1088 lines
43 KiB
Rust
1088 lines
43 KiB
Rust
// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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#![unstable(feature = "allocator_api",
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reason = "the precise API and guarantees it provides may be tweaked \
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slightly, especially to possibly take into account the \
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types being stored to make room for a future \
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tracing garbage collector",
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issue = "32838")]
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use cmp;
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use fmt;
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use mem;
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use usize;
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use ptr::{self, NonNull};
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extern {
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/// An opaque, unsized type. Used for pointers to allocated memory.
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///
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/// This type can only be used behind a pointer like `*mut Void` or `ptr::NonNull<Void>`.
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/// Such pointers are similar to C’s `void*` type.
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pub type Void;
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}
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impl Void {
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/// Similar to `std::ptr::null`, which requires `T: Sized`.
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pub fn null() -> *const Self {
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0 as _
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}
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/// Similar to `std::ptr::null_mut`, which requires `T: Sized`.
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pub fn null_mut() -> *mut Self {
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0 as _
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}
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}
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/// Represents the combination of a starting address and
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/// a total capacity of the returned block.
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#[derive(Debug)]
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pub struct Excess(pub *mut u8, pub usize);
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fn size_align<T>() -> (usize, usize) {
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(mem::size_of::<T>(), mem::align_of::<T>())
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}
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/// Layout of a block of memory.
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///
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/// An instance of `Layout` describes a particular layout of memory.
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/// You build a `Layout` up as an input to give to an allocator.
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///
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/// All layouts have an associated non-negative size and a
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/// power-of-two alignment.
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///
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/// (Note however that layouts are *not* required to have positive
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/// size, even though many allocators require that all memory
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/// requests have positive size. A caller to the `Alloc::alloc`
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/// method must either ensure that conditions like this are met, or
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/// use specific allocators with looser requirements.)
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#[derive(Clone, Debug, PartialEq, Eq)]
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pub struct Layout {
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// size of the requested block of memory, measured in bytes.
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size: usize,
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// alignment of the requested block of memory, measured in bytes.
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// we ensure that this is always a power-of-two, because API's
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// like `posix_memalign` require it and it is a reasonable
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// constraint to impose on Layout constructors.
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//
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// (However, we do not analogously require `align >= sizeof(void*)`,
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// even though that is *also* a requirement of `posix_memalign`.)
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align: usize,
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}
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// FIXME: audit default implementations for overflow errors,
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// (potentially switching to overflowing_add and
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// overflowing_mul as necessary).
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impl Layout {
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/// Constructs a `Layout` from a given `size` and `align`,
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/// or returns `None` if either of the following conditions
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/// are not met:
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///
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/// * `align` must be a power of two,
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///
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/// * `size`, when rounded up to the nearest multiple of `align`,
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/// must not overflow (i.e. the rounded value must be less than
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/// `usize::MAX`).
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#[inline]
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pub fn from_size_align(size: usize, align: usize) -> Option<Layout> {
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if !align.is_power_of_two() {
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return None;
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}
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// (power-of-two implies align != 0.)
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// Rounded up size is:
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// size_rounded_up = (size + align - 1) & !(align - 1);
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//
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// We know from above that align != 0. If adding (align - 1)
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// does not overflow, then rounding up will be fine.
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//
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// Conversely, &-masking with !(align - 1) will subtract off
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// only low-order-bits. Thus if overflow occurs with the sum,
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// the &-mask cannot subtract enough to undo that overflow.
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//
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// Above implies that checking for summation overflow is both
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// necessary and sufficient.
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if size > usize::MAX - (align - 1) {
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return None;
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}
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unsafe {
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Some(Layout::from_size_align_unchecked(size, align))
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}
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}
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/// Creates a layout, bypassing all checks.
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///
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/// # Safety
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///
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/// This function is unsafe as it does not verify that `align` is
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/// a power-of-two nor `size` aligned to `align` fits within the
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/// address space (i.e. the `Layout::from_size_align` preconditions).
