diff options
Diffstat (limited to 'third_party/rust/bumpalo/src/lib.rs')
| -rw-r--r-- | third_party/rust/bumpalo/src/lib.rs | 2023 |
1 files changed, 2023 insertions, 0 deletions
diff --git a/third_party/rust/bumpalo/src/lib.rs b/third_party/rust/bumpalo/src/lib.rs new file mode 100644 index 0000000000..74dfcd4361 --- /dev/null +++ b/third_party/rust/bumpalo/src/lib.rs @@ -0,0 +1,2023 @@ +#![doc = include_str!("../README.md")] +#![deny(missing_debug_implementations)] +#![deny(missing_docs)] +#![no_std] +#![cfg_attr( + feature = "allocator_api", + feature(allocator_api, nonnull_slice_from_raw_parts) +)] + +#[doc(hidden)] +pub extern crate alloc as core_alloc; + +#[cfg(feature = "boxed")] +pub mod boxed; +#[cfg(feature = "collections")] +pub mod collections; + +mod alloc; + +use core::cell::Cell; +use core::fmt::Display; +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}; +#[cfg(feature = "allocator_api")] +use core_alloc::alloc::{AllocError, Allocator}; + +pub use alloc::AllocErr; + +/// An error returned from [`Bump::try_alloc_try_with`]. +#[derive(Clone, PartialEq, Eq, Debug)] +pub enum AllocOrInitError<E> { + /// Indicates that the initial allocation failed. + Alloc(AllocErr), + /// Indicates that the initializer failed with the contained error after + /// allocation. + /// + /// It is possible but not guaranteed that the allocated memory has been + /// released back to the allocator at this point. + Init(E), +} +impl<E> From<AllocErr> for AllocOrInitError<E> { + fn from(e: AllocErr) -> Self { + Self::Alloc(e) + } +} +impl<E: Display> Display for AllocOrInitError<E> { + fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result { + match self { + AllocOrInitError::Alloc(err) => err.fmt(f), + AllocOrInitError::Init(err) => write!(f, "initialization failed: {}", err), + } + } +} + +/// 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: +/// +/// * Using [`bumpalo::boxed::Box::new_in`] instead of [`Bump::alloc`], that +/// will drop wrapped values similarly to [`std::boxed::Box`]. Note that this +/// requires enabling the `"boxed"` Cargo feature for this crate. **This is +/// often the easiest solution.** +/// +/// * 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`]. +/// +/// * 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`]: https://doc.rust-lang.org/std/ops/trait.Drop.html +/// [`Vec<T>`]: https://doc.rust-lang.org/std/vec/struct.Vec.html +/// [`std::fs::File`]: https://doc.rust-lang.org/std/fs/struct.File.html +/// [drop_in_place]: https://doc.rust-lang.org/std/ptr/fn.drop_in_place.html +/// [manuallydrop]: https://doc.rust-lang.org/std/mem/struct.ManuallyDrop.html +/// [`bumpalo::collections::Vec`]: collections/vec/struct.Vec.html +/// [`std::vec::Vec`]: https://doc.rust-lang.org/std/vec/struct.Vec.html +/// [`bumpalo::boxed::Box::new_in`]: boxed/struct.Box.html#method.new_in +/// [`std::boxed::Box`]: https://doc.rust-lang.org/std/boxed/struct.Box.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"; +/// ``` +/// +/// ## Allocation Methods Come in Many Flavors +/// +/// There are various allocation methods on `Bump`, the simplest being +/// [`alloc`][Bump::alloc]. The others exist to satisfy some combination of +/// fallible allocation and initialization. The allocation methods are +/// summarized in the following table: +/// +/// <table> +/// <thead> +/// <tr> +/// <th></th> +/// <th>Infallible Allocation</th> +/// <th>Fallible Allocation</th> +/// </tr> +/// </thead> +/// <tr> +/// <th>By Value</th> +/// <td><a href="#method.alloc"><code>alloc</code></a></td> +/// <td><a href="#method.try_alloc"><code>try_alloc</code></a></td> +/// </tr> +/// <tr> +/// <th>Infallible Initializer Function</th> +/// <td><a href="#method.alloc_with"><code>alloc_with</code></a></td> +/// <td><a href="#method.try_alloc_with"><code>try_alloc_with</code></a></td> +/// </tr> +/// <tr> +/// <th>Fallible Initializer Function</th> +/// <td><a href="#method.alloc_try_with"><code>alloc_try_with</code></a></td> +/// <td><a href="#method.try_alloc_try_with"><code>try_alloc_try_with</code></a></td> +/// </tr> +/// <tbody> +/// </tbody> +/// </table> +/// +/// ### Fallible Allocation: The `try_alloc_` Method Prefix +/// +/// These allocation methods let you recover from out-of-memory (OOM) +/// scenarioes, rather than raising a panic on OOM. +/// +/// ``` +/// use bumpalo::Bump; +/// +/// let bump = Bump::new(); +/// +/// match bump.try_alloc(MyStruct { +/// // ... +/// }) { +/// Ok(my_struct) => { +/// // Allocation succeeded. +/// } +/// Err(e) => { +/// // Out of memory. +/// } +/// } +/// +/// struct MyStruct { +/// // ... +/// } +/// ``` +/// +/// ### Initializer Functions: The `_with` Method Suffix +/// +/// Calling one of the generic `…alloc(x)` methods is essentially equivalent to +/// the matching [`…alloc_with(|| x)`](?search=alloc_with). 