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//! Memory allocation APIs
#![stable(feature = "alloc_module", since = "1.28.0")]
mod global;
mod layout;
#[stable(feature = "global_alloc", since = "1.28.0")]
pub use self::global::GlobalAlloc;
#[stable(feature = "alloc_layout", since = "1.28.0")]
pub use self::layout::Layout;
#[stable(feature = "alloc_layout", since = "1.28.0")]
#[deprecated(
since = "1.52.0",
note = "Name does not follow std convention, use LayoutError",
suggestion = "LayoutError"
)]
#[allow(deprecated, deprecated_in_future)]
pub use self::layout::LayoutErr;
#[stable(feature = "alloc_layout_error", since = "1.50.0")]
pub use self::layout::LayoutError;
use crate::fmt;
use crate::ptr::{self, NonNull};
/// The `AllocError` 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(Copy, Clone, PartialEq, Eq, Debug)]
pub struct AllocError;
// (we need this for downstream impl of trait Error)
#[unstable(feature = "allocator_api", issue = "32838")]
impl fmt::Display for AllocError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.write_str("memory allocation failed")
}
}
/// An implementation of `Allocator` can allocate, grow, shrink, and deallocate arbitrary blocks of
/// data described via [`Layout`][].
///
/// `Allocator` is designed to be implemented on ZSTs, references, or smart pointers because having
/// an allocator like `MyAlloc([u8; N])` cannot be moved, without updating the pointers to the
/// allocated memory.
///
/// Unlike [`GlobalAlloc`][], zero-sized allocations are allowed in `Allocator`. If an underlying
/// allocator does not support this (like jemalloc) or return a null pointer (such as
/// `libc::malloc`), this must be caught by the implementation.
///
/// ### Currently allocated memory
///
/// 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 [`allocate`], [`grow`], or
/// [`shrink`], and
///
/// * the memory block has not been subsequently deallocated, where blocks are either deallocated
/// directly by being passed to [`deallocate`] or were changed by being passed to [`grow`] or
/// [`shrink`] that returns `Ok`. If `grow` or `shrink` have returned `Err`, the passed pointer
/// remains valid.
///
/// [`allocate`]: Allocator::allocate
/// [`grow`]: Allocator::grow
/// [`shrink`]: Allocator::shrink
/// [`deallocate`]: Allocator::deallocate
///
/// ### Memory fitting
///
/// 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 conditions must hold:
///
/// * The block must be allocated with the same alignment as [`layout.align()`], and
///
/// * The provided [`layout.size()`] must fall in the range `min ..= max`, where:
/// - `min` is the size of the layout most recently used to allocate the block, and
/// - `max` is the latest actual size returned from [`allocate`], [`grow`], or [`shrink`].
///
/// [`layout.align()`]: Layout::align
/// [`layout.size()`]: Layout::size
///
/// # Safety
///
/// * Memory blocks returned from an allocator must point to valid memory and retain their validity
/// until the instance and all of its clones are dropped,
///
/// * cloning or moving the allocator must not invalidate memory blocks returned from this
/// allocator. A cloned allocator must behave like the same allocator, and
///
/// * any pointer to a memory block which is [*currently allocated*] may be passed to any other
/// method of the allocator.
///
/// [*currently allocated*]: #currently-allocated-memory
#[unstable(feature = "allocator_api", issue = "32838")]
pub unsafe trait Allocator {
/// Attempts to allocate a block of memory.
///
/// On success, returns a [`NonNull<[u8]>`][NonNull] meeting the size and alignment guarantees of `layout`.
///
/// The returned block may have a larger size than specified by `layout.size()`, and may or may
/// not have its contents initialized.
///
/// # 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
fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError>;
/// Behaves like `allocate`, but also ensures that the returned memory is zero-initialized.
///
/// # 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
fn allocate_zeroed(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
let ptr = self.allocate(layout)?;
// SAFETY: `alloc` returns a valid memory block
unsafe { ptr.as_non_null_ptr().as_ptr().write_bytes(0, ptr.len()) }
Ok(ptr)
}
/// Deallocates the memory referenced by `ptr`.
