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Diffstat (limited to 'library/alloc/src/raw_vec/mod.rs')
| -rw-r--r-- | library/alloc/src/raw_vec/mod.rs | 822 |
1 files changed, 822 insertions, 0 deletions
diff --git a/library/alloc/src/raw_vec/mod.rs b/library/alloc/src/raw_vec/mod.rs new file mode 100644 index 00000000000..99ebc5c4bfc --- /dev/null +++ b/library/alloc/src/raw_vec/mod.rs @@ -0,0 +1,822 @@ +#![unstable(feature = "raw_vec_internals", reason = "unstable const warnings", issue = "none")] +#![cfg_attr(test, allow(dead_code))] + +// Note: This module is also included in the alloctests crate using #[path] to +// run the tests. See the comment there for an explanation why this is the case. + +use core::marker::PhantomData; +use core::mem::{ManuallyDrop, MaybeUninit, SizedTypeProperties}; +use core::ptr::{self, NonNull, Unique}; +use core::{cmp, hint}; + +#[cfg(not(no_global_oom_handling))] +use crate::alloc::handle_alloc_error; +use crate::alloc::{Allocator, Global, Layout}; +use crate::boxed::Box; +use crate::collections::TryReserveError; +use crate::collections::TryReserveErrorKind::*; + +#[cfg(test)] +mod tests; + +// One central function responsible for reporting capacity overflows. This'll +// ensure that the code generation related to these panics is minimal as there's +// only one location which panics rather than a bunch throughout the module. +#[cfg(not(no_global_oom_handling))] +#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))] +#[track_caller] +fn capacity_overflow() -> ! { + panic!("capacity overflow"); +} + +enum AllocInit { + /// The contents of the new memory are uninitialized. + Uninitialized, + #[cfg(not(no_global_oom_handling))] + /// The new memory is guaranteed to be zeroed. + Zeroed, +} + +type Cap = core::num::niche_types::UsizeNoHighBit; + +const ZERO_CAP: Cap = unsafe { Cap::new_unchecked(0) }; + +/// `Cap(cap)`, except if `T` is a ZST then `Cap::ZERO`. +/// +/// # Safety: cap must be <= `isize::MAX`. +unsafe fn new_cap<T>(cap: usize) -> Cap { + if T::IS_ZST { ZERO_CAP } else { unsafe { Cap::new_unchecked(cap) } } +} + +/// A low-level utility for more ergonomically allocating, reallocating, and deallocating +/// a buffer of memory on the heap without having to worry about all the corner cases +/// involved. This type is excellent for building your own data structures like Vec and VecDeque. +/// In particular: +/// +/// * Produces `Unique::dangling()` on zero-sized types. +/// * Produces `Unique::dangling()` on zero-length allocations. +/// * Avoids freeing `Unique::dangling()`. +/// * Catches all overflows in capacity computations (promotes them to "capacity overflow" panics). +/// * Guards against 32-bit systems allocating more than `isize::MAX` bytes. +/// * Guards against overflowing your length. +/// * Calls `handle_alloc_error` for fallible allocations. +/// * Contains a `ptr::Unique` and thus endows the user with all related benefits. +/// * Uses the excess returned from the allocator to use the largest available capacity. +/// +/// This type does not in anyway inspect the memory that it manages. When dropped it *will* +/// free its memory, but it *won't* try to drop its contents. It is up to the user of `RawVec` +/// to handle the actual things *stored* inside of a `RawVec`. +/// +/// Note that the excess of a zero-sized types is always infinite, so `capacity()` always returns +/// `usize::MAX`. This means that you need to be careful when round-tripping this type with a +/// `Box<[T]>`, since `capacity()` won't yield the length. +#[allow(missing_debug_implementations)] +pub(crate) struct RawVec<T, A: Allocator = Global> { + inner: RawVecInner<A>, + _marker: PhantomData<T>, +} + +/// Like a `RawVec`, but only generic over the allocator, not the type. +/// +/// As such, all the methods need the layout passed-in as a parameter. +/// +/// Having this separation reduces the amount of code we need to monomorphize, +/// as most operations don't need the actual type, just its layout. +#[allow(missing_debug_implementations)] +struct RawVecInner<A: Allocator = Global> { + ptr: Unique<u8>, + /// Never used for ZSTs; it's `capacity()`'s responsibility to return usize::MAX in that case. + /// + /// # Safety + /// + /// `cap` must be in the `0..