| // Maximum typical overhead per allocation imposed by allocators. |
| const MALLOC_OVERHEAD: usize = 16; |
| |
| // This is the overhead from malloc, footer and alignment. For instance, if |
| // we want to request a chunk of memory that has at least X bytes usable for |
| // allocations (where X is aligned to CHUNK_ALIGN), then we expect that the |
| // after adding a footer, malloc overhead and alignment, the chunk of memory |
| // the allocator actually sets asside for us is X+OVERHEAD rounded up to the |
| // nearest suitable size boundary. |
| const OVERHEAD: usize = (MALLOC_OVERHEAD + FOOTER_SIZE + (CHUNK_ALIGN - 1)) & !(CHUNK_ALIGN - 1); |
| |
| // Choose a relatively small default initial chunk size, since we double chunk |
| // sizes as we grow bump arenas to amortize costs of hitting the global |
| // allocator. |
| const FIRST_ALLOCATION_GOAL: usize = 1 << 9; |
| |
| // The actual size of the first allocation is going to be a bit smaller |
| // than the goal. We need to make room for the footer, and we also need |
| // take the alignment into account. |
| const DEFAULT_CHUNK_SIZE_WITHOUT_FOOTER: usize = FIRST_ALLOCATION_GOAL - OVERHEAD; |
| |
| #[inline] |
| fn layout_for_array<T>(len: usize) -> Option<Layout> { |
| // TODO: use Layout::array once the rust feature `alloc_layout_extra` |
| // gets stabilized |
| // |
| // According to https://doc.rust-lang.org/reference/type-layout.html#size-and-alignment |
| // the size of a value is always a multiple of it's alignment. But that does not seem to match |
| // with https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.from_size_align |
| // |
| // Let's be on the safe size and round up to the padding in any case. |
| // |
| // An interesting question is whether there needs to be padding at the end of |
| // the last object in the array. Again, we take the safe approach and include it. |
| |
| let layout = Layout::new::<T>(); |
| let size_rounded_up = round_up_to(layout.size(), layout.align())?; |
| let total_size = len.checked_mul(size_rounded_up)?; |
| |
| Layout::from_size_align(total_size, layout.align()).ok() |
| } |
| |
| /// Wrapper around `Layout::from_size_align` that adds debug assertions. |
| #[inline] |
| unsafe fn layout_from_size_align(size: usize, align: usize) -> Layout { |
| if cfg!(debug_assertions) { |
| Layout::from_size_align(size, align).unwrap() |
| } else { |
| Layout::from_size_align_unchecked(size, align) |
| } |
| } |
| |
| #[inline(never)] |
| fn allocation_size_overflow<T>() -> T { |
| panic!("requested allocation size overflowed") |
| } |
| |
| impl Bump { |
| /// Construct a new arena to bump allocate into. |
| /// |
| /// ## Example |
| /// |
| /// ``` |
| /// let bump = bumpalo::Bump::new(); |
| /// # let _ = bump; |
| /// ``` |
| pub fn new() -> Bump { |
| Self::with_capacity(0) |
| } |
| |
| /// Construct a new arena with the specified capacity to bump allocate into. |
| /// |
| /// ## Example |
| /// |
| /// ``` |
| /// let bump = bumpalo::Bump::with_capacity(100); |
| /// # let _ = bump; |
| /// ``` |
| pub fn with_capacity(capacity: usize) -> Bump { |
| let chunk_footer = Self::new_chunk( |
| None, |
| Some(unsafe { layout_from_size_align(capacity, 1) }), |
| None, |
| ); |
| Bump { |
| current_chunk_footer: Cell::new(chunk_footer), |
| } |
| } |
| |
| /// Allocate a new chunk and return its initialized footer. |
| /// |
| /// If given, `layouts` is a tuple of the current chunk size and the |
| /// layout of the allocation request that triggered us to fall back to |
| /// allocating a new chunk of memory. |
| fn new_chunk( |
| old_size_with_footer: Option<usize>, |
| requested_layout: Option<Layout>, |
| prev: Option<NonNull<ChunkFooter>>, |
| ) -> NonNull<ChunkFooter> { |
| unsafe { |
| // As a sane default, we want our new allocation to be about twice as |
| // big as the previous allocation |
| let mut new_size_without_footer = |
| if let Some(old_size_with_footer) = old_size_with_footer { |
| let old_size_without_footer = old_size_with_footer - FOOTER_SIZE; |
| old_size_without_footer |
| .checked_mul(2) |
| .unwrap_or_else(|| oom()) |
| } else { |