///
/// # Safety
///
/// * `ptr` must denote a block of memory [*currently allocated*] via this allocator, and
/// * `layout` must [*fit*] that block of memory.
///
/// [*currently allocated*]: #currently-allocated-memory
/// [*fit*]: #memory-fitting
unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout);
/// Attempts to extend the memory block.
///
/// Returns a new [`NonNull<[u8]>`][NonNull] containing a pointer and the actual size of the allocated
/// memory. The pointer is suitable for holding data described by `new_layout`. To accomplish
/// this, the allocator may extend 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.
///
/// 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
///
/// * `ptr` must denote a block of memory [*currently allocated*] via this allocator.
/// * `old_layout` must [*fit*] that block of memory (The `new_layout` argument need not fit it.).
/// * `new_layout.size()` must be greater than or equal to `old_layout.size()`.
///
/// Note that `new_layout.align()` need not be the same as `old_layout.align()`.
///
/// [*currently allocated*]: #currently-allocated-memory
/// [*fit*]: #memory-fitting
///
/// # Errors
///
/// Returns `Err` if the new layout does not meet the allocator's size and alignment
/// constraints of the allocator, or if growing 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 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 grow(
&self,
ptr: NonNull<u8>,
old_layout: Layout,
new_layout: Layout,
) -> Result<NonNull<[u8]>, AllocError> {
debug_assert!(
new_layout.size() >= old_layout.size(),
"`new_layout.size()` must be greater than or equal to `old_layout.size()`"
);
let new_ptr = self.allocate(new_layout)?;
// SAFETY: because `new_layout.size()` must be greater than or equal to
// `old_layout.size()`, both the old and new memory allocation are valid for reads and
// writes for `old_layout.size()` bytes. Also, because the old allocation wasn't yet
// deallocated, it cannot overlap `new_ptr`. Thus, the call to `copy_nonoverlapping` is
// safe. The safety contract for `dealloc` must be upheld by the caller.
unsafe {
ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), old_layout.size());
self.deallocate(ptr, old_layout);
}
Ok(new_ptr)
}
/// Behaves like `grow`, but also ensures that the new contents are set to zero before being
/// returned.
///
/// The memory block will contain the following contents after a successful call to
/// `grow_zeroed`:
/// * Bytes `0..old_layout.size()` are preserved from the original allocation.
/// * Bytes `old_layout.size()..old_size` will either be preserved or zeroed, depending on
/// the allocator implementation. `old_size` refers to the size of the memory block prior
/// to the `grow_zeroed` call, which may be larger than the size that was originally
/// requested when it was allocated.
/// * Bytes `old_size..new_size` are zeroed. `new_size` refers to the size of the memory
/// block returned by the `grow_zeroed` call.
///
/// # Safety
///
/// * `ptr` must denote a block of memory [*currently allocated*] via this allocator.
/// * `old_layout` must [*fit*] that block of memory (The `new_layout` argument need not fit it.).
/// * `new_layout.size()` must be greater than or equal to `old_layout.size()`.
///
/// Note that `new_layout.align()` need not be the same as `old_layout.align()`.
///
/// [*currently allocated*]: #currently-allocated-memory
/// [*fit*]: #memory-fitting
///
/// # Errors
///
/// Returns `Err` if the new layout does not meet the allocator's size and alignment
/// constraints of the allocator, or if growing 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 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 grow_zeroed(
&self,
ptr: NonNull<u8>,
old_layout: Layout,
new_layout: Layout,
) -> Result<NonNull<[u8]>, AllocError> {
debug_assert!(
new_layout.size() >= old_layout.size(),
"`new_layout.size()` must be greater than or equal to `old_layout.size()`"
);
let new_ptr = self.allocate_zeroed(new_layout)?;
// SAFETY: because `new_layout.size()` must be greater than or equal to
// `old_layout.size()`, both the old and new memory allocation are valid for reads and
// writes for `old_layout.size()` bytes. Also, because the old allocation wasn't yet
// deallocated, it cannot overlap `new_ptr`. Thus, the call to `copy_nonoverlapping` is
// safe. The safety contract for `dealloc` must be upheld by the caller.
unsafe {
ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), old_layout.size());
self.deallocate(ptr, old_layout);
}
Ok(new_ptr)
}
/// Attempts to shrink the memory block.
