Source code
Revision control
Copy as Markdown
Other Tools
// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// option. This file may not be copied, modified, or distributed
// except according to those terms.
#![allow(unstable_name_collisions)]
#![allow(dead_code)]
#![allow(deprecated)]
//! Memory allocation APIs
use core::cmp;
use core::fmt;
use core::mem;
use core::ptr::{self, NonNull};
use core::usize;
pub use core::alloc::{Layout, LayoutErr};
fn new_layout_err() -> LayoutErr {
Layout::from_size_align(1, 3).unwrap_err()
}
pub fn handle_alloc_error(layout: Layout) -> ! {
panic!("encountered allocation error: {:?}", layout)
}
pub trait UnstableLayoutMethods {
fn padding_needed_for(&self, align: usize) -> usize;
fn repeat(&self, n: usize) -> Result<(Layout, usize), LayoutErr>;
fn array<T>(n: usize) -> Result<Layout, LayoutErr>;
}
impl UnstableLayoutMethods for Layout {
fn padding_needed_for(&self, align: usize) -> usize {
let len = self.size();
// Rounded up value is:
// len_rounded_up = (len + align - 1) & !(align - 1);
// and then we return the padding difference: `len_rounded_up - len`.
//
// We use modular arithmetic throughout:
//
// 1. align is guaranteed to be > 0, so align - 1 is always
// valid.
//
// 2. `len + align - 1` can overflow by at most `align - 1`,
// so the &-mask with `!(align - 1)` will ensure that in the
// case of overflow, `len_rounded_up` will itself be 0.
// Thus the returned padding, when added to `len`, yields 0,
// which trivially satisfies the alignment `align`.
//
// (Of course, attempts to allocate blocks of memory whose
// size and padding overflow in the above manner should cause
// the allocator to yield an error anyway.)
let len_rounded_up = len.wrapping_add(align).wrapping_sub(1) & !align.wrapping_sub(1);
len_rounded_up.wrapping_sub(len)
}
fn repeat(&self, n: usize) -> Result<(Layout, usize), LayoutErr> {
let padded_size = self
.size()
.checked_add(self.padding_needed_for(self.align()))
.ok_or_else(new_layout_err)?;
let alloc_size = padded_size.checked_mul(n).ok_or_else(new_layout_err)?;
unsafe {
// self.align is already known to be valid and alloc_size has been
// padded already.
Ok((
Layout::from_size_align_unchecked(alloc_size, self.align()),
padded_size,
))
}
}
fn array<T>(n: usize) -> Result<Layout, LayoutErr> {
Layout::new::<T>().repeat(n).map(|(k, offs)| {
debug_assert!(offs == mem::size_of::<T>());
k
})
}
}
/// Represents the combination of a starting address and
/// a total capacity of the returned block.
// #[unstable(feature = "allocator_api", issue = "32838")]
#[derive(Debug)]
pub struct Excess(pub NonNull<u8>, pub usize);
fn size_align<T>() -> (usize, usize) {
(mem::size_of::<T>(), mem::align_of::<T>())
}
/// The `AllocErr` error indicates an allocation failure
/// that may be due to resource exhaustion or to
/// something wrong when combining the given input arguments with this
/// allocator.
// #[unstable(feature = "allocator_api", issue = "32838")]
#[derive(Clone, PartialEq, Eq, Debug)]
pub struct AllocErr;
// (we need this for downstream impl of trait Error)
// #[unstable(feature = "allocator_api", issue = "32838")]
impl fmt::Display for AllocErr {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.write_str("memory allocation failed")
}
}
/// The `CannotReallocInPlace` error is used when `grow_in_place` or
/// `shrink_in_place` were unable to reuse the given memory block for
/// a requested layout.