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#[inline]
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pub unsafe fn from_size_align_unchecked(size: usize, align: usize) -> Layout {
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Layout { size: size, align: align }
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}
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/// The minimum size in bytes for a memory block of this layout.
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#[inline]
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pub fn size(&self) -> usize { self.size }
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/// The minimum byte alignment for a memory block of this layout.
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#[inline]
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pub fn align(&self) -> usize { self.align }
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/// Constructs a `Layout` suitable for holding a value of type `T`.
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pub fn new<T>() -> Self {
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let (size, align) = size_align::<T>();
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Layout::from_size_align(size, align).unwrap()
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}
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/// Produces layout describing a record that could be used to
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/// allocate backing structure for `T` (which could be a trait
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/// or other unsized type like a slice).
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pub fn for_value<T: ?Sized>(t: &T) -> Self {
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let (size, align) = (mem::size_of_val(t), mem::align_of_val(t));
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Layout::from_size_align(size, align).unwrap()
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}
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/// Creates a layout describing the record that can hold a value
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/// of the same layout as `self`, but that also is aligned to
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/// alignment `align` (measured in bytes).
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///
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/// If `self` already meets the prescribed alignment, then returns
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/// `self`.
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///
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/// Note that this method does not add any padding to the overall
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/// size, regardless of whether the returned layout has a different
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/// alignment. In other words, if `K` has size 16, `K.align_to(32)`
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/// will *still* have size 16.
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///
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/// # Panics
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///
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/// Panics if the combination of `self.size` and the given `align`
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/// violates the conditions listed in `from_size_align`.
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#[inline]
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pub fn align_to(&self, align: usize) -> Self {
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Layout::from_size_align(self.size, cmp::max(self.align, align)).unwrap()
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}
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/// Returns the amount of padding we must insert after `self`
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/// to ensure that the following address will satisfy `align`
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/// (measured in bytes).
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///
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/// E.g. if `self.size` is 9, then `self.padding_needed_for(4)`
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/// returns 3, because that is the minimum number of bytes of
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/// padding required to get a 4-aligned address (assuming that the
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/// corresponding memory block starts at a 4-aligned address).
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///
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/// The return value of this function has no meaning if `align` is
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/// not a power-of-two.
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///
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/// Note that the utility of the returned value requires `align`
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/// to be less than or equal to the alignment of the starting
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/// address for the whole allocated block of memory. One way to
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/// satisfy this constraint is to ensure `align <= self.align`.
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#[inline]
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pub fn padding_needed_for(&self, align: usize) -> usize {
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let len = self.size();
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// Rounded up value is:
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// len_rounded_up = (len + align - 1) & !(align - 1);
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// and then we return the padding difference: `len_rounded_up - len`.
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//
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// We use modular arithmetic throughout:
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//
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// 1. align is guaranteed to be > 0, so align - 1 is always
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// valid.
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//
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// 2. `len + align - 1` can overflow by at most `align - 1`,
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// so the &-mask wth `!(align - 1)` will ensure that in the
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// case of overflow, `len_rounded_up` will itself be 0.
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// Thus the returned padding, when added to `len`, yields 0,
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// which trivially satisfies the alignment `align`.
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//
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// (Of course, attempts to allocate blocks of memory whose
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// size and padding overflow in the above manner should cause
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// the allocator to yield an error anyway.)
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let len_rounded_up = len.wrapping_add(align).wrapping_sub(1) & !align.wrapping_sub(1);
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return len_rounded_up.wrapping_sub(len);
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}
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/// Creates a layout describing the record for `n` instances of
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/// `self`, with a suitable amount of padding between each to
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/// ensure that each instance is given its requested size and
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/// alignment. On success, returns `(k, offs)` where `k` is the
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/// layout of the array and `offs` is the distance between the start
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/// of each element in the array.
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///
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/// On arithmetic overflow, returns `None`.
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#[inline]
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pub fn repeat(&self, n: usize) -> Option<(Self, usize)> {
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let padded_size = self.size.checked_add(self.padding_needed_for(self.align))?;
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let alloc_size = padded_size.checked_mul(n)?;
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// We can assume that `self.align` is a power-of-two.
