1 #![unstable(feature = "raw_vec_internals", reason = "implementation detail", issue = "none")]
4 use core::alloc::LayoutError;
7 use core::mem::{self, ManuallyDrop, MaybeUninit};
9 use core::ptr::{self, NonNull, Unique};
12 #[cfg(not(no_global_oom_handling))]
13 use crate::alloc::handle_alloc_error;
14 use crate::alloc::{Allocator, Global, Layout};
15 use crate::boxed::Box;
16 use crate::collections::TryReserveError;
17 use crate::collections::TryReserveErrorKind::*;
22 #[cfg(not(no_global_oom_handling))]
24 /// The contents of the new memory are uninitialized.
26 /// The new memory is guaranteed to be zeroed.
30 /// A low-level utility for more ergonomically allocating, reallocating, and deallocating
31 /// a buffer of memory on the heap without having to worry about all the corner cases
32 /// involved. This type is excellent for building your own data structures like Vec and VecDeque.
35 /// * Produces `Unique::dangling()` on zero-sized types.
36 /// * Produces `Unique::dangling()` on zero-length allocations.
37 /// * Avoids freeing `Unique::dangling()`.
38 /// * Catches all overflows in capacity computations (promotes them to "capacity overflow" panics).
39 /// * Guards against 32-bit systems allocating more than isize::MAX bytes.
40 /// * Guards against overflowing your length.
41 /// * Calls `handle_alloc_error` for fallible allocations.
42 /// * Contains a `ptr::Unique` and thus endows the user with all related benefits.
43 /// * Uses the excess returned from the allocator to use the largest available capacity.
45 /// This type does not in anyway inspect the memory that it manages. When dropped it *will*
46 /// free its memory, but it *won't* try to drop its contents. It is up to the user of `RawVec`
47 /// to handle the actual things *stored* inside of a `RawVec`.
49 /// Note that the excess of a zero-sized types is always infinite, so `capacity()` always returns
50 /// `usize::MAX`. This means that you need to be careful when round-tripping this type with a
51 /// `Box<[T]>`, since `capacity()` won't yield the length.
52 #[allow(missing_debug_implementations)]
53 pub struct RawVec<T, A: Allocator = Global> {
59 impl<T> RawVec<T, Global> {
60 /// HACK(Centril): This exists because stable `const fn` can only call stable `const fn`, so
61 /// they cannot call `Self::new()`.
63 /// If you change `RawVec<T>::new` or dependencies, please take care to not introduce anything
64 /// that would truly const-call something unstable.
65 pub const NEW: Self = Self::new();
67 /// Creates the biggest possible `RawVec` (on the system heap)
68 /// without allocating. If `T` has positive size, then this makes a
69 /// `RawVec` with capacity `0`. If `T` is zero-sized, then it makes a
70 /// `RawVec` with capacity `usize::MAX`. Useful for implementing
71 /// delayed allocation.
73 pub const fn new() -> Self {
77 /// Creates a `RawVec` (on the system heap) with exactly the
78 /// capacity and alignment requirements for a `[T; capacity]`. This is
79 /// equivalent to calling `RawVec::new` when `capacity` is `0` or `T` is
80 /// zero-sized. Note that if `T` is zero-sized this means you will
81 /// *not* get a `RawVec` with the requested capacity.
85 /// Panics if the requested capacity exceeds `isize::MAX` bytes.
90 #[cfg(not(no_global_oom_handling))]
93 pub fn with_capacity(capacity: usize) -> Self {
94 Self::with_capacity_in(capacity, Global)
97 /// Like `with_capacity`, but guarantees the buffer is zeroed.
98 #[cfg(not(no_global_oom_handling))]
101 pub fn with_capacity_zeroed(capacity: usize) -> Self {
102 Self::with_capacity_zeroed_in(capacity, Global)
105 /// Reconstitutes a `RawVec` from a pointer and capacity.
109 /// The `ptr` must be allocated (on the system heap), and with the given `capacity`.