// #[unstable(feature = "allocator_api", issue = "32838")]
#[derive(Clone, PartialEq, Eq, Debug)]
pub struct CannotReallocInPlace;
// #[unstable(feature = "allocator_api", issue = "32838")]
impl CannotReallocInPlace {
pub fn description(&self) -> &str {
"cannot reallocate allocator's memory in place"
}
}
// (we need this for downstream impl of trait Error)
// #[unstable(feature = "allocator_api", issue = "32838")]
impl fmt::Display for CannotReallocInPlace {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(f, "{}", self.description())
}
}
/// An implementation of `Alloc` can allocate, reallocate, and
/// deallocate arbitrary blocks of data described via `Layout`.
///
/// Some of the methods require that a memory block be *currently
/// allocated* via an allocator. This means that:
///
/// * the starting address for that memory block was previously
/// returned by a previous call to an allocation method (`alloc`,
/// `alloc_zeroed`, `alloc_excess`, `alloc_one`, `alloc_array`) or
/// reallocation method (`realloc`, `realloc_excess`, or
/// `realloc_array`), and
///
/// * the memory block has not been subsequently deallocated, where
/// blocks are deallocated either by being passed to a deallocation
/// method (`dealloc`, `dealloc_one`, `dealloc_array`) or by being
/// passed to a reallocation method (see above) that returns `Ok`.
///
/// A note regarding zero-sized types and zero-sized layouts: many
/// methods in the `Alloc` trait state that allocation requests
/// must be non-zero size, or else undefined behavior can result.
///
/// * However, some higher-level allocation methods (`alloc_one`,
/// `alloc_array`) are well-defined on zero-sized types and can
/// optionally support them: it is left up to the implementor
/// whether to return `Err`, or to return `Ok` with some pointer.
///
/// * If an `Alloc` implementation chooses to return `Ok` in this
/// case (i.e. the pointer denotes a zero-sized inaccessible block)
/// then that returned pointer must be considered "currently
/// allocated". On such an allocator, *all* methods that take
/// currently-allocated pointers as inputs must accept these
/// zero-sized pointers, *without* causing undefined behavior.
///
/// * In other words, if a zero-sized pointer can flow out of an
/// allocator, then that allocator must likewise accept that pointer
/// flowing back into its deallocation and reallocation methods.
///
/// Some of the methods require that a layout *fit* a memory block.
/// What it means for a layout to "fit" a memory block means (or
/// equivalently, for a memory block to "fit" a layout) is that the
/// following two conditions must hold:
///
/// 1. The block's starting address must be aligned to `layout.align()`.
///
/// 2. The block's size must fall in the range `[use_min, use_max]`, where:
///
/// * `use_min` is `self.usable_size(layout).0`, and
///
/// * `use_max` is the capacity that was (or would have been)
/// returned when (if) the block was allocated via a call to
/// `alloc_excess` or `realloc_excess`.
///
/// Note that:
///
/// * the size of the layout most recently used to allocate the block
/// is guaranteed to be in the range `[use_min, use_max]`, and
///
/// * a lower-bound on `use_max` can be safely approximated by a call to
/// `usable_size`.
///
/// * if a layout `k` fits a memory block (denoted by `ptr`)
/// currently allocated via an allocator `a`, then it is legal to
/// use that layout to deallocate it, i.e. `a.dealloc(ptr, k);`.
///
/// # Unsafety
///
/// The `Alloc` trait is an `unsafe` trait for a number of reasons, and
/// implementors must ensure that they adhere to these contracts:
///
/// * Pointers returned from allocation functions must point to valid memory and
/// retain their validity until at least the instance of `Alloc` is dropped
/// itself.
///
/// * `Layout` queries and calculations in general must be correct. Callers of
/// this trait are allowed to rely on the contracts defined on each method,
/// and implementors must ensure such contracts remain true.
///
/// Note that this list may get tweaked over time as clarifications are made in
/// the future.
// #[unstable(feature = "allocator_api", issue = "32838")]
pub unsafe trait Alloc {
// (Note: some existing allocators have unspecified but well-defined
// behavior in response to a zero size allocation request ;
// e.g. in C, `malloc` of 0 will either return a null pointer or a
// unique pointer, but will not have arbitrary undefined
// behavior.
