1 #![unstable(feature = "raw_vec_internals", reason = "unstable const warnings", issue = "none")]
3 use core::alloc::LayoutError;
6 use core::mem::{self, ManuallyDrop, MaybeUninit};
8 use core::ptr::{self, NonNull, Unique};
11 #[cfg(not(no_global_oom_handling))]
12 use crate::alloc::handle_alloc_error;
13 use crate::alloc::{Allocator, Global, Layout};
14 use crate::boxed::Box;
15 use crate::collections::TryReserveError;
16 use crate::collections::TryReserveErrorKind::*;
21 #[cfg(not(no_global_oom_handling))]
23 /// The contents of the new memory are uninitialized.
25 /// The new memory is guaranteed to be zeroed.
29 /// A low-level utility for more ergonomically allocating, reallocating, and deallocating
30 /// a buffer of memory on the heap without having to worry about all the corner cases
31 /// involved. This type is excellent for building your own data structures like Vec and VecDeque.
34 /// * Produces `Unique::dangling()` on zero-sized types.
35 /// * Produces `Unique::dangling()` on zero-length allocations.
36 /// * Avoids freeing `Unique::dangling()`.
37 /// * Catches all overflows in capacity computations (promotes them to "capacity overflow" panics).
38 /// * Guards against 32-bit systems allocating more than isize::MAX bytes.
39 /// * Guards against overflowing your length.
40 /// * Calls `handle_alloc_error` for fallible allocations.
41 /// * Contains a `ptr::Unique` and thus endows the user with all related benefits.
42 /// * Uses the excess returned from the allocator to use the largest available capacity.
44 /// This type does not in anyway inspect the memory that it manages. When dropped it *will*
45 /// free its memory, but it *won't* try to drop its contents. It is up to the user of `RawVec`
46 /// to handle the actual things *stored* inside of a `RawVec`.
48 /// Note that the excess of a zero-sized types is always infinite, so `capacity()` always returns
49 /// `usize::MAX`. This means that you need to be careful when round-tripping this type with a
50 /// `Box<[T]>`, since `capacity()` won't yield the length.
51 #[allow(missing_debug_implementations)]
52 pub(crate) struct RawVec<T, A: Allocator = Global> {
58 impl<T> RawVec<T, Global> {
59 /// HACK(Centril): This exists because stable `const fn` can only call stable `const fn`, so
60 /// they cannot call `Self::new()`.
62 /// If you change `RawVec<T>::new` or dependencies, please take care to not introduce anything
63 /// that would truly const-call something unstable.
64 pub const NEW: Self = Self::new();
66 /// Creates the biggest possible `RawVec` (on the system heap)
67 /// without allocating. If `T` has positive size, then this makes a
68 /// `RawVec` with capacity `0`. If `T` is zero-sized, then it makes a
69 /// `RawVec` with capacity `usize::MAX`. Useful for implementing
70 /// delayed allocation.
72 pub const fn new() -> Self {
76 /// Creates a `RawVec` (on the system heap) with exactly the
77 /// capacity and alignment requirements for a `[T; capacity]`. This is
78 /// equivalent to calling `RawVec::new` when `capacity` is `0` or `T` is
79 /// zero-sized. Note that if `T` is zero-sized this means you will
80 /// *not* get a `RawVec` with the requested capacity.
84 /// Panics if the requested capacity exceeds `isize::MAX` bytes.
89 #[cfg(not(any(no_global_oom_handling, test)))]
92 pub fn with_capacity(capacity: usize) -> Self {
93 Self::with_capacity_in(capacity, Global)
96 /// Like `with_capacity`, but guarantees the buffer is zeroed.
97 #[cfg(not(any(no_global_oom_handling, test)))]
100 pub fn with_capacity_zeroed(capacity: usize) -> Self {
101 Self::with_capacity_zeroed_in(capacity, Global)
105 impl<T, A: Allocator> RawVec<T, A> {
106 // Tiny Vecs are dumb. Skip to:
107 // - 8 if the element size is 1, because any heap allocators is likely
108 // to round up a request of less than 8 bytes to at least 8 bytes.
109 // - 4 if elements are moderate-sized (<= 1 KiB).
110 // - 1 otherwise, to avoid wasting too much space for very short Vecs.
111 pub(crate) const MIN_NON_ZERO_CAP: usize = if mem::size_of::<T>() == 1 {
113 } else if mem::size_of::<T>() <= 1024 {
119 /// Like `new`, but parameterized over the choice of allocator for
120 /// the returned `RawVec`.
121 #[rustc_allow_const_fn_unstable(const_fn)]
122 pub const fn new_in(alloc: A) -> Self {
123 // `cap: 0` means "unallocated". zero-sized types are ignored.