=isize::MAX` range. + cap: Cap, + alloc: A, +} + +impl<T> RawVec<T, Global> { + /// Creates the biggest possible `RawVec` (on the system heap) + /// without allocating. If `T` has positive size, then this makes a + /// `RawVec` with capacity `0`. If `T` is zero-sized, then it makes a + /// `RawVec` with capacity `usize::MAX`. Useful for implementing + /// delayed allocation. + #[must_use] + pub(crate) const fn new() -> Self { + Self::new_in(Global) + } + + /// Creates a `RawVec` (on the system heap) with exactly the + /// capacity and alignment requirements for a `[T; capacity]`. This is + /// equivalent to calling `RawVec::new` when `capacity` is `0` or `T` is + /// zero-sized. Note that if `T` is zero-sized this means you will + /// *not* get a `RawVec` with the requested capacity. + /// + /// Non-fallible version of `try_with_capacity` + /// + /// # Panics + /// + /// Panics if the requested capacity exceeds `isize::MAX` bytes. + /// + /// # Aborts + /// + /// Aborts on OOM. + #[cfg(not(any(no_global_oom_handling, test)))] + #[must_use] + #[inline] + #[track_caller] + pub(crate) fn with_capacity(capacity: usize) -> Self { + Self { inner: RawVecInner::with_capacity(capacity, T::LAYOUT), _marker: PhantomData } + } + + /// Like `with_capacity`, but guarantees the buffer is zeroed. + #[cfg(not(any(no_global_oom_handling, test)))] + #[must_use] + #[inline] + #[track_caller] + pub(crate) fn with_capacity_zeroed(capacity: usize) -> Self { + Self { + inner: RawVecInner::with_capacity_zeroed_in(capacity, Global, T::LAYOUT), + _marker: PhantomData, + } + } +} + +impl RawVecInner<Global> { + #[cfg(not(any(no_global_oom_handling, test)))] + #[must_use] + #[inline] + #[track_caller] + fn with_capacity(capacity: usize, elem_layout: Layout) -> Self { + match Self::try_allocate_in(capacity, AllocInit::Uninitialized, Global, elem_layout) { + Ok(res) => res, + Err(err) => handle_error(err), + } + } +} + +// Tiny Vecs are dumb. Skip to: +// - 8 if the element size is 1, because any heap allocators is likely +// to round up a request of less than 8 bytes to at least 8 bytes. +// - 4 if elements are moderate-sized (<= 1 KiB). +// - 1 otherwise, to avoid wasting too much space for very short Vecs. +const fn min_non_zero_cap(size: usize) -> usize { + if size == 1 { + 8 + } else if size <= 1024 { + 4 + } else { + 1 + } +} + +impl<T, A: Allocator> RawVec<T, A> { + #[cfg(not(no_global_oom_handling))] + pub(crate) const MIN_NON_ZERO_CAP: usize = min_non_zero_cap(size_of::<T>()); + + /// Like `new`, but parameterized over the choice of allocator for + /// the returned `RawVec`. + #[inline] + pub(crate) const fn new_in(alloc: A) -> Self { + Self { inner: RawVecInner::new_in(alloc, align_of::<T>()), _marker: PhantomData } + } + + /// Like `with_capacity`, but parameterized over the choice of + /// allocator for the returned `RawVec`. + #[cfg(not(no_global_oom_handling))] + #[inline] + #[track_caller] + pub(crate) fn with_capacity_in(capacity: usize, alloc: A) -> Self { + Self { + inner: RawVecInner::with_capacity_in(capacity, alloc, T::LAYOUT), + _marker: PhantomData, + } + } + + /// Like `try_with_capacity`, but parameterized over the choice of + /// allocator for the returned `RawVec`. + #[inline] + pub(crate) fn try_with_capacity_in(capacity: usize, alloc: A) -> Result<Self, TryReserveError> { + match RawVecInner::try_with_capacity_in(capacity, alloc, T::LAYOUT) { + Ok(inner) => Ok(Self { inner, _marker: PhantomData }), + Err(e) => Err(e), + } + } + + /// Like `with_capacity_zeroed`, but parameterized over the choice + /// of allocator for the returned `RawVec`. + #[cfg(not(no_global_oom_handling))] + #[inline] + #[track_caller] + pub(crate) fn