| DEFAULT_CHUNK_SIZE_WITHOUT_FOOTER |
| }; |
| |
| // We want to have CHUNK_ALIGN or better alignment |
| let mut align = CHUNK_ALIGN; |
| |
| // If we already know we need to fulfill some request, |
| // make sure we allocate at least enough to satisfy it |
| if let Some(requested_layout) = requested_layout { |
| align = align.max(requested_layout.align()); |
| let requested_size = round_up_to(requested_layout.size(), align) |
| .unwrap_or_else(allocation_size_overflow); |
| new_size_without_footer = new_size_without_footer.max(requested_size); |
| } |
| |
| // We want our allocations to play nice with the memory allocator, |
| // and waste as little memory as possible. |
| // For small allocations, this means that the entire allocation |
| // including the chunk footer and mallocs internal overhead is |
| // as close to a power of two as we can go without going over. |
| // For larger allocations, we only need to get close to a page |
| // boundary without going over. |
| if new_size_without_footer < PAGE_STRATEGY_CUTOFF { |
| new_size_without_footer = |
| (new_size_without_footer + OVERHEAD).next_power_of_two() - OVERHEAD; |
| } else { |
| new_size_without_footer = round_up_to(new_size_without_footer + OVERHEAD, 0x1000) |
| .unwrap_or_else(|| oom()) |
| - OVERHEAD; |
| } |
| |
| debug_assert_eq!(align % CHUNK_ALIGN, 0); |
| debug_assert_eq!(new_size_without_footer % CHUNK_ALIGN, 0); |
| let size = new_size_without_footer |
| .checked_add(FOOTER_SIZE) |
| .unwrap_or_else(allocation_size_overflow); |
| let layout = layout_from_size_align(size, align); |
| |
| debug_assert!(size >= old_size_with_footer.unwrap_or(0) * 2); |
| |
| let data = alloc(layout); |
| let data = NonNull::new(data).unwrap_or_else(|| oom()); |
| |
| // The `ChunkFooter` is at the end of the chunk. |
| let footer_ptr = data.as_ptr() as usize + new_size_without_footer; |
| debug_assert_eq!((data.as_ptr() as usize) % align, 0); |
| debug_assert_eq!(footer_ptr % CHUNK_ALIGN, 0); |
| let footer_ptr = footer_ptr as *mut ChunkFooter; |
| |
| // The bump pointer is initialized to the end of the range we will |
| // bump out of. |
| let ptr = Cell::new(NonNull::new_unchecked(footer_ptr as *mut u8)); |
| |
| ptr::write( |
| footer_ptr, |
| ChunkFooter { |
| data, |
| layout, |
| prev: Cell::new(prev), |
| ptr, |
| }, |
| ); |
| |
| NonNull::new_unchecked(footer_ptr) |
| } |
| } |
| |
| /// Reset this bump allocator. |
| /// |
| /// Performs mass deallocation on everything allocated in this arena by |
| /// resetting the pointer into the underlying chunk of memory to the start |
| /// of the chunk. Does not run any `Drop` implementations on deallocated |
| /// objects; see [the `Bump` type's top-level |
| /// documentation](./struct.Bump.html) for details. |
| /// |
| /// If this arena has allocated multiple chunks to bump allocate into, then |
| /// the excess chunks are returned to the global allocator. |
| /// |
| /// ## Example |
| /// |
| /// ``` |
| /// let mut bump = bumpalo::Bump::new(); |
| /// |
| /// // Allocate a bunch of things. |
| /// { |
| /// for i in 0..100 { |
| /// bump.alloc(i); |
| /// } |
| /// } |
| /// |
| /// // Reset the arena. |
| /// bump.reset(); |
| /// |
| /// // Allocate some new things in the space previously occupied by the |
| /// // original things. |
| /// for j in 200..400 { |
| /// bump.alloc(j); |
| /// } |
| ///``` |
| pub fn reset(&mut self) { |
| // Takes `&mut self` so `self` must be unique and there can't be any |
| // borrows active that would get invalidated by resetting. |
| unsafe { |
| let cur_chunk = self.current_chunk_footer.get(); |
| |
| // Deallocate all chunks except the current one |
| let prev_chunk = cur_chunk.as_ref().prev.replace(None); |
| dealloc_chunk_list(prev_chunk); |
| |
| // Reset the bump finger to the end of the chunk. |
| cur_chunk.as_ref().ptr.set(cur_chunk.cast()); |
| |
| debug_assert!( |
| self.current_chunk_footer |
| .get() |
| .as_ref() |
| .prev |
| .get() |
| .is_none(), |
| "We should only have a single chunk" |
| ); |
| debug_assert_eq!( |
| self.current_chunk_footer.get().as_ref().ptr.get(), |
| self.current_chunk_footer.get().cast(), |