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 for example `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 `…alloc_with` functions try to help the compiler be smarter. In most +/// cases doing for example `bump.try_alloc_with(|| x)` on release mode will be +/// enough to help the compiler realize that this optimization is valid and +/// to construct `x` directly onto the heap. +/// +/// #### Warning +/// +/// These functions critically depend on compiler optimizations to achieve their +/// desired effect. This means that it is not an effective tool when compiling +/// without optimizations on. +/// +/// Even when optimizations are on, these functions do 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 1.54. +/// +/// ### Fallible Initialization: The `_try_with` Method Suffix +/// +/// The generic [`…alloc_try_with(|| x)`](?search=_try_with) methods behave +/// like the purely `_with` suffixed methods explained above. However, they +/// allow for fallible initialization by accepting a closure that returns a +/// [`Result`] and will attempt to undo the initial allocation if this closure +/// returns [`Err`]. +/// +/// #### Warning +/// +/// If the inner closure returns [`Ok`], space for the entire [`Result`] remains +/// allocated inside `self`. This can be a problem especially if the [`Err`] +/// variant is larger, but even otherwise there may be overhead for the +/// [`Result`]'s discriminant. +/// +/// <p><details><summary>Undoing the allocation in the <code>Err</code> case +/// always fails if <code>f</code> successfully made any additional allocations +/// in <code>self</code>.</summary> +/// +/// For example, the following will always leak also space for the [`Result`] +/// into this `Bump`, even though the inner reference isn't kept and the [`Err`] +/// payload is returned semantically by value: +/// +/// ```rust +/// let bump = bumpalo::Bump::new(); +/// +/// let r: Result<&mut [u8; 1000], ()> = bump.alloc_try_with(|| { +/// let _ = bump.alloc(0_u8); +/// Err(()) +/// }); +/// +/// assert!(r.is_err()); +/// ``` +/// +///</details></p> +/// +/// Since [`Err`] payloads are first placed on the heap and then moved to the +/// stack, `bump.…alloc_try_with(|| x)?` is likely to execute more slowly than +/// the matching `bump.…alloc(x?)` in case of initialization failure. If this +/// happens frequently, using the plain un-suffixed method may perform better. +/// +/// [`Result`]: https://doc.rust-lang.org/std/result/enum.Result.html +/// [`Ok`]: https://doc.rust-lang.org/std/result/enum.Result.html#variant.Ok +/// [`Err`]: https://doc.rust-lang.org/std/result/enum.Result.html#variant.Err +/// +/// ### `Bump` Allocation Limits +/// +/// `bumpalo` supports setting a limit on the maximum bytes of memory that can +/// be allocated for use in a particular `Bump` arena. This limit can be set and removed with +/// [`set_allocation_limit`][Bump::set_allocation_limit]. +/// The allocation limit is only enforced when allocating new backing chunks for +/// a `Bump`. Updating the allocation limit will not affect existing allocations +/// or any future allocations within the `Bump`'s current chunk. +/// +/// #### Example +/// +/// ``` +/// let bump = bumpalo::Bump::new(); +/// +/// assert_eq!(bump.allocation_limit(), None); +/// bump.set_allocation_limit(Some(0)); +/// +/// assert!(bump.try_alloc(5).is_err()); +/// +/// bump.set_allocation_limit(Some(6)); +/// +/// assert_eq!(bump.allocation_limit(), Some(6)); +/// +/// bump.set_allocation_limit(None); +/// +/// assert_eq!(bump.allocation_limit(), None); +/// ``` +/// +/// #### Warning +/// +/// Because of backwards compatibility, allocations that fail +/// due to allocation limits will not present differently than +/// errors due to resource exhaustion. + +#[derive(Debug)] +pub struct Bump { + // The current chunk we are bump allocating within. + current_chunk_footer: Cell<NonNull<ChunkFooter>>, + allocation_limit: Cell<Option<usize>>, +} + +#[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. + // + // Note that the last node in the `prev` linked list is the canonical empty + // chunk, whose `prev` link points to itself. + prev: Cell<NonNull<ChunkFooter>>, + + // Bump allocation finger that is always in the range `self.data..=self`. + ptr: Cell<NonNull<u8>>, + + // The bytes allocated in all chunks so far, the canonical empty chunk has + // a size of 0 and for all other chunks, `allocated_bytes` will be + // the allocated_bytes of the current chunk plus the allocated bytes + // of the `prev` chunk. + allocated_bytes: usize, +} + +/// A wrapper type for the canonical, statically allocated empty chunk. +/// +/// For the canonical empty chunk to be `static`, its type must be `Sync`, which +/// is the purpose of this wrapper type. This is safe because the empty chunk is +/// immutable and never actually modified. +#[repr(transparent)] +struct EmptyChunkFooter(ChunkFooter); + +unsafe impl Sync for EmptyChunkFooter {} + +static EMPTY_CHUNK: EmptyChunkFooter = EmptyChunkFooter(ChunkFooter { + // This chunk is empty (except the foot itself). + layout: Layout::new::<ChunkFooter>(), + + // The start of the (empty) allocatable region for this chunk is itself. + data: unsafe { NonNull::new_unchecked(&EMPTY_CHUNK as *const EmptyChunkFooter as *mut u8) }, + + // The end of the (empty) allocatable region for this chunk is also itself. + ptr: Cell::new(unsafe { + NonNull::new_unchecked(&EMPTY_CHUNK as *const EmptyChunkFooter as *mut u8) + }), + + // Invariant: the last chunk footer in all `ChunkFooter::prev` linked lists + // is the empty chunk footer, whose `prev` points to itself. + prev: Cell::new(unsafe { + NonNull::new_unchecked(&EMPTY_CHUNK as *const EmptyChunkFooter as *mut ChunkFooter) + }), + + // Empty chunks count as 0 allocated bytes in an arena. + allocated_bytes: 0, +}); + +impl EmptyChunkFooter { + fn get(&'static self) -> NonNull<ChunkFooter> { + unsafe { NonNull::new_unchecked(&self.0 as *const ChunkFooter as *mut ChunkFooter) } + } +} + +impl ChunkFooter { + // Returns the start and length of the currently allocated region of this + // chunk. + fn as_raw_parts(&self) -> (*const u8, usize) { + let data = self.data.as_ptr() as *const u8; + let ptr = self.ptr.get().as_ptr() as *const u8; + debug_assert!