// However in jemalloc for example,
// `mallocx(0)` is documented as undefined behavior.)
/// Returns a pointer meeting the size and alignment guarantees of
/// `layout`.
///
/// If this method returns an `Ok(addr)`, then the `addr` returned
/// will be non-null address pointing to a block of storage
/// suitable for holding an instance of `layout`.
///
/// The returned block of storage may or may not have its contents
/// initialized. (Extension subtraits might restrict this
/// behavior, e.g. to ensure initialization to particular sets of
/// bit patterns.)
///
/// # Safety
///
/// This function is unsafe because undefined behavior can result
/// if the caller does not ensure that `layout` has non-zero size.
///
/// (Extension subtraits might provide more specific bounds on
/// behavior, e.g. guarantee a sentinel address or a null pointer
/// in response to a zero-size allocation request.)
///
/// # Errors
///
/// Returning `Err` indicates that either memory is exhausted or
/// `layout` does not meet allocator's size or alignment
/// constraints.
///
/// Implementations are encouraged to return `Err` on memory
/// exhaustion rather than panicking or aborting, but this is not
/// a strict requirement. (Specifically: it is *legal* to
/// implement this trait atop an underlying native allocation
/// library that aborts on memory exhaustion.)
///
/// Clients wishing to abort computation in response to an
/// allocation error are encouraged to call the [`handle_alloc_error`] function,
/// rather than directly invoking `panic!` or similar.
///
/// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
unsafe fn alloc(&mut self, layout: Layout) -> Result<NonNull<u8>, AllocErr>;
/// Deallocate the memory referenced by `ptr`.
///
/// # Safety
///
/// This function is unsafe because undefined behavior can result
/// if the caller does not ensure all of the following:
///
/// * `ptr` must denote a block of memory currently allocated via
/// this allocator,
///
/// * `layout` must *fit* that block of memory,
///
/// * In addition to fitting the block of memory `layout`, the
/// alignment of the `layout` must match the alignment used
/// to allocate that block of memory.
unsafe fn dealloc(&mut self, ptr: NonNull<u8>, layout: Layout);
// == ALLOCATOR-SPECIFIC QUANTITIES AND LIMITS ==
// usable_size
/// Returns bounds on the guaranteed usable size of a successful
/// allocation created with the specified `layout`.
///
/// In particular, if one has a memory block allocated via a given
/// allocator `a` and layout `k` where `a.usable_size(k)` returns
/// `(l, u)`, then one can pass that block to `a.dealloc()` with a
/// layout in the size range [l, u].
///
/// (All implementors of `usable_size` must ensure that
/// `l <= k.size() <= u`)
///
/// Both the lower- and upper-bounds (`l` and `u` respectively)
/// are provided, because an allocator based on size classes could
/// misbehave if one attempts to deallocate a block without
/// providing a correct value for its size (i.e., one within the
/// range `[l, u]`).
///
/// Clients who wish to make use of excess capacity are encouraged
/// to use the `alloc_excess` and `realloc_excess` instead, as
/// this method is constrained to report conservative values that
/// serve as valid bounds for *all possible* allocation method
/// calls.
///
/// However, for clients that do not wish to track the capacity
/// returned by `alloc_excess` locally, this method is likely to
/// produce useful results.
#[inline]
fn usable_size(&self, layout: &Layout) -> (usize, usize) {
(layout.size(), layout.size())
}
// == METHODS FOR MEMORY REUSE ==
// realloc. alloc_excess, realloc_excess
/// Returns a pointer suitable for holding data described by
/// a new layout with `layout`’s alignment and a size given
/// by `new_size`. To
/// accomplish this, this may extend or shrink the allocation
/// referenced by `ptr` to fit the new layout.