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// Furthermore, `alloc_size` has already been rounded up
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// to a multiple of `self.align`; therefore, the call to
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// `Layout::from_size_align` below should never panic.
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Some((Layout::from_size_align(alloc_size, self.align).unwrap(), padded_size))
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}
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/// Creates a layout describing the record for `self` followed by
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/// `next`, including any necessary padding to ensure that `next`
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/// will be properly aligned. Note that the result layout will
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/// satisfy the alignment properties of both `self` and `next`.
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///
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/// Returns `Some((k, offset))`, where `k` is layout of the concatenated
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/// record and `offset` is the relative location, in bytes, of the
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/// start of the `next` embedded within the concatenated record
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/// (assuming that the record itself starts at offset 0).
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///
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/// On arithmetic overflow, returns `None`.
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pub fn extend(&self, next: Self) -> Option<(Self, usize)> {
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let new_align = cmp::max(self.align, next.align);
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let realigned = Layout::from_size_align(self.size, new_align)?;
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let pad = realigned.padding_needed_for(next.align);
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let offset = self.size.checked_add(pad)?;
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let new_size = offset.checked_add(next.size)?;
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let layout = Layout::from_size_align(new_size, new_align)?;
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Some((layout, offset))
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}
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/// Creates a layout describing the record for `n` instances of
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/// `self`, with no padding between each instance.
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///
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/// Note that, unlike `repeat`, `repeat_packed` does not guarantee
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/// that the repeated instances of `self` will be properly
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/// aligned, even if a given instance of `self` is properly
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/// aligned. In other words, if the layout returned by
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/// `repeat_packed` is used to allocate an array, it is not
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/// guaranteed that all elements in the array will be properly
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/// aligned.
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///
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/// On arithmetic overflow, returns `None`.
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pub fn repeat_packed(&self, n: usize) -> Option<Self> {
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let size = self.size().checked_mul(n)?;
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Layout::from_size_align(size, self.align)
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}
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/// Creates a layout describing the record for `self` followed by
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/// `next` with no additional padding between the two. Since no
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/// padding is inserted, the alignment of `next` is irrelevant,
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/// and is not incorporated *at all* into the resulting layout.
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///
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/// Returns `(k, offset)`, where `k` is layout of the concatenated
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/// record and `offset` is the relative location, in bytes, of the
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/// start of the `next` embedded within the concatenated record
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/// (assuming that the record itself starts at offset 0).
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///
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/// (The `offset` is always the same as `self.size()`; we use this
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/// signature out of convenience in matching the signature of
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/// `extend`.)
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///
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/// On arithmetic overflow, returns `None`.
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pub fn extend_packed(&self, next: Self) -> Option<(Self, usize)> {
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let new_size = self.size().checked_add(next.size())?;
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let layout = Layout::from_size_align(new_size, self.align)?;
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Some((layout, self.size()))
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}
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/// Creates a layout describing the record for a `[T; n]`.
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///
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/// On arithmetic overflow, returns `None`.
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pub fn array<T>(n: usize) -> Option<Self> {
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Layout::new::<T>()
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.repeat(n)
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.map(|(k, offs)| {
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debug_assert!(offs == mem::size_of::<T>());
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k
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})
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}
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}
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/// The `AllocErr` error specifies whether an allocation failure is
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/// specifically due to resource exhaustion or if it is due to
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/// something wrong when combining the given input arguments with this
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/// allocator.
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#[derive(Clone, PartialEq, Eq, Debug)]
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pub struct AllocErr;
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// (we need this for downstream impl of trait Error)
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impl fmt::Display for AllocErr {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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f.write_str("memory allocation failed")
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}
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}
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/// The `CannotReallocInPlace` error is used when `grow_in_place` or
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/// `shrink_in_place` were unable to reuse the given memory block for
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/// a requested layout.