110 /// The `capacity` cannot exceed `isize::MAX` for sized types. (only a concern on 32-bit
111 /// systems). ZST vectors may have a capacity up to `usize::MAX`.
112 /// If the `ptr` and `capacity` come from a `RawVec`, then this is guaranteed.
114 pub unsafe fn from_raw_parts(ptr: *mut T, capacity: usize) -> Self {
115 unsafe { Self::from_raw_parts_in(ptr, capacity, Global) }
119 impl<T, A: Allocator> RawVec<T, A> {
120 // Tiny Vecs are dumb. Skip to:
121 // - 8 if the element size is 1, because any heap allocators is likely
122 // to round up a request of less than 8 bytes to at least 8 bytes.
123 // - 4 if elements are moderate-sized (<= 1 KiB).
124 // - 1 otherwise, to avoid wasting too much space for very short Vecs.
125 const MIN_NON_ZERO_CAP: usize = if mem::size_of::<T>() == 1 {
127 } else if mem::size_of::<T>() <= 1024 {
133 /// Like `new`, but parameterized over the choice of allocator for
134 /// the returned `RawVec`.
135 #[rustc_allow_const_fn_unstable(const_fn)]
136 pub const fn new_in(alloc: A) -> Self {
137 // `cap: 0` means "unallocated". zero-sized types are ignored.
138 Self { ptr: Unique::dangling(), cap: 0, alloc }
141 /// Like `with_capacity`, but parameterized over the choice of
142 /// allocator for the returned `RawVec`.
143 #[cfg(not(no_global_oom_handling))]
145 pub fn with_capacity_in(capacity: usize, alloc: A) -> Self {
146 Self::allocate_in(capacity, AllocInit::Uninitialized, alloc)
149 /// Like `with_capacity_zeroed`, but parameterized over the choice
150 /// of allocator for the returned `RawVec`.
151 #[cfg(not(no_global_oom_handling))]
153 pub fn with_capacity_zeroed_in(capacity: usize, alloc: A) -> Self {
154 Self::allocate_in(capacity, AllocInit::Zeroed, alloc)
157 /// Converts a `Box<[T]>` into a `RawVec<T>`.
158 pub fn from_box(slice: Box<[T], A>) -> Self {
160 let (slice, alloc) = Box::into_raw_with_allocator(slice);
161 RawVec::from_raw_parts_in(slice.as_mut_ptr(), slice.len(), alloc)
165 /// Converts the entire buffer into `Box<[MaybeUninit<T>]>` with the specified `len`.
167 /// Note that this will correctly reconstitute any `cap` changes
168 /// that may have been performed. (See description of type for details.)
172 /// * `len` must be greater than or equal to the most recently requested capacity, and
173 /// * `len` must be less than or equal to `self.capacity()`.
175 /// Note, that the requested capacity and `self.capacity()` could differ, as
176 /// an allocator could overallocate and return a greater memory block than requested.
177 pub unsafe fn into_box(self, len: usize) -> Box<[MaybeUninit<T>], A> {
178 // Sanity-check one half of the safety requirement (we cannot check the other half).
180 len <= self.capacity(),
181 "`len` must be smaller than or equal to `self.capacity()`"
184 let me = ManuallyDrop::new(self);
186 let slice = slice::from_raw_parts_mut(me.ptr() as *mut MaybeUninit<T>, len);
187 Box::from_raw_in(slice, ptr::read(&me.alloc))
191 #[cfg(not(no_global_oom_handling))]
192 fn allocate_in(capacity: usize, init: AllocInit, alloc: A) -> Self {
193 if mem::size_of::<T>() == 0 {
196 // We avoid `unwrap_or_else` here because it bloats the amount of
197 // LLVM IR generated.