(data <= ptr); + debug_assert!(ptr <= self as *const ChunkFooter as *const u8); + let len = unsafe { (self as *const ChunkFooter as *const u8).offset_from(ptr) as usize }; + (ptr, len) + } + + /// Is this chunk the last empty chunk? + fn is_empty(&self) -> bool { + ptr::eq(self, EMPTY_CHUNK.get().as_ptr()) + } +} + +impl Default for Bump { + fn default() -> Bump { + Bump::new() + } +} + +impl Drop for Bump { + fn drop(&mut self) { + unsafe { + dealloc_chunk_list(self.current_chunk_footer.get()); + } + } +} + +#[inline] +unsafe fn dealloc_chunk_list(mut footer: NonNull<ChunkFooter>) { + while !footer.as_ref().is_empty() { + let 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)) +} + +#[inline] +pub(crate) fn round_down_to(n: usize, divisor: usize) -> usize { + debug_assert!(divisor > 0); + debug_assert!(divisor.is_power_of_two()); + n & !(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 aside 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; + +/// The memory size and alignment details for a potential new chunk +/// allocation. +#[derive(Debug, Clone, Copy)] +struct NewChunkMemoryDetails { + new_size_without_footer: usize, + align: usize, + size: usize, +} + +/// 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") +} + +// This can be migrated to directly use `usize::abs_diff` when the MSRV +// reaches `1.60` +fn abs_diff(a: usize, b: usize) -> usize { + usize::max(a, b) - usize::min(a, b) +} + +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) + } + + /// Attempt to construct a new arena to bump allocate into. + /// + /// ## Example + /// + /// ``` + /// let bump = bumpalo::Bump::try_new(); + /// # let _ = bump.unwrap(); + /// ``` + pub fn try_new() -> Result<Bump, AllocErr> { + Bump::try_with_capacity(0) + } + + /// Construct a new arena with the specified byte capacity to bump allocate into. + /// + /// ## Example + /// + /// ``` + /// let bump = bumpalo::Bump::with_capacity(100); + /// # let _ = bump; + /// ``` + pub fn with_capacity(capacity: usize) -> Bump { + Bump::try_with_capacity(capacity).unwrap_or_else(|_| oom()) + } + + /// Attempt to construct a new arena with the specified byte capacity to bump allocate into. + /// + /// ## Example + /// + /// ``` + /// let bump = bumpalo::Bump::try_with_capacity(100); + /// # let _ = bump.unwrap(); + /// ``` + pub fn try_with_capacity(capacity: usize) -> Result<Self, AllocErr> { + if capacity == 0 { + return Ok(Bump { + current_chunk_footer: Cell::new(EMPTY_CHUNK.get()), + allocation_limit: Cell::new(None), + }); + } + + let layout = unsafe { layout_from_size_align(capacity, 1) }; + + let chunk_footer = unsafe { + Self::new_chunk( + Bump::new_chunk_memory_details(None, layout).ok_or(AllocErr)?, + layout, + EMPTY_CHUNK.get(), + ) + .ok_or(AllocErr)? + }; + + Ok(Bump { + current_chunk_footer: Cell::new(chunk_footer), + allocation_limit: Cell::new(None), + }) + } + + /// The allocation limit for this arena in bytes. + /// + /// ## Example + /// + /// ``` + /// let bump = bumpalo::Bump::with_capacity(0); + /// + /// assert_eq!(bump.allocation_limit(), None); + /// + /// bump.set_allocation_limit(Some(6)); + /// + /// assert_eq!(bump.allocation_limit(), Some(6)); + /// + /// bump.set_allocation_limit(None); + /// + /// assert_eq!(bump.allocation_limit(), None); + /// ``` + pub fn allocation_limit(&self) -> Option<usize> { + self.allocation_limit.get() + } + + /// Set the allocation limit in bytes for this arena. + /// + /// The allocation limit is only enforced when allocating new backing chunks for + /// a `Bump`. Updating the allocation limit will not affect existing allocations + /// or any future allocations within the `Bump`'s current chunk. + /// + /// ## Example + /// + /// ``` + /// let bump = bumpalo::Bump::with_capacity(0); + /// + /// bump.set_allocation_limit(Some(0)); + /// + /// assert!(bump.try_alloc(5).is_err()); + /// ``` + pub fn set_allocation_limit(&self, limit: Option<usize>) { + self.allocation_limit.set(limit) + } + + /// How much headroom an arena has before it hits its allocation + /// limit. + fn allocation_limit_remaining(&self) -> Option<usize> { + self.allocation_limit.get().and_then(|allocation_limit| { + let allocated_bytes = self.allocated_bytes(); + if allocated_bytes > allocation_limit { + None + } else { + Some(abs_diff(allocation_limit, allocated_bytes)) + } + }) + } + + /// Whether a request to allocate a new chunk with a given size for a given + /// requested layout will fit under the allocation limit set on a `Bump`. + fn chunk_fits_under_limit( + allocation_limit_remaining: Option<usize>, + new_chunk_memory_details: NewChunkMemoryDetails, + ) -> bool { + allocation_limit_remaining + .map(|allocation_limit_left| { + allocation_limit_left >= new_chunk_memory_details.new_size_without_footer + }) + .unwrap_or(true) + } + + /// Determine the memory details including final size, alignment and + /// final size