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527 lines
20 KiB
527 lines
20 KiB
// SPDX-License-Identifier: Apache-2.0 OR MIT |
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#![unstable(feature = "raw_vec_internals", reason = "unstable const warnings", issue = "none")] |
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use core::alloc::LayoutError; |
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use core::cmp; |
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use core::intrinsics; |
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use core::mem::{self, ManuallyDrop, MaybeUninit}; |
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use core::ops::Drop; |
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use core::ptr::{self, NonNull, Unique}; |
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use core::slice; |
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#[cfg(not(no_global_oom_handling))] |
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use crate::alloc::handle_alloc_error; |
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use crate::alloc::{Allocator, Global, Layout}; |
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use crate::boxed::Box; |
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use crate::collections::TryReserveError; |
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use crate::collections::TryReserveErrorKind::*; |
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#[cfg(test)] |
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mod tests; |
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#[cfg(not(no_global_oom_handling))] |
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enum AllocInit { |
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/// The contents of the new memory are uninitialized. |
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Uninitialized, |
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/// The new memory is guaranteed to be zeroed. |
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Zeroed, |
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} |
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/// A low-level utility for more ergonomically allocating, reallocating, and deallocating |
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/// a buffer of memory on the heap without having to worry about all the corner cases |
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/// involved. This type is excellent for building your own data structures like Vec and VecDeque. |
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/// In particular: |
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/// |
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/// * Produces `Unique::dangling()` on zero-sized types. |
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/// * Produces `Unique::dangling()` on zero-length allocations. |
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/// * Avoids freeing `Unique::dangling()`. |
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/// * Catches all overflows in capacity computations (promotes them to "capacity overflow" panics). |
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/// * Guards against 32-bit systems allocating more than isize::MAX bytes. |
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/// * Guards against overflowing your length. |
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/// * Calls `handle_alloc_error` for fallible allocations. |
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/// * Contains a `ptr::Unique` and thus endows the user with all related benefits. |
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/// * Uses the excess returned from the allocator to use the largest available capacity. |
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/// |
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/// This type does not in anyway inspect the memory that it manages. When dropped it *will* |
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/// free its memory, but it *won't* try to drop its contents. It is up to the user of `RawVec` |
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/// to handle the actual things *stored* inside of a `RawVec`. |
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/// |
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/// Note that the excess of a zero-sized types is always infinite, so `capacity()` always returns |
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/// `usize::MAX`. This means that you need to be careful when round-tripping this type with a |
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/// `Box<[T]>`, since `capacity()` won't yield the length. |
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#[allow(missing_debug_implementations)] |
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pub(crate) struct RawVec<T, A: Allocator = Global> { |
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ptr: Unique<T>, |
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cap: usize, |
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alloc: A, |
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} |
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impl<T> RawVec<T, Global> { |
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/// HACK(Centril): This exists because stable `const fn` can only call stable `const fn`, so |
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/// they cannot call `Self::new()`. |
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/// |
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/// If you change `RawVec<T>::new` or dependencies, please take care to not introduce anything |
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/// that would truly const-call something unstable. |
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pub const NEW: Self = Self::new(); |
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/// Creates the biggest possible `RawVec` (on the system heap) |
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/// without allocating. If `T` has positive size, then this makes a |
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/// `RawVec` with capacity `0`. If `T` is zero-sized, then it makes a |
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/// `RawVec` with capacity `usize::MAX`. Useful for implementing |
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/// delayed allocation. |
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#[must_use] |
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pub const fn new() -> Self { |
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Self::new_in(Global) |
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} |
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/// Creates a `RawVec` (on the system heap) with exactly the |
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/// capacity and alignment requirements for a `[T; capacity]`. This is |
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/// equivalent to calling `RawVec::new` when `capacity` is `0` or `T` is |
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/// zero-sized. Note that if `T` is zero-sized this means you will |
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/// *not* get a `RawVec` with the requested capacity. |
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/// |
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/// # Panics |
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/// |
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/// Panics if the requested capacity exceeds `isize::MAX` bytes. |
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/// |
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/// # Aborts |
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/// |
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/// Aborts on OOM. |
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#[cfg(not(any(no_global_oom_handling, test)))] |
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#[must_use] |
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#[inline] |
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pub fn with_capacity(capacity: usize) -> Self { |
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Self::with_capacity_in(capacity, Global) |
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} |
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/// Like `with_capacity`, but guarantees the buffer is zeroed. |
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#[cfg(not(any(no_global_oom_handling, test)))] |
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#[must_use] |
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#[inline] |
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pub fn with_capacity_zeroed(capacity: usize) -> Self { |