with_capacity_zeroed_in(capacity: usize, alloc: A) -> Self { + Self { + inner: RawVecInner::with_capacity_zeroed_in(capacity, alloc, T::LAYOUT), + _marker: PhantomData, + } + } + + /// Converts the entire buffer into `Box<[MaybeUninit<T>]>` with the specified `len`. + /// + /// Note that this will correctly reconstitute any `cap` changes + /// that may have been performed. (See description of type for details.) + /// + /// # Safety + /// + /// * `len` must be greater than or equal to the most recently requested capacity, and + /// * `len` must be less than or equal to `self.capacity()`. + /// + /// Note, that the requested capacity and `self.capacity()` could differ, as + /// an allocator could overallocate and return a greater memory block than requested. + pub(crate) unsafe fn into_box(self, len: usize) -> Box<[MaybeUninit<T>], A> { + // Sanity-check one half of the safety requirement (we cannot check the other half). + debug_assert!( + len <= self.capacity(), + "`len` must be smaller than or equal to `self.capacity()`" + ); + + let me = ManuallyDrop::new(self); + unsafe { + let slice = ptr::slice_from_raw_parts_mut(me.ptr() as *mut MaybeUninit<T>, len); + Box::from_raw_in(slice, ptr::read(&me.inner.alloc)) + } + } + + /// Reconstitutes a `RawVec` from a pointer, capacity, and allocator. + /// + /// # Safety + /// + /// The `ptr` must be allocated (via the given allocator `alloc`), and with the given + /// `capacity`. + /// The `capacity` cannot exceed `isize::MAX` for sized types. (only a concern on 32-bit + /// systems). For ZSTs capacity is ignored. + /// If the `ptr` and `capacity` come from a `RawVec` created via `alloc`, then this is + /// guaranteed. + #[inline] + pub(crate) unsafe fn from_raw_parts_in(ptr: *mut T, capacity: usize, alloc: A) -> Self { + // SAFETY: Precondition passed to the caller + unsafe { + let ptr = ptr.cast(); + let capacity = new_cap::<T>(capacity); + Self { + inner: RawVecInner::from_raw_parts_in(ptr, capacity, alloc), + _marker: PhantomData, + } + } + } + + /// A convenience method for hoisting the non-null precondition out of [`RawVec::from_raw_parts_in`]. + /// + /// # Safety + /// + /// See [`RawVec::from_raw_parts_in`]. + #[inline] + pub(crate) unsafe fn from_nonnull_in(ptr: NonNull<T>, capacity: usize, alloc: A) -> Self { + // SAFETY: Precondition passed to the caller + unsafe { + let ptr = ptr.cast(); + let capacity = new_cap::<T>(capacity); + Self { inner: RawVecInner::from_nonnull_in(ptr, capacity, alloc), _marker: PhantomData } + } + } + + /// Gets a raw pointer to the start of the allocation. Note that this is + /// `Unique::dangling()` if `capacity == 0` or `T` is zero-sized. In the former case, you must + /// be careful. + #[inline] + pub(crate) const fn ptr(&self) -> *mut T { + self.inner.ptr() + } + + #[inline] + pub(crate) fn non_null(&self) -> NonNull<T> { + self.inner.non_null() + } + + /// Gets the capacity of the allocation. + /// + /// This will always be `usize::MAX` if `T` is zero-sized. + #[inline] + pub(crate) const fn capacity(&self) -> usize { + self.inner.capacity(size_of::<T>()) + } + + /// Returns a shared reference to the allocator backing this `RawVec`. + #[inline] + pub(crate) fn allocator(&self) -> &A { + self.inner.allocator() + } + + /// Ensures that the buffer contains at least enough space to hold `len + + /// additional` elements. If it doesn't already have enough capacity, will + /// reallocate enough space plus comfortable slack space to get amortized + /// *O*(1) behavior. Will limit this behavior if it would needlessly cause + /// itself to panic. + /// + /// If `len` exceeds `self.capacity()`, this may fail to actually allocate + /// the requested space. This is not really unsafe, but the unsafe + /// code *you* write that relies on the behavior of this function may break. + /// + /// This is ideal for implementing a bulk-push operation like `extend`. + /// + /// # Panics + /// + /// Panics if the new capacity exceeds `isize::MAX` _bytes_. + /// + /// # Aborts + /// + /// Aborts on OOM. + #[cfg(not(no_global_oom_handling))] + #[inline] + #[track_caller] + pub(crate) fn reserve(&mut self, len: usize, additional: usize) { + self.inner.reserve(len, additional, T::LAYOUT) + } + + /// A specialized version of `self.reserve(len, 1)` which requires the + /// caller to ensure `len == self.capacity()`. + #[cfg(not(no_global_oom_handling))] + #[inline(never)] + #[track_caller] + pub(crate) fn grow_one(&mut self) { + self.inner.grow_one(T::LAYOUT) + } + + /// The same as `reserve`, but returns on errors instead of panicking or aborting. + pub(crate) fn try_reserve( + &mut self, + len: usize, + additional: usize, + ) -> Result<(), TryReserveError> { + self.inner.try_reserve(len, additional, T::LAYOUT) + } + + /// Ensures that the buffer contains at least enough space to hold `len + + /// additional` elements. If it doesn't already, will reallocate the + /// minimum possible amount of memory necessary. Generally this will be + /// exactly the amount of memory necessary, but in principle the allocator + /// is free to give back more than we asked for. + /// + /// If `len` exceeds `self.capacity()`, this may fail to actually allocate + /// the requested space. This is not really unsafe, but the unsafe code + /// *you* write that relies on the behavior of this function may break. + /// + /// # Panics + /// + /// Panics if the new capacity exceeds `isize::MAX` _bytes_. + /// + /// # Aborts + /// + /// Aborts on OOM. + #[cfg(not(no_global_oom_handling))] + #[track_caller] + pub(crate) fn reserve_exact(&mut self, len: usize, additional: usize) { + self.inner.reserve_exact(len, additional, T::LAYOUT) + } + + /// The same as `reserve_exact`, but returns on errors instead of panicking or aborting. + pub(crate) fn try_reserve_exact( + &mut self, + len: usize, + additional: usize, + ) -> Result<(), TryReserveError> { + self.inner.try_reserve_exact(len, additional, T::LAYOUT) + } + + /// Shrinks the buffer down to the specified capacity. If the given amount + /// is 0, actually completely deallocates. + /// + /// # Panics + /// + /// Panics if the given amount is *larger* than the current capacity. + /// + /// # Aborts + /// + /// Aborts on OOM. + #[cfg(not(no_global_oom_handling))] + #[track_caller] + #[inline] + pub(crate) fn shrink_to_fit(&mut self, cap: usize) { + self.inner.shrink_to_fit(cap, T::LAYOUT) + } +} + +unsafe impl<#[may_dangle] T, A: Allocator> Drop for RawVec<T, A> { + /// Frees the memory owned by the `RawVec` *without* trying to drop its contents. + fn drop(&mut self) { + // SAFETY: We are in a Drop impl, self.inner will not be used again. + unsafe { self.inner.deallocate(T::LAYOUT) } + } +} + +impl<A: Allocator> RawVecInner<A> { + #[inline] + const fn new_in(alloc: A, align: usize) -> Self { + let ptr = unsafe { core::mem::transmute(align) }; + // `cap: 0` means "unallocated". zero-sized types are ignored. + Self { ptr, cap: ZERO_CAP, alloc } + } + + #[cfg(not(no_global_oom_handling))] + #[inline] + #[track_caller] + fn with_capacity_in(capacity: usize, alloc: A, elem_layout: Layout) -> Self { + match Self::try_allocate_in(capacity, AllocInit::Uninitialized, alloc, elem_layout) { + Ok(this) => { + unsafe { + // Make it more obvious that a subsequent Vec::reserve(capacity) will not allocate. + hint::assert_unchecked(!this.needs_to_grow(0, capacity, elem_layout)); + } + this + } + Err(err) => handle_error(err), + } + } + + #[inline] + fn try_with_capacity_in( + capacity: usize, + alloc: A, + elem_layout: Layout, + ) -> Result<Self, TryReserveError> { + Self::try_allocate_in(capacity, AllocInit::Uninitialized, alloc, elem_layout) + } + + #[cfg(not(no_global_oom_handling))] + #[inline] + #[track_caller] + fn with_capacity_zeroed_in(capacity: usize, alloc: A, elem_layout: Layout) -> Self { + match Self::try_allocate_in(capacity, AllocInit::Zeroed, alloc, elem_layout) { + Ok(res) => res, + Err(err) => handle_error(err), + } + } + + fn