without footer for a new chunk that would be allocated + /// to fulfill an allocation request. + fn new_chunk_memory_details( + new_size_without_footer: Option<usize>, + requested_layout: Layout, + ) -> Option<NewChunkMemoryDetails> { + let mut new_size_without_footer = + new_size_without_footer.unwrap_or(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 + 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)? - 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); + + Some(NewChunkMemoryDetails { + new_size_without_footer, + size, + align, + }) + } + + /// 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. + unsafe fn new_chunk( + new_chunk_memory_details: NewChunkMemoryDetails, + requested_layout: Layout, + prev: NonNull<ChunkFooter>, + ) -> Option<NonNull<ChunkFooter>> { + let NewChunkMemoryDetails { + new_size_without_footer, + align, + size, + } = new_chunk_memory_details; + + let layout = layout_from_size_align(size, align); + + debug_assert!(size >= requested_layout.size()); + + let data = alloc(layout); + let data = NonNull::new(data)?; + + // The `ChunkFooter` is at the end of the chunk. + let footer_ptr = data.as_ptr().add(new_size_without_footer); + debug_assert_eq!((data.as_ptr() as usize) % align, 0); + debug_assert_eq!(footer_ptr as usize % 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)); + + // The `allocated_bytes` of a new chunk counts the total size + // of the chunks, not how much of the chunks are used. + let allocated_bytes = prev.as_ref().allocated_bytes + new_size_without_footer; + + ptr::write( + footer_ptr, + ChunkFooter { + data, + layout, + prev: Cell::new(prev), + ptr, + allocated_bytes, + }, + ); + + Some(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 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 { + if self.current_chunk_footer.get().as_ref().is_empty() { + return; + } + + let mut cur_chunk = self.current_chunk_footer.get(); + + // Deallocate all chunks except the current one + let prev_chunk = cur_chunk.as_ref().prev.replace(EMPTY_CHUNK.get()); + dealloc_chunk_list(prev_chunk); + + // Reset the bump finger to the end of the chunk. + cur_chunk.as_ref().ptr.set(cur_chunk.cast()); + + // Reset the allocated size of the chunk. + cur_chunk.as_mut().allocated_bytes = cur_chunk.as_ref().layout.size(); + + debug_assert!( + self.current_chunk_footer + .get() + .as_ref() + .prev + .get() + .as_ref() + .is_empty(), + "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` fails. + /// + /// ## 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) + } + + /// Try to allocate an object in this `Bump` and return an exclusive + /// reference to it. + /// + /// ## Errors + /// + /// Errors if reserving space for `T` fails. + /// + /// ## Example + /// + /// ``` + /// let bump = bumpalo::Bump::new(); + /// let x = bump.try_alloc("hello"); + /// assert_eq!(x, Ok(&mut "hello")); + /// ``` + #[inline(always)] + #[allow(clippy::mut_from_ref)] + pub fn try_alloc<T>(&self, val: T) -> Result<&mut T, AllocErr> { + self.try_alloc_with(|| val) + } + + /// Pre-allocate space for an object in this `Bump`, initializes it using + /// the closure, then returns an exclusive reference to it. + /// + /// See [The `_with` Method Suffix](#initializer-functions-the-_with-method-suffix) for a + /// discussion on the differences between the `_with` suffixed methods and + /// those methods without it, their performance characteristics, and when + /// you might or might not choose a `_with` suffixed method. + /// + /// ## Panics + /// + /// Panics if reserving space for `T` fails. + /// + /// ## 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 + } + } + + /// Tries to pre-allocate space for an object in this `Bump`, initializes + /// it using the closure, then returns an exclusive reference to it. + /// + /// See [The `_with` Method Suffix](#initializer-functions-the-_with-method-suffix) for a + /// discussion on the differences between the `_with` suffixed methods and + /// those methods without it, their performance characteristics, and when + /// you might or might not choose a `_with` suffixed method. + /// + /// ## Errors + /// + /// Errors if reserving space for `T` fails. + /// + /// ## Example + /// + /// ``` + /// let bump = bumpalo::Bump::new(); + /// let x = bump.try_alloc_with(|| "hello"); + /// assert_eq!(x, Ok(&mut "hello")); + /// ``` + #[inline(always)] + #[allow(clippy::mut_from_ref)] + pub fn try_alloc_with<F, T>(&self, f: F) -> Result<&mut T, AllocErr> + 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()) + } + + //SAFETY: Self-contained: + // `p` is allocated for `T` and then a `T` is written. + let layout = Layout::new::<T>(); + let p = self.try_alloc_layout(layout)?; + let p = p.as_ptr() as *mut T; + + unsafe { + inner_writer(p, f); + Ok(&mut *p) + } + } + + /// Pre-allocates space for a [`Result`] in this `Bump`, initializes it using + /// the closure, then returns an exclusive reference to its `T` if [`Ok`]. + /// + /// Iff the allocation fails, the closure is not run. + /// + /// Iff [`Err`], an allocator rewind is *attempted* and the `E` instance is + /// moved out of the allocator to be consumed or dropped as normal. + /// + /// See [The `_with` Method Suffix](#initializer-functions-the-_with-method-suffix) for a + /// discussion on the differences between the `_with` suffixed