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Self::with_capacity_zeroed_in(capacity, Global) |
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} |
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} |
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impl<T, A: Allocator> RawVec<T, A> { |
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// Tiny Vecs are dumb. Skip to: |
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// - 8 if the element size is 1, because any heap allocators is likely |
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// to round up a request of less than 8 bytes to at least 8 bytes. |
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// - 4 if elements are moderate-sized (<= 1 KiB). |
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// - 1 otherwise, to avoid wasting too much space for very short Vecs. |
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pub(crate) const MIN_NON_ZERO_CAP: usize = if mem::size_of::<T>() == 1 { |
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8 |
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} else if mem::size_of::<T>() <= 1024 { |
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4 |
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} else { |
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1 |
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}; |
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/// Like `new`, but parameterized over the choice of allocator for |
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/// the returned `RawVec`. |
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pub const fn new_in(alloc: A) -> Self { |
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// `cap: 0` means "unallocated". zero-sized types are ignored. |
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Self { ptr: Unique::dangling(), cap: 0, alloc } |
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} |
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/// Like `with_capacity`, but parameterized over the choice of |
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/// allocator for the returned `RawVec`. |
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#[cfg(not(no_global_oom_handling))] |
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#[inline] |
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pub fn with_capacity_in(capacity: usize, alloc: A) -> Self { |
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Self::allocate_in(capacity, AllocInit::Uninitialized, alloc) |
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} |
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/// Like `with_capacity_zeroed`, but parameterized over the choice |
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/// of allocator for the returned `RawVec`. |
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#[cfg(not(no_global_oom_handling))] |
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#[inline] |
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pub fn with_capacity_zeroed_in(capacity: usize, alloc: A) -> Self { |
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Self::allocate_in(capacity, AllocInit::Zeroed, alloc) |
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} |
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/// Converts the entire buffer into `Box<[MaybeUninit<T>]>` with the specified `len`. |
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/// |
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/// Note that this will correctly reconstitute any `cap` changes |
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/// that may have been performed. (See description of type for details.) |
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/// |
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/// # Safety |
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/// |
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/// * `len` must be greater than or equal to the most recently requested capacity, and |
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/// * `len` must be less than or equal to `self.capacity()`. |
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/// |
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/// Note, that the requested capacity and `self.capacity()` could differ, as |
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/// an allocator could overallocate and return a greater memory block than requested. |
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pub unsafe fn into_box(self, len: usize) -> Box<[MaybeUninit<T>], A> { |
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// Sanity-check one half of the safety requirement (we cannot check the other half). |
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debug_assert!( |
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len <= self.capacity(), |
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"`len` must be smaller than or equal to `self.capacity()`" |
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); |
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let me = ManuallyDrop::new(self); |
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unsafe { |
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let slice = slice::from_raw_parts_mut(me.ptr() as *mut MaybeUninit<T>, len); |
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Box::from_raw_in(slice, ptr::read(&me.alloc)) |
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} |
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} |
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#[cfg(not(no_global_oom_handling))] |
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fn allocate_in(capacity: usize, init: AllocInit, alloc: A) -> Self { |
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// Don't allocate here because `Drop` will not deallocate when `capacity` is 0. |
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if mem::size_of::<T>() == 0 || capacity == 0 { |
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Self::new_in(alloc) |
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} else { |
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// We avoid `unwrap_or_else` here because it bloats the amount of |
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// LLVM IR generated. |
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let layout = match Layout::array::<T>(capacity) { |
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Ok(layout) => layout, |
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Err(_) => capacity_overflow(), |
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}; |
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match alloc_guard(layout.size()) { |
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Ok(_) => {} |
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Err(_) => capacity_overflow(), |
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} |
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let result = match init { |
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AllocInit::Uninitialized => alloc.allocate(layout), |
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AllocInit::Zeroed => alloc.allocate_zeroed(layout), |
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}; |
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let ptr = match result { |
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Ok(ptr) => ptr, |
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Err(_) => handle_alloc_error(layout), |
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}; |
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// Allocators currently return a `NonNull<[u8]>` whose length |
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// matches the size requested. If that ever changes, the capacity |
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// here should change to `ptr.len() / mem::size_of::<T>()`. |
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Self { |
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ptr: unsafe { Unique::new_unchecked(ptr.cast().as_ptr()) }, |
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cap: capacity, |
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alloc, |
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} |
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} |
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} |
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/// Reconstitutes a `RawVec` from a pointer, capacity, and allocator. |
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/// |
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/// # Safety |
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/// |
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/// The `ptr` must be allocated (via the given allocator `alloc`), and with the given |