198 let layout = match Layout::array::<T>(capacity) {
199 Ok(layout) => layout,
200 Err(_) => capacity_overflow(),
202 match alloc_guard(layout.size()) {
204 Err(_) => capacity_overflow(),
206 let result = match init {
207 AllocInit::Uninitialized => alloc.allocate(layout),
208 AllocInit::Zeroed => alloc.allocate_zeroed(layout),
210 let ptr = match result {
212 Err(_) => handle_alloc_error(layout),
216 ptr: unsafe { Unique::new_unchecked(ptr.cast().as_ptr()) },
217 cap: Self::capacity_from_bytes(ptr.len()),
223 /// Reconstitutes a `RawVec` from a pointer, capacity, and allocator.
227 /// The `ptr` must be allocated (via the given allocator `alloc`), and with the given
229 /// The `capacity` cannot exceed `isize::MAX` for sized types. (only a concern on 32-bit
230 /// systems). ZST vectors may have a capacity up to `usize::MAX`.
231 /// If the `ptr` and `capacity` come from a `RawVec` created via `alloc`, then this is
234 pub unsafe fn from_raw_parts_in(ptr: *mut T, capacity: usize, alloc: A) -> Self {
235 Self { ptr: unsafe { Unique::new_unchecked(ptr) }, cap: capacity, alloc }
238 /// Gets a raw pointer to the start of the allocation. Note that this is
239 /// `Unique::dangling()` if `capacity == 0` or `T` is zero-sized. In the former case, you must
242 pub fn ptr(&self) -> *mut T {
246 /// Gets the capacity of the allocation.
248 /// This will always be `usize::MAX` if `T` is zero-sized.
250 pub fn capacity(&self) -> usize {
251 if mem::size_of::<T>() == 0 { usize::MAX } else { self.cap }
254 /// Returns a shared reference to the allocator backing this `RawVec`.
255 pub fn allocator(&self) -> &A {
259 fn current_memory(&self) -> Option<(NonNull<u8>, Layout)> {
260 if mem::size_of::<T>() == 0 || self.cap == 0 {
263 // We have an allocated chunk of memory, so we can bypass runtime
264 // checks to get our current layout.
266 let align = mem::align_of::<T>();
267 let size = mem::size_of::<T>() * self.cap;
268 let layout = Layout::from_size_align_unchecked(size, align);
269 Some((self.ptr.cast().into(), layout))
274 /// Ensures that the buffer contains at least enough space to hold `len +
275 /// additional` elements. If it doesn't already have enough capacity, will
276 /// reallocate enough space plus comfortable slack space to get amortized
277 /// *O*(1) behavior. Will limit this behavior if it would needlessly cause
280 /// If `len` exceeds `self.capacity()`, this may fail to actually allocate
281 /// the requested space. This is not really unsafe, but the unsafe
282 /// code *you* write that relies on the behavior of this function may break.
284 /// This is ideal for implementing a bulk-push operation like `extend`.
288 /// Panics if the new capacity exceeds `isize::MAX` bytes.
297 /// # #![feature(raw_vec_internals)]
298 /// # extern crate alloc;
300 /// # use alloc::raw_vec::RawVec;
301 /// struct MyVec<T> {
306 /// impl<T: Clone> MyVec<T> {
307 /// pub fn push_all(&mut self, elems: &[T]) {
308 /// self.buf.reserve(self.len, elems.len());
309 /// // reserve would have aborted or panicked if the len exceeded
310 /// // `isize::MAX` so this is safe to do unchecked now.
313 /// ptr::write(self.buf.ptr().add(self.len), x.clone());
320 /// # let mut vector = MyVec { buf: RawVec::new(), len: 0 };
321 /// # vector.push_all(&[1, 3, 5, 7, 9]);
324 #[cfg(not(no_global_oom_handling))]
326 pub fn reserve(&mut self, len: usize, additional: usize) {
327 // Callers expect this function to be very cheap when there is already sufficient capacity.
328 // Therefore, we move all the resizing and error-handling logic from grow_amortized and
329 // handle_reserve behind a call, while making sure that this function is likely to be
330 // inlined as just a comparison and a call if the comparison fails.