methods and + /// those methods without it, their performance characteristics, and when + /// you might or might not choose a `_with` suffixed method. + /// + /// For caveats specific to fallible initialization, see + /// [The `_try_with` Method Suffix](#fallible-initialization-the-_try_with-method-suffix). + /// + /// [`Result`]: https://doc.rust-lang.org/std/result/enum.Result.html + /// [`Ok`]: https://doc.rust-lang.org/std/result/enum.Result.html#variant.Ok + /// [`Err`]: https://doc.rust-lang.org/std/result/enum.Result.html#variant.Err + /// + /// ## Errors + /// + /// Iff the allocation succeeds but `f` fails, that error is forwarded by value. + /// + /// ## Panics + /// + /// Panics if reserving space for `Result<T, E>` fails. + /// + /// ## Example + /// + /// ``` + /// let bump = bumpalo::Bump::new(); + /// let x = bump.alloc_try_with(|| Ok("hello"))?; + /// assert_eq!(*x, "hello"); + /// # Result::<_, ()>::Ok(()) + /// ``` + #[inline(always)] + #[allow(clippy::mut_from_ref)] + pub fn alloc_try_with<F, T, E>(&self, f: F) -> Result<&mut T, E> + where + F: FnOnce() -> Result<T, E>, + { + let rewind_footer = self.current_chunk_footer.get(); + let rewind_ptr = unsafe { rewind_footer.as_ref() }.ptr.get(); + let mut inner_result_ptr = NonNull::from(self.alloc_with(f)); + match unsafe { inner_result_ptr.as_mut() } { + Ok(t) => Ok(unsafe { + //SAFETY: + // The `&mut Result<T, E>` returned by `alloc_with` may be + // lifetime-limited by `E`, but the derived `&mut T` still has + // the same validity as in `alloc_with` since the error variant + // is already ruled out here. + + // We could conditionally truncate the allocation here, but + // since it grows backwards, it seems unlikely that we'd get + // any more than the `Result`'s discriminant this way, if + // anything at all. + &mut *(t as *mut _) + }), + Err(e) => unsafe { + // If this result was the last allocation in this arena, we can + // reclaim its space. In fact, sometimes we can do even better + // than simply calling `dealloc` on the result pointer: we can + // reclaim any alignment padding we might have added (which + // `dealloc` cannot do) if we didn't allocate a new chunk for + // this result. + if self.is_last_allocation(inner_result_ptr.cast()) { + let current_footer_p = self.current_chunk_footer.get(); + let current_ptr = ¤t_footer_p.as_ref().ptr; + if current_footer_p == rewind_footer { + // It's still the same chunk, so reset the bump pointer + // to its original value upon entry to this method + // (reclaiming any alignment padding we may have + // added). + current_ptr.set(rewind_ptr); + } else { + // We allocated a new chunk for this result. + // + // We know the result is the only allocation in this + // chunk: Any additional allocations since the start of + // this method could only have happened when running + // the initializer function, which is called *after* + // reserving space for this result. Therefore, since we + // already determined via the check above that this + // result was the last allocation, there must not have + // been any other allocations, and this result is the + // only allocation in this chunk. + // + // Because this is the only allocation in this chunk, + // we can reset the chunk's bump finger to the start of + // the chunk. + current_ptr.set(current_footer_p.as_ref().data); + } + } + //SAFETY: + // As we received `E` semantically by value from `f`, we can + // just copy that value here as long as we avoid a double-drop + // (which can't happen as any specific references to the `E`'s + // data in `self` are destroyed when this function returns). + // + // The order between this and the deallocation doesn't matter + // because `Self: !Sync`. + Err(ptr::read(e as *const _)) + }, + } + } + + /// Tries to pre-allocates space for a [`Result`] in this `Bump`, + /// initializes it using the closure, then returns an exclusive reference + /// to its `T` if all [`Ok`]. + /// + /// Iff the allocation fails, the closure is not run. + /// + /// Iff the closure returns [`Err`], an allocator rewind is *attempted* and + /// the `E` instance is moved out of the allocator to be consumed or dropped + /// as normal. + /// + /// See [The `_with` Method Suffix](#initializer-functions-the-_with-method-suffix) for a + /// discussion on the differences between the `_with` suffixed methods and + /// those methods without it, their performance characteristics, and when + /// you might or might not choose a `_with` suffixed method. + /// + /// For caveats specific to fallible initialization, see + /// [The `_try_with` Method Suffix](#fallible-initialization-the-_try_with-method-suffix). + /// + /// [`Result`]: https://doc.rust-lang.org/std/result/enum.Result.html + /// [`Ok`]: https://doc.rust-lang.org/std/result/enum.Result.html#variant.Ok + /// [`Err`]: https://doc.rust-lang.org/std/result/enum.Result.html#variant.Err + /// + /// ## Errors + /// + /// Errors with the [`Alloc`](`AllocOrInitError::Alloc`) variant iff + /// reserving space for `Result<T, E>` fails. + /// + /// Iff the allocation succeeds but `f` fails, that error is forwarded by + /// value inside the [`Init`](`AllocOrInitError::Init`) variant. + /// + /// ## Example + /// + /// ``` + /// let bump = bumpalo::Bump::new(); + /// let x = bump.try_alloc_try_with(|| Ok("hello"))?; + /// assert_eq!