| "Our chunk's bump finger should be reset to the start of its allocation" |
| ); |
| } |
| } |
| |
| /// Allocate an object in this `Bump` and return an exclusive reference to |
| /// it. |
| /// |
| /// ## Panics |
| /// |
| /// Panics if reserving space for `T` would cause an overflow. |
| /// |
| /// ## Example |
| /// |
| /// ``` |
| /// let bump = bumpalo::Bump::new(); |
| /// let x = bump.alloc("hello"); |
| /// assert_eq!(*x, "hello"); |
| /// ``` |
| #[inline(always)] |
| #[allow(clippy::mut_from_ref)] |
| pub fn alloc<T>(&self, val: T) -> &mut T { |
| self.alloc_with(|| val) |
| } |
| |
| /// Pre-allocate space for an object in this `Bump`, initializes it using |
| /// the closure, then returns an exclusive reference to it. |
| /// |
| /// Calling `bump.alloc(x)` is essentially equivalent to calling |
| /// `bump.alloc_with(|| x)`. However if you use `alloc_with`, then the |
| /// closure will not be invoked until after allocating space for storing |
| /// `x` on the heap. |
| /// |
| /// This can be useful in certain edge-cases related to compiler |
| /// optimizations. When evaluating `bump.alloc(x)`, semantically `x` is |
| /// first put on the stack and then moved onto the heap. In some cases, |
| /// the compiler is able to optimize this into constructing `x` directly |
| /// on the heap, however in many cases it does not. |
| /// |
| /// The function `alloc_with` tries to help the compiler be smarter. In |
| /// most cases doing `bump.alloc_with(|| x)` on release mode will be |
| /// enough to help the compiler to realize this optimization is valid |
| /// and construct `x` directly onto the heap. |
| /// |
| /// ## Warning |
| /// |
| /// This function critically depends on compiler optimizations to achieve |
| /// its desired effect. This means that it is not an effective tool when |
| /// compiling without optimizations on. |
| /// |
| /// Even when optimizations are on, this function does not **guarantee** |
| /// that the value is constructed on the heap. To the best of our |
| /// knowledge no such guarantee can be made in stable Rust as of 1.33. |
| /// |
| /// ## Panics |
| /// |
| /// Panics if reserving space for `T` would cause an overflow. |
| /// |
| /// ## Example |
| /// |
| /// ``` |
| /// let bump = bumpalo::Bump::new(); |
| /// let x = bump.alloc_with(|| "hello"); |
| /// assert_eq!(*x, "hello"); |
| /// ``` |
| #[inline(always)] |
| #[allow(clippy::mut_from_ref)] |
| pub fn alloc_with<F, T>(&self, f: F) -> &mut T |
| where |
| F: FnOnce() -> T, |
| { |
| #[inline(always)] |
| unsafe fn inner_writer<T, F>(ptr: *mut T, f: F) |
| where |
| F: FnOnce() -> T, |
| { |
| // This function is translated as: |
| // - allocate space for a T on the stack |
| // - call f() with the return value being put onto this stack space |
| // - memcpy from the stack to the heap |
| // |
| // Ideally we want LLVM to always realize that doing a stack |
| // allocation is unnecessary and optimize the code so it writes |
| // directly into the heap instead. It seems we get it to realize |
| // this most consistently if we put this critical line into it's |
| // own function instead of inlining it into the surrounding code. |
| ptr::write(ptr, f()) |
| } |
| |
| let layout = Layout::new::<T>(); |
| |
| unsafe { |
| let p = self.alloc_layout(layout); |
| let p = p.as_ptr() as *mut T; |
| inner_writer(p, f); |
| &mut *p |
| } |
| } |
| |
| /// `Copy` a slice into this `Bump` and return an exclusive reference to |
| /// the copy. |
| /// |
| /// ## Panics |
| /// |
| /// Panics if reserving space for the slice would cause an overflow. |
| /// |
| /// ## Example |
| /// |
| /// ``` |
| /// let bump = bumpalo::Bump::new(); |
| /// let x = bump.alloc_slice_copy(&[1, 2, 3]); |
| /// assert_eq!(x, &[1, 2, 3]); |
| /// ``` |
| #[inline(always)] |
| #[allow(clippy::mut_from_ref)] |
| pub fn alloc_slice_copy<T>(&self, src: &[T]) -> &mut [T] |
| where |
| T: Copy, |
| { |
| let layout = Layout::for_value(src); |
| let dst = self.alloc_layout(layout).cast::<T>(); |
| |
| unsafe { |
| ptr::copy_nonoverlapping(src.as_ptr(), dst.as_ptr(), src.len()); |
| slice::from_raw_parts_mut(dst.as_ptr(), src.len()) |
