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Diffstat (limited to 'rust/alloc/raw_vec.rs')
| -rw-r--r-- | rust/alloc/raw_vec.rs | 611 |
1 files changed, 0 insertions, 611 deletions
diff --git a/rust/alloc/raw_vec.rs b/rust/alloc/raw_vec.rs deleted file mode 100644 index 98b6abf30af6..000000000000 --- a/rust/alloc/raw_vec.rs +++ /dev/null @@ -1,611 +0,0 @@ -// SPDX-License-Identifier: Apache-2.0 OR MIT - -#![unstable(feature = "raw_vec_internals", reason = "unstable const warnings", issue = "none")] - -use core::alloc::LayoutError; -use core::cmp; -use core::intrinsics; -use core::mem::{self, ManuallyDrop, MaybeUninit, SizedTypeProperties}; -use core::ptr::{self, NonNull, Unique}; -use core::slice; - -#[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; - -enum AllocInit { - /// The contents of the new memory are uninitialized. - Uninitialized, - /// The new memory is guaranteed to be zeroed. - #[allow(dead_code)] - Zeroed, -} - -#[repr(transparent)] -#[cfg_attr(target_pointer_width = "16", rustc_layout_scalar_valid_range_end(0x7fff))] -#[cfg_attr(target_pointer_width = "32", rustc_layout_scalar_valid_range_end(0x7fff_ffff))] -#[cfg_attr(target_pointer_width = "64", rustc_layout_scalar_valid_range_end(0x7fff_ffff_ffff_ffff))] -struct Cap(usize); - -impl Cap { - const ZERO: Cap = unsafe { Cap(0) }; -} - -/// 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> { - ptr: Unique<T>, - /// 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> { - /// HACK(Centril): This exists because stable `const fn` can only call stable `const fn`, so - /// they cannot call `Self::new()`. - /// - /// If you change `RawVec<T>::new` or dependencies, please take care to not introduce anything - /// that would truly const-call something unstable. - pub const NEW: Self = Self::new(); - - /// 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 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. - /// - /// # 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] - pub fn with_capacity(capacity: usize) -> Self { - Self::with_capacity_in(capacity, Global) - } - - /// Like `with_capacity`, but guarantees the buffer is zeroed. - #[cfg(not(any(no_global_oom_handling, test)))] - #[must_use] - #[inline] - pub fn with_capacity_zeroed(capacity: usize) -> Self { - Self::with_capacity_zeroed_in(capacity, Global) - } -} - -impl<T, A: Allocator> RawVec<T, A> { - // 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. - pub(crate) const MIN_NON_ZERO_CAP: usize = if mem::size_of::<T>() == 1 { - 8 - } else if mem::size_of::<T>() <= 1024 { - 4 - } else { - 1 - }; - - /// Like `new`, but parameterized over the choice of allocator for - /// the returned `RawVec`. - pub const fn new_in(alloc: A) -> Self { - // `cap: 0` means "unallocated". zero-sized types are ignored. - Self { ptr: Unique::dangling(), cap: Cap::ZERO, alloc } - } - - /// Like `with_capacity`, but parameterized over the choice of - /// allocator for the returned `RawVec`. - #[cfg(not(no_global_oom_handling))] - #[inline] - pub fn with_capacity_in(capacity: usize, alloc: A) -> Self { - Self::allocate_in(capacity, AllocInit::Uninitialized, alloc) - } - - /// Like `try_with_capacity`, but parameterized over the choice of - /// allocator for the returned `RawVec`. - #[inline] - pub fn try_with_capacity_in(capacity: usize, alloc: A) -> Result<Self, TryReserveError> { - Self::try_allocate_in(capacity, AllocInit::Uninitialized, alloc) - } - - /// Like `with_capacity_zeroed`, but parameterized over the choice - /// of allocator for the returned `RawVec`. - #[cfg(not(no_global_oom_handling))] - #[inline] - pub fn with_capacity_zeroed_in(capacity: usize, alloc: A) -> Self { - Self::allocate_in(capacity, AllocInit::Zeroed, alloc) - } - - /// 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 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 = slice::from_raw_parts_mut(me.ptr() as *mut MaybeUninit<T>, len); - Box::from_raw_in(slice, ptr::read(&me.alloc)) - } - } - - #[cfg(not(no_global_oom_handling))] - fn allocate_in(capacity: usize, init: AllocInit, alloc: A) -> Self { - // Don't allocate here because `Drop` will not deallocate when `capacity` is 0. - if T::IS_ZST || capacity == 0 { - Self::new_in(alloc) - } else { - // We avoid `unwrap_or_else` here because it bloats the amount of - // LLVM IR generated. - let layout = match Layout::array::<T>(capacity) { - Ok(layout) => layout, - Err(_) => capacity_overflow(), - }; - match alloc_guard(layout.size()) { - Ok(_) => {} - Err(_) => capacity_overflow(), - } - let result = match init { - AllocInit::Uninitialized => alloc.allocate(layout), - AllocInit::Zeroed => alloc.allocate_zeroed(layout), - }; - let ptr = match result { - Ok(ptr) => ptr, - Err(_) => handle_alloc_error(layout), - }; - - // Allocators currently return a `NonNull<[u8]>` whose length - // matches the size requested. If that ever changes, the capacity - // here should change to `ptr.len() / mem::size_of::<T>()`. - Self { - ptr: unsafe { Unique::new_unchecked(ptr.cast().as_ptr()) }, - cap: unsafe { Cap(capacity) }, - alloc, - } - } - } - - fn try_allocate_in(capacity: usize, init: AllocInit, alloc: A) -> Result<Self, TryReserveError> { - // Don't allocate here because `Drop` will not deallocate when `capacity` is 0. - if T::IS_ZST || capacity == 0 { - return Ok(Self::new_in(alloc)); - } - - let layout = Layout::array::<T>(capacity).map_err(|_| CapacityOverflow)?; - alloc_guard(layout.size())?; - let result = match init { - AllocInit::Uninitialized => alloc.allocate(layout), - AllocInit::Zeroed => alloc.allocate_zeroed(layout), - }; - let ptr = result.map_err(|_| AllocError { layout, non_exhaustive: () })?; - - // Allocators currently return a `NonNull<[u8]>` whose length - // matches the size requested. If that ever changes, the capacity - // here should change to `ptr.len() / mem::size_of::<T>()`. - Ok(Self { - ptr: unsafe { Unique::new_unchecked(ptr.cast().as_ptr()) }, - cap: unsafe { Cap(capacity) }, - 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 unsafe fn from_raw_parts_in(ptr: *mut T, capacity: usize, alloc: A) -> Self { - let cap = if T::IS_ZST { Cap::ZERO } else { unsafe { Cap(capacity) } }; - Self { ptr: unsafe { Unique::new_unchecked(ptr) }, cap, alloc } - } - - /// 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 fn ptr(&self) -> *mut T { - self.ptr.as_ptr() - } - - /// Gets the capacity of the allocation. - /// - /// This will always be `usize::MAX` if `T` is zero-sized. - #[inline(always)] - pub fn capacity(&self) -> usize { - if T::IS_ZST { usize::MAX } else { self.cap.0 } - } - - /// Returns a shared reference to the allocator backing this `RawVec`. - pub fn allocator(&self) -> &A { - &self.alloc - } - - fn current_memory(&self) -> Option<(NonNull<u8>, Layout)> { - if T::IS_ZST || self.cap.0 == 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. - let _: () = const { assert!(mem::size_of::<T>() % mem::align_of::<T>() == 0) }; - unsafe { - let align = mem::align_of::<T>(); - let size = mem::size_of::<T>().unchecked_mul(self.cap.0); - let layout = Layout::from_size_align_unchecked(size, align); - Some((self.ptr.cast().into(), layout)) - } - } - } - - /// 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] - pub fn reserve(&mut self, len: usize, additional: usize) { - // 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<T, A: Allocator>( - slf: &mut RawVec<T, A>, - len: usize, - additional: usize, - ) { - handle_reserve(slf.grow_amortized(len, additional)); - } - - if self.needs_to_grow(len, additional) { - do_reserve_and_handle(self, len, additional); - } - } - - /// A specialized version of `reserve()` used only by the hot and - /// oft-instantiated `Vec::push()`, which does its own capacity check. - #[cfg(not(no_global_oom_handling))] - #[inline(never)] - pub fn reserve_for_push(&mut self, len: usize) { - handle_reserve(self.grow_amortized(len, 1)); - } - - /// The same as `reserve`, but returns on errors instead of panicking or aborting. - pub fn try_reserve(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> { - if self.needs_to_grow(len, additional) { - self.grow_amortized(len, additional)?; - } - unsafe { - // Inform the optimizer that the reservation has succeeded or wasn't needed - core::intrinsics::assume(!self.needs_to_grow(len, additional)); - } - Ok(()) - } - - /// The same as `reserve_for_push`, but returns on errors instead of panicking or aborting. - #[inline(never)] - pub fn try_reserve_for_push(&mut self, len: usize) -> Result<(), TryReserveError> { - self.grow_amortized(len, 1) - } - - /// 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))] - pub fn reserve_exact(&mut self, len: usize, additional: usize) { - handle_reserve(self.try_reserve_exact(len, additional)); - } - - /// The same as `reserve_exact`, but returns on errors instead of panicking or aborting. - pub fn try_reserve_exact( - &mut self, - len: usize, - additional: usize, - ) -> Result<(), TryReserveError> { - if self.needs_to_grow(len, additional) { - self.grow_exact(len, additional)?; - } - unsafe { - // Inform the optimizer that the reservation has succeeded