(*x, "hello"); + /// # Result::<_, bumpalo::AllocOrInitError<()>>::Ok(()) + /// ``` + #[inline(always)] + #[allow(clippy::mut_from_ref)] + pub fn try_alloc_try_with<F, T, E>(&self, f: F) -> Result<&mut T, AllocOrInitError<E>> + where + F: FnOnce() -> Result<T, E>, + { + let rewind_footer = self.current_chunk_footer.get(); + let rewind_ptr = unsafe { rewind_footer.as_ref() }.ptr.get(); + let mut inner_result_ptr = NonNull::from(self.try_alloc_with(f)?); + match unsafe { inner_result_ptr.as_mut() } { + Ok(t) => Ok(unsafe { + //SAFETY: + // The `&mut Result<T, E>` returned by `alloc_with` may be + // lifetime-limited by `E`, but the derived `&mut T` still has + // the same validity as in `alloc_with` since the error variant + // is already ruled out here. + + // We could conditionally truncate the allocation here, but + // since it grows backwards, it seems unlikely that we'd get + // any more than the `Result`'s discriminant this way, if + // anything at all. + &mut *(t as *mut _) + }), + Err(e) => unsafe { + // If this result was the last allocation in this arena, we can + // reclaim its space. In fact, sometimes we can do even better + // than simply calling `dealloc` on the result pointer: we can + // reclaim any alignment padding we might have added (which + // `dealloc` cannot do) if we didn't allocate a new chunk for + // this result. + if self.is_last_allocation(inner_result_ptr.cast()) { + let current_footer_p = self.current_chunk_footer.get(); + let current_ptr = ¤t_footer_p.as_ref().ptr; + if current_footer_p == rewind_footer { + // It's still the same chunk, so reset the bump pointer + // to its original value upon entry to this method + // (reclaiming any alignment padding we may have + // added). + current_ptr.set(rewind_ptr); + } else { + // We allocated a new chunk for this result. + // + // We know the result is the only allocation in this + // chunk: Any additional allocations since the start of + // this method could only have happened when running + // the initializer function, which is called *after* + // reserving space for this result. Therefore, since we + // already determined via the check above that this + // result was the last allocation, there must not have + // been any other allocations, and this result is the + // only allocation in this chunk. + // + // Because this is the only allocation in this chunk, + // we can reset the chunk's bump finger to the start of + // the chunk. + current_ptr.set(current_footer_p.as_ref().data); + } + } + //SAFETY: + // As we received `E` semantically by value from `f`, we can + // just copy that value here as long as we avoid a double-drop + // (which can't happen as any specific references to the `E`'s + // data in `self` are destroyed when this function returns). + // + // The order between this and the deallocation doesn't matter + // because `Self: !Sync`. + Err(AllocOrInitError::Init(ptr::read(e as *const _))) + }, + } + } + + /// `Copy` a slice into this `Bump` and return an exclusive reference to + /// the copy. + /// + /// ## Panics + /// + /// Panics if reserving space for the slice fails. + /// + /// ## 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`](#method.alloc_slice_copy) if `T` is `Copy`. + /// + /// ## Panics + /// + /// Panics if reserving space for the slice fails. + /// + /// ## Example + /// + /// ``` + /// #[derive(Clone, Debug, Eq, PartialEq)] + /// struct Sheep { + /// name: String, + /// } + /// + /// let originals = [ + /// 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 fails. + /// + /// ## 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 fails. + /// + /// ## 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::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 fails. + /// + /// ## 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 fails. + /// + /// ## 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 fails, 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()`]. + /// + /// [`T::default()`]: https://doc.rust-lang.org/std/default/trait.Default.html#tymethod.default + /// + /// ## Panics + /// + /// Panics if reserving space for the slice fails. + /// + /// ## 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/std/ptr/fn.write.html). + /// + /// # Panics + /// + /// Panics if reserving space matching `layout` fails. + #[inline(always)] + pub fn alloc_layout(&self, layout: Layout) -> NonNull<u8> { + self.try_alloc_layout(layout).unwrap_or_else(|_| oom()) + } + + /// Attempts to allocate space for an object with the given `Layout` or else returns + /// an `Err`. + /// + /// The returned pointer points at uninitialized memory, and should be + /// initialized with + /// [`std::ptr::write`](https://doc.rust-lang.org/std/ptr/fn.write.html). + /// + /// # Errors + /// + /// Errors if reserving space matching `layout` fails. + #[inline(always)] + pub fn try_alloc_layout(&self, layout: Layout) -> Result<NonNull<u8>, AllocErr> { + if let Some(p) = self.try_alloc_layout_fast(layout) { + Ok(p) + } else { + self.alloc_layout_slow(layout).ok_or(AllocErr) + } + } + + #[inline(always)] + fn try_alloc_layout_fast(&self, layout: Layout) -> Option<NonNull<u8>> { + // We don't need to check for ZSTs here since they will automatically + // be handled properly: the pointer will be bumped by zero bytes, + // modulo alignment. This keeps the fast path optimized for non-ZSTs, + // which are much more common. + unsafe { + let footer = self.current_chunk_footer.get(); + let footer = footer.as_ref(); + let ptr = footer.ptr.get().as_ptr(); + let start = footer.data.as_ptr(); + debug_assert!