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//!
//! Scoped-Arena provides arena allocator with explicit scopes.
//!
//! ## Arena allocation
//!
//! Arena allocators are simple and provides ludicrously fast allocation.\
//! Basically allocation requires only increment of internal pointer in the memory block to alignment of allocated object and then to size of allocated object and that's it.\
//! When memory block is exhausted arena will allocate new bigger memory block.\
//! Then arena can be reset after all allocated objects are not used anymore, keeping only last memory block and reuse it.\
//! After several warmup iterations the only memory block is large enough to handle all allocations until next reset.
//!
//!
//! ### Example
//!
//! ```rust
//! use scoped_arena::Scope;
//!
//! struct Cat {
//! name: String,
//! hungry: bool,
//! }
//!
//! /// Create new arena with `Global` allocator.
//! let mut scope = Scope::new();
//!
//! /// Construct a cat and move it to the scope.
//! let cat: &mut Cat = scope.to_scope(Cat {
//! name: "Fluffy".to_owned(),
//! hungry: true,
//! });
//!
//! // Now `cat` is a mutable reference bound to scope borrow lifetime.
//!
//! assert_eq!(&cat.name, "Fluffy");
//! assert!(cat.hungry);
//!
//! cat.hungry = false;
//!
//! // This cat instance on scope will be automatically dropped when `scope` is dropped or reset.
//! // It is impossible to reset before last usage of `cat`.
//!
//! // Next line will drop cat value and free memory occupied by it.
//! scope.reset();
//!
//! // If there were more cats or any other objects put on scope they all would be dropped and memory freed.
//! ```
//!
//! ## Scopes
//!
//! To reuse memory earlier this crates provides `Scope` with methods to create sub-`Scope`s.\
//! When sub-`Scope` is reset or dropped it will `Drop` all stored values and free memory allocated by the scope and flush last of new allocated memory block into parent.\
//! While objects allocated with parent `Scope` are unchanged and still valid.
//!
//! Well placed scopes can significantly reduce memory consumption.\
//! For example if few function calls use a lot of dynamic memory but don't need it to be available in caller\
//! they can be provided with sub-scope.\
//! At the same time any memory allocated in parent scope stays allocated.
//!
//! Creating sub-scope is cheap and allocating within sub-scope is as fast as allocating in parent scope.\
//!
//! ### Example
//!
//! ```rust
//! use scoped_arena::{Scope, ScopeProxy};
//!
//!
//! fn heavy_on_memory(mut scope: Scope<'_>, foobar: &String) {
//! for _ in 0 .. 42 {
//! let foobar: &mut String = scope.to_scope(foobar.clone());
//! }
//!
//! // new `scope` is dropped here and drops all allocated strings and frees memory.
//! }
//!
//! let mut scope = Scope::new();
//!
//! // Proxy is required to be friends with borrow checker.
//! // Creating sub-scope must lock parent `Scope` from being used, which requires mutable borrow, but any allocation borrows `Scope`.
//! // `Proxy` relaxes this a bit. `Proxy` borrows `Scope` mutably and tie allocated objects lifetime to scopes' borrow lifetime.
//! // So sub-scope can borrow proxy mutably while there are objects allocated from it.
//! let mut proxy = scope.proxy();
//!
//! let foobar: &mut String = proxy.to_scope("foobar".to_owned());
//!
//! // Make sub-scope for the call.
//! heavy_on_memory(proxy.scope(), &*foobar);
//!
//! // If `heavy_on_memory` didn't trigger new memory object allocation in the scope,
//! // sub-scope drop would rewind scope's internals to exactly the same state.
//! // Otherwise last of new blocks will become current block in parent scope.
//! //
//! // Note that `foobar` is still alive.
//!
//! heavy_on_memory(proxy.scope(), &*foobar);
//! heavy_on_memory(proxy.scope(), &*foobar);
//! heavy_on_memory(proxy.scope(), &*foobar);
//! heavy_on_memory(proxy.scope(), &*foobar);
//!
//! // Once peak memory consumption is reached, any number of `heavy_on_memory` calls would not require new memory blocks to be allocated.
//! // Even `loop { heavy_on_memory(proxy.scope(), &*foobar) }` will settle on some big enough block.
//! ```
//!
//! ## Dropping
//!
//! `to_scope` and `try_to_scope` methods store drop-glue for values that `needs_drop`.
//! On reset or drop scope iterates and properly drops all values.
//! No drop-glue is added for types that doesn't need drop. `Scope` allocates enough memory and writes value there, no bookkeeping overhead.
//!
//! ## Iterator collecting
//!
//! `to_scope_from_iter` method acts as `to_scope` but works on iterators and returns slices.
//! The limitation is that `to_scope_from_iter` need to allocate memory enough for upper bound of what iterator can yield.
//! If upper bound is too large or iterator is unbounded it will always fail.
//! One can use `try_to_scope_from_iter` so fail is `Err` and not panic.
//! It is safe for iterator to yield more items then upper bound it reports, `to_scope_from_iter` would not iterate past upper bound.
