| #![unstable(feature = "raw_vec_internals", reason = "implementation detail", issue = "none")] |
| #![doc(hidden)] |
| |
| use core::alloc::LayoutErr; |
| use core::cmp; |
| use core::intrinsics; |
| use core::mem::{self, ManuallyDrop, MaybeUninit}; |
| use core::ops::Drop; |
| use core::ptr::{NonNull, Unique}; |
| use core::slice; |
| |
| use crate::alloc::{handle_alloc_error, AllocRef, Global, Layout}; |
| use crate::boxed::Box; |
| use crate::collections::TryReserveError::{self, *}; |
| |
| #[cfg(test)] |
| mod tests; |
| |
| enum AllocInit { |
| /// The contents of the new memory are uninitialized. |
| Uninitialized, |
| /// The new memory is guaranteed to be zeroed. |
| Zeroed, |
| } |
| |
| /// 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 struct RawVec<T, A: AllocRef = Global> { |
| ptr: Unique<T>, |
| cap: usize, |
| alloc: A, |
| } |
| |
| impl<T> RawVec<T, Global> { |
| /// HACK(Centril): This exists because `#[unstable]` `const fn`s needn't conform |
| /// to `min_const_fn` and so they cannot be called in `min_const_fn`s either. |
| /// |
| /// If you change `RawVec<T>::new` or dependencies, please take care to not |
| /// introduce anything that would truly violate `min_const_fn`. |
| /// |
| /// NOTE: We could avoid this hack and check conformance with some |
| /// `#[rustc_force_min_const_fn]` attribute which requires conformance |
| /// with `min_const_fn` but does not necessarily allow calling it in |
| /// `stable(...) const fn` / user code not enabling `foo` when |
| /// `#[rustc_const_unstable(feature = "foo", issue = "01234")]` is present. |
| 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. |
| 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. |
| #[inline] |
| pub fn with_capacity(capacity: usize) -> Self { |
| Self::with_capacity_in(capacity, Global) |
| } |
| |
| /// Like `with_capacity`, but guarantees the buffer is zeroed. |
| #[inline] |
| pub fn with_capacity_zeroed(capacity: usize) -> Self { |
| Self::with_capacity_zeroed_in(capacity, Global) |
| } |
| |
| /// Reconstitutes a `RawVec` from a pointer and capacity. |
| /// |
| /// # Safety |
| /// |
| /// The `ptr` must be allocated (on the system heap), and with the given `capacity`. |
| /// The `capacity` cannot exceed `isize::MAX` for sized types. (only a concern on 32-bit |
| /// systems). ZST vectors may have a capacity up to `usize::MAX`. |
| /// If the `ptr` and `capacity` come from a `RawVec`, then this is guaranteed. |
| #[inline] |
| pub unsafe fn from_raw_parts(ptr: *mut T, capacity: usize) -> Self { |
| unsafe { Self::from_raw_parts_in(ptr, capacity, Global) } |
| } |
| |
| /// Converts a `Box<[T]>` into a `RawVec<T>`. |
| pub fn from_box(slice: Box<[T]>) -> Self { |
| unsafe { |
| let mut slice = ManuallyDrop::new(slice); |
| RawVec::from_raw_parts(slice.as_mut_ptr(), slice.len()) |
| } |
| } |
| |
| /// 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>]> { |
| // 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(slice) |
| } |
| } |
| } |
| |
| impl<T, A: AllocRef> RawVec<T, A> { |
| /// Like `new`, but parameterized over the choice of allocator for |
| /// the returned `RawVec`. |
| #[allow_internal_unstable(const_fn)] |
| pub const fn new_in(alloc: A) -> Self { |
| // `cap: 0` means "unallocated". zero-sized types are ignored. |
| Self { ptr: Unique::dangling(), cap: 0, alloc } |
| } |
| |
| /// Like `with_capacity`, but parameterized over the choice of |
| /// allocator for the returned `RawVec`. |
| #[inline] |
| pub fn with_capacity_in(capacity: usize, alloc: A) -> Self { |
| Self::allocate_in(capacity, AllocInit::Uninitialized, alloc) |
| } |
| |
| /// Like `with_capacity_zeroed`, but parameterized over the choice |
| /// of allocator for the returned `RawVec`. |
| #[inline] |
| pub fn with_capacity_zeroed_in(capacity: usize, alloc: A) -> Self { |
| Self::allocate_in(capacity, AllocInit::Zeroed, alloc) |
| } |
| |
| fn allocate_in(capacity: usize, init: AllocInit, alloc: A) -> Self { |
| if mem::size_of::<T>() == 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.alloc(layout), |
| AllocInit::Zeroed => alloc.alloc_zeroed(layout), |
| }; |
| let ptr = match result { |
| Ok(ptr) => ptr, |
| Err(_) => handle_alloc_error(layout), |
| }; |
| |
| Self { |
| ptr: unsafe { Unique::new_unchecked(ptr.cast().as_ptr()) }, |
| cap: Self::capacity_from_bytes(ptr.len()), |
| 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). ZST vectors may have a capacity up to `usize::MAX`. |
| /// 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 { |
| Self { ptr: unsafe { Unique::new_unchecked(ptr) }, cap: capacity, 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. |
| 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 mem::size_of::<T>() == 0 { usize::MAX } else { self.cap } |
| } |
| |
| /// Returns a shared reference to the allocator backing this `RawVec`. |