(start <= ptr); + debug_assert!(ptr as *const u8 <= footer as *const _ as *const u8); + + if (ptr as usize) < layout.size() { + return None; + } + + let ptr = ptr.wrapping_sub(layout.size()); + let rem = ptr as usize % layout.align(); + let aligned_ptr = ptr.wrapping_sub(rem); + + 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 + } + } + } + + /// Gets the remaining capacity in the current chunk (in bytes). + /// + /// ## Example + /// + /// ``` + /// use bumpalo::Bump; + /// + /// let bump = Bump::with_capacity(100); + /// + /// let capacity = bump.chunk_capacity(); + /// assert!(capacity >= 100); + /// ``` + pub fn chunk_capacity(&self) -> usize { + let current_footer = self.current_chunk_footer.get(); + let current_footer = unsafe { current_footer.as_ref() }; + + current_footer as *const _ as usize - current_footer.data.as_ptr() as usize + } + + /// 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) -> Option<NonNull<u8>> { + unsafe { + let size = layout.size(); + let allocation_limit_remaining = self.allocation_limit_remaining(); + + // Get a new chunk from the global allocator. + let current_footer = self.current_chunk_footer.get(); + let current_layout = current_footer.as_ref().layout; + + // By default, we want our new chunk to be about twice as big + // as the previous chunk. If the global allocator refuses it, + // we try to divide it by half until it works or the requested + // size is smaller than the default footer size. + let min_new_chunk_size = layout.size().max(DEFAULT_CHUNK_SIZE_WITHOUT_FOOTER); + let mut base_size = (current_layout.size() - FOOTER_SIZE) + .checked_mul(2)? + .max(min_new_chunk_size); + let chunk_memory_details = iter::from_fn(|| { + let bypass_min_chunk_size_for_small_limits = match self.allocation_limit() { + Some(limit) + if layout.size() < limit + && base_size >= layout.size() + && limit < DEFAULT_CHUNK_SIZE_WITHOUT_FOOTER + && self.allocated_bytes() == 0 => + { + true + } + _ => false, + }; + + if base_size >= min_new_chunk_size || bypass_min_chunk_size_for_small_limits { + let size = base_size; + base_size = base_size / 2; + Bump::new_chunk_memory_details(Some(size), layout) + } else { + None + } + }); + + let new_footer = chunk_memory_details + .filter_map(|chunk_memory_details| { + if Bump::chunk_fits_under_limit( + allocation_limit_remaining, + chunk_memory_details, + ) { + Bump::new_chunk(chunk_memory_details, layout, current_footer) + } else { + None + } + }) + .next()?; + + 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 mut ptr = new_footer.ptr.get().as_ptr().sub(size); + // Round the pointer down to the requested alignment. + ptr = ptr.sub(ptr as usize % layout.align()); + debug_assert!( + ptr as *const _ <= new_footer, + "{:p} <= {:p}", + ptr, + new_footer + ); + 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. + Some(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. + /// + /// Finally, you must also ensure that any values allocated into the bump + /// arena have not had their `Drop` implementations called on them, + /// e.g. after dropping a [`bumpalo::boxed::Box<T>`][crate::boxed::Box]. + /// + /// ## 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[0].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<'_> { + // SAFE: Ensured by mutable borrow of `self`. + let raw = unsafe { self.iter_allocated_chunks_raw() }; + ChunkIter { + raw, + bump: PhantomData, + } + } + + /// Returns an iterator over raw pointers to chunks of allocated memory that + /// this arena has bump allocated into. + /// + /// This is an unsafe version of [`iter_allocated_chunks()`](Bump::iter_allocated_chunks), + /// with the caller responsible for safe usage of the returned pointers as + /// well as ensuring that the iterator is not invalidated by new + /// allocations. + /// + /// ## Safety + /// + /// Allocations from this arena must not be performed while the returned + /// iterator is alive. If reading the chunk data (or casting to a reference) + /// the caller must ensure that there exist no mutable references to + /// previously allocated data. + /// + /// In addition, all of the caveats when reading the chunk data from + /// [`iter_allocated_chunks()`](Bump::iter_allocated_chunks) still apply. + pub unsafe fn iter_allocated_chunks_raw(&self) -> ChunkRawIter<'_> { + ChunkRawIter { + footer: self.current_chunk_footer.get(), + bump: PhantomData, + } + } + + /// Calculates the number of bytes currently allocated across all chunks in + /// this bump arena. + /// + /// 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. + /// + /// The allocated bytes do not include the size of bumpalo's metadata, + /// so the amount of memory requested from the Rust allocator is higher + /// than the returned value. + /// + /// ## 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 footer = self.current_chunk_footer.get(); + + unsafe { footer.as_ref().allocated_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 + } + + #[inline] + unsafe fn dealloc(&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 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 