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/// `capacity`. |
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/// The `capacity` cannot exceed `isize::MAX` for sized types. (only a concern on 32-bit |
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/// systems). ZST vectors may have a capacity up to `usize::MAX`. |
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/// If the `ptr` and `capacity` come from a `RawVec` created via `alloc`, then this is |
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/// guaranteed. |
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#[inline] |
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pub unsafe fn from_raw_parts_in(ptr: *mut T, capacity: usize, alloc: A) -> Self { |
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Self { ptr: unsafe { Unique::new_unchecked(ptr) }, cap: capacity, alloc } |
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} |
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/// Gets a raw pointer to the start of the allocation. Note that this is |
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/// `Unique::dangling()` if `capacity == 0` or `T` is zero-sized. In the former case, you must |
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/// be careful. |
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#[inline] |
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pub fn ptr(&self) -> *mut T { |
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self.ptr.as_ptr() |
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} |
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/// Gets the capacity of the allocation. |
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/// |
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/// This will always be `usize::MAX` if `T` is zero-sized. |
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#[inline(always)] |
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pub fn capacity(&self) -> usize { |
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if mem::size_of::<T>() == 0 { usize::MAX } else { self.cap } |
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} |
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/// Returns a shared reference to the allocator backing this `RawVec`. |
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pub fn allocator(&self) -> &A { |
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&self.alloc |
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} |
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fn current_memory(&self) -> Option<(NonNull<u8>, Layout)> { |
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if mem::size_of::<T>() == 0 || self.cap == 0 { |
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None |
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} else { |
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// We have an allocated chunk of memory, so we can bypass runtime |
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// checks to get our current layout. |
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unsafe { |
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let layout = Layout::array::<T>(self.cap).unwrap_unchecked(); |
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Some((self.ptr.cast().into(), layout)) |
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} |
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} |
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} |
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/// Ensures that the buffer contains at least enough space to hold `len + |
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/// additional` elements. If it doesn't already have enough capacity, will |
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/// reallocate enough space plus comfortable slack space to get amortized |
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/// *O*(1) behavior. Will limit this behavior if it would needlessly cause |
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/// itself to panic. |
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/// |
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/// If `len` exceeds `self.capacity()`, this may fail to actually allocate |
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/// the requested space. This is not really unsafe, but the unsafe |
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/// code *you* write that relies on the behavior of this function may break. |
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/// |
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/// This is ideal for implementing a bulk-push operation like `extend`. |
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/// |
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/// # Panics |
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/// |
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/// Panics if the new capacity exceeds `isize::MAX` bytes. |
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/// |
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/// # Aborts |
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/// |
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/// Aborts on OOM. |
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#[cfg(not(no_global_oom_handling))] |
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#[inline] |
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pub fn reserve(&mut self, len: usize, additional: usize) { |
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// Callers expect this function to be very cheap when there is already sufficient capacity. |
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// Therefore, we move all the resizing and error-handling logic from grow_amortized and |
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// handle_reserve behind a call, while making sure that this function is likely to be |
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// inlined as just a comparison and a call if the comparison fails. |
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#[cold] |
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fn do_reserve_and_handle<T, A: Allocator>( |
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slf: &mut RawVec<T, A>, |
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len: usize, |
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additional: usize, |
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) { |
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handle_reserve(slf.grow_amortized(len, additional)); |
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} |
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if self.needs_to_grow(len, additional) { |
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do_reserve_and_handle(self, len, additional); |
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} |
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} |
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/// A specialized version of `reserve()` used only by the hot and |
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/// oft-instantiated `Vec::push()`, which does its own capacity check. |
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#[cfg(not(no_global_oom_handling))] |
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#[inline(never)] |
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pub fn reserve_for_push(&mut self, len: usize) { |
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handle_reserve(self.grow_amortized(len, 1)); |
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} |
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/// The same as `reserve`, but returns on errors instead of panicking or aborting. |
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pub fn try_reserve(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> { |
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if self.needs_to_grow(len, additional) { |
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self.grow_amortized(len, additional) |
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} else { |
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Ok(()) |
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} |
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} |
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/// The same as `reserve_for_push`, but returns on errors instead of panicking or aborting. |
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#[inline(never)] |
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pub fn try_reserve_for_push(&mut self, len: usize) -> Result<(), TryReserveError> { |
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self.grow_amortized(len, 1) |