332 fn do_reserve_and_handle<T, A: Allocator>(
333 slf: &mut RawVec<T, A>,
337 handle_reserve(slf.grow_amortized(len, additional));
340 if self.needs_to_grow(len, additional) {
341 do_reserve_and_handle(self, len, additional);
345 /// The same as `reserve`, but returns on errors instead of panicking or aborting.
346 pub fn try_reserve(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
347 if self.needs_to_grow(len, additional) {
348 self.grow_amortized(len, additional)
354 /// Ensures that the buffer contains at least enough space to hold `len +
355 /// additional` elements. If it doesn't already, will reallocate the
356 /// minimum possible amount of memory necessary. Generally this will be
357 /// exactly the amount of memory necessary, but in principle the allocator
358 /// is free to give back more than we asked for.
360 /// If `len` exceeds `self.capacity()`, this may fail to actually allocate
361 /// the requested space. This is not really unsafe, but the unsafe code
362 /// *you* write that relies on the behavior of this function may break.
366 /// Panics if the new capacity exceeds `isize::MAX` bytes.
371 #[cfg(not(no_global_oom_handling))]
372 pub fn reserve_exact(&mut self, len: usize, additional: usize) {
373 handle_reserve(self.try_reserve_exact(len, additional));
376 /// The same as `reserve_exact`, but returns on errors instead of panicking or aborting.
377 pub fn try_reserve_exact(
381 ) -> Result<(), TryReserveError> {
382 if self.needs_to_grow(len, additional) { self.grow_exact(len, additional) } else { Ok(()) }
385 /// Shrinks the allocation down to the specified amount. If the given amount
386 /// is 0, actually completely deallocates.
390 /// Panics if the given amount is *larger* than the current capacity.
395 #[cfg(not(no_global_oom_handling))]
396 pub fn shrink_to_fit(&mut self, amount: usize) {
397 handle_reserve(self.shrink(amount));
401 impl<T, A: Allocator> RawVec<T, A> {
402 /// Returns if the buffer needs to grow to fulfill the needed extra capacity.
403 /// Mainly used to make inlining reserve-calls possible without inlining `grow`.
404 fn needs_to_grow(&self, len: usize, additional: usize) -> bool {
405 additional > self.capacity().wrapping_sub(len)
408 fn capacity_from_bytes(excess: usize) -> usize {
409 debug_assert_ne!(mem::size_of::<T>(), 0);
410 excess / mem::size_of::<T>()
413 fn set_ptr(&mut self, ptr: NonNull<[u8]>) {
414 self.ptr = unsafe { Unique::new_unchecked(ptr.cast().as_ptr()) };
415 self.cap = Self::capacity_from_bytes(ptr.len());
418 // This method is usually instantiated many times. So we want it to be as
419 // small as possible, to improve compile times. But we also want as much of
420 // its contents to be statically computable as possible, to make the
421 // generated code run faster. Therefore, this method is carefully written
422 // so that all of the code that depends on `T` is within it, while as much
423 // of the code that doesn't depend on `T` as possible is in functions that
424 // are non-generic over `T`.
425 fn grow_amortized(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
426 // This is ensured by the calling contexts.
427 debug_assert!(additional > 0);
429 if mem::size_of::<T>() == 0 {
430 // Since we return a capacity of `usize::MAX` when `elem_size` is
431 // 0, getting to here necessarily means the `RawVec` is overfull.
432 return Err(CapacityOverflow.into());
435 // Nothing we can really do about these checks, sadly.
436 let required_cap = len.checked_add(additional).ok_or(CapacityOverflow)?;
438 // This guarantees exponential growth. The doubling cannot overflow
439 // because `cap <= isize::MAX` and the type of `cap` is `usize`.
440 let cap = cmp::max(self.cap * 2, required_cap);
441 let cap = cmp::max(Self::MIN_NON_ZERO_CAP, cap);
443 let new_layout = Layout::array::<T>(cap);
445 // `finish_grow` is non-generic over `T`.
446 let ptr = finish_grow(new_layout, self.current_memory(), &mut self.alloc)?;
451 // The constraints on this method are much the same as those on
452 // `grow_amortized`, but this method is usually instantiated less often so
453 // it's less critical.