| } |
| } |
| |
| /// `Clone` a slice into this `Bump` and return an exclusive reference to |
| /// the clone. Prefer `alloc_slice_copy` if `T` is `Copy`. |
| /// |
| /// ## Panics |
| /// |
| /// Panics if reserving space for the slice would cause an overflow. |
| /// |
| /// ## Example |
| /// |
| /// ``` |
| /// #[derive(Clone, Debug, Eq, PartialEq)] |
| /// struct Sheep { |
| /// name: String, |
| /// } |
| /// |
| /// let originals = vec![ |
| /// Sheep { name: "Alice".into() }, |
| /// Sheep { name: "Bob".into() }, |
| /// Sheep { name: "Cathy".into() }, |
| /// ]; |
| /// |
| /// let bump = bumpalo::Bump::new(); |
| /// let clones = bump.alloc_slice_clone(&originals); |
| /// assert_eq!(originals, clones); |
| /// ``` |
| #[inline(always)] |
| #[allow(clippy::mut_from_ref)] |
| pub fn alloc_slice_clone<T>(&self, src: &[T]) -> &mut [T] |
| where |
| T: Clone, |
| { |
| let layout = Layout::for_value(src); |
| let dst = self.alloc_layout(layout).cast::<T>(); |
| |
| unsafe { |
| for (i, val) in src.iter().cloned().enumerate() { |
| ptr::write(dst.as_ptr().add(i), val); |
| } |
| |
| slice::from_raw_parts_mut(dst.as_ptr(), src.len()) |
| } |
| } |
| |
| /// `Copy` a string slice into this `Bump` and return an exclusive reference to it. |
| /// |
| /// ## Panics |
| /// |
| /// Panics if reserving space for the string would cause an overflow. |
| /// |
| /// ## Example |
| /// |
| /// ``` |
| /// let bump = bumpalo::Bump::new(); |
| /// let hello = bump.alloc_str("hello world"); |
| /// assert_eq!("hello world", hello); |
| /// ``` |
| #[inline(always)] |
| #[allow(clippy::mut_from_ref)] |
| pub fn alloc_str(&self, src: &str) -> &mut str { |
| let buffer = self.alloc_slice_copy(src.as_bytes()); |
| unsafe { |
| // This is OK, because it already came in as str, so it is guaranteed to be utf8 |
| str::from_utf8_unchecked_mut(buffer) |
| } |
| } |
| |
| /// Allocates a new slice of size `len` into this `Bump` and returns an |
| /// exclusive reference to the copy. |
| /// |
| /// The elements of the slice are initialized using the supplied closure. |
| /// The closure argument is the position in the slice. |
| /// |
| /// ## Panics |
| /// |
| /// Panics if reserving space for the slice would cause an overflow. |
| /// |
| /// ## Example |
| /// |
| /// ``` |
| /// let bump = bumpalo::Bump::new(); |
| /// let x = bump.alloc_slice_fill_with(5, |i| 5*(i+1)); |
| /// assert_eq!(x, &[5, 10, 15, 20, 25]); |
| /// ``` |
| #[inline(always)] |
| #[allow(clippy::mut_from_ref)] |
| pub fn alloc_slice_fill_with<T, F>(&self, len: usize, mut f: F) -> &mut [T] |
| where |
| F: FnMut(usize) -> T, |
| { |
| let layout = layout_for_array::<T>(len).unwrap_or_else(|| oom()); |
| let dst = self.alloc_layout(layout).cast::<T>(); |
| |
| unsafe { |
| for i in 0..len { |
| ptr::write(dst.as_ptr().add(i), f(i)); |
| } |
| |
| let result = slice::from_raw_parts_mut(dst.as_ptr(), len); |
| debug_assert_eq!(Layout::for_value(result), layout); |
| result |
| } |
| } |
| |
| /// Allocates a new slice of size `len` into this `Bump` and returns an |
| /// exclusive reference to the copy. |
| /// |
| /// All elements of the slice are initialized to `value`. |
| /// |
| /// ## Panics |
| /// |
| /// Panics if reserving space for the slice would cause an overflow. |
| /// |
| /// ## Example |
| /// |
| /// ``` |
| /// let bump = bumpalo::Bump::new(); |
| /// let x = bump.alloc_slice_fill_copy(5, 42); |
| /// assert_eq!(x, &[42, 42, 42, 42, 42]); |
| /// ``` |
| #[inline(always)] |
| #[allow(clippy::mut_from_ref)] |
| pub fn alloc_slice_fill_copy<T: Copy>(&self, len: usize, value: T) -> &mut [T] { |
| self.alloc_slice_fill_with(len, |_| value) |
| } |
| |
| /// Allocates a new slice of size `len` slice into this `Bump` and return an |
| /// exclusive reference to the copy. |
| /// |
| /// All elements of the slice are initialized to `value.clone()`. |
| /// |
| /// ## Panics |
| /// |
| /// Panics if reserving space for the slice would cause an overflow. |
| /// |
| /// ## Example |
| /// |
| /// ``` |
| /// let bump = bumpalo::Bump::new(); |
| /// let s: String = "Hello Bump!".to_string(); |