124 Self { ptr: Unique::dangling(), cap: 0, alloc }
127 /// Like `with_capacity`, but parameterized over the choice of
128 /// allocator for the returned `RawVec`.
129 #[cfg(not(no_global_oom_handling))]
131 pub fn with_capacity_in(capacity: usize, alloc: A) -> Self {
132 Self::allocate_in(capacity, AllocInit::Uninitialized, alloc)
135 /// Like `with_capacity_zeroed`, but parameterized over the choice
136 /// of allocator for the returned `RawVec`.
137 #[cfg(not(no_global_oom_handling))]
139 pub fn with_capacity_zeroed_in(capacity: usize, alloc: A) -> Self {
140 Self::allocate_in(capacity, AllocInit::Zeroed, alloc)
143 /// Converts the entire buffer into `Box<[MaybeUninit<T>]>` with the specified `len`.
145 /// Note that this will correctly reconstitute any `cap` changes
146 /// that may have been performed. (See description of type for details.)
150 /// * `len` must be greater than or equal to the most recently requested capacity, and
151 /// * `len` must be less than or equal to `self.capacity()`.
153 /// Note, that the requested capacity and `self.capacity()` could differ, as
154 /// an allocator could overallocate and return a greater memory block than requested.
155 pub unsafe fn into_box(self, len: usize) -> Box<[MaybeUninit<T>], A> {
156 // Sanity-check one half of the safety requirement (we cannot check the other half).
158 len <= self.capacity(),
159 "`len` must be smaller than or equal to `self.capacity()`"
162 let me = ManuallyDrop::new(self);
164 let slice = slice::from_raw_parts_mut(me.ptr() as *mut MaybeUninit<T>, len);
165 Box::from_raw_in(slice, ptr::read(&me.alloc))
169 #[cfg(not(no_global_oom_handling))]
170 fn allocate_in(capacity: usize, init: AllocInit, alloc: A) -> Self {
171 // Don't allocate here because `Drop` will not deallocate when `capacity` is 0.
172 if mem::size_of::<T>() == 0 || capacity == 0 {
175 // We avoid `unwrap_or_else` here because it bloats the amount of
176 // LLVM IR generated.
177 let layout = match Layout::array::<T>(capacity) {
178 Ok(layout) => layout,
179 Err(_) => capacity_overflow(),
181 match alloc_guard(layout.size()) {
183 Err(_) => capacity_overflow(),
185 let result = match init {
186 AllocInit::Uninitialized => alloc.allocate(layout),
187 AllocInit::Zeroed => alloc.allocate_zeroed(layout),
189 let ptr = match result {
191 Err(_) => handle_alloc_error(layout),
194 // Allocators currently return a `NonNull<[u8]>` whose length
195 // matches the size requested. If that ever changes, the capacity
196 // here should change to `ptr.len() / mem::size_of::<T>()`.
198 ptr: unsafe { Unique::new_unchecked(ptr.cast().as_ptr()) },
205 /// Reconstitutes a `RawVec` from a pointer, capacity, and allocator.
209 /// The `ptr` must be allocated (via the given allocator `alloc`), and with the given
211 /// The `capacity` cannot exceed `isize::MAX` for sized types. (only a concern on 32-bit
212 /// systems). ZST vectors may have a capacity up to `usize::MAX`.
213 /// If the `ptr` and `capacity` come from a `RawVec` created via `alloc`, then this is
216 pub unsafe fn from_raw_parts_in(ptr: *mut T, capacity: usize, alloc: A) -> Self {
217 Self { ptr: unsafe { Unique::new_unchecked(ptr) }, cap: capacity, alloc }
220 /// Gets a raw pointer to the start of the allocation. Note that this is
221 /// `Unique::dangling()` if `capacity == 0` or `T` is zero-sized. In the former case, you must
224 pub fn ptr(&self) -> *mut T {
228 /// Gets the capacity of the allocation.
230 /// This will always be `usize::MAX` if `T` is zero-sized.
232 pub fn capacity(&self) -> usize {
233 if mem::size_of::<T>() == 0 { usize::MAX } else { self.cap }
236 /// Returns a shared reference to the allocator backing this `RawVec`.
237 pub fn allocator(&self) -> &A {
241 fn current_memory(&self) -> Option<(NonNull<u8>, Layout)> {
242 if mem::size_of::<T>() == 0 || self.cap == 0 {
245 // We have an allocated chunk of memory, so we can bypass runtime
246 // checks to get our current layout.
