#![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 { /// 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 From for AllocOrInitError { fn from(e: AllocErr) -> Self { Self::Alloc(e) } } impl Display for AllocOrInitError { 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`]), /// * 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`]: 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: /// /// /// /// /// /// /// /// /// /// /// /// /// /// /// /// /// /// /// /// /// /// /// /// /// /// ///
Infallible AllocationFallible Allocation
By Valuealloctry_alloc
Infallible Initializer Functionalloc_withtry_alloc_with
Fallible Initializer Functionalloc_try_withtry_alloc_try_with
/// /// ### 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. /// ///

Undoing the allocation in the Err case /// always fails if f successfully made any additional allocations /// in self. /// /// 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()); /// ``` /// ///

/// /// 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>, allocation_limit: Cell>, } #[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, // 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>, // Bump allocation finger that is always in the range `self.data..=self`. ptr: Cell>, // 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::(), // 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 { 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) { 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 { 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::(); // 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::() <= 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 { 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::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 { 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 { 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) { self.allocation_limit.set(limit) } /// How much headroom an arena has before it hits its allocation /// limit. fn allocation_limit_remaining(&self) -> Option { 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, 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, requested_layout: Layout, ) -> Option { 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, ) -> Option> { 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(&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(&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(&self, f: F) -> &mut T where F: FnOnce() -> T, { #[inline(always)] unsafe fn inner_writer(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::(); 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(&self, f: F) -> Result<&mut T, AllocErr> where F: FnOnce() -> T, { #[inline(always)] unsafe fn inner_writer(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::(); 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` 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(&self, f: F) -> Result<&mut T, E> where F: FnOnce() -> Result, { 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` 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` 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(&self, f: F) -> Result<&mut T, AllocOrInitError> where F: FnOnce() -> Result, { 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` 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(&self, src: &[T]) -> &mut [T] where T: Copy, { let layout = Layout::for_value(src); let dst = self.alloc_layout(layout).cast::(); 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(&self, src: &[T]) -> &mut [T] where T: Clone, { let layout = Layout::for_value(src); let dst = self.alloc_layout(layout).cast::(); 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(&self, len: usize, mut f: F) -> &mut [T] where F: FnMut(usize) -> T, { let layout = Layout::array::(len).unwrap_or_else(|_| oom()); let dst = self.alloc_layout(layout).cast::(); 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(&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(&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(&self, iter: I) -> &mut [T] where I: IntoIterator, 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::(5); /// assert_eq!(x, &[0, 0, 0, 0, 0]); /// ``` #[inline(always)] #[allow(clippy::mut_from_ref)] pub fn alloc_slice_fill_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 { 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, 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> { // 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> { 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]`, 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`][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::(5); /// let bytes = bump.allocated_bytes(); /// assert!(bytes >= core::mem::size_of::() * 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) -> bool { let footer = self.current_chunk_footer.get(); let footer = footer.as_ref(); footer.ptr.get() == ptr } #[inline] unsafe fn dealloc(&self, ptr: NonNull, 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, old_layout: Layout, new_layout: Layout, ) -> Result, 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, old_layout: Layout, new_layout: Layout, ) -> Result, 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]; fn next(&mut self) -> Option<&'a [mem::MaybeUninit]> { unsafe { let (ptr, len) = self.raw.next()?; let slice = slice::from_raw_parts(ptr as *const mem::MaybeUninit, 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, 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, AllocErr> { self.try_alloc_layout(layout) } #[inline] unsafe fn dealloc(&mut self, ptr: NonNull, layout: Layout) { Bump::dealloc(self, ptr, layout) } #[inline] unsafe fn realloc( &mut self, ptr: NonNull, layout: Layout, new_size: usize, ) -> Result, 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, 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, layout: Layout) { Bump::dealloc(self, ptr, layout) } unsafe fn shrink( &self, ptr: NonNull, old_layout: Layout, new_layout: Layout, ) -> Result, 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, old_layout: Layout, new_layout: Layout, ) -> Result, 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, old_layout: Layout, new_layout: Layout, ) -> Result, 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::(), mem::size_of::() * 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(); } } }