| pub fn alloc(&self) -> &A { |
| &self.alloc |
| } |
| |
| /// Returns a mutable reference to the allocator backing this `RawVec`. |
| pub fn alloc_mut(&mut self) -> &mut A { |
| &mut self.alloc |
| } |
| |
| fn current_memory(&self) -> Option<(NonNull<u8>, Layout)> { |
| if mem::size_of::<T>() == 0 || self.cap == 0 { |
| None |
| } else { |
| // We have an allocated chunk of memory, so we can bypass runtime |
| // checks to get our current layout. |
| unsafe { |
| let align = mem::align_of::<T>(); |
| let size = mem::size_of::<T>() * self.cap; |
| 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. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// # #![feature(raw_vec_internals)] |
| /// # extern crate alloc; |
| /// # use std::ptr; |
| /// # use alloc::raw_vec::RawVec; |
| /// struct MyVec<T> { |
| /// buf: RawVec<T>, |
| /// len: usize, |
| /// } |
| /// |
| /// impl<T: Clone> MyVec<T> { |
| /// pub fn push_all(&mut self, elems: &[T]) { |
| /// self.buf.reserve(self.len, elems.len()); |
| /// // reserve would have aborted or panicked if the len exceeded |
| /// // `isize::MAX` so this is safe to do unchecked now. |
| /// for x in elems { |
| /// unsafe { |
| /// ptr::write(self.buf.ptr().add(self.len), x.clone()); |
| /// } |
| /// self.len += 1; |
| /// } |
| /// } |
| /// } |
| /// # fn main() { |
| /// # let mut vector = MyVec { buf: RawVec::new(), len: 0 }; |
| /// # vector.push_all(&[1, 3, 5, 7, 9]); |
| /// # } |
| /// ``` |
| pub fn reserve(&mut self, len: usize, additional: usize) { |
| handle_reserve(self.try_reserve(len, additional)); |
| } |
| |
| /// 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) |
| } else { |
| Ok(()) |
| } |
| } |
| |
| /// 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. |
| 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) } else { Ok(()) } |
| } |
| |
| /// Shrinks the allocation down to the specified amount. 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. |
| pub fn shrink_to_fit(&mut self, amount: usize) { |
| handle_reserve(self.shrink(amount)); |
| } |
| } |
| |
| impl<T, A: AllocRef> 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) |
| } |
| |
| fn capacity_from_bytes(excess: usize) -> usize { |
| debug_assert_ne!(mem::size_of::<T>(), 0); |
| excess / mem::size_of::<T>() |
| } |
| |
| fn set_ptr(&mut self, ptr: NonNull<[u8]>) { |
| self.ptr = unsafe { Unique::new_unchecked(ptr.cast().as_ptr()) }; |
| self.cap = Self::capacity_from_bytes(ptr.len()); |
| } |
| |
| // 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 mem::size_of::<T>() == 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); |
| } |
| |
| // 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 * 2, required_cap); |
| |
| // 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. |
| // Note that `min_non_zero_cap` is computed statically. |
| let elem_size = mem::size_of::<T>(); |
| let min_non_zero_cap = if elem_size == 1 { |
| 8 |
| } else if elem_size <= 1024 { |
| 4 |
| } else { |
| 1 |
| }; |
| let cap = cmp::max(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)?; |
| self.set_ptr(ptr); |
| 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 mem::size_of::<T>() == 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); |
| } |
| |
| 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)?; |
| self.set_ptr(ptr); |
| Ok(()) |
| } |
| |
| fn shrink(&mut self, amount: usize) -> Result<(), TryReserveError> { |
| assert!(amount <= self.capacity(), "Tried to shrink to a larger capacity"); |
| |
| let (ptr, layout) = if let Some(mem) = self.current_memory() { mem } else { return Ok(()) }; |
| let new_size = amount * mem::size_of::<T>(); |
| |
| let ptr = unsafe { |
| let new_layout = Layout::from_size_align_unchecked(new_size, layout.align()); |
| self.alloc.shrink(ptr, layout, new_layout).map_err(|_| TryReserveError::AllocError { |
| layout: new_layout, |
| non_exhaustive: (), |
| })? |
| }; |
| self.set_ptr(ptr); |
| 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.) |
| fn finish_grow<A>( |
| new_layout: Result<Layout, LayoutErr>, |
| current_memory: Option<(NonNull<u8>, Layout)>, |
| alloc: &mut A, |
| ) -> Result<NonNull<[u8]>, TryReserveError> |
| where |
| A: AllocRef, |
| { |
| // 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.alloc(new_layout) |
| }; |
| |
| memory.map_err(|_| AllocError { layout: new_layout, non_exhaustive: () }) |
| } |
| |
| unsafe impl<#[may_dangle] T, A: AllocRef> 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.dealloc(ptr, layout) } |
| } |
| } |
| } |
| |
| // Central function for reserve error handling. |
| #[inline] |
| fn handle_reserve(result: Result<(), TryReserveError>) { |
| match result { |
| 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) |
| } 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. |
| fn capacity_overflow() -> ! { |
| panic!("capacity overflow"); |
| } |