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} |
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/// Ensures that the buffer contains at least enough space to hold `len + |
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/// additional` elements. If it doesn't already, will reallocate the |
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/// minimum possible amount of memory necessary. Generally this will be |
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/// exactly the amount of memory necessary, but in principle the allocator |
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/// is free to give back more than we asked for. |
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/// |
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/// If `len` exceeds `self.capacity()`, this may fail to actually allocate |
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/// the requested space. This is not really unsafe, but the unsafe code |
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/// *you* write that relies on the behavior of this function may break. |
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/// |
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/// # Panics |
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/// |
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/// Panics if the new capacity exceeds `isize::MAX` bytes. |
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/// |
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/// # Aborts |
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/// |
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/// Aborts on OOM. |
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#[cfg(not(no_global_oom_handling))] |
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pub fn reserve_exact(&mut self, len: usize, additional: usize) { |
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handle_reserve(self.try_reserve_exact(len, additional)); |
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} |
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/// The same as `reserve_exact`, but returns on errors instead of panicking or aborting. |
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pub fn try_reserve_exact( |
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&mut self, |
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len: usize, |
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additional: usize, |
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) -> Result<(), TryReserveError> { |
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if self.needs_to_grow(len, additional) { self.grow_exact(len, additional) } else { Ok(()) } |
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} |
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/// Shrinks the buffer down to the specified capacity. If the given amount |
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/// is 0, actually completely deallocates. |
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/// |
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/// # Panics |
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/// |
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/// Panics if the given amount is *larger* than the current capacity. |
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/// |
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/// # Aborts |
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/// |
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/// Aborts on OOM. |
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#[cfg(not(no_global_oom_handling))] |
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pub fn shrink_to_fit(&mut self, cap: usize) { |
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handle_reserve(self.shrink(cap)); |
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} |
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} |
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impl<T, A: Allocator> RawVec<T, A> { |
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/// Returns if the buffer needs to grow to fulfill the needed extra capacity. |
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/// Mainly used to make inlining reserve-calls possible without inlining `grow`. |
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fn needs_to_grow(&self, len: usize, additional: usize) -> bool { |
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additional > self.capacity().wrapping_sub(len) |
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} |
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fn set_ptr_and_cap(&mut self, ptr: NonNull<[u8]>, cap: usize) { |
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// Allocators currently return a `NonNull<[u8]>` whose length matches |
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// the size requested. If that ever changes, the capacity here should |
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// change to `ptr.len() / mem::size_of::<T>()`. |
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self.ptr = unsafe { Unique::new_unchecked(ptr.cast().as_ptr()) }; |
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self.cap = cap; |
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} |
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// This method is usually instantiated many times. So we want it to be as |
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// small as possible, to improve compile times. But we also want as much of |
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// its contents to be statically computable as possible, to make the |
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// generated code run faster. Therefore, this method is carefully written |
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// so that all of the code that depends on `T` is within it, while as much |
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// of the code that doesn't depend on `T` as possible is in functions that |
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// are non-generic over `T`. |
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fn grow_amortized(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> { |
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// This is ensured by the calling contexts. |
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debug_assert!(additional > 0); |
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if mem::size_of::<T>() == 0 { |
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// Since we return a capacity of `usize::MAX` when `elem_size` is |
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// 0, getting to here necessarily means the `RawVec` is overfull. |
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return Err(CapacityOverflow.into()); |
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} |
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// Nothing we can really do about these checks, sadly. |
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let required_cap = len.checked_add(additional).ok_or(CapacityOverflow)?; |
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// This guarantees exponential growth. The doubling cannot overflow |
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// because `cap <= isize::MAX` and the type of `cap` is `usize`. |
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let cap = cmp::max(self.cap * 2, required_cap); |
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let cap = cmp::max(Self::MIN_NON_ZERO_CAP, cap); |
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let new_layout = Layout::array::<T>(cap); |
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// `finish_grow` is non-generic over `T`. |
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let ptr = finish_grow(new_layout, self.current_memory(), &mut self.alloc)?; |
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self.set_ptr_and_cap(ptr, cap); |
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Ok(()) |
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} |
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// The constraints on this method are much the same as those on |
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// `grow_amortized`, but this method is usually instantiated less often so |
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// it's less critical. |
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fn grow_exact(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> { |
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if mem::size_of::<T>() == 0 { |
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// Since we return a capacity of `usize::MAX` when the type size is |