try_allocate_in( + capacity: usize, + init: AllocInit, + alloc: A, + elem_layout: Layout, + ) -> Result<Self, TryReserveError> { + // We avoid `unwrap_or_else` here because it bloats the amount of + // LLVM IR generated. + let layout = match layout_array(capacity, elem_layout) { + Ok(layout) => layout, + Err(_) => return Err(CapacityOverflow.into()), + }; + + // Don't allocate here because `Drop` will not deallocate when `capacity` is 0. + if layout.size() == 0 { + return Ok(Self::new_in(alloc, elem_layout.align())); + } + + if let Err(err) = alloc_guard(layout.size()) { + return Err(err); + } + + let result = match init { + AllocInit::Uninitialized => alloc.allocate(layout), + #[cfg(not(no_global_oom_handling))] + AllocInit::Zeroed => alloc.allocate_zeroed(layout), + }; + let ptr = match result { + Ok(ptr) => ptr, + Err(_) => return Err(AllocError { layout, non_exhaustive: () }.into()), + }; + + // Allocators currently return a `NonNull<[u8]>` whose length + // matches the size requested. If that ever changes, the capacity + // here should change to `ptr.len() / size_of::<T>()`. + Ok(Self { + ptr: Unique::from(ptr.cast()), + cap: unsafe { Cap::new_unchecked(capacity) }, + alloc, + }) + } + + #[inline] + unsafe fn from_raw_parts_in(ptr: *mut u8, cap: Cap, alloc: A) -> Self { + Self { ptr: unsafe { Unique::new_unchecked(ptr) }, cap, alloc } + } + + #[inline] + unsafe fn from_nonnull_in(ptr: NonNull<u8>, cap: Cap, alloc: A) -> Self { + Self { ptr: Unique::from(ptr), cap, alloc } + } + + #[inline] + const fn ptr<T>(&self) -> *mut T { + self.non_null::<T>().as_ptr() + } + + #[inline] + const fn non_null<T>(&self) -> NonNull<T> { + self.ptr.cast().as_non_null_ptr() + } + + #[inline] + const fn capacity(&self, elem_size: usize) -> usize { + if elem_size == 0 { usize::MAX } else { self.cap.as_inner() } + } + + #[inline] + fn allocator(&self) -> &A { + &self.alloc + } + + #[inline] + fn current_memory(&self, elem_layout: Layout) -> Option<(NonNull<u8>, Layout)> { + if elem_layout.size() == 0 || self.cap.as_inner() == 0 { + None + } else { + // We could use Layout::array here which ensures the absence of isize and usize overflows + // and could hypothetically handle differences between stride and size, but this memory + // has already been allocated so we know it can't overflow and currently Rust does not + // support such types. So we can do better by skipping some checks and avoid an unwrap. + unsafe { + let alloc_size = elem_layout.size().unchecked_mul(self.cap.as_inner()); + let layout = Layout::from_size_align_unchecked(alloc_size, elem_layout.align()); + Some((self.ptr.into(), layout)) + } + } + } + + #[cfg(not(no_global_oom_handling))] + #[inline] + #[track_caller] + fn reserve(&mut self, len: usize, additional: usize, elem_layout: Layout) { + // Callers expect this function to be very cheap when there is already sufficient capacity. + // Therefore, we move all the resizing and error-handling logic from grow_amortized and + // handle_reserve behind a call, while making sure that this function is likely to be + // inlined as just a comparison and a call if the comparison fails. + #[cold] + fn do_reserve_and_handle<A: Allocator>( + slf: &mut RawVecInner<A>, + len: usize, + additional: usize, + elem_layout: Layout, + ) { + if let Err(err) = slf.grow_amortized(len, additional, elem_layout) { + handle_error(err); + } + } + + if self.needs_to_grow(len, additional, elem_layout) { + do_reserve_and_handle(self, len, additional, elem_layout); + } + } + + #[cfg(not(no_global_oom_handling))] + #[inline] + #[track_caller] + fn grow_one(&mut self, elem_layout: Layout) { + if let Err(err) = self.grow_amortized(self.cap.as_inner(), 1, elem_layout) { + handle_error(err); + } + } + + fn try_reserve( + &mut self, + len: usize, + additional: usize, + elem_layout: Layout, + ) -> Result<(), TryReserveError> { + if self.needs_to_grow(len, additional, elem_layout) { + self.grow_amortized(len, additional, elem_layout)?; + } + unsafe { + // Inform the optimizer that the reservation has succeeded or wasn't needed + hint::assert_unchecked(!self.needs_to_grow(len, additional, elem_layout)); + } + Ok(()) + } + + #[cfg(not(no_global_oom_handling))] + #[track_caller] + fn reserve_exact(&mut self, len: usize, additional: usize, elem_layout: Layout) { + if let Err(err) = self.try_reserve_exact(len, additional, elem_layout) { + handle_error(err); + } + } + + fn try_reserve_exact( + &mut self, + len: usize, + additional: usize, + elem_layout: Layout, + ) -> Result<(), TryReserveError> { + if self.needs_to_grow(len, additional, elem_layout) { + self.grow_exact(len, additional, elem_layout)?; + } + unsafe { + // Inform the optimizer that the reservation has succeeded or wasn't needed + hint::assert_unchecked(!self.needs_to_grow(len, additional, elem_layout)); + } + Ok(()) + } + + #[cfg(not(no_global_oom_handling))] + #[inline] + #[track_caller] + fn shrink_to_fit(&mut self, cap: usize, elem_layout: Layout) { + if let Err(err) = self.shrink(cap, elem_layout) { + handle_error(err); + } + } + + #[inline] + fn needs_to_grow(&self, len: usize, additional: usize, elem_layout: Layout) -> bool { + additional > self.capacity(elem_layout.size()).wrapping_sub(len) + } + + #[inline] + unsafe fn set_ptr_and_cap(&mut self, ptr: NonNull<[u8]>, cap: usize) { + // Allocators currently return a `NonNull<[u8]>` whose length matches + // the size requested. If that ever changes, the capacity here should + // change to `ptr.len() / size_of::<T>()`. + self.ptr = Unique::from(ptr.cast()); + self.cap = unsafe { Cap::new_unchecked(cap) }; + } + + fn grow_amortized( + &mut self, + len: usize, + additional: usize, + elem_layout: Layout, + ) -> Result<(), TryReserveError> { + // This is ensured by the calling contexts. + debug_assert!(additional > 0); + + if elem_layout.size() == 0 { + // Since we return a capacity of `usize::MAX` when `elem_size` is + // 0, getting to here necessarily means the `RawVec` is overfull. + return Err(CapacityOverflow.into()); + } + + // Nothing we can really do about these checks, sadly. + let required_cap = len.checked_add(additional).ok_or(CapacityOverflow)?; + + // This guarantees exponential growth. The doubling cannot overflow + // because `cap <= isize::MAX` and the type of `cap` is `usize`. + let cap = cmp::max(self.cap.as_inner() * 2, required_cap); + let cap = cmp::max(min_non_zero_cap(elem_layout.size()), cap); + + let new_layout = layout_array(cap, elem_layout)?; + + let ptr = finish_grow(new_layout, self.current_memory(elem_layout), &mut self.alloc)?; + // SAFETY: finish_grow would have resulted in a capacity overflow if we tried to allocate more than `isize::MAX` items + + unsafe { self.set_ptr_and_cap(ptr, cap) }; + Ok(()) + } + + fn grow_exact( + &mut self, + len: usize, + additional: usize, + elem_layout: Layout, + ) -> Result<(), TryReserveError> { + if elem_layout.size() == 0 { + // Since we return a capacity of `usize::MAX` when the type size is + // 0, getting to here necessarily means the `RawVec` is overfull. + return Err(CapacityOverflow.into()); + } + + let cap = len.checked_add(additional).ok_or(CapacityOverflow)?; + let new_layout = layout_array(cap, elem_layout)?; + + let ptr = finish_grow(new_layout, self.current_memory(elem_layout), &mut self.alloc)?; + // SAFETY: finish_grow would have resulted in a capacity overflow if we tried to allocate more than `isize::MAX` items + unsafe { + self.set_ptr_and_cap(ptr, cap); + } + Ok(()) + } + + #[cfg(not(no_global_oom_handling))] + #[inline] + fn shrink(&mut self, cap: usize, elem_layout: Layout) -> Result<(), TryReserveError> { + assert!