| /// let x: &[String] = bump.alloc_slice_fill_clone(2, &s); |
| /// assert_eq!(x.len(), 2); |
| /// assert_eq!(&x[0], &s); |
| /// assert_eq!(&x[1], &s); |
| /// ``` |
| #[inline(always)] |
| #[allow(clippy::mut_from_ref)] |
| pub fn alloc_slice_fill_clone<T: Clone>(&self, len: usize, value: &T) -> &mut [T] { |
| self.alloc_slice_fill_with(len, |_| value.clone()) |
| } |
| |
| /// Allocates a new slice of size `len` slice into this `Bump` and return an |
| /// exclusive reference to the copy. |
| /// |
| /// The elements are initialized using the supplied iterator. |
| /// |
| /// ## Panics |
| /// |
| /// Panics if reserving space for the slice would cause an overflow, or if the supplied |
| /// iterator returns fewer elements than it promised. |
| /// |
| /// ## Example |
| /// |
| /// ``` |
| /// let bump = bumpalo::Bump::new(); |
| /// let x: &[i32] = bump.alloc_slice_fill_iter([2, 3, 5].iter().cloned().map(|i| i * i)); |
| /// assert_eq!(x, [4, 9, 25]); |
| /// ``` |
| #[inline(always)] |
| #[allow(clippy::mut_from_ref)] |
| pub fn alloc_slice_fill_iter<T, I>(&self, iter: I) -> &mut [T] |
| where |
| I: IntoIterator<Item = T>, |
| I::IntoIter: ExactSizeIterator, |
| { |
| let mut iter = iter.into_iter(); |
| self.alloc_slice_fill_with(iter.len(), |_| { |
| iter.next().expect("Iterator supplied too few elements") |
| }) |
| } |
| |
| /// Allocates a new slice of size `len` slice into this `Bump` and return an |
| /// exclusive reference to the copy. |
| /// |
| /// All elements of the slice are initialized to `T::default()`. |
| /// |
| /// ## Panics |
| /// |
| /// Panics if reserving space for the slice would cause an overflow. |
| /// |
| /// ## Example |
| /// |
| /// ``` |
| /// let bump = bumpalo::Bump::new(); |
| /// let x = bump.alloc_slice_fill_default::<u32>(5); |
| /// assert_eq!(x, &[0, 0, 0, 0, 0]); |
| /// ``` |
| #[inline(always)] |
| #[allow(clippy::mut_from_ref)] |
| pub fn alloc_slice_fill_default<T: Default>(&self, len: usize) -> &mut [T] { |
| self.alloc_slice_fill_with(len, |_| T::default()) |
| } |
| |
| /// Allocate space for an object with the given `Layout`. |
| /// |
| /// The returned pointer points at uninitialized memory, and should be |
| /// initialized with |
| /// [`std::ptr::write`](https://doc.rust-lang.org/stable/std/ptr/fn.write.html). |
| #[inline(always)] |
| pub fn alloc_layout(&self, layout: Layout) -> NonNull<u8> { |
| if let Some(p) = self.try_alloc_layout_fast(layout) { |
| p |
| } else { |
| self.alloc_layout_slow(layout) |
| } |
| } |
| |
| #[inline(always)] |
| fn try_alloc_layout_fast(&self, layout: Layout) -> Option<NonNull<u8>> { |
| unsafe { |
| if layout.size() == 0 { |
| // We want to use NonNull::dangling here, but that function uses mem::align_of::<T> |
| // internally. For our use-case we cannot call dangling::<T>, since we are not generic |
| // over T; we only have access to the Layout of T. Instead we re-implement the |
| // functionality here. |
| // |
| // See https://github.com/rust-lang/rust/blob/9966af3/src/libcore/ptr/non_null.rs#L70 |
| // for the reference implementation. |
| let ptr = layout.align() as *mut u8; |
| return Some(NonNull::new_unchecked(ptr)); |
| } |
| |
| let footer = self.current_chunk_footer.get(); |
| let footer = footer.as_ref(); |
| let ptr = footer.ptr.get().as_ptr() as usize; |
| let start = footer.data.as_ptr() as usize; |
| debug_assert!(start <= ptr); |
| debug_assert!(ptr <= footer as *const _ as usize); |
| |
| let ptr = ptr.checked_sub(layout.size())?; |
| let aligned_ptr = ptr & !(layout.align() - 1); |
| |
| if aligned_ptr >= start { |
| let aligned_ptr = NonNull::new_unchecked(aligned_ptr as *mut u8); |
| footer.ptr.set(aligned_ptr); |
| Some(aligned_ptr) |
| } else { |
| None |
| } |
| } |
| } |
| |
| // Slow path allocation for when we need to allocate a new chunk from the |
| // parent bump set because there isn't enough room in our current chunk. |
| #[inline(never)] |
| fn alloc_layout_slow(&self, layout: Layout) -> NonNull<u8> { |
| unsafe { |
| let size = layout.size(); |
| |
| // Get a new chunk from the global allocator. |
| let current_footer = self.current_chunk_footer.get(); |