///
/// If this returns `Ok`, then ownership of the memory block
/// referenced by `ptr` has been transferred to this
/// allocator. The memory may or may not have been freed, and
/// should be considered unusable (unless of course it was
/// transferred back to the caller again via the return value of
/// this method).
///
/// If this method returns `Err`, then ownership of the memory
/// block has not been transferred to this allocator, and the
/// contents of the memory block are unaltered.
///
/// # Safety
///
/// This function is unsafe because undefined behavior can result
/// if the caller does not ensure all of the following:
///
/// * `ptr` must be currently allocated via this allocator,
///
/// * `layout` must *fit* the `ptr` (see above). (The `new_size`
/// argument need not fit it.)
///
/// * `new_size` must be greater than zero.
///
/// * `new_size`, when rounded up to the nearest multiple of `layout.align()`,
/// must not overflow (i.e. the rounded value must be less than `usize::MAX`).
///
/// (Extension subtraits might provide more specific bounds on
/// behavior, e.g. guarantee a sentinel address or a null pointer
/// in response to a zero-size allocation request.)
///
/// # Errors
///
/// Returns `Err` only if the new layout
/// does not meet the allocator's size
/// and alignment constraints of the allocator, or if reallocation
/// otherwise fails.
///
/// Implementations are encouraged to return `Err` on memory
/// exhaustion rather than panicking or aborting, but this is not
/// a strict requirement. (Specifically: it is *legal* to
/// implement this trait atop an underlying native allocation
/// library that aborts on memory exhaustion.)
///
/// Clients wishing to abort computation in response to a
/// reallocation error are encouraged to call the [`handle_alloc_error`] function,
/// rather than directly invoking `panic!` or similar.
///
/// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
unsafe fn realloc(
&mut self,
ptr: NonNull<u8>,
layout: Layout,
new_size: usize,
) -> Result<NonNull<u8>, AllocErr> {
let old_size = layout.size();
if new_size >= old_size {
if let Ok(()) = self.grow_in_place(ptr, layout, new_size) {
return Ok(ptr);
}
} else if new_size < old_size {
if let Ok(()) = self.shrink_in_place(ptr, layout, new_size) {
return Ok(ptr);
}
}
// otherwise, fall back on alloc + copy + dealloc.
let new_layout = Layout::from_size_align_unchecked(new_size, layout.align());
let result = self.alloc(new_layout);
if let Ok(new_ptr) = result {
ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_ptr(), cmp::min(old_size, new_size));
self.dealloc(ptr, layout);
}
result
}
/// Behaves like `alloc`, but also ensures that the contents
/// are set to zero before being returned.
///
/// # Safety
///
/// This function is unsafe for the same reasons that `alloc` is.
///
/// # Errors
///
/// Returning `Err` indicates that either memory is exhausted or
/// `layout` does not meet allocator's size or alignment
/// constraints, just as in `alloc`.
///
/// Clients wishing to abort computation in response to an
/// allocation error are encouraged to call the [`handle_alloc_error`] function,
/// rather than directly invoking `panic!` or similar.
///
/// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
unsafe fn alloc_zeroed(&mut self, layout: Layout) -> Result<NonNull<u8>, AllocErr> {
let size = layout.size();
let p = self.alloc(layout);
if let Ok(p) = p {
ptr::write_bytes(p.as_ptr(), 0, size);
}
p
}
/// Behaves like `alloc`, but also returns the whole size of
/// the returned block. For some `layout` inputs, like arrays, this
/// may include extra storage usable for additional data.
///
/// # Safety
///
/// This function is unsafe for the same reasons that `alloc` is.
///
/// # Errors
///
/// Returning `Err` indicates that either memory is exhausted or
/// `layout` does not meet allocator's size or alignment
/// constraints, just as in `alloc`.
///
/// Clients wishing to abort computation in response to an
/// allocation error are encouraged to call the [`handle_alloc_error`] function,
/// rather than directly invoking `panic!` or similar.