///
/// Returns a new [`NonNull<[u8]>`][NonNull] containing a pointer and the actual size of the allocated
/// memory. The pointer is suitable for holding data described by `new_layout`. To accomplish
/// this, the allocator may 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.
///
/// 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
///
/// * `ptr` must denote a block of memory [*currently allocated*] via this allocator.
/// * `old_layout` must [*fit*] that block of memory (The `new_layout` argument need not fit it.).
/// * `new_layout.size()` must be smaller than or equal to `old_layout.size()`.
///
/// Note that `new_layout.align()` need not be the same as `old_layout.align()`.
///
/// [*currently allocated*]: #currently-allocated-memory
/// [*fit*]: #memory-fitting
///
/// # Errors
///
/// Returns `Err` if the new layout does not meet the allocator's size and alignment
/// constraints of the allocator, or if shrinking 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 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 shrink(
&self,
ptr: NonNull<u8>,
old_layout: Layout,
new_layout: Layout,
) -> Result<NonNull<[u8]>, AllocError> {
debug_assert!(
new_layout.size() <= old_layout.size(),
"`new_layout.size()` must be smaller than or equal to `old_layout.size()`"
);
let new_ptr = self.allocate(new_layout)?;
// SAFETY: because `new_layout.size()` must be lower than or equal to
// `old_layout.size()`, both the old and new memory allocation are valid for reads and
// writes for `new_layout.size()` bytes. Also, because the old allocation wasn't yet
// deallocated, it cannot overlap `new_ptr`. Thus, the call to `copy_nonoverlapping` is
// safe. The safety contract for `dealloc` must be upheld by the caller.
unsafe {
ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), new_layout.size());
self.deallocate(ptr, old_layout);
}
Ok(new_ptr)
}
/// Creates a "by reference" adapter for this instance of `Allocator`.
///
/// The returned adapter also implements `Allocator` and will simply borrow this.
#[inline(always)]
fn by_ref(&self) -> &Self
where
Self: Sized,
{
self
}
}
#[unstable(feature = "allocator_api", issue = "32838")]
unsafe impl<A> Allocator for &A
where
A: Allocator + ?Sized,
{
#[inline]
fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
(**self).allocate(layout)
}
#[inline]
fn allocate_zeroed(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
(**self).allocate_zeroed(layout)
}
#[inline]
unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout) {
// SAFETY: the safety contract must be upheld by the caller
unsafe { (**self).deallocate(ptr, layout) }
}
#[inline]
unsafe fn grow(
&self,
ptr: NonNull<u8>,
old_layout: Layout,
new_layout: Layout,
) -> Result<NonNull<[u8]>, AllocError> {
// SAFETY: the safety contract must be upheld by the caller
unsafe { (**self).grow(ptr, old_layout, new_layout) }
}
#[inline]
unsafe fn grow_zeroed(
&self,
ptr: NonNull<u8>,
old_layout: Layout,
new_layout: Layout,
) -> Result<NonNull<[u8]>, AllocError> {
// SAFETY: the safety contract must be upheld by the caller
unsafe { (**self).grow_zeroed(ptr, old_layout, new_layout) }
}
#[inline]
unsafe fn shrink(
&self,
ptr: NonNull<u8>,
old_layout: Layout,
new_layout: Layout,
) -> Result<NonNull<[u8]>, AllocError> {
// SAFETY: the safety contract must be upheld by the caller
unsafe { (**self).shrink(ptr, old_layout, new_layout) }
}
}