1 #![unstable(feature = "raw_vec_internals", reason = "implementation detail", issue = "none")]
4 use core::alloc::{LayoutErr, MemoryBlock};
6 use core::mem::{self, ManuallyDrop, MaybeUninit};
8 use core::ptr::{NonNull, Unique};
12 handle_alloc_error, AllocErr,
14 AllocRef, Global, Layout,
15 ReallocPlacement::{self, *},
17 use crate::boxed::Box;
18 use crate::collections::TryReserveError::{self, *};
23 /// A low-level utility for more ergonomically allocating, reallocating, and deallocating
24 /// a buffer of memory on the heap without having to worry about all the corner cases
25 /// involved. This type is excellent for building your own data structures like Vec and VecDeque.
28 /// * Produces `Unique::dangling()` on zero-sized types.
29 /// * Produces `Unique::dangling()` on zero-length allocations.
30 /// * Avoids freeing `Unique::dangling()`.
31 /// * Catches all overflows in capacity computations (promotes them to "capacity overflow" panics).
32 /// * Guards against 32-bit systems allocating more than isize::MAX bytes.
33 /// * Guards against overflowing your length.
34 /// * Calls `handle_alloc_error` for fallible allocations.
35 /// * Contains a `ptr::Unique` and thus endows the user with all related benefits.
36 /// * Uses the excess returned from the allocator to use the largest available capacity.
38 /// This type does not in anyway inspect the memory that it manages. When dropped it *will*
39 /// free its memory, but it *won't* try to drop its contents. It is up to the user of `RawVec`
40 /// to handle the actual things *stored* inside of a `RawVec`.
42 /// Note that the excess of a zero-sized types is always infinite, so `capacity()` always returns
43 /// `usize::MAX`. This means that you need to be careful when round-tripping this type with a
44 /// `Box<[T]>`, since `capacity()` won't yield the length.
45 #[allow(missing_debug_implementations)]
46 pub struct RawVec<T, A: AllocRef = Global> {
52 impl<T> RawVec<T, Global> {
53 /// HACK(Centril): This exists because `#[unstable]` `const fn`s needn't conform
54 /// to `min_const_fn` and so they cannot be called in `min_const_fn`s either.
56 /// If you change `RawVec<T>::new` or dependencies, please take care to not
57 /// introduce anything that would truly violate `min_const_fn`.
59 /// NOTE: We could avoid this hack and check conformance with some
60 /// `#[rustc_force_min_const_fn]` attribute which requires conformance
61 /// with `min_const_fn` but does not necessarily allow calling it in
62 /// `stable(...) const fn` / user code not enabling `foo` when
63 /// `#[rustc_const_unstable(feature = "foo", ..)]` is present.
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.
71 pub const fn new() -> Self {
75 /// Creates a `RawVec` (on the system heap) with exactly the
76 /// capacity and alignment requirements for a `[T; capacity]`. This is
77 /// equivalent to calling `RawVec::new` when `capacity` is `0` or `T` is
78 /// zero-sized. Note that if `T` is zero-sized this means you will
79 /// *not* get a `RawVec` with the requested capacity.
83 /// * Panics if the requested capacity exceeds `usize::MAX` bytes.
84 /// * Panics on 32-bit platforms if the requested capacity exceeds
85 /// `isize::MAX` bytes.
91 pub fn with_capacity(capacity: usize) -> Self {
92 Self::with_capacity_in(capacity, Global)
95 /// Like `with_capacity`, but guarantees the buffer is zeroed.
97 pub fn with_capacity_zeroed(capacity: usize) -> Self {
98 Self::with_capacity_zeroed_in(capacity, Global)
101 /// Reconstitutes a `RawVec` from a pointer and capacity.
105 /// The `ptr` must be allocated (on the system heap), and with the given `capacity`.
106 /// The `capacity` cannot exceed `isize::MAX` for sized types. (only a concern on 32-bit
107 /// systems). ZST vectors may have a capacity up to `usize::MAX`.
108 /// If the `ptr` and `capacity` come from a `RawVec`, then this is guaranteed.