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#[derive(Clone, PartialEq, Eq, Debug)]
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pub struct CannotReallocInPlace;
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impl CannotReallocInPlace {
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pub fn description(&self) -> &str {
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"cannot reallocate allocator's memory in place"
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}
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}
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// (we need this for downstream impl of trait Error)
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impl fmt::Display for CannotReallocInPlace {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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write!(f, "{}", self.description())
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}
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}
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/// Augments `AllocErr` with a CapacityOverflow variant.
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#[derive(Clone, PartialEq, Eq, Debug)]
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#[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
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pub enum CollectionAllocErr {
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/// Error due to the computed capacity exceeding the collection's maximum
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/// (usually `isize::MAX` bytes).
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CapacityOverflow,
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/// Error due to the allocator (see the `AllocErr` type's docs).
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AllocErr(AllocErr),
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}
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#[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
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impl From<AllocErr> for CollectionAllocErr {
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fn from(err: AllocErr) -> Self {
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CollectionAllocErr::AllocErr(err)
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}
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}
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// FIXME: docs
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pub unsafe trait GlobalAlloc {
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unsafe fn alloc(&self, layout: Layout) -> *mut Void;
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unsafe fn dealloc(&self, ptr: *mut Void, layout: Layout);
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unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut Void {
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let size = layout.size();
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let ptr = self.alloc(layout);
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if !ptr.is_null() {
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ptr::write_bytes(ptr as *mut u8, 0, size);
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}
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ptr
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}
|
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/// # Safety
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///
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/// `new_size`, when rounded up to the nearest multiple of `old_layout.align()`,
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/// must not overflow (i.e. the rounded value must be less than `usize::MAX`).
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unsafe fn realloc(&self, ptr: *mut Void, old_layout: Layout, new_size: usize) -> *mut Void {
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let new_layout = Layout::from_size_align_unchecked(new_size, old_layout.align());
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let new_ptr = self.alloc(new_layout);
|
||
if !new_ptr.is_null() {
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||
ptr::copy_nonoverlapping(
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||
ptr as *const u8,
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new_ptr as *mut u8,
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cmp::min(old_layout.size(), new_size),
|
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);
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self.dealloc(ptr, old_layout);
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||
}
|
||
new_ptr
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||
}
|
||
}
|
||
|
||
/// 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.
|
||
///
|
||
/// * It's undefined behavior if global allocators unwind. This restriction may
|
||
/// be lifted in the future, but currently a panic from any of these
|
||
/// functions may lead to memory unsafety. Note that as of the time of this
|
||
/// writing allocators *not* intending to be global allocators can still panic
|
||
/// in their implementation without violating memory safety.
|
||
///
|
||
/// * `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. Additionally global allocators may gain unique requirements for
|
||
/// how to safely implement one in the future as well.
|
||
pub unsafe trait Alloc {
|
||
|
||
// (Note: 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. Rust should consider revising the alloc::heap crate
|
||
// to reflect this reality.)
|
||
|
||
/// 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 allocator's `oom`
|
||
/// method, rather than directly invoking `panic!` or similar.
|
||
unsafe fn alloc(&mut self, layout: Layout) -> Result<*mut 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: *mut u8, layout: Layout);
|
||
|
||
/// Allocator-specific method for signaling an out-of-memory
|
||
/// condition.
|
||
///
|
||
/// `oom` aborts the thread or process, optionally performing
|
||
/// cleanup or logging diagnostic information before panicking or
|
||
/// aborting.
|
||
///
|
||
/// `oom` is meant to be used by clients unable to cope with an
|
||
/// unsatisfied allocation request, and wish to abandon
|
||
/// computation rather than attempt to recover locally.
|
||
///
|
||
/// Implementations of the `oom` method are discouraged from
|
||
/// infinitely regressing in nested calls to `oom`. In
|
||
/// practice this means implementors should eschew allocating,
|
||
/// especially from `self` (directly or indirectly).
