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#![doc = include_str!("../README.md")]
#![deny(missing_debug_implementations)]
#![deny(missing_docs)]
#![cfg_attr(not(feature = "std"), no_std)]
#![cfg_attr(feature = "allocator_api", feature(allocator_api))]
#[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};
#[cfg(all(feature = "allocator-api2", not(feature = "allocator_api")))]
use allocator_api2::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.
///
/// [`bumpalo::collections::Vec`]: collections/vec/struct.Vec.html
/// [`bumpalo::boxed::Box::new_in`]: boxed/struct.Box.html#method.new_in
///
/// ## 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.
///
///
/// ### `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> {
NonNull::from(&self.0)
}
}
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]
fn is_pointer_aligned_to<T>(pointer: *mut T, align: usize) -> bool {
debug_assert!(align.is_power_of_two());
let pointer = pointer as usize;
let pointer_aligned = round_down_to(pointer, align);
pointer == pointer_aligned
}
#[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)
}
/// Same as `round_down_to` but preserves pointer provenance.
#[inline]
pub(crate) fn round_mut_ptr_down_to(ptr: *mut u8, divisor: usize) -> *mut u8 {
debug_assert!(divisor > 0);
debug_assert!(divisor.is_power_of_two());
ptr.wrapping_sub(ptr as usize & (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]
fn layout_from_size_align(size: usize, align: usize) -> Result<Layout, AllocErr> {
Layout::from_size_align(size, align).map_err(|_| AllocErr)
}
#[inline(never)]
fn allocation_size_overflow<T>() -> T {
panic!("requested allocation size overflowed")
}
impl Bump {
/// Construct a new arena to bump allocate into.
///
/// ## Example
///
/// ```
/// let bump = bumpalo::Bump::new();
/// # let _ = bump;
/// ```
pub fn new() -> Bump {
Self::with_capacity(0)
}
/// 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 = 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(usize::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).ok()?;
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)]
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)]
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)]
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)]
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).
///
///
/// ## 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)]
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).
///
///
/// ## 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)]
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)]
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)]
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)]
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)]
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)]
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)]
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)]
pub fn alloc_slice_fill_iter<T, I>(&self, iter: I) -> &mut [T]
where
I: IntoIterator<Item = T>,
I::IntoIter: ExactSizeIterator,
{
let mut iter = iter.into_iter();
self.alloc_slice_fill_with(iter.len(), |_| {
iter.next().expect("Iterator supplied too few elements")
})
}
/// Allocates a new slice of size `len` slice into this `Bump` and return an
/// exclusive reference to the copy.
///
/// All elements of the slice are initialized to [`T::default()`].
///
///
/// ## Panics
///
/// Panics if reserving space for the slice 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)]
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
///
/// # 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
///
/// # 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 aligned_ptr = round_mut_ptr_down_to(ptr, layout.align());
if aligned_ptr >= start {
let aligned_ptr = NonNull::new_unchecked(aligned_ptr);
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.ptr.get().as_ptr() 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)]
#[cold]
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 = matches!(self.allocation_limit(), Some(limit) if layout.size() < limit
&& base_size >= layout.size()
&& limit < DEFAULT_CHUNK_SIZE_WITHOUT_FOOTER
&& self.allocated_bytes() == 0);
if base_size >= min_new_chunk_size || bypass_min_chunk_size_for_small_limits {
let 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 = round_mut_ptr_down_to(ptr, layout.align());
debug_assert!(
ptr as *const _ <= new_footer,
"{:p} <= {:p}",
ptr,
new_footer
);
let ptr = NonNull::new_unchecked(ptr);
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 }
}
/// Calculates the number of bytes requested from the Rust allocator for this `Bump`.
///
/// This number is equal to the [`allocated_bytes()`](Self::allocated_bytes) plus
/// the size of the bump metadata.
pub fn allocated_bytes_including_metadata(&self) -> usize {
let metadata_size =
unsafe { self.iter_allocated_chunks_raw().count() * mem::size_of::<ChunkFooter>() };
self.allocated_bytes() + metadata_size
}
#[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> {
// If the new layout demands greater alignment than the old layout has,
// then either
//
// 1. the pointer happens to satisfy the new layout's alignment, so we
// got lucky and can return the pointer as-is, or
//
// 2. the pointer is not aligned to the new layout's demanded alignment,
// and we are unlucky.
//
// In the case of (2), to successfully "shrink" the allocation, we would
// have to allocate a whole new region for the new layout, without being
// able to free the old region. That is unacceptable, so simply return
// an allocation failure error instead.
if old_layout.align() < new_layout.align() {
if is_pointer_aligned_to(ptr.as_ptr(), new_layout.align()) {
return Ok(ptr);
} else {
return Err(AllocErr);
}
}
debug_assert!(is_pointer_aligned_to(ptr.as_ptr(), new_layout.align()));
let old_size = old_layout.size();
let new_size = new_layout.size();
// 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.
//
// We do `(old_size + 1) / 2` so division rounds up rather than
// down. Consider when:
//
// old_size = 5
// new_size = 3
//
// If we do not take care to round up, this will result in:
//
// delta = 2
// (old_size / 2) = (5 / 2) = 2
//
// And the the check will succeed even though we are have
// overlapping ranges:
//
// |--------old-allocation-------|
// |------from-------|
// |-------to--------|
// +-----+-----+-----+-----+-----+
// | a | b | c | . | . |
// +-----+-----+-----+-----+-----+
//
// But we MUST NOT have overlapping ranges because we use
// `copy_nonoverlapping` below! Therefore, we round the division
// up to avoid this issue.
&& delta >= (old_size + 1) / 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);
}
// If this wasn't the last allocation, or shrinking wasn't worth it,
// simply return the old pointer as-is.
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(any(feature = "allocator_api", feature = "allocator-api2"))]
unsafe impl<'a> Allocator for &'a Bump {
#[inline]
fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
self.try_alloc_layout(layout)
.map(|p| unsafe {
NonNull::new_unchecked(ptr::slice_from_raw_parts_mut(p.as_ptr(), layout.size()))
})
.map_err(|_| AllocError)
}
#[inline]
unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout) {
Bump::dealloc(self, ptr, layout)
}
#[inline]
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| unsafe {
NonNull::new_unchecked(ptr::slice_from_raw_parts_mut(p.as_ptr(), new_layout.size()))
})
.map_err(|_| AllocError)
}
#[inline]
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| unsafe {
NonNull::new_unchecked(ptr::slice_from_raw_parts_mut(p.as_ptr(), new_layout.size()))
})
.map_err(|_| AllocError)
}
#[inline]
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]
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();
}
}
}