///
/// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
unsafe fn alloc_excess(&mut self, layout: Layout) -> Result<Excess, AllocErr> {
let usable_size = self.usable_size(&layout);
self.alloc(layout).map(|p| Excess(p, usable_size.1))
}
/// Behaves like `realloc`, but also returns the whole size of
/// the returned block. For some `layout` inputs, like arrays, this
/// may include extra storage usable for additional data.
///
/// # Safety
///
/// This function is unsafe for the same reasons that `realloc` is.
///
/// # Errors
///
/// Returning `Err` indicates that either memory is exhausted or
/// `layout` does not meet allocator's size or alignment
/// constraints, just as in `realloc`.
///
/// Clients wishing to abort computation in response to a
/// reallocation error are encouraged to call the [`handle_alloc_error`] function,
/// rather than directly invoking `panic!` or similar.
///
/// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
unsafe fn realloc_excess(
&mut self,
ptr: NonNull<u8>,
layout: Layout,
new_size: usize,
) -> Result<Excess, AllocErr> {
let new_layout = Layout::from_size_align_unchecked(new_size, layout.align());
let usable_size = self.usable_size(&new_layout);
self.realloc(ptr, layout, new_size)
.map(|p| Excess(p, usable_size.1))
}
/// Attempts to extend the allocation referenced by `ptr` to fit `new_size`.
///
/// If this returns `Ok`, then the allocator has asserted that the
/// memory block referenced by `ptr` now fits `new_size`, and thus can
/// be used to carry data of a layout of that size and same alignment as
/// `layout`. (The allocator is allowed to
/// expend effort to accomplish this, such as extending the memory block to
/// include successor blocks, or virtual memory tricks.)
///
/// Regardless of what this method returns, ownership of the
/// memory block referenced by `ptr` has not been transferred, and
/// the contents of the memory block are unaltered.
///
/// # Safety
///
/// This function is unsafe because undefined behavior can result
/// if the caller does not ensure all of the following:
///
/// * `ptr` must be currently allocated via this allocator,
///
/// * `layout` must *fit* the `ptr` (see above); note the
/// `new_size` argument need not fit it,
///
/// * `new_size` must not be less than `layout.size()`,
///
/// # Errors
///
/// Returns `Err(CannotReallocInPlace)` when the allocator is
/// unable to assert that the memory block referenced by `ptr`
/// could fit `layout`.
///
/// Note that one cannot pass `CannotReallocInPlace` to the `handle_alloc_error`
/// function; clients are expected either to be able to recover from
/// `grow_in_place` failures without aborting, or to fall back on
/// another reallocation method before resorting to an abort.
unsafe fn grow_in_place(
&mut self,
ptr: NonNull<u8>,
layout: Layout,
new_size: usize,
) -> Result<(), CannotReallocInPlace> {
let _ = ptr; // this default implementation doesn't care about the actual address.
debug_assert!(new_size >= layout.size());
let (_l, u) = self.usable_size(&layout);
// _l <= layout.size() [guaranteed by usable_size()]
// layout.size() <= new_layout.size() [required by this method]
if new_size <= u {
Ok(())
} else {
Err(CannotReallocInPlace)
}
}
/// Attempts to shrink the allocation referenced by `ptr` to fit `new_size`.
///
/// If this returns `Ok`, then the allocator has asserted that the
/// memory block referenced by `ptr` now fits `new_size`, and
/// thus can only be used to carry data of that smaller
/// layout. (The allocator is allowed to take advantage of this,
/// carving off portions of the block for reuse elsewhere.) The
/// truncated contents of the block within the smaller layout are
/// unaltered, and ownership of block has not been transferred.
///
/// If this returns `Err`, then the memory block is considered to
/// still represent the original (larger) `layout`. None of the
/// block has been carved off for reuse elsewhere, ownership of
/// the memory block has not been transferred, and the contents of
/// the memory block are unaltered.