| let current_layout = current_footer.as_ref().layout; |
| let new_footer = Bump::new_chunk( |
| Some(current_layout.size()), |
| Some(layout), |
| Some(current_footer), |
| ); |
| debug_assert_eq!( |
| new_footer.as_ref().data.as_ptr() as usize % layout.align(), |
| 0 |
| ); |
| |
| // Set the new chunk as our new current chunk. |
| self.current_chunk_footer.set(new_footer); |
| |
| let new_footer = new_footer.as_ref(); |
| |
| // Move the bump ptr finger down to allocate room for `val`. We know |
| // this can't overflow because we successfully allocated a chunk of |
| // at least the requested size. |
| let ptr = new_footer.ptr.get().as_ptr() as usize - size; |
| // Round the pointer down to the requested alignment. |
| let ptr = ptr & !(layout.align() - 1); |
| debug_assert!( |
| ptr <= new_footer as *const _ as usize, |
| "{:#x} <= {:#x}", |
| ptr, |
| new_footer as *const _ as usize |
| ); |
| let ptr = NonNull::new_unchecked(ptr as *mut u8); |
| new_footer.ptr.set(ptr); |
| |
| // Return a pointer to the freshly allocated region in this chunk. |
| ptr |
| } |
| } |
| |
| /// Returns an iterator over each chunk of allocated memory that |
| /// this arena has bump allocated into. |
| /// |
| /// The chunks are returned ordered by allocation time, with the most |
| /// recently allocated chunk being returned first, and the least recently |
| /// allocated chunk being returned last. |
| /// |
| /// The values inside each chunk are also ordered by allocation time, with |
| /// the most recent allocation being earlier in the slice, and the least |
| /// recent allocation being towards the end of the slice. |
| /// |
| /// ## Safety |
| /// |
| /// Because this method takes `&mut self`, we know that the bump arena |
| /// reference is unique and therefore there aren't any active references to |
| /// any of the objects we've allocated in it either. This potential aliasing |
| /// of exclusive references is one common footgun for unsafe code that we |
| /// don't need to worry about here. |
| /// |
| /// However, there could be regions of uninitialized memory used as padding |
| /// between allocations, which is why this iterator has items of type |
| /// `[MaybeUninit<u8>]`, instead of simply `[u8]`. |
| /// |
| /// The only way to guarantee that there is no padding between allocations |
| /// or within allocated objects is if all of these properties hold: |
| /// |
| /// 1. Every object allocated in this arena has the same alignment, |
| /// and that alignment is at most 16. |
| /// 2. Every object's size is a multiple of its alignment. |
| /// 3. None of the objects allocated in this arena contain any internal |
| /// padding. |
| /// |
| /// If you want to use this `iter_allocated_chunks` method, it is *your* |
| /// responsibility to ensure that these properties hold before calling |
| /// `MaybeUninit::assume_init` or otherwise reading the returned values. |
| /// |
| /// ## Example |
| /// |
| /// ``` |
| /// let mut bump = bumpalo::Bump::new(); |
| /// |
| /// // Allocate a bunch of `i32`s in this bump arena, potentially causing |
| /// // additional memory chunks to be reserved. |
| /// for i in 0..10000 { |
| /// bump.alloc(i); |
| /// } |
| /// |
| /// // Iterate over each chunk we've bump allocated into. This is safe |
| /// // because we have only allocated `i32`s in this arena, which fulfills |
| /// // the above requirements. |
| /// for ch in bump.iter_allocated_chunks() { |
| /// println!("Used a chunk that is {} bytes long", ch.len()); |
| /// println!("The first byte is {:?}", unsafe { |
| /// ch.get(0).unwrap().assume_init() |
| /// }); |
| /// } |
| /// |
| /// // Within a chunk, allocations are ordered from most recent to least |
| /// // recent. If we allocated 'a', then 'b', then 'c', when we iterate |
| /// // through the chunk's data, we get them in the order 'c', then 'b', |
| /// // then 'a'. |
| /// |
| /// bump.reset(); |
| /// bump.alloc(b'a'); |
| /// bump.alloc(b'b'); |
| /// bump.alloc(b'c'); |
| /// |
| /// assert_eq!(bump.iter_allocated_chunks().count(), 1); |
| /// let chunk = bump.iter_allocated_chunks().nth(0).unwrap(); |