110 pub unsafe fn from_raw_parts(ptr: *mut T, capacity: usize) -> Self {
111 Self::from_raw_parts_in(ptr, capacity, Global)
114 /// Converts a `Box<[T]>` into a `RawVec<T>`.
115 pub fn from_box(slice: Box<[T]>) -> Self {
117 let mut slice = ManuallyDrop::new(slice);
118 RawVec::from_raw_parts(slice.as_mut_ptr(), slice.len())
123 impl<T, A: AllocRef> RawVec<T, A> {
124 /// Like `new`, but parameterized over the choice of allocator for
125 /// the returned `RawVec`.
126 pub const fn new_in(alloc: A) -> Self {
127 // `cap: 0` means "unallocated". zero-sized types are ignored.
128 Self { ptr: Unique::dangling(), cap: 0, alloc }
131 /// Like `with_capacity`, but parameterized over the choice of
132 /// allocator for the returned `RawVec`.
134 pub fn with_capacity_in(capacity: usize, alloc: A) -> Self {
135 Self::allocate_in(capacity, Uninitialized, alloc)
138 /// Like `with_capacity_zeroed`, but parameterized over the choice
139 /// of allocator for the returned `RawVec`.
141 pub fn with_capacity_zeroed_in(capacity: usize, alloc: A) -> Self {
142 Self::allocate_in(capacity, Zeroed, alloc)
145 fn allocate_in(capacity: usize, init: AllocInit, mut alloc: A) -> Self {
146 if mem::size_of::<T>() == 0 {
149 let layout = Layout::array::<T>(capacity).unwrap_or_else(|_| capacity_overflow());
150 alloc_guard(layout.size()).unwrap_or_else(|_| capacity_overflow());
152 let memory = alloc.alloc(layout, init).unwrap_or_else(|_| handle_alloc_error(layout));
154 ptr: unsafe { Unique::new_unchecked(memory.ptr.cast().as_ptr()) },
155 cap: Self::capacity_from_bytes(memory.size),
161 /// Reconstitutes a `RawVec` from a pointer, capacity, and allocator.
165 /// The `ptr` must be allocated (via the given allocator `a`), and with the given `capacity`.
166 /// The `capacity` cannot exceed `isize::MAX` for sized types. (only a concern on 32-bit
167 /// systems). ZST vectors may have a capacity up to `usize::MAX`.
168 /// If the `ptr` and `capacity` come from a `RawVec` created via `a`, then this is guaranteed.
170 pub unsafe fn from_raw_parts_in(ptr: *mut T, capacity: usize, a: A) -> Self {
171 Self { ptr: Unique::new_unchecked(ptr), cap: capacity, alloc: a }
174 /// Gets a raw pointer to the start of the allocation. Note that this is
175 /// `Unique::dangling()` if `capacity == 0` or `T` is zero-sized. In the former case, you must
177 pub fn ptr(&self) -> *mut T {
181 /// Gets the capacity of the allocation.
183 /// This will always be `usize::MAX` if `T` is zero-sized.
185 pub fn capacity(&self) -> usize {
186 if mem::size_of::<T>() == 0 { usize::MAX } else { self.cap }
189 /// Returns a shared reference to the allocator backing this `RawVec`.
190 pub fn alloc(&self) -> &A {
194 /// Returns a mutable reference to the allocator backing this `RawVec`.
195 pub fn alloc_mut(&mut self) -> &mut A {
199 fn current_memory(&self) -> Option<(NonNull<u8>, Layout)> {
200 if mem::size_of::<T>() == 0 || self.cap == 0 {
203 // We have an allocated chunk of memory, so we can bypass runtime
204 // checks to get our current layout.
206 let align = mem::align_of::<T>();
207 let size = mem::size_of::<T>() * self.cap;
208 let layout = Layout::from_size_align_unchecked(size, align);
209 Some((self.ptr.cast().into(), layout))
214 /// Ensures that the buffer contains at least enough space to hold
215 /// `used_capacity + needed_extra_capacity` elements. If it doesn't already have
216 /// enough capacity, will reallocate enough space plus comfortable slack
217 /// space to get amortized `O(1)` behavior. Will limit this behavior
218 /// if it would needlessly cause itself to panic.