///
/// # Safety
///
/// This function is unsafe because undefined behavior can result
/// if the caller does not ensure all of the following:
///
/// * `ptr` must be currently allocated via this allocator,
///
/// * `layout` must *fit* the `ptr` (see above); note the
/// `new_size` argument need not fit it,
///
/// * `new_size` must not be greater than `layout.size()`
/// (and must be greater than zero),
///
/// # Errors
///
/// Returns `Err(CannotReallocInPlace)` when the allocator is
/// unable to assert that the memory block referenced by `ptr`
/// could fit `layout`.
///
/// Note that one cannot pass `CannotReallocInPlace` to the `handle_alloc_error`
/// function; clients are expected either to be able to recover from
/// `shrink_in_place` failures without aborting, or to fall back
/// on another reallocation method before resorting to an abort.
unsafe fn shrink_in_place(
&mut self,
ptr: NonNull<u8>,
layout: Layout,
new_size: usize,
) -> Result<(), CannotReallocInPlace> {
let _ = ptr; // this default implementation doesn't care about the actual address.
debug_assert!(new_size <= layout.size());
let (l, _u) = self.usable_size(&layout);
// layout.size() <= _u [guaranteed by usable_size()]
// new_layout.size() <= layout.size() [required by this method]
if l <= new_size {
Ok(())
} else {
Err(CannotReallocInPlace)
}
}
// == COMMON USAGE PATTERNS ==
// alloc_one, dealloc_one, alloc_array, realloc_array. dealloc_array
/// Allocates a block suitable for holding an instance of `T`.
///
/// Captures a common usage pattern for allocators.
///
/// The returned block is suitable for passing to the
/// `alloc`/`realloc` methods of this allocator.
///
/// Note to implementors: If this returns `Ok(ptr)`, then `ptr`
/// must be considered "currently allocated" and must be
/// acceptable input to methods such as `realloc` or `dealloc`,
/// *even if* `T` is a zero-sized type. In other words, if your
/// `Alloc` implementation overrides this method in a manner
/// that can return a zero-sized `ptr`, then all reallocation and
/// deallocation methods need to be similarly overridden to accept
/// such values as input.
///
/// # Errors
///
/// Returning `Err` indicates that either memory is exhausted or
/// `T` does not meet allocator's size or alignment constraints.
///
/// For zero-sized `T`, may return either of `Ok` or `Err`, but
/// will *not* yield undefined behavior.
///
/// Clients wishing to abort computation in response to an
/// allocation error are encouraged to call the [`handle_alloc_error`] function,
/// rather than directly invoking `panic!` or similar.
///
/// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
fn alloc_one<T>(&mut self) -> Result<NonNull<T>, AllocErr>
where
Self: Sized,
{
let k = Layout::new::<T>();
if k.size() > 0 {
unsafe { self.alloc(k).map(|p| p.cast()) }
} else {
Err(AllocErr)
}
}
/// Deallocates a block suitable for holding an instance of `T`.
///
/// The given block must have been produced by this allocator,
/// and must be suitable for storing a `T` (in terms of alignment
/// as well as minimum and maximum size); otherwise yields
/// undefined behavior.
///
/// Captures a common usage pattern for allocators.
///
/// # Safety
///
/// This function is unsafe because undefined behavior can result
/// if the caller does not ensure both:
///
/// * `ptr` must denote a block of memory currently allocated via this allocator
///
/// * the layout of `T` must *fit* that block of memory.
unsafe fn dealloc_one<T>(&mut self, ptr: NonNull<T>)
where
Self: Sized,
{
let k = Layout::new::<T>();
if k.size() > 0 {
self.dealloc(ptr.cast(), k);
}
}
/// Allocates a block suitable for holding `n` instances of `T`.
///
/// Captures a common usage pattern for allocators.
///
/// The returned block is suitable for passing to the
/// `alloc`/`realloc` methods of this allocator.