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// 0, getting to here necessarily means the `RawVec` is overfull. |
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return Err(CapacityOverflow.into()); |
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} |
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let cap = len.checked_add(additional).ok_or(CapacityOverflow)?; |
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let new_layout = Layout::array::<T>(cap); |
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// `finish_grow` is non-generic over `T`. |
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let ptr = finish_grow(new_layout, self.current_memory(), &mut self.alloc)?; |
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self.set_ptr_and_cap(ptr, cap); |
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Ok(()) |
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} |
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#[allow(dead_code)] |
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fn shrink(&mut self, cap: usize) -> Result<(), TryReserveError> { |
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assert!(cap <= self.capacity(), "Tried to shrink to a larger capacity"); |
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let (ptr, layout) = if let Some(mem) = self.current_memory() { mem } else { return Ok(()) }; |
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let ptr = unsafe { |
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// `Layout::array` cannot overflow here because it would have |
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// overflowed earlier when capacity was larger. |
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let new_layout = Layout::array::<T>(cap).unwrap_unchecked(); |
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self.alloc |
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.shrink(ptr, layout, new_layout) |
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.map_err(|_| AllocError { layout: new_layout, non_exhaustive: () })? |
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}; |
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self.set_ptr_and_cap(ptr, cap); |
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Ok(()) |
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} |
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} |
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// This function is outside `RawVec` to minimize compile times. See the comment |
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// above `RawVec::grow_amortized` for details. (The `A` parameter isn't |
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// significant, because the number of different `A` types seen in practice is |
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// much smaller than the number of `T` types.) |
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#[inline(never)] |
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fn finish_grow<A>( |
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new_layout: Result<Layout, LayoutError>, |
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current_memory: Option<(NonNull<u8>, Layout)>, |
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alloc: &mut A, |
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) -> Result<NonNull<[u8]>, TryReserveError> |
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where |
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A: Allocator, |
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{ |
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// Check for the error here to minimize the size of `RawVec::grow_*`. |
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let new_layout = new_layout.map_err(|_| CapacityOverflow)?; |
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alloc_guard(new_layout.size())?; |
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let memory = if let Some((ptr, old_layout)) = current_memory { |
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debug_assert_eq!(old_layout.align(), new_layout.align()); |
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unsafe { |
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// The allocator checks for alignment equality |
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intrinsics::assume(old_layout.align() == new_layout.align()); |
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alloc.grow(ptr, old_layout, new_layout) |
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} |
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} else { |
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alloc.allocate(new_layout) |
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}; |
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memory.map_err(|_| AllocError { layout: new_layout, non_exhaustive: () }.into()) |
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} |
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unsafe impl<#[may_dangle] T, A: Allocator> Drop for RawVec<T, A> { |
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/// Frees the memory owned by the `RawVec` *without* trying to drop its contents. |
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fn drop(&mut self) { |
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if let Some((ptr, layout)) = self.current_memory() { |
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unsafe { self.alloc.deallocate(ptr, layout) } |
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} |
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} |
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} |
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// Central function for reserve error handling. |
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#[cfg(not(no_global_oom_handling))] |
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#[inline] |
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fn handle_reserve(result: Result<(), TryReserveError>) { |
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match result.map_err(|e| e.kind()) { |
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Err(CapacityOverflow) => capacity_overflow(), |
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Err(AllocError { layout, .. }) => handle_alloc_error(layout), |
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Ok(()) => { /* yay */ } |
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} |
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} |
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// We need to guarantee the following: |
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// * We don't ever allocate `> isize::MAX` byte-size objects. |
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// * We don't overflow `usize::MAX` and actually allocate too little. |
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// |
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// On 64-bit we just need to check for overflow since trying to allocate |
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// `> isize::MAX` bytes will surely fail. On 32-bit and 16-bit we need to add |
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// an extra guard for this in case we're running on a platform which can use |
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// all 4GB in user-space, e.g., PAE or x32. |
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|
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#[inline] |
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fn alloc_guard(alloc_size: usize) -> Result<(), TryReserveError> { |
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if usize::BITS < 64 && alloc_size > isize::MAX as usize { |
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Err(CapacityOverflow.into()) |
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} else { |
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Ok(()) |
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} |
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} |
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|
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// One central function responsible for reporting capacity overflows. This'll |
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// ensure that the code generation related to these panics is minimal as there's |
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// only one location which panics rather than a bunch throughout the module. |
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#[cfg(not(no_global_oom_handling))] |
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fn capacity_overflow() -> ! { |
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panic!("capacity overflow"); |
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}
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