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Diffstat (limited to 'library/core/src/alloc/mod.rs')
| -rw-r--r-- | library/core/src/alloc/mod.rs | 410 |
1 files changed, 410 insertions, 0 deletions
diff --git a/library/core/src/alloc/mod.rs b/library/core/src/alloc/mod.rs new file mode 100644 index 000000000..6cc6e359e --- /dev/null +++ b/library/core/src/alloc/mod.rs @@ -0,0 +1,410 @@ +//! 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) } + } +} |