248 let layout = Layout::array::<T>(self.cap).unwrap_unchecked();
249 Some((self.ptr.cast().into(), layout))
254 /// Ensures that the buffer contains at least enough space to hold `len +
255 /// additional` elements. If it doesn't already have enough capacity, will
256 /// reallocate enough space plus comfortable slack space to get amortized
257 /// *O*(1) behavior. Will limit this behavior if it would needlessly cause
260 /// If `len` exceeds `self.capacity()`, this may fail to actually allocate
261 /// the requested space. This is not really unsafe, but the unsafe
262 /// code *you* write that relies on the behavior of this function may break.
264 /// This is ideal for implementing a bulk-push operation like `extend`.
268 /// Panics if the new capacity exceeds `isize::MAX` bytes.
273 #[cfg(not(no_global_oom_handling))]
275 pub fn reserve(&mut self, len: usize, additional: usize) {
276 // Callers expect this function to be very cheap when there is already sufficient capacity.
277 // Therefore, we move all the resizing and error-handling logic from grow_amortized and
278 // handle_reserve behind a call, while making sure that this function is likely to be
279 // inlined as just a comparison and a call if the comparison fails.
281 fn do_reserve_and_handle<T, A: Allocator>(
282 slf: &mut RawVec<T, A>,
286 handle_reserve(slf.grow_amortized(len, additional));
289 if self.needs_to_grow(len, additional) {
290 do_reserve_and_handle(self, len, additional);
294 /// A specialized version of `reserve()` used only by the hot and
295 /// oft-instantiated `Vec::push()`, which does its own capacity check.
296 #[cfg(not(no_global_oom_handling))]
298 pub fn reserve_for_push(&mut self, len: usize) {
299 handle_reserve(self.grow_amortized(len, 1));
302 /// The same as `reserve`, but returns on errors instead of panicking or aborting.
303 pub fn try_reserve(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
304 if self.needs_to_grow(len, additional) {
305 self.grow_amortized(len, additional)
311 /// Ensures that the buffer contains at least enough space to hold `len +
312 /// additional` elements. If it doesn't already, will reallocate the
313 /// minimum possible amount of memory necessary. Generally this will be
314 /// exactly the amount of memory necessary, but in principle the allocator
315 /// is free to give back more than we asked for.
317 /// If `len` exceeds `self.capacity()`, this may fail to actually allocate
318 /// the requested space. This is not really unsafe, but the unsafe code
319 /// *you* write that relies on the behavior of this function may break.
323 /// Panics if the new capacity exceeds `isize::MAX` bytes.
328 #[cfg(not(no_global_oom_handling))]
329 pub fn reserve_exact(&mut self, len: usize, additional: usize) {
330 handle_reserve(self.try_reserve_exact(len, additional));
333 /// The same as `reserve_exact`, but returns on errors instead of panicking or aborting.
334 pub fn try_reserve_exact(
338 ) -> Result<(), TryReserveError> {
339 if self.needs_to_grow(len, additional) { self.grow_exact(len, additional) } else { Ok(()) }
342 /// Shrinks the buffer down to the specified capacity. If the given amount
343 /// is 0, actually completely deallocates.
347 /// Panics if the given amount is *larger* than the current capacity.
352 #[cfg(not(no_global_oom_handling))]
353 pub fn shrink_to_fit(&mut self, cap: usize) {
354 handle_reserve(self.shrink(cap));
358 impl<T, A: Allocator> RawVec<T, A> {
359 /// Returns if the buffer needs to grow to fulfill the needed extra capacity.
360 /// Mainly used to make inlining reserve-calls possible without inlining `grow`.
361 fn needs_to_grow(&self, len: usize, additional: usize) -> bool {
362 additional > self.capacity().wrapping_sub(len)
365 fn set_ptr_and_cap(&mut self, ptr: NonNull<[u8]>, cap: usize) {
366 // Allocators currently return a `NonNull<[u8]>` whose length matches
367 // the size requested. If that ever changes, the capacity here should
368 // change to `ptr.len() / mem::size_of::<T>()`.
369 self.ptr = unsafe { Unique::new_unchecked(ptr.cast().as_ptr()) };
373 // This method is usually instantiated many times. So we want it to be as
374 // small as possible, to improve compile times. But we also want as much of
375 // its contents to be statically computable as possible, to make the
376 // generated code run faster. Therefore, this method is carefully written
377 // so that all of the code that depends on `T` is within it, while as much
378 // of the code that doesn't depend on `T` as possible is in functions that
379 // are non-generic over `T`.
380 fn grow_amortized(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
381 // This is ensured by the calling contexts.
382 debug_assert!(additional > 0);
384 if mem::size_of::<T>() == 0 {
385 // Since we return a capacity of `usize::MAX` when `elem_size` is
386 // 0, getting to here necessarily means the `RawVec` is overfull.
387 return Err(CapacityOverflow.into());
390 // Nothing we can really do about these checks, sadly.