454 fn grow_exact(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
455 if mem::size_of::<T>() == 0 {
456 // Since we return a capacity of `usize::MAX` when the type size is
457 // 0, getting to here necessarily means the `RawVec` is overfull.
458 return Err(CapacityOverflow.into());
461 let cap = len.checked_add(additional).ok_or(CapacityOverflow)?;
462 let new_layout = Layout::array::<T>(cap);
464 // `finish_grow` is non-generic over `T`.
465 let ptr = finish_grow(new_layout, self.current_memory(), &mut self.alloc)?;
470 fn shrink(&mut self, amount: usize) -> Result<(), TryReserveError> {
471 assert!(amount <= self.capacity(), "Tried to shrink to a larger capacity");
473 let (ptr, layout) = if let Some(mem) = self.current_memory() { mem } else { return Ok(()) };
474 let new_size = amount * mem::size_of::<T>();
477 let new_layout = Layout::from_size_align_unchecked(new_size, layout.align());
479 .shrink(ptr, layout, new_layout)
480 .map_err(|_| AllocError { layout: new_layout, non_exhaustive: () })?
487 // This function is outside `RawVec` to minimize compile times. See the comment
488 // above `RawVec::grow_amortized` for details. (The `A` parameter isn't
489 // significant, because the number of different `A` types seen in practice is
490 // much smaller than the number of `T` types.)
493 new_layout: Result<Layout, LayoutError>,
494 current_memory: Option<(NonNull<u8>, Layout)>,
496 ) -> Result<NonNull<[u8]>, TryReserveError>
500 // Check for the error here to minimize the size of `RawVec::grow_*`.
501 let new_layout = new_layout.map_err(|_| CapacityOverflow)?;
503 alloc_guard(new_layout.size())?;
505 let memory = if let Some((ptr, old_layout)) = current_memory {
506 debug_assert_eq!(old_layout.align(), new_layout.align());
508 // The allocator checks for alignment equality
509 intrinsics::assume(old_layout.align() == new_layout.align());
510 alloc.grow(ptr, old_layout, new_layout)
513 alloc.allocate(new_layout)
516 memory.map_err(|_| AllocError { layout: new_layout, non_exhaustive: () }.into())
519 unsafe impl<#[may_dangle] T, A: Allocator> Drop for RawVec<T, A> {
520 /// Frees the memory owned by the `RawVec` *without* trying to drop its contents.
522 if let Some((ptr, layout)) = self.current_memory() {
523 unsafe { self.alloc.deallocate(ptr, layout) }
528 // Central function for reserve error handling.
529 #[cfg(not(no_global_oom_handling))]
531 fn handle_reserve(result: Result<(), TryReserveError>) {
532 match result.map_err(|e| e.kind()) {
533 Err(CapacityOverflow) => capacity_overflow(),
534 Err(AllocError { layout, .. }) => handle_alloc_error(layout),
535 Ok(()) => { /* yay */ }
539 // We need to guarantee the following:
540 // * We don't ever allocate `> isize::MAX` byte-size objects.
541 // * We don't overflow `usize::MAX` and actually allocate too little.
543 // On 64-bit we just need to check for overflow since trying to allocate
544 // `> isize::MAX` bytes will surely fail. On 32-bit and 16-bit we need to add
545 // an extra guard for this in case we're running on a platform which can use
546 // all 4GB in user-space, e.g., PAE or x32.
549 fn alloc_guard(alloc_size: usize) -> Result<(), TryReserveError> {
550 if usize::BITS < 64 && alloc_size > isize::MAX as usize {
551 Err(CapacityOverflow.into())
557 // One central function responsible for reporting capacity overflows. This'll
558 // ensure that the code generation related to these panics is minimal as there's
559 // only one location which panics rather than a bunch throughout the module.
560 #[cfg(not(no_global_oom_handling))]
561 fn capacity_overflow() -> ! {
562 panic!("capacity overflow");