220 /// If `used_capacity` exceeds `self.capacity()`, this may fail to actually allocate
221 /// the requested space. This is not really unsafe, but the unsafe
222 /// code *you* write that relies on the behavior of this function may break.
224 /// This is ideal for implementing a bulk-push operation like `extend`.
228 /// * Panics if the requested capacity exceeds `usize::MAX` bytes.
229 /// * Panics on 32-bit platforms if the requested capacity exceeds
230 /// `isize::MAX` bytes.
239 /// # #![feature(raw_vec_internals)]
240 /// # extern crate alloc;
242 /// # use alloc::raw_vec::RawVec;
243 /// struct MyVec<T> {
248 /// impl<T: Clone> MyVec<T> {
249 /// pub fn push_all(&mut self, elems: &[T]) {
250 /// self.buf.reserve(self.len, elems.len());
251 /// // reserve would have aborted or panicked if the len exceeded
252 /// // `isize::MAX` so this is safe to do unchecked now.
255 /// ptr::write(self.buf.ptr().add(self.len), x.clone());
262 /// # let mut vector = MyVec { buf: RawVec::new(), len: 0 };
263 /// # vector.push_all(&[1, 3, 5, 7, 9]);
266 pub fn reserve(&mut self, used_capacity: usize, needed_extra_capacity: usize) {
267 match self.try_reserve(used_capacity, needed_extra_capacity) {
268 Err(CapacityOverflow) => capacity_overflow(),
269 Err(AllocError { layout, .. }) => handle_alloc_error(layout),
270 Ok(()) => { /* yay */ }
274 /// The same as `reserve`, but returns on errors instead of panicking or aborting.
277 used_capacity: usize,
278 needed_extra_capacity: usize,
279 ) -> Result<(), TryReserveError> {
280 if self.needs_to_grow(used_capacity, needed_extra_capacity) {
281 self.grow_amortized(used_capacity, needed_extra_capacity, MayMove)
287 /// Attempts to ensure that the buffer contains at least enough space to hold
288 /// `used_capacity + needed_extra_capacity` elements. If it doesn't already have
289 /// enough capacity, will reallocate in place enough space plus comfortable slack
290 /// space to get amortized `O(1)` behavior. Will limit this behaviour
291 /// if it would needlessly cause itself to panic.
293 /// If `used_capacity` exceeds `self.capacity()`, this may fail to actually allocate
294 /// the requested space. This is not really unsafe, but the unsafe
295 /// code *you* write that relies on the behavior of this function may break.
297 /// Returns `true` if the reallocation attempt has succeeded.
301 /// * Panics if the requested capacity exceeds `usize::MAX` bytes.
302 /// * Panics on 32-bit platforms if the requested capacity exceeds
303 /// `isize::MAX` bytes.
304 pub fn reserve_in_place(&mut self, used_capacity: usize, needed_extra_capacity: usize) -> bool {
305 // This is more readable than putting this in one line:
306 // `!self.needs_to_grow(...) || self.grow(...).is_ok()`
307 if self.needs_to_grow(used_capacity, needed_extra_capacity) {
308 self.grow_amortized(used_capacity, needed_extra_capacity, InPlace).is_ok()
314 /// Ensures that the buffer contains at least enough space to hold
315 /// `used_capacity + needed_extra_capacity` elements. If it doesn't already,
316 /// will reallocate the minimum possible amount of memory necessary.
317 /// Generally this will be exactly the amount of memory necessary,
318 /// but in principle the allocator is free to give back more than
321 /// If `used_capacity` exceeds `self.capacity()`, this may fail to actually allocate
322 /// the requested space. This is not really unsafe, but the unsafe
323 /// code *you* write that relies on the behavior of this function may break.
327 /// * Panics if the requested capacity exceeds `usize::MAX` bytes.
328 /// * Panics on 32-bit platforms if the requested capacity exceeds
329 /// `isize::MAX` bytes.