| /// assert_eq!(chunk.len(), 3); |
| /// |
| /// // Safe because we've only allocated `u8`s in this arena, which |
| /// // fulfills the above requirements. |
| /// unsafe { |
| /// assert_eq!(chunk[0].assume_init(), b'c'); |
| /// assert_eq!(chunk[1].assume_init(), b'b'); |
| /// assert_eq!(chunk[2].assume_init(), b'a'); |
| /// } |
| /// ``` |
| pub fn iter_allocated_chunks(&mut self) -> ChunkIter<'_> { |
| ChunkIter { |
| footer: Some(self.current_chunk_footer.get()), |
| bump: PhantomData, |
| } |
| } |
| |
| /// Calculates the number of bytes currently allocated across all chunks. |
| /// |
| /// If you allocate types of different alignments or types with |
| /// larger-than-typical alignment in the same arena, some padding |
| /// bytes might get allocated in the bump arena. Note that those padding |
| /// bytes will add to this method's resulting sum, so you cannot rely |
| /// on it only counting the sum of the sizes of the things |
| /// you've allocated in the arena. |
| /// |
| /// ## Example |
| /// |
| /// ``` |
| /// let bump = bumpalo::Bump::new(); |
| /// let _x = bump.alloc_slice_fill_default::<u32>(5); |
| /// let bytes = bump.allocated_bytes(); |
| /// assert!(bytes >= core::mem::size_of::<u32>() * 5); |
| /// ``` |
| pub fn allocated_bytes(&self) -> usize { |
| let mut footer = Some(self.current_chunk_footer.get()); |
| |
| let mut bytes = 0; |
| |
| while let Some(f) = footer { |
| let foot = unsafe { f.as_ref() }; |
| |
| let ptr = foot.ptr.get().as_ptr() as usize; |
| debug_assert!(ptr <= foot as *const _ as usize); |
| |
| bytes += foot as *const _ as usize - ptr; |
| |
| footer = foot.prev.get(); |
| } |
| |
| bytes |
| } |
| |
| #[inline] |
| unsafe fn is_last_allocation(&self, ptr: NonNull<u8>) -> bool { |
| let footer = self.current_chunk_footer.get(); |
| let footer = footer.as_ref(); |
| footer.ptr.get() == ptr |
| } |
| } |
| |
| /// An iterator over each chunk of allocated memory that |
| /// an arena has bump allocated into. |
| /// |
| /// The chunks are returned ordered by allocation time, with the most recently |
| /// allocated chunk being returned first. |
| /// |
| /// The values inside each chunk is also ordered by allocation time, with the most |
| /// recent allocation being earlier in the slice. |
| /// |
| /// This struct is created by the [`iter_allocated_chunks`] method on |
| /// [`Bump`]. See that function for a safety description regarding reading from the returned items. |
| /// |
| /// [`Bump`]: ./struct.Bump.html |
| /// [`iter_allocated_chunks`]: ./struct.Bump.html#method.iter_allocated_chunks |
| #[derive(Debug)] |
| pub struct ChunkIter<'a> { |
| footer: Option<NonNull<ChunkFooter>>, |
| bump: PhantomData<&'a mut Bump>, |
| } |
| |
| impl<'a> Iterator for ChunkIter<'a> { |
| type Item = &'a [mem::MaybeUninit<u8>]; |
| fn next(&mut self) -> Option<&'a [mem::MaybeUninit<u8>]> { |
| unsafe { |
| let foot = self.footer?; |
| let foot = foot.as_ref(); |
| let data = foot.data.as_ptr() as usize; |
| let ptr = foot.ptr.get().as_ptr() as usize; |
| debug_assert!(data <= ptr); |
| debug_assert!(ptr <= foot as *const _ as usize); |
| |
| let len = foot as *const _ as usize - ptr; |
| let slice = slice::from_raw_parts(ptr as *const mem::MaybeUninit<u8>, len); |
| self.footer = foot.prev.get(); |
| Some(slice) |
| } |
| } |
| } |
| |
| impl<'a> iter::FusedIterator for ChunkIter<'a> {} |
| |
| #[inline(never)] |
| #[cold] |
| fn oom() -> ! { |
| panic!("out of memory") |
| } |
| |
| unsafe impl<'a> alloc::Alloc for &'a Bump { |
| #[inline(always)] |
| unsafe fn alloc(&mut self, layout: Layout) -> Result<NonNull<u8>, alloc::AllocErr> { |
| Ok(self.alloc_layout(layout)) |
| } |
| |
| #[inline] |
| unsafe fn dealloc(&mut self, ptr: NonNull<u8>, layout: Layout) { |
| // If the pointer is the last allocation we made, we can reuse the bytes, |
| // otherwise they are simply leaked -- at least until somebody calls reset(). |
| if layout.size() != 0 && self.is_last_allocation(ptr) { |
| let ptr = NonNull::new_unchecked(ptr.as_ptr().add(layout.size())); |
| self.current_chunk_footer.get().as_ref().ptr.set(ptr); |
| } |
| } |