shrink( + &self, + ptr: NonNull<u8>, + old_layout: Layout, + new_layout: Layout, + ) -> Result<NonNull<u8>, AllocErr> { + let old_size = old_layout.size(); + let new_size = new_layout.size(); + let align_is_compatible = old_layout.align() >= new_layout.align(); + + if !align_is_compatible { + return Err(AllocErr); + } + + // This is how much space we would *actually* reclaim while satisfying + // the requested alignment. + let delta = round_down_to(old_size - new_size, new_layout.align()); + + 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. + && delta >= old_size / 2 + { + let footer = self.current_chunk_footer.get(); + let footer = footer.as_ref(); + + // NB: new_ptr is aligned, because ptr *has to* be aligned, and we + // made sure delta is aligned. + let new_ptr = NonNull::new_unchecked(footer.ptr.get().as_ptr().add(delta)); + footer.ptr.set(new_ptr); + + // 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); + } + } + + #[inline] + unsafe fn grow( + &self, + ptr: NonNull<u8>, + old_layout: Layout, + new_layout: Layout, + ) -> Result<NonNull<u8>, AllocErr> { + let old_size = old_layout.size(); + let new_size = new_layout.size(); + let align_is_compatible = old_layout.align() >= new_layout.align(); + + if align_is_compatible && 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, old_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_ptr = self.try_alloc_layout(new_layout)?; + ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_ptr(), old_size); + Ok(new_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 are 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> { + raw: ChunkRawIter<'a>, + 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 (ptr, len) = self.raw.next()?; + let slice = slice::from_raw_parts(ptr as *const mem::MaybeUninit<u8>, len); + Some(slice) + } + } +} + +impl<'a> iter::FusedIterator for ChunkIter<'a> {} + +/// An iterator over raw pointers to chunks of allocated memory that this +/// arena has bump allocated into. +/// +/// See [`ChunkIter`] for details regarding the returned chunks. +/// +/// This struct is created by the [`iter_allocated_chunks_raw`] method on +/// [`Bump`]. See that function for a safety description regarding reading from +/// the returned items. +/// +/// [`Bump`]: struct.Bump.html +/// [`iter_allocated_chunks_raw`]: struct.Bump.html#method.iter_allocated_chunks_raw +#[derive(Debug)] +pub struct ChunkRawIter<'a> { + footer: NonNull<ChunkFooter>, + bump: PhantomData<&'a Bump>, +} + +impl Iterator for ChunkRawIter<'_> { + type Item = (*mut u8, usize); + fn next(&mut self) -> Option<(*mut u8, usize)> { + unsafe { + let foot = self.footer.as_ref(); + if foot.is_empty() { + return None; + } + let (ptr, len) = foot.as_raw_parts(); + self.footer = foot.prev.get(); + Some((ptr as *mut u8, len)) + } + } +} + +impl iter::FusedIterator for ChunkRawIter<'_> {} + +#[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>, AllocErr> { + self.try_alloc_layout(layout) + } + + #[inline] + unsafe fn dealloc(&mut self, ptr: NonNull<u8>, layout: Layout) { + Bump::dealloc(self, ptr, layout) + } + + #[inline] + unsafe fn realloc( + &mut self, + ptr: NonNull<u8>, + layout: Layout, + new_size: usize, + ) -> Result<NonNull<u8>, AllocErr> { + let old_size = layout.size(); + + if old_size == 0 { + return self.try_alloc_layout(layout); + } + + let new_layout = layout_from_size_align(new_size, layout.align()); + if new_size <= old_size { + self.shrink(ptr, layout, new_layout) + } else { + self.grow(ptr, layout, new_layout) + } + } +} + +#[cfg(feature = "allocator_api")] +unsafe impl<'a> Allocator for &'a Bump { + fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> { + self.try_alloc_layout(layout) + .map(|p| NonNull::slice_from_raw_parts(p, layout.size())) + .map_err(|_| AllocError) + } + + unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout) { + Bump::dealloc(self, ptr, layout) + } + + unsafe fn shrink( + &self, + ptr: NonNull<u8>, + old_layout: Layout, + new_layout: Layout, + ) -> Result<NonNull<[u8]>, AllocError> { + Bump::shrink(self, ptr, old_layout, new_layout) + .map(|p| NonNull::slice_from_raw_parts(p, new_layout.size())) + .map_err(|_| AllocError) + } + + unsafe fn grow( + &self, + ptr: NonNull<u8>, + old_layout: Layout, + new_layout: Layout, + ) -> Result<NonNull<[u8]>, AllocError> { + Bump::grow(self, ptr, old_layout, new_layout) + .map(|p| NonNull::slice_from_raw_parts(p, new_layout.size())) + .map_err(|_| AllocError) + } + + unsafe fn grow_zeroed( + &self, + ptr: NonNull<u8>, + old_layout: Layout, + new_layout: Layout, + ) -> Result<NonNull<[u8]>, AllocError> { + let mut ptr = self.grow(ptr, old_layout, new_layout)?; + ptr.as_mut()[old_layout.size()..].fill(0); + Ok(ptr) + } +} + +// NB: Only tests which require private types, fields, or methods should be in +// here. Anything that can just be tested via public API surface should be in +// `bumpalo/tests/all/*`. +#[cfg(test)] +mod tests { + use super::*; + + // Uses private type `ChunkFooter`. + #[test] + fn chunk_footer_is_five_words() { + assert_eq!(mem::size_of::<ChunkFooter>(), mem::size_of::<usize>() * 6); + } + + // Uses private `alloc` module. + #[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(); + } + } + + // Uses our private `alloc` module. + #[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(); + } + } +} |