|
||
///
|
||
/// Implementations of the allocation and reallocation methods
|
||
/// (e.g. `alloc`, `alloc_one`, `realloc`) are discouraged from
|
||
/// panicking (or aborting) in the event of memory exhaustion;
|
||
/// instead they should return an appropriate error from the
|
||
/// invoked method, and let the client decide whether to invoke
|
||
/// this `oom` method in response.
|
||
fn oom(&mut self) -> ! {
|
||
unsafe { ::intrinsics::abort() }
|
||
}
|
||
|
||
// == 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
|
||
/// `new_layout`, meeting its size and alignment guarantees. To
|
||
/// accomplish this, this may extend or shrink the allocation
|
||
/// referenced by `ptr` to fit `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.
|
||
///
|
||
/// For best results, `new_layout` should not impose a different
|
||
/// alignment constraint than `layout`. (In other words,
|
||
/// `new_layout.align()` should equal `layout.align()`.) However,
|
||
/// behavior is well-defined (though underspecified) when this
|
||
/// constraint is violated; further discussion below.
|
||
///
|
||
/// # 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_layout`
|
||
/// argument need not fit it.)
|
||
///
|
||
/// * `new_layout` must have size greater than zero.
|
||
///
|
||
/// * the alignment of `new_layout` is non-zero.
|
||
///
|
||
/// (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 `new_layout` does not match the
|
||
/// alignment of `layout`, or does not meet the allocator's size
|
||
/// and alignment constraints of the allocator, or if reallocation
|
||
/// otherwise fails.
|
||
///
|
||
/// (Note the previous sentence did not say "if and only if" -- in
|
||
/// particular, an implementation of this method *can* return `Ok`
|
||
/// if `new_layout.align() != old_layout.align()`; or it can
|
||
/// return `Err` in that scenario, depending on whether this
|
||
/// allocator can dynamically adjust the alignment constraint for
|
||
/// the block.)
|
||
///
|
||
/// 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
|
||
/// reallocation error are encouraged to call the allocator's `oom`
|
||
/// method, rather than directly invoking `panic!` or similar.
|
||
unsafe fn realloc(&mut self,
|
||
ptr: *mut u8,
|
||
layout: Layout,
|
||
new_layout: Layout) -> Result<*mut u8, AllocErr> {
|
||
let new_size = new_layout.size();
|
||
let old_size = layout.size();
|
||
let aligns_match = layout.align == new_layout.align;
|
||
|
||
if new_size >= old_size && aligns_match {
|
||
if let Ok(()) = self.grow_in_place(ptr, layout.clone(), new_layout.clone()) {
|
||
return Ok(ptr);
|
||
}
|
||
} else if new_size < old_size && aligns_match {
|
||
if let Ok(()) = self.shrink_in_place(ptr, layout.clone(), new_layout.clone()) {
|
||
return Ok(ptr);
|
||
}
|
||
}
|
||
|
||
// otherwise, fall back on alloc + copy + dealloc.
|
||
let result = self.alloc(new_layout);
|
||
if let Ok(new_ptr) = result {
|
||
ptr::copy_nonoverlapping(ptr as *const u8, new_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 allocator's `oom`
|
||
/// method, rather than directly invoking `panic!` or similar.
|
||
unsafe fn alloc_zeroed(&mut self, layout: Layout) -> Result<*mut u8, AllocErr> {
|
||
let size = layout.size();
|
||
let p = self.alloc(layout);
|
||
if let Ok(p) = p {
|
||
ptr::write_bytes(p, 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 allocator's `oom`
|
||
/// method, rather than directly invoking `panic!` or similar.
|
||
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 an
|
||
/// reallocation error are encouraged to call the allocator's `oom`
|
||
/// method, rather than directly invoking `panic!` or similar.
|
||
unsafe fn realloc_excess(&mut self,
|
||
ptr: *mut u8,
|
||
layout: Layout,
|
||
new_layout: Layout) -> Result<Excess, AllocErr> {
|
||
let usable_size = self.usable_size(&new_layout);
|
||
self.realloc(ptr, layout, new_layout)
|
||
.map(|p| Excess(p, usable_size.1))
|
||
}
|
||
|
||
/// Attempts to extend the allocation referenced by `ptr` to fit `new_layout`.
