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Diffstat (limited to 'third_party/rust/bumpalo/src/alloc.rs')
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diff --git a/third_party/rust/bumpalo/src/alloc.rs b/third_party/rust/bumpalo/src/alloc.rs new file mode 100644 index 0000000000..0bcc21f22c --- /dev/null +++ b/third_party/rust/bumpalo/src/alloc.rs @@ -0,0 +1,794 @@ +// Copyright 2015 The Rust Project Developers. See the COPYRIGHT +// file at the top-level directory of this distribution and at +// http://rust-lang.org/COPYRIGHT. +// +// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or +// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license +// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your +// 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.clone(), 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), + } + } +} |