///
/// Note to implementors: If this returns `Ok(ptr)`, then `ptr`
/// must be considered "currently allocated" and must be
/// acceptable input to methods such as `realloc` or `dealloc`,
/// *even if* `T` is a zero-sized type. In other words, if your
/// `Alloc` implementation overrides this method in a manner
/// that can return a zero-sized `ptr`, then all reallocation and
/// deallocation methods need to be similarly overridden to accept
/// such values as input.
///
/// # Errors
///
/// Returning `Err` indicates that either memory is exhausted or
/// `[T; n]` does not meet allocator's size or alignment
/// constraints.
///
/// For zero-sized `T` or `n == 0`, may return either of `Ok` or
/// `Err`, but will *not* yield undefined behavior.
///
/// Always returns `Err` on arithmetic overflow.
///
/// Clients wishing to abort computation in response to an
/// allocation error are encouraged to call the [`handle_alloc_error`] function,
/// rather than directly invoking `panic!` or similar.
///
/// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
fn alloc_array<T>(&mut self, n: usize) -> Result<NonNull<T>, AllocErr>
where
Self: Sized,
{
match Layout::array::<T>(n) {
Ok(layout) if layout.size() > 0 => unsafe { self.alloc(layout).map(|p| p.cast()) },
_ => Err(AllocErr),
}
}
/// Reallocates a block previously suitable for holding `n_old`
/// instances of `T`, returning a block suitable for holding
/// `n_new` instances of `T`.
///
/// Captures a common usage pattern for allocators.
///
/// The returned block is suitable for passing to the
/// `alloc`/`realloc` methods of this allocator.
///
/// # Safety
///
/// This function is unsafe because undefined behavior can result
/// if the caller does not ensure all of the following:
///
/// * `ptr` must be currently allocated via this allocator,
///
/// * the layout of `[T; n_old]` must *fit* that block of memory.
///
/// # Errors
///
/// Returning `Err` indicates that either memory is exhausted or
/// `[T; n_new]` does not meet allocator's size or alignment
/// constraints.
///
/// For zero-sized `T` or `n_new == 0`, may return either of `Ok` or
/// `Err`, but will *not* yield undefined behavior.
///
/// Always returns `Err` on arithmetic overflow.
///
/// Clients wishing to abort computation in response to a
/// reallocation error are encouraged to call the [`handle_alloc_error`] function,
/// rather than directly invoking `panic!` or similar.
///
/// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
unsafe fn realloc_array<T>(
&mut self,
ptr: NonNull<T>,
n_old: usize,
n_new: usize,
) -> Result<NonNull<T>, AllocErr>
where
Self: Sized,
{
match (Layout::array::<T>(n_old), Layout::array::<T>(n_new)) {
(Ok(ref k_old), Ok(ref k_new)) if k_old.size() > 0 && k_new.size() > 0 => {
debug_assert!(k_old.align() == k_new.align());
self.realloc(ptr.cast(), *k_old, k_new.size())
.map(NonNull::cast)
}
_ => Err(AllocErr),
}
}
/// Deallocates a block suitable for holding `n` instances of `T`.
///
/// Captures a common usage pattern for allocators.
///
/// # Safety
///
/// This function is unsafe because undefined behavior can result
/// if the caller does not ensure both:
///
/// * `ptr` must denote a block of memory currently allocated via this allocator
///
/// * the layout of `[T; n]` must *fit* that block of memory.
///
/// # Errors
///
/// Returning `Err` indicates that either `[T; n]` or the given
/// memory block does not meet allocator's size or alignment
/// constraints.
///
/// Always returns `Err` on arithmetic overflow.
unsafe fn dealloc_array<T>(&mut self, ptr: NonNull<T>, n: usize) -> Result<(), AllocErr>
where
Self: Sized,
{
match Layout::array::<T>(n) {
Ok(k) if k.size() > 0 => {
self.dealloc(ptr.cast(), k);
Ok(())
}
_ => Err(AllocErr),
}
}
}