(cap <= self.capacity(elem_layout.size()), "Tried to shrink to a larger capacity"); + // SAFETY: Just checked this isn't trying to grow + unsafe { self.shrink_unchecked(cap, elem_layout) } + } + + /// `shrink`, but without the capacity check. + /// + /// This is split out so that `shrink` can inline the check, since it + /// optimizes out in things like `shrink_to_fit`, without needing to + /// also inline all this code, as doing that ends up failing the + /// `vec-shrink-panic` codegen test when `shrink_to_fit` ends up being too + /// big for LLVM to be willing to inline. + /// + /// # Safety + /// `cap <= self.capacity()` + #[cfg(not(no_global_oom_handling))] + unsafe fn shrink_unchecked( + &mut self, + cap: usize, + elem_layout: Layout, + ) -> Result<(), TryReserveError> { + let (ptr, layout) = + if let Some(mem) = self.current_memory(elem_layout) { mem } else { return Ok(()) }; + + // If shrinking to 0, deallocate the buffer. We don't reach this point + // for the T::IS_ZST case since current_memory() will have returned + // None. + if cap == 0 { + unsafe { self.alloc.deallocate(ptr, layout) }; + self.ptr = + unsafe { Unique::new_unchecked(ptr::without_provenance_mut(elem_layout.align())) }; + self.cap = ZERO_CAP; + } else { + let ptr = unsafe { + // Layout cannot overflow here because it would have + // overflowed earlier when capacity was larger. + let new_size = elem_layout.size().unchecked_mul(cap); + let new_layout = Layout::from_size_align_unchecked(new_size, layout.align()); + self.alloc + .shrink(ptr, layout, new_layout) + .map_err(|_| AllocError { layout: new_layout, non_exhaustive: () })? + }; + // SAFETY: if the allocation is valid, then the capacity is too + unsafe { + self.set_ptr_and_cap(ptr, cap); + } + } + Ok(()) + } + + /// # Safety + /// + /// This function deallocates the owned allocation, but does not update `ptr` or `cap` to + /// prevent double-free or use-after-free. Essentially, do not do anything with the caller + /// after this function returns. + /// Ideally this function would take `self` by move, but it cannot because it exists to be + /// called from a `Drop` impl. + unsafe fn deallocate(&mut self, elem_layout: Layout) { + if let Some((ptr, layout)) = self.current_memory(elem_layout) { + unsafe { + self.alloc.deallocate(ptr, layout); + } + } + } +} + +// not marked inline(never) since we want optimizers to be able to observe the specifics of this +// function, see tests/codegen/vec-reserve-extend.rs. +#[cold] +fn finish_grow<A>( + new_layout: Layout, + current_memory: Option<(NonNull<u8>, Layout)>, + alloc: &mut A, +) -> Result<NonNull<[u8]>, TryReserveError> +where + A: Allocator, +{ + alloc_guard(new_layout.size())?; + + let memory = if let Some((ptr, old_layout)) = current_memory { + debug_assert_eq!(old_layout.align(), new_layout.align()); + unsafe { + // The allocator checks for alignment equality + hint::assert_unchecked(old_layout.align() == new_layout.align()); + alloc.grow(ptr, old_layout, new_layout) + } + } else { + alloc.allocate(new_layout) + }; + + memory.map_err(|_| AllocError { layout: new_layout, non_exhaustive: () }.into()) +} + +// Central function for reserve error handling. +#[cfg(not(no_global_oom_handling))] +#[cold] +#[optimize(size)] +#[track_caller] +fn handle_error(e: TryReserveError) -> ! { + match e.kind() { + CapacityOverflow => capacity_overflow(), + AllocError { layout, .. } => handle_alloc_error(layout), + } +} + +// We need to guarantee the following: +// * We don't ever allocate `> isize::MAX` byte-size objects. +// * We don't overflow `usize::MAX` and actually allocate too little. +// +// On 64-bit we just need to check for overflow since trying to allocate +// `> isize::MAX` bytes will surely fail. On 32-bit and 16-bit we need to add +// an extra guard for this in case we're running on a platform which can use +// all 4GB in user-space, e.g., PAE or x32. +#[inline] +fn alloc_guard(alloc_size: usize) -> Result<(), TryReserveError> { + if usize::BITS < 64 && alloc_size > isize::MAX as usize { + Err(CapacityOverflow.into()) + } else { + Ok(()) + } +} + +#[inline] +fn layout_array(cap: usize, elem_layout: Layout) -> Result<Layout, TryReserveError> { + elem_layout.repeat(cap).map(|(layout, _pad)| layout).map_err(|_| CapacityOverflow.into()) +} |