|
||
///
|
||
/// If this returns `Ok`, then the allocator has asserted that the
|
||
/// memory block referenced by `ptr` now fits `new_layout`, and thus can
|
||
/// be used to carry data of that 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_layout` argument need not fit it,
|
||
///
|
||
/// * `new_layout.size()` must not be less than `layout.size()`,
|
||
///
|
||
/// * `new_layout.align()` must equal `layout.align()`.
|
||
///
|
||
/// # 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 `oom`
|
||
/// method; 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: *mut u8,
|
||
layout: Layout,
|
||
new_layout: Layout) -> Result<(), CannotReallocInPlace> {
|
||
let _ = ptr; // this default implementation doesn't care about the actual address.
|
||
debug_assert!(new_layout.size >= layout.size);
|
||
debug_assert!(new_layout.align == layout.align);
|
||
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_layout.size <= u {
|
||
return Ok(());
|
||
} else {
|
||
return Err(CannotReallocInPlace);
|
||
}
|
||
}
|
||
|
||
/// Attempts to shrink the allocation referenced by `ptr` to fit `new_layout`.
|
||
///
|
||
/// If this returns `Ok`, then the allocator has asserted that the
|
||
/// memory block referenced by `ptr` now fits `new_layout`, 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_layout` argument need not fit it,
|
||
///
|
||
/// * `new_layout.size()` must not be greater than `layout.size()`
|
||
/// (and must be greater than zero),
|
||
///
|
||
/// * `new_layout.align()` must equal `layout.align()`.
|
||
///
|
||
/// # 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 `oom`
|
||
/// method; 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: *mut u8,
|
||
layout: Layout,
|
||
new_layout: Layout) -> Result<(), CannotReallocInPlace> {
|
||
let _ = ptr; // this default implementation doesn't care about the actual address.
|
||
debug_assert!(new_layout.size <= layout.size);
|
||
debug_assert!(new_layout.align == layout.align);
|
||
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_layout.size {
|
||
return Ok(());
|
||
} else {
|
||
return 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 allocator's `oom`
|
||
/// method, rather than directly invoking `panic!` or similar.
|
||
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| NonNull::new_unchecked(p as *mut T)) }
|
||
} 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 raw_ptr = ptr.as_ptr() as *mut u8;
|
||
let k = Layout::new::<T>();
|
||
if k.size() > 0 {
|
||
self.dealloc(raw_ptr, 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 allocator's `oom`
|
||
/// method, rather than directly invoking `panic!` or similar.
|
||
fn alloc_array<T>(&mut self, n: usize) -> Result<NonNull<T>, AllocErr>
|
||
where Self: Sized
|
||
{
|
||
match Layout::array::<T>(n) {
|
||
Some(ref layout) if layout.size() > 0 => {
|
||
unsafe {
|
||
self.alloc(layout.clone())
|
||
.map(|p| {
|
||
NonNull::new_unchecked(p as *mut T)
|
||
})
|
||
}
|
||
}
|
||
_ => 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 an
|
||
/// reallocation error are encouraged to call the allocator's `oom`
|
||
/// method, rather than directly invoking `panic!` or similar.
|
||
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), ptr.as_ptr()) {
|
||
(Some(ref k_old), Some(ref k_new), ptr) if k_old.size() > 0 && k_new.size() > 0 => {
|
||
self.realloc(ptr as *mut u8, k_old.clone(), k_new.clone())
|
||
.map(|p| NonNull::new_unchecked(p as *mut T))
|
||
}
|
||
_ => {
|
||
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
|
||
{
|
||
let raw_ptr = ptr.as_ptr() as *mut u8;
|
||
match Layout::array::<T>(n) {
|
||
Some(ref k) if k.size() > 0 => {
|
||
Ok(self.dealloc(raw_ptr, k.clone()))
|
||
}
|
||
_ => {
|
||
Err(AllocErr)
|
||
}
|
||
}
|
||
}
|
||
}
|