334 pub fn reserve_exact(&mut self, used_capacity: usize, needed_extra_capacity: usize) {
335 match self.try_reserve_exact(used_capacity, needed_extra_capacity) {
336 Err(CapacityOverflow) => capacity_overflow(),
337 Err(AllocError { layout, .. }) => handle_alloc_error(layout),
338 Ok(()) => { /* yay */ }
342 /// The same as `reserve_exact`, but returns on errors instead of panicking or aborting.
343 pub fn try_reserve_exact(
345 used_capacity: usize,
346 needed_extra_capacity: usize,
347 ) -> Result<(), TryReserveError> {
348 if self.needs_to_grow(used_capacity, needed_extra_capacity) {
349 self.grow_exact(used_capacity, needed_extra_capacity)
355 /// Shrinks the allocation down to the specified amount. If the given amount
356 /// is 0, actually completely deallocates.
360 /// Panics if the given amount is *larger* than the current capacity.
365 pub fn shrink_to_fit(&mut self, amount: usize) {
366 match self.shrink(amount, MayMove) {
367 Err(CapacityOverflow) => capacity_overflow(),
368 Err(AllocError { layout, .. }) => handle_alloc_error(layout),
369 Ok(()) => { /* yay */ }
374 impl<T, A: AllocRef> RawVec<T, A> {
375 /// Returns if the buffer needs to grow to fulfill the needed extra capacity.
376 /// Mainly used to make inlining reserve-calls possible without inlining `grow`.
377 fn needs_to_grow(&self, used_capacity: usize, needed_extra_capacity: usize) -> bool {
378 needed_extra_capacity > self.capacity().wrapping_sub(used_capacity)
381 fn capacity_from_bytes(excess: usize) -> usize {
382 debug_assert_ne!(mem::size_of::<T>(), 0);
383 excess / mem::size_of::<T>()
386 fn set_memory(&mut self, memory: MemoryBlock) {
387 self.ptr = unsafe { Unique::new_unchecked(memory.ptr.cast().as_ptr()) };
388 self.cap = Self::capacity_from_bytes(memory.size);
391 // This method is usually instantiated many times. So we want it to be as
392 // small as possible, to improve compile times. But we also want as much of
393 // its contents to be statically computable as possible, to make the
394 // generated code run faster. Therefore, this method is carefully written
395 // so that all of the code that depends on `T` is within it, while as much
396 // of the code that doesn't depend on `T` as possible is in functions that
397 // are non-generic over `T`.
400 used_capacity: usize,
401 needed_extra_capacity: usize,
402 placement: ReallocPlacement,
403 ) -> Result<(), TryReserveError> {
404 if mem::size_of::<T>() == 0 {
405 // Since we return a capacity of `usize::MAX` when `elem_size` is
406 // 0, getting to here necessarily means the `RawVec` is overfull.
407 return Err(CapacityOverflow);
410 // Nothing we can really do about these checks, sadly.
412 used_capacity.checked_add(needed_extra_capacity).ok_or(CapacityOverflow)?;
413 // Cannot overflow, because `cap <= isize::MAX`, and type of `cap` is `usize`.
414 let double_cap = self.cap * 2;
415 // `double_cap` guarantees exponential growth.
416 let cap = cmp::max(double_cap, required_cap);
417 let new_layout = Layout::array::<T>(cap);
419 // `finish_grow` is non-generic over `T`.
420 let memory = finish_grow(new_layout, placement, self.current_memory(), &mut self.alloc)?;
421 self.set_memory(memory);
425 // The constraints on this method are much the same as those on
426 // `grow_amortized`, but this method is usually instantiated less often so
427 // it's less critical.
430 used_capacity: usize,
431 needed_extra_capacity: usize,
432 ) -> Result<(), TryReserveError> {
433 if mem::size_of::<T>() == 0 {
434 // Since we return a capacity of `usize::MAX` when the type size is
435 // 0, getting to here necessarily means the `RawVec` is overfull.
436 return Err(CapacityOverflow);
439 let cap = used_capacity.checked_add