or wasn't needed - core::intrinsics::assume(!self.needs_to_grow(len, additional)); - } - Ok(()) - } - - /// 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))] - pub fn shrink_to_fit(&mut self, cap: usize) { - handle_reserve(self.shrink(cap)); - } -} - -impl<T, A: Allocator> RawVec<T, A> { - /// Returns if the buffer needs to grow to fulfill the needed extra capacity. - /// Mainly used to make inlining reserve-calls possible without inlining `grow`. - fn needs_to_grow(&self, len: usize, additional: usize) -> bool { - additional > self.capacity().wrapping_sub(len) - } - - /// # Safety: - /// - /// `cap` must not exceed `isize::MAX`. - 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() / mem::size_of::<T>()`. - self.ptr = unsafe { Unique::new_unchecked(ptr.cast().as_ptr()) }; - self.cap = unsafe { Cap(cap) }; - } - - // This method is usually instantiated many times. So we want it to be as - // small as possible, to improve compile times. But we also want as much of - // its contents to be statically computable as possible, to make the - // generated code run faster. Therefore, this method is carefully written - // so that all of the code that depends on `T` is within it, while as much - // of the code that doesn't depend on `T` as possible is in functions that - // are non-generic over `T`. - fn grow_amortized(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> { - // This is ensured by the calling contexts. - debug_assert!(additional > 0); - - if T::IS_ZST { - // 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.0 * 2, required_cap); - let cap = cmp::max(Self::MIN_NON_ZERO_CAP, cap); - - let new_layout = Layout::array::<T>(cap); - - // `finish_grow` is non-generic over `T`. - let ptr = finish_grow(new_layout, self.current_memory(), &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(()) - } - - // The constraints on this method are much the same as those on - // `grow_amortized`, but this method is usually instantiated less often so - // it's less critical. - fn grow_exact(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> { - if T::IS_ZST { - // 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::<T>(cap); - - // `finish_grow` is non-generic over `T`. - let ptr = finish_grow(new_layout, self.current_memory(), &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))] - fn shrink(&mut self, cap: usize) -> Result<(), TryReserveError> { - assert!(cap <= self.capacity(), "Tried to shrink to a larger capacity"); - - let (ptr, layout) = if let Some(mem) = self.current_memory() { mem } else { return Ok(()) }; - // See current_memory() why this assert is here - let _: () = const { assert!(mem::size_of::<T>() % mem::align_of::<T>() == 0) }; - - // 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 = Unique::dangling(); - self.cap = Cap::ZERO; - } else { - let ptr = unsafe { - // `Layout::array` cannot overflow here because it would have - // overflowed earlier when capacity was larger. - let new_size = mem::size_of::<T>().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(()) - } -} - -// This function is outside `RawVec` to minimize compile times. See the comment -// above `RawVec::grow_amortized` for details. (The `A` parameter isn't -// significant, because the number of different `A` types seen in practice is -// much smaller than the number of `T` types.) -#[inline(never)] -fn finish_grow<A>( - new_layout: Result<Layout, LayoutError>, - current_memory: Option<(NonNull<u8>, Layout)>, - alloc: &mut A, -) -> Result<NonNull<[u8]>, TryReserveError> -where - A: Allocator, -{ - // Check for the error here to minimize the size of `RawVec::grow_*`. - let new_layout = new_layout.map_err(|_| CapacityOverflow)?; - - 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 - intrinsics::assume(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()) -} - -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) { - if let Some((ptr, layout)) = self.current_memory() { - unsafe { self.alloc.deallocate(ptr, layout) } - } - } -} - -// Central function for reserve error handling. -#[cfg(not(no_global_oom_handling))] -#[inline] -fn handle_reserve(result: Result<(), TryReserveError>) { - match result.map_err(|e| e.kind()) { - Err(CapacityOverflow) => capacity_overflow(), - Err(AllocError { layout, .. }) => handle_alloc_error(layout), - Ok(()) => { /* yay */ } - } -} - -// 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(()) - } -} - -// 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))] -fn capacity_overflow() -> ! { - panic!("capacity overflow"); -} |