//! On success it returns mutable reference to slice with items from iterator in order.
//! All values will be dropped on scope reset or drop, same as with `to_scope`.
//!
//! This method is especially useful to deal with API that requires slices (*glares at FFI*), collecting into temporary `Vec` would cost much more.
//!
#![no_std]
#![cfg(any(feature = "allocator_api", feature = "alloc"))]
#![cfg_attr(feature = "allocator_api", feature(allocator_api))]
#[cfg(feature = "alloc")]
extern crate alloc;
mod allocator_api;
mod bucket;
mod drop;
use core::{
alloc::Layout,
fmt::{self, Debug},
iter::IntoIterator,
mem::{align_of, needs_drop, MaybeUninit},
ptr::{self, write, NonNull},
slice,
};
#[cfg(all(not(no_global_oom_handling), feature = "alloc"))]
use alloc::alloc::handle_alloc_error;
use self::{
bucket::Buckets,
drop::{DropList, WithDrop},
};
use self::allocator_api::{AllocError, Allocator};
#[cfg(feature = "alloc")]
use self::allocator_api::Global;
/// Scope associated with `Scope` allocator.
/// Allows placing values on the scope returning reference bound to scope borrow.
/// On drop scope drops all values placed onto it.
/// On drop scope frees all memory allocated from it.
#[cfg(not(feature = "alloc"))]
pub struct Scope<'arena, A: Allocator> {
buckets: Buckets<'arena>,
alloc: &'arena A,
drop_list: DropList<'static>,
}
/// Scope associated with `Scope` allocator.
/// Allows placing values on the scope returning reference bound to scope borrow.
/// On drop scope drops all values placed onto it.
/// On drop scope frees all memory allocated from it.
#[cfg(feature = "alloc")]
pub struct Scope<'arena, A: Allocator = Global> {
buckets: Buckets<'arena>,
alloc: A,
drop_list: DropList<'static>,
}
impl<A> Debug for Scope<'_, A>
where
A: Allocator,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("Scope")
.field("buckets", &self.buckets)
.finish_non_exhaustive()
}
}
impl<A> Drop for Scope<'_, A>
where
A: Allocator,
{
#[inline(always)]
fn drop(&mut self) {
unsafe {
self.drop_list.reset();
self.buckets.reset(&self.alloc, false);
}
}
}
#[cfg(feature = "alloc")]
impl Scope<'_, Global> {
/// Returns new instance of arena allocator based on [`Global`] allocator.
#[inline(always)]
pub fn new() -> Self {
Scope::new_in(Global)
}
/// Returns new instance of arena allocator based on [`Global`] allocator
/// with preallocated capacity in bytes.
#[inline(always)]
pub fn with_capacity(capacity: usize) -> Self {
Scope::with_capacity_in(capacity, Global)
}
}
impl<A> Scope<'_, A>
where
A: Allocator,
{
/// Returns new instance of arena allocator based on provided allocator.
#[inline(always)]
pub fn new_in(alloc: A) -> Self {
Scope::with_capacity_in(0, alloc)
}
/// Returns new instance of arena allocator based on provided allocator
/// with preallocated capacity in bytes.
#[inline(always)]
pub fn with_capacity_in(capacity: usize, alloc: A) -> Self {
Scope {
buckets: Buckets::new(capacity, &alloc).expect(ALLOCATOR_CAPACITY_OVERFLOW),
alloc,
drop_list: DropList::new(),
}
}
}
impl<A> Scope<'_, A>
where
A: Allocator,
{
#[inline(always)]
pub fn reset(&mut self) {
unsafe {
self.drop_list.reset();
self.buckets.reset(&self.alloc, true);
}
}
/// Allocates a block of memory.
/// Returns a [`&mut [MaybeUninit<u8>]`] meeting the size and alignment guarantees of layout.
/// Actual size of the returned size MAY be larger than requested.
/// The returned block should be initialized before use.
///
/// Returned block will be deallocated when scope is dropped.
#[cfg(all(not(no_global_oom_handling), feature = "alloc"))]
#[inline(always)]
pub fn alloc(&self, layout: Layout) -> &mut [MaybeUninit<u8>] {
match self.try_alloc(layout) {
Ok(buf) => buf,
Err(_) => handle_alloc_error(layout),
}
}
/// Attempts to allocate a block of memory.
/// On success, returns a [`&mut [MaybeUninit<u8>]`] meeting the size and alignment guarantees of layout.
/// Actual size of the returned size MAY be larger than requested.
/// The returned block should be initialized before use.
///
/// Returned block will be deallocated when scope is dropped.
///
/// # Errors
///
/// Returning `Err` indicates that memory is exhausted.
#[inline(always)]
pub fn try_alloc(&self, layout: Layout) -> Result<&mut [MaybeUninit<u8>], AllocError> {
unsafe { self.buckets.allocate(layout, &self.alloc) }
}
/// Allocates a block of memory.