| |
| #[inline] |
| unsafe fn realloc( |
| &mut self, |
| ptr: NonNull<u8>, |
| layout: Layout, |
| new_size: usize, |
| ) -> Result<NonNull<u8>, alloc::AllocErr> { |
| let old_size = layout.size(); |
| |
| if old_size == 0 { |
| return self.alloc(layout); |
| } |
| |
| if new_size <= old_size { |
| if self.is_last_allocation(ptr) |
| // Only reclaim the excess space (which requires a copy) if it |
| // is worth it: we are actually going to recover "enough" space |
| // and we can do a non-overlapping copy. |
| && new_size <= old_size / 2 |
| { |
| let delta = old_size - new_size; |
| let footer = self.current_chunk_footer.get(); |
| let footer = footer.as_ref(); |
| footer |
| .ptr |
| .set(NonNull::new_unchecked(footer.ptr.get().as_ptr().add(delta))); |
| let new_ptr = footer.ptr.get(); |
| // NB: we know it is non-overlapping because of the size check |
| // in the `if` condition. |
| ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_ptr(), new_size); |
| return Ok(new_ptr); |
| } else { |
| return Ok(ptr); |
| } |
| } |
| |
| if self.is_last_allocation(ptr) { |
| // Try to allocate the delta size within this same block so we can |
| // reuse the currently allocated space. |
| let delta = new_size - old_size; |
| if let Some(p) = |
| self.try_alloc_layout_fast(layout_from_size_align(delta, layout.align())) |
| { |
| ptr::copy(ptr.as_ptr(), p.as_ptr(), old_size); |
| return Ok(p); |
| } |
| } |
| |
| // Fallback: do a fresh allocation and copy the existing data into it. |
| let new_layout = layout_from_size_align(new_size, layout.align()); |
| let new_ptr = self.alloc_layout(new_layout); |
| ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_ptr(), old_size); |
| Ok(new_ptr) |
| } |
| } |
| |
| #[cfg(test)] |
| mod tests { |
| use super::*; |
| |
| #[test] |
| fn chunk_footer_is_five_words() { |
| assert_eq!(mem::size_of::<ChunkFooter>(), mem::size_of::<usize>() * 5); |
| } |
| |
| #[test] |
| #[allow(clippy::cognitive_complexity)] |
| fn test_realloc() { |
| use crate::alloc::Alloc; |
| |
| unsafe { |
| const CAPACITY: usize = 1024 - OVERHEAD; |
| let mut b = Bump::with_capacity(CAPACITY); |
| |
| // `realloc` doesn't shrink allocations that aren't "worth it". |
| let layout = Layout::from_size_align(100, 1).unwrap(); |
| let p = b.alloc_layout(layout); |
| let q = (&b).realloc(p, layout, 51).unwrap(); |
| assert_eq!(p, q); |
| b.reset(); |
| |
| // `realloc` will shrink allocations that are "worth it". |
| let layout = Layout::from_size_align(100, 1).unwrap(); |
| let p = b.alloc_layout(layout); |
| let q = (&b).realloc(p, layout, 50).unwrap(); |
| assert!(p != q); |
| b.reset(); |
| |
| // `realloc` will reuse the last allocation when growing. |
| let layout = Layout::from_size_align(10, 1).unwrap(); |
| let p = b.alloc_layout(layout); |
| let q = (&b).realloc(p, layout, 11).unwrap(); |
| assert_eq!(q.as_ptr() as usize, p.as_ptr() as usize - 1); |
| b.reset(); |
| |
| // `realloc` will allocate a new chunk when growing the last |
| // allocation, if need be. |
| let layout = Layout::from_size_align(1, 1).unwrap(); |
| let p = b.alloc_layout(layout); |
| let q = (&b).realloc(p, layout, CAPACITY + 1).unwrap(); |
| assert!(q.as_ptr() as usize != p.as_ptr() as usize - CAPACITY); |
| b = Bump::with_capacity(CAPACITY); |
| |
| // `realloc` will allocate and copy when reallocating anything that |
| // wasn't the last allocation. |
| let layout = Layout::from_size_align(1, 1).unwrap(); |
| let p = b.alloc_layout(layout); |
| let _ = b.alloc_layout(layout); |
| let q = (&b).realloc(p, layout, 2).unwrap(); |
| assert!(q.as_ptr() as usize != p.as_ptr() as usize - 1); |
| b.reset(); |
| } |
| } |
| |
| #[test] |
| fn invalid_read() { |
| use alloc::Alloc; |
| |
| let mut b = &Bump::new(); |
| |
| unsafe { |
| let l1 = Layout::from_size_align(12000, 4).unwrap(); |
| let p1 = Alloc::alloc(&mut b, l1).unwrap(); |
| |
| let l2 = Layout::from_size_align(1000, 4).unwrap(); |
| Alloc::alloc(&mut b, l2).unwrap(); |
| |
| let p1 = b.realloc(p1, l1, 24000).unwrap(); |
| let l3 = Layout::from_size_align(24000, 4).unwrap(); |
| b.realloc(p1, l3, 48000).unwrap(); |
| } |
| } |
| } |