391 let required_cap = len.checked_add(additional).ok_or(CapacityOverflow)?;
393 // This guarantees exponential growth. The doubling cannot overflow
394 // because `cap <= isize::MAX` and the type of `cap` is `usize`.
395 let cap = cmp::max(self.cap * 2, required_cap);
396 let cap = cmp::max(Self::MIN_NON_ZERO_CAP, cap);
398 let new_layout = Layout::array::<T>(cap);
400 // `finish_grow` is non-generic over `T`.
401 let ptr = finish_grow(new_layout, self.current_memory(), &mut self.alloc)?;
402 self.set_ptr_and_cap(ptr, cap);
406 // The constraints on this method are much the same as those on
407 // `grow_amortized`, but this method is usually instantiated less often so
408 // it's less critical.
409 fn grow_exact(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
410 if mem::size_of::<T>() == 0 {
411 // Since we return a capacity of `usize::MAX` when the type size is
412 // 0, getting to here necessarily means the `RawVec` is overfull.
413 return Err(CapacityOverflow.into());
416 let cap = len.checked_add(additional).ok_or(CapacityOverflow)?;
417 let new_layout = Layout::array::<T>(cap);
419 // `finish_grow` is non-generic over `T`.
420 let ptr = finish_grow(new_layout, self.current_memory(), &mut self.alloc)?;
421 self.set_ptr_and_cap(ptr, cap);
425 fn shrink(&mut self, cap: usize) -> Result<(), TryReserveError> {
426 assert!(cap <= self.capacity(), "Tried to shrink to a larger capacity");
428 let (ptr, layout) = if let Some(mem) = self.current_memory() { mem } else { return Ok(()) };
431 // `Layout::array` cannot overflow here because it would have
432 // overflowed earlier when capacity was larger.
433 let new_layout = Layout::array::<T>(cap).unwrap_unchecked();
435 .shrink(ptr, layout, new_layout)
436 .map_err(|_| AllocError { layout: new_layout, non_exhaustive: () })?
438 self.set_ptr_and_cap(ptr, cap);
443 // This function is outside `RawVec` to minimize compile times. See the comment
444 // above `RawVec::grow_amortized` for details. (The `A` parameter isn't
445 // significant, because the number of different `A` types seen in practice is
446 // much smaller than the number of `T` types.)
449 new_layout: Result<Layout, LayoutError>,
450 current_memory: Option<(NonNull<u8>, Layout)>,
452 ) -> Result<NonNull<[u8]>, TryReserveError>
456 // Check for the error here to minimize the size of `RawVec::grow_*`.
457 let new_layout = new_layout.map_err(|_| CapacityOverflow)?;
459 alloc_guard(new_layout.size())?;
461 let memory = if let Some((ptr, old_layout)) = current_memory {
462 debug_assert_eq!(old_layout.align(), new_layout.align());
464 // The allocator checks for alignment equality
465 intrinsics::assume(old_layout.align() == new_layout.align());
466 alloc.grow(ptr, old_layout, new_layout)
469 alloc.allocate(new_layout)
472 memory.map_err(|_| AllocError { layout: new_layout, non_exhaustive: () }.into())
475 unsafe impl<#[may_dangle] T, A: Allocator> Drop for RawVec<T, A> {
476 /// Frees the memory owned by the `RawVec` *without* trying to drop its contents.
478 if let Some((ptr, layout)) = self.current_memory() {
479 unsafe { self.alloc.deallocate(ptr, layout) }
484 // Central function for reserve error handling.
485 #[cfg(not(no_global_oom_handling))]
487 fn handle_reserve(result: Result<(), TryReserveError>) {
488 match result.map_err(|e| e.kind()) {
489 Err(CapacityOverflow) => capacity_overflow(),
490 Err(AllocError { layout, .. }) => handle_alloc_error(layout),
491 Ok(()) => { /* yay */ }
495 // We need to guarantee the following:
496 // * We don't ever allocate `> isize::MAX` byte-size objects.
497 // * We don't overflow `usize::MAX` and actually allocate too little.
499 // On 64-bit we just need to check for overflow since trying to allocate
500 // `> isize::MAX` bytes will surely fail. On 32-bit and 16-bit we need to add
501 // an extra guard for this in case we're running on a platform which can use
502 // all 4GB in user-space, e.g., PAE or x32.
505 fn alloc_guard(alloc_size: usize) -> Result<(), TryReserveError> {
506 if usize::BITS < 64 && alloc_size > isize::MAX as usize {
507 Err(CapacityOverflow.into())
513 // One central function responsible for reporting capacity overflows. This'll
514 // ensure that the code generation related to these panics is minimal as there's
515 // only one location which panics rather than a bunch throughout the module.
516 #[cfg(not(no_global_oom_handling))]
517 fn capacity_overflow() -> ! {
518 panic!("capacity overflow");