/// Returns a [`&mut [u8]`] meeting the size and alignment guarantees of layout.
/// Actual size of the returned size MAY be larger than requested.
/// The returned block contents is zero-initialized.
///
/// Returned block will be deallocated when scope is dropped.
#[cfg(all(not(no_global_oom_handling), feature = "alloc"))]
#[inline(always)]
pub fn alloc_zeroed(&self, layout: Layout) -> &mut [u8] {
match self.try_alloc_zeroed(layout) {
Ok(buf) => buf,
Err(_) => handle_alloc_error(layout),
}
}
/// Attempts to allocate a block of memory.
/// On success, returns a [`&mut [u8]`] meeting the size and alignment guarantees of layout.
/// Actual size of the returned size MAY be larger than requested.
/// The returned block contents is zero-initialized.
///
/// Returned block will be deallocated when scope is dropped.
///
/// # Errors
///
/// Returning `Err` indicates that memory is exhausted.
#[inline(always)]
pub fn try_alloc_zeroed(&self, layout: Layout) -> Result<&mut [u8], AllocError> {
let buf = unsafe { self.buckets.allocate(layout, &self.alloc) }?;
let buf = unsafe {
// Zeroing bytes buffer should be safe.
ptr::write_bytes(buf.as_mut_ptr(), 0, buf.len());
// Zero-initialized.
slice::from_raw_parts_mut(buf.as_mut_ptr() as *mut u8, buf.len())
};
Ok(buf)
}
/// Move value onto the scope.
/// Returns mutable reference to value with lifetime equal to scope borrow lifetime.
/// Value on scope will be dropped when scope is dropped.
///
/// This method is as cheap as allocation if value does not needs dropping as reported by [`core::mem::needs_drop`].
#[cfg(all(not(no_global_oom_handling), feature = "alloc"))]
#[inline(always)]
pub fn to_scope<T>(&self, value: T) -> &mut T {
self.to_scope_with(|| value)
}
/// Places value returned from function onto the scope.
/// Returns mutable reference to value with lifetime equal to scope borrow lifetime.
/// Value on scope will be dropped when scope is dropped.
///
/// This method is as cheap as allocation if value does not needs dropping as reported by [`core::mem::needs_drop`].
#[cfg(all(not(no_global_oom_handling), feature = "alloc"))]
#[inline(always)]
pub fn to_scope_with<F, T>(&self, f: F) -> &mut T
where
F: FnOnce() -> T,
{
match self.try_to_scope_with(f) {
Ok(value) => value,
Err(_) => handle_alloc_error(Layout::new::<T>()),
}
}
/// Tries to move value onto the scope.
/// On success, returns mutable reference to value with lifetime equal to scope borrow lifetime.
/// Value on scope will be dropped when scope is dropped.
///
/// This method is as cheap as allocation if value does not needs dropping as reported by [`core::mem::needs_drop`].
///
/// # Errors
///
/// Returning `Err` indicates that memory is exhausted.
/// Returning `Err` contains original value.
#[inline(always)]
pub fn try_to_scope<T>(&self, value: T) -> Result<&mut T, (AllocError, T)> {
self.try_to_scope_with(|| value)
.map_err(|(err, f)| (err, f()))
}
/// Tries to place value return from function onto the scope.
/// On success, returns mutable reference to value with lifetime equal to scope borrow lifetime.
/// Value on scope will be dropped when scope is dropped.
///
/// This method is as cheap as allocation if value does not needs dropping as reported by [`core::mem::needs_drop`].
///
/// # Errors
///
/// Returning `Err` indicates that memory is exhausted.
/// Returning `Err` contains original value.
#[inline(always)]
pub fn try_to_scope_with<F, T>(&self, f: F) -> Result<&mut T, (AllocError, F)>
where
F: FnOnce() -> T,
{
try_to_scope_with(|layout| self.try_alloc(layout), &self.drop_list, f)
}
/// Move values from iterator onto the scope.
/// Returns mutable reference to slice with lifetime equal to scope borrow lifetime.
/// Values on scope will be dropped when scope is dropped.
///
/// This method is as cheap as allocation if value does not needs dropping as reported by [`core::mem::needs_drop`].
///
/// This method allocates memory to hold iterator's upper bound number of items. See [`core::iter::Iterator::size_hint`].
/// It will not consume more items.
/// This method will always fail for unbound iterators.
#[cfg(all(not(no_global_oom_handling), feature = "alloc"))]
#[inline(always)]
pub fn to_scope_from_iter<T, I>(&self, iter: I) -> &mut [T]
where
I: IntoIterator<Item = T>,
{
let too_large_layout = unsafe {
Layout::from_size_align_unchecked(usize::MAX - align_of::<T>(), align_of::<T>())
};
let iter = iter.into_iter();
let upper_bound = iter
.size_hint()
.1
.unwrap_or_else(|| handle_alloc_error(too_large_layout));
match self.try_to_scope_from_iter(iter) {
Ok(slice) => slice,
Err(_) => {
handle_alloc_error(Layout::array::<T>(upper_bound).unwrap_or(too_large_layout))
}
}
}
/// Tries to move values from iterator onto the scope.
/// On success, returns mutable reference to slice with lifetime equal to scope borrow lifetime.
/// Values on scope will be dropped when scope is dropped.
///
/// This method is as cheap as allocation if value does not needs dropping as reported by [`core::mem::needs_drop`].
///
/// This method allocates memory to hold iterator's upper bound number of items. See [`core::iter::Iterator::size_hint`].
/// It will not consume more items.
/// This method will always fail for unbound iterators.
///
/// # Errors
///
/// Returning `Err` indicates that memory is exhausted.
/// Returning `Err` contains original iterator.
#[inline(always)]
pub fn try_to_scope_from_iter<T, I>(
&self,
iter: I,
) -> Result<&mut [T], (AllocError, I::IntoIter)>
where
I: IntoIterator<Item = T>,
{
try_to_scope_from_iter(|layout| self.try_alloc(layout), &self.drop_list, iter)
}
/// Put multiple clones of the value onto the scope.
/// Returns mutable reference to slice with lifetime equal to scope borrow lifetime.
/// Values on scope will be dropped when scope is dropped.
///
/// This method is as cheap as allocation if value does not needs dropping as reported by [`core::mem::needs_drop`].
#[inline(always)]
pub fn to_scope_many<T>(&self, count: usize, value: T) -> &mut [T]
where
T: Clone,
{
let too_large_layout = unsafe {
Layout::from_size_align_unchecked(usize::MAX - align_of::<T>(), align_of::<T>())
};
match self.try_to_scope_many(count, value) {
Ok(slice) => slice,
Err(_) => handle_alloc_error(Layout::array::<T>(count).unwrap_or(too_large_layout)),
}
}
/// Tries to put multiple clones of the value onto the scope.
/// On success, returns mutable reference to slice with lifetime equal to scope borrow lifetime.
/// Returns mutable reference to slice with lifetime equal to scope borrow lifetime.
/// Values on scope will be dropped when scope is dropped.
///
/// This method is as cheap as allocation if value does not needs dropping as reported by [`core::mem::needs_drop`].
#[inline(always)]
pub fn try_to_scope_many<T>(&self, count: usize, value: T) -> Result<&mut [T], AllocError>
where
T: Clone,
{
self.try_to_scope_many_with(count, || value.clone())
}
/// Put multiple values created by calls to the specified function onto the scope.
/// Returns mutable reference to slice with lifetime equal to scope borrow lifetime.
/// Values on scope will be dropped when scope is dropped.
///
/// This method is as cheap as allocation if value does not needs dropping as reported by [`core::mem::needs_drop`].
#[inline(always)]
pub fn to_scope_many_with<T, F>(&self, count: usize, f: F) -> &mut [T]
where
F: FnMut() -> T,
{
let too_large_layout = unsafe {
Layout::from_size_align_unchecked(usize::MAX - align_of::<T>(), align_of::<T>())
};
match self.try_to_scope_many_with(count, f) {
Ok(slice) => slice,
Err(_) => handle_alloc_error(Layout::array::<T>(count).unwrap_or(too_large_layout)),
}
}
/// Tries to put multiple values created by calls to the specified function onto the scope.
/// On success, returns mutable reference to slice with lifetime equal to scope borrow lifetime.
/// Returns mutable reference to slice with lifetime equal to scope borrow lifetime.
/// Values on scope will be dropped when scope is dropped.
///
/// This method is as cheap as allocation if value does not needs dropping as reported by [`core::mem::needs_drop`].
#[inline(always)]
pub fn try_to_scope_many_with<T, F>(&self, count: usize, f: F) -> Result<&mut [T], AllocError>
where
F: FnMut() -> T,
{
try_to_scope_many_with(|layout| self.try_alloc(layout), &self.drop_list, count, f)
}
/// Reports total memory allocated from underlying allocator by associated arena.
#[inline(always)]
pub fn total_memory_usage(&self) -> usize {
self.buckets.total_memory_usage()
}
/// Creates scope proxy bound to the scope.
/// Any objects allocated through proxy will be attached to the scope.
/// Returned proxy will use reference to the underlying allocator.
#[inline(always)]
pub fn proxy_ref<'a>(&'a mut self) -> ScopeProxy<'a, &'a A> {
ScopeProxy {
buckets: self.buckets.fork(),
alloc: &self.alloc,
drop_list: self.drop_list.fork(),
}
}
}
impl<A> Scope<'_, A>
where
A: Allocator + Clone,
{
/// Creates scope proxy bound to the scope.
/// Any objects allocated through proxy will be attached to the scope.
/// Returned proxy will use clone of the underlying allocator.
#[inline(always)]
pub fn proxy<'a>(&'a mut self) -> ScopeProxy<'a, A> {
ScopeProxy {
buckets: self.buckets.fork(),
alloc: self.alloc.clone(),
drop_list: self.drop_list.fork(),
}
}
}
/// Proxy for `Scope` which allocates memory bound to the scope lifetime and not itself.
/// This allows to create sub-scopes while keeping references to scoped values.
/// Does not frees memory and does not drops values moved on scope when dropped.
/// Parent `Scope` will do this.
#[cfg(not(feature = "alloc"))]
pub struct ScopeProxy<'scope, A: Allocator> {
buckets: Buckets<'scope>,
alloc: &'scope A,
drop_list: DropList<'scope>,
}
/// Proxy for `Scope` which allocates memory bound to the scope lifetime and not itself.
/// This allows to create sub-scopes while keeping references to scoped values.
/// Does not frees memory and does not drops values moved on scope when dropped.
/// Parent `Scope` will do this.
#[cfg(feature = "alloc")]
pub struct ScopeProxy<'scope, A: Allocator = Global> {
buckets: Buckets<'scope>,
alloc: A,
drop_list: DropList<'scope>,
}
impl<A> Debug for ScopeProxy<'_, A>
where
A: Allocator,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("ScopeProxy")
.field("buckets", &self.buckets)
.finish_non_exhaustive()
}
}
impl<A> Drop for ScopeProxy<'_, A>
where
A: Allocator,
{
#[inline(always)]
fn drop(&mut self) {
unsafe {
self.drop_list.flush_fork();
self.buckets.flush_fork();
}
}
}
impl<'scope, A> ScopeProxy<'scope, A>
where
A: Allocator,
{
/// Allocates a block of memory.
/// Returns a [`&mut [MaybeUninit<u8>]`] meeting the size and alignment guarantees of layout.
/// The returned block should be initialized before use.
///
/// Returned block will be deallocated when scope is dropped.
#[cfg(all(not(no_global_oom_handling), feature = "alloc"))]
#[inline(always)]
pub fn alloc(&self, layout: Layout) -> &'scope mut [MaybeUninit<u8>] {
match self.try_alloc(layout) {
Ok(buf) => buf,
Err(_) => handle_alloc_error(layout),
}
}
/// Attempts to allocate a block of memory.
/// On success, returns a [`&mut [MaybeUninit<u8>]`] meeting the size and alignment guarantees of layout.
/// The returned block should be initialized before use.
///
/// Returned block will be deallocated when scope is dropped.
///
/// # Errors
///
/// Returning `Err` indicates that memory is exhausted.
#[inline(always)]
pub fn try_alloc(&self, layout: Layout) -> Result<&'scope mut [MaybeUninit<u8>], AllocError> {
unsafe { self.buckets.allocate(layout, &self.alloc) }
}
/// Allocates a block of memory.
/// Returns a [`&mut [u8]`] meeting the size and alignment guarantees of layout.
/// The returned block contents is zero-initialized.
///
/// Returned block will be deallocated when scope is dropped.
#[cfg(all(not(no_global_oom_handling), feature = "alloc"))]
#[inline(always)]
pub fn alloc_zeroed(&self, layout: Layout) -> &mut [u8] {
match self.try_alloc_zeroed(layout) {
Ok(buf) => buf,
Err(_) => handle_alloc_error(layout),
}
}
/// Attempts to allocate a block of memory.
/// On success, returns a [`&mut [u8]`] meeting the size and alignment guarantees of layout.
/// The returned block contents is zero-initialized.
///
/// Returned block will be deallocated when scope is dropped.
///
/// # Errors
///
/// Returning `Err` indicates that memory is exhausted.
#[inline(always)]
pub fn try_alloc_zeroed(&self, layout: Layout) -> Result<&mut [u8], AllocError> {
let buf = unsafe { self.buckets.allocate(layout, &self.alloc) }?;
let buf = unsafe {
// Zeroing bytes buffer should be safe.
ptr::write_bytes(buf.as_mut_ptr(), 0, buf.len());
// Zero-initialized.
slice::from_raw_parts_mut(buf.as_mut_ptr() as *mut u8, buf.len())
};
Ok(buf)
}
/// Move value onto the scope.
/// Returns mutable reference to value with lifetime equal to 'scope lifetime.
/// Value on scope will be dropped when scope is dropped.
///
/// This method is as cheap as allocation if value does not needs dropping as reported by [`core::mem::needs_drop`].
#[cfg(all(not(no_global_oom_handling), feature = "alloc"))]
#[inline(always)]
pub fn to_scope<T>(&self, value: T) -> &'scope mut T {
self.to_scope_with(|| value)
}
/// Places value returned from function onto the scope.
/// Returns mutable reference to value with lifetime equal to scope borrow lifetime.
/// Value on scope will be dropped when scope is dropped.
///
/// This method is as cheap as allocation if value does not needs dropping as reported by [`core::mem::needs_drop`].
#[cfg(all(not(no_global_oom_handling), feature = "alloc"))]
#[inline(always)]
pub fn to_scope_with<F, T>(&self, f: F) -> &'scope mut T
where
F: FnOnce() -> T,
{
match self.try_to_scope_with(f) {
Ok(value) => value,
Err(_) => handle_alloc_error(Layout::new::<T>()),
}
}
/// Tries to move value onto the scope.
/// On success, returns mutable reference to value with lifetime to equal 'scope lifetime.
/// Value on scope will be dropped when scope is dropped.
///
/// This method is as cheap as allocation if value does not needs dropping as reported by [`core::mem::needs_drop`].
///
/// # Errors
///
/// Returning `Err` indicates that memory is exhausted.
/// Returning `Err` contains original value.
#[inline(always)]
pub fn try_to_scope<T>(&self, value: T) -> Result<&'scope mut T, (AllocError, T)> {
self.try_to_scope_with(|| value)
.map_err(|(err, f)| (err, f()))
}
/// Tries to place value return from function onto the scope.
/// On success, returns mutable reference to value with lifetime equal to scope borrow lifetime.
/// Value on scope will be dropped when scope is dropped.
///
/// This method is as cheap as allocation if value does not needs dropping as reported by [`core::mem::needs_drop`].
///
/// # Errors
///
/// Returning `Err` indicates that memory is exhausted.
/// Returning `Err` contains original value.
#[inline(always)]
pub fn try_to_scope_with<F, T>(&self, f: F) -> Result<&'scope mut T, (AllocError, F)>
where
F: FnOnce() -> T,
{
try_to_scope_with(|layout| self.try_alloc(layout), &self.drop_list, f)
}
/// Move values from iterator onto the scope.
/// Returns mutable reference to slice with lifetime equal to 'scope lifetime.
/// Values on scope will be dropped when scope is dropped.
///
/// This method is as cheap as allocation if value does not needs dropping as reported by [`core::mem::needs_drop`].
///
/// This method allocates memory to hold iterator's upper bound number of items. See [`core::iter::Iterator::size_hint`].
/// It will not consume more items.
/// This method will always fail for unbound iterators.
#[cfg(all(not(no_global_oom_handling), feature = "alloc"))]
#[inline(always)]
pub fn to_scope_from_iter<T, I>(&self, iter: I) -> &'scope mut [T]
where
I: IntoIterator<Item = T>,
{
let too_large_layout = unsafe {
Layout::from_size_align_unchecked(usize::MAX - align_of::<T>(), align_of::<T>())
};
let iter = iter.into_iter();
let upper_bound = iter
.size_hint()
.1
.unwrap_or_else(|| handle_alloc_error(too_large_layout));
match self.try_to_scope_from_iter(iter) {
Ok(slice) => slice,
Err(_) => {
handle_alloc_error(Layout::array::<T>(upper_bound).unwrap_or(too_large_layout))
}
}
}
/// Tries to move values from iterator onto the scope.
/// On success, returns mutable reference to slice with lifetime equal to 'scope lifetime.
/// Values on scope will be dropped when scope is dropped.
///
/// This method is as cheap as allocation if value does not needs dropping as reported by [`core::mem::needs_drop`].
///
/// This method allocates memory to hold iterator's upper bound number of items. See [`core::iter::Iterator::size_hint`].
/// It will not consume more items.
/// This method will always fail for unbound iterators.
///
/// # Errors
///
/// Returning `Err` indicates that memory is exhausted.
/// Returning `Err` contains original iterator.
#[inline(always)]
pub fn try_to_scope_from_iter<T, I>(
&self,
iter: I,
) -> Result<&'scope mut [T], (AllocError, I::IntoIter)>
where
I: IntoIterator<Item = T>,
{
try_to_scope_from_iter(|layout| self.try_alloc(layout), &self.drop_list, iter)
}
/// Put multiple clones of the value onto the scope.
/// Returns mutable reference to slice with lifetime equal to scope borrow lifetime.
/// Values on scope will be dropped when scope is dropped.
///
/// This method is as cheap as allocation if value does not needs dropping as reported by [`core::mem::needs_drop`].
#[inline(always)]
pub fn to_scope_many<T>(&self, count: usize, value: T) -> &'scope mut [T]
where
T: Clone,
{
let too_large_layout = unsafe {
Layout::from_size_align_unchecked(usize::MAX - align_of::<T>(), align_of::<T>())
};
match self.try_to_scope_many(count, value) {
Ok(slice) => slice,
Err(_) => handle_alloc_error(Layout::array::<T>(count).unwrap_or(too_large_layout)),
}
}
/// Tries to put multiple clones of the value onto the scope.
/// On success, returns mutable reference to slice with lifetime equal to scope borrow lifetime.
/// Returns mutable reference to slice with lifetime equal to scope borrow lifetime.
/// Values on scope will be dropped when scope is dropped.
///
/// This method is as cheap as allocation if value does not needs dropping as reported by [`core::mem::needs_drop`].
#[inline(always)]
pub fn try_to_scope_many<T>(
&self,
count: usize,
value: T,
) -> Result<&'scope mut [T], AllocError>
where
T: Clone,
{
self.try_to_scope_many_with(count, || value.clone())
}
/// Put multiple values created by calls to the specified function onto the scope.
/// Returns mutable reference to slice with lifetime equal to scope borrow lifetime.
/// Values on scope will be dropped when scope is dropped.
///
/// This method is as cheap as allocation if value does not needs dropping as reported by [`core::mem::needs_drop`].
#[inline(always)]
pub fn to_scope_many_with<T, F>(&self, count: usize, f: F) -> &'scope mut [T]
where
F: FnMut() -> T,
{
let too_large_layout = unsafe {
Layout::from_size_align_unchecked(usize::MAX - align_of::<T>(), align_of::<T>())
};
match self.try_to_scope_many_with(count, f) {
Ok(slice) => slice,
Err(_) => handle_alloc_error(Layout::array::<T>(count).unwrap_or(too_large_layout)),
}
}
/// Tries to put multiple values created by calls to the specified function onto the scope.
/// On success, returns mutable reference to slice with lifetime equal to scope borrow lifetime.
/// Returns mutable reference to slice with lifetime equal to scope borrow lifetime.
/// Values on scope will be dropped when scope is dropped.
///
/// This method is as cheap as allocation if value does not needs dropping as reported by [`core::mem::needs_drop`].
#[inline(always)]
pub fn try_to_scope_many_with<T, F>(
&self,
count: usize,
f: F,
) -> Result<&'scope mut [T], AllocError>
where
F: FnMut() -> T,
{
try_to_scope_many_with(|layout| self.try_alloc(layout), &self.drop_list, count, f)
}
/// Reports total memory allocated from underlying allocator by associated arena.
#[inline(always)]
pub fn total_memory_usage(&self) -> usize {
self.buckets.total_memory_usage()
}
/// Creates new scope which inherits from the proxy's scope.
/// This scope becomes locked until returned scope is dropped.
/// Returned scope will use reference to the underlying allocator.
#[inline(always)]
pub fn scope_ref<'a>(&'a mut self) -> Scope<'a, &'a A> {
Scope {
buckets: self.buckets.fork(),
alloc: &self.alloc,
drop_list: DropList::new(),
}
}
}
impl<A> ScopeProxy<'_, A>
where
A: Allocator + Clone,
{
/// Creates new scope which inherits from the proxy's scope.
/// This scope becomes locked until returned scope is dropped.
/// Returned scope will use clone of the underlying allocator.
#[inline(always)]
pub fn scope<'a>(&'a mut self) -> Scope<'a, A> {
Scope {
buckets: self.buckets.fork(),
alloc: self.alloc.clone(),
drop_list: DropList::new(),
}
}
}
const ALLOCATOR_CAPACITY_OVERFLOW: &'static str = "Allocator capacity overflow";
unsafe impl<A> Allocator for &'_ Scope<'_, A>
where
A: Allocator,
{
#[inline(always)]
fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
let buf = self.try_alloc(layout)?;
let ptr = unsafe {
NonNull::new_unchecked(core::ptr::slice_from_raw_parts_mut(
buf.as_mut_ptr() as *mut u8,
buf.len(),
))
};
Ok(ptr)
}
#[inline(always)]
unsafe fn deallocate(&self, _ptr: NonNull<u8>, _layout: Layout) {
// Will be deallocated on scope drop.
}
#[cfg(feature = "allocator_api")]
#[inline(always)]
unsafe fn shrink(
&self,
ptr: NonNull<u8>,
old_layout: Layout,
new_layout: Layout,
) -> Result<NonNull<[u8]>, AllocError> {
debug_assert!(
new_layout.size() <= old_layout.size(),
"`new_layout.size()` must be smaller than or equal to `old_layout.size()`"
);
// Returns same memory unchanged.
// This is valid behavior as change in layout won't affect deallocation
// and for `grow{_zeroed}` methods new layout with smaller size will only affect numbers of bytes copied.
Ok(NonNull::new_unchecked(core::slice::from_raw_parts_mut(
ptr.as_ptr(),
old_layout.size(),
)))
}
}
unsafe impl<A> Allocator for ScopeProxy<'_, A>
where
A: Allocator,
{
#[inline(always)]
fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
let buf = self.try_alloc(layout)?;
let ptr = unsafe {
NonNull::new_unchecked(core::ptr::slice_from_raw_parts_mut(
buf.as_mut_ptr() as *mut u8,
buf.len(),
))
};
Ok(ptr)
}
#[inline(always)]
unsafe fn deallocate(&self, _ptr: NonNull<u8>, _layout: Layout) {
// Will be deallocated on scope drop.
}
#[cfg(feature = "allocator_api")]
#[inline(always)]
unsafe fn shrink(
&self,
ptr: NonNull<u8>,
old_layout: Layout,
new_layout: Layout,
) -> Result<NonNull<[u8]>, AllocError> {
debug_assert!(
new_layout.size() <= old_layout.size(),
"`new_layout.size()` must be smaller than or equal to `old_layout.size()`"
);
// Returns same memory unchanged.
// This is valid behavior as change in layout won't affect deallocation
// and for `grow{_zeroed}` methods new layout with smaller size will only affect numbers of bytes copied.
Ok(NonNull::new_unchecked(core::slice::from_raw_parts_mut(
ptr.as_ptr(),
old_layout.size(),
)))
}
}
#[inline(always)]
fn try_to_scope_with<'a, F, T>(
try_alloc: impl FnOnce(Layout) -> Result<&'a mut [MaybeUninit<u8>], AllocError>,
drop_list: &DropList,
f: F,
) -> Result<&'a mut T, (AllocError, F)>
where
F: FnOnce() -> T,
{
if needs_drop::<T>() {
match try_alloc(Layout::new::<WithDrop<T>>()) {
Ok(buf) => {
let value = unsafe { WithDrop::init(buf, f(), drop_list) };
Ok(value)
}
Err(err) => Err((err, f)),
}
} else {
match try_alloc(Layout::new::<T>()) {
Ok(buf) => {
let uninit = unsafe { cast_buf(buf) };
unsafe { write(uninit.as_mut_ptr(), f()) };
Ok(unsafe { uninit.assume_init_mut() })
}
Err(err) => Err((err, f)),
}
}
}
fn try_to_scope_from_iter<'a, T, I>(
try_alloc: impl FnOnce(Layout) -> Result<&'a mut [MaybeUninit<u8>], AllocError>,
drop_list: &DropList,
iter: I,
) -> Result<&'a mut [T], (AllocError, I::IntoIter)>
where
I: IntoIterator<Item = T>,
{
let iter = iter.into_iter();
let upper_bound = match iter.size_hint().1 {
Some(upper_bound) => upper_bound,
None => return Err((AllocError, iter)),
};
if needs_drop::<T>() {
match WithDrop::<T>::array_layout(upper_bound) {
Some(layout) => match try_alloc(layout) {
Ok(buf) => {
let slice = unsafe { WithDrop::init_iter(buf, iter, drop_list) };
Ok(slice)
}
Err(err) => Err((err, iter)),
},
None => Err((AllocError, iter)),
}
} else {
match Layout::array::<T>(upper_bound) {
Ok(layout) => match try_alloc(layout) {
Ok(buf) => {
let (uninit, _) = unsafe {
// Buffer with layout for `[T; upper_bound]` was requested.
cast_buf_array::<T>(buf)
};
let item_count = iter.take(uninit.len()).fold(0, |idx, item| {
uninit[idx].write(item);
idx + 1
});
let slice = unsafe {
// First `item_count` elements of the array were initialized from iterator
core::slice::from_raw_parts_mut(uninit.as_mut_ptr() as *mut T, item_count)
};
Ok(slice)
}
Err(err) => Err((err, iter)),
},
Err(_) => Err((AllocError, iter)),
}
}
}
fn try_to_scope_many_with<'a, T>(
try_alloc: impl FnOnce(Layout) -> Result<&'a mut [MaybeUninit<u8>], AllocError>,
drop_list: &DropList,
count: usize,
mut f: impl FnMut() -> T,
) -> Result<&'a mut [T], AllocError> {
if needs_drop::<T>() {
match WithDrop::<T>::array_layout(count) {
Some(layout) => match try_alloc(layout) {
Ok(buf) => {
let slice = unsafe { WithDrop::init_many(buf, count, f, drop_list) };
Ok(slice)
}
Err(err) => Err(err),
},
None => Err(AllocError),
}
} else {
match Layout::array::<T>(count) {
Ok(layout) => match try_alloc(layout) {
Ok(buf) => {
let (uninit, _) = unsafe {
// Buffer with layout for `[T; upper_bound]` was requested.
cast_buf_array::<T>(buf)
};
for i in 0..count {
uninit[i].write(f());
}
let slice = unsafe {
// First `item_count` elements of the array were initialized from iterator
core::slice::from_raw_parts_mut(uninit.as_mut_ptr() as *mut T, count)
};
Ok(slice)
}
Err(err) => Err(err),
},
Err(_) => Err(AllocError),
}
}
}
unsafe fn cast_buf<T>(buf: &mut [MaybeUninit<u8>]) -> &mut MaybeUninit<T> {
let layout = Layout::new::<T>();
debug_assert_eq!(0, buf.as_mut_ptr() as usize % layout.align());
debug_assert!(buf.len() >= layout.size());
&mut *(buf.as_mut_ptr() as *mut MaybeUninit<T>)
}
unsafe fn cast_buf_array<T>(
buf: &mut [MaybeUninit<u8>],
) -> (&mut [MaybeUninit<T>], &mut [MaybeUninit<u8>]) {
let layout = Layout::new::<T>();
debug_assert_eq!(0, buf.as_mut_ptr() as usize % layout.align());
let len = buf.len() / layout.size();
let (head, tail) = buf.split_at_mut(len * layout.size());
let head = slice::from_raw_parts_mut(head.as_mut_ptr() as *mut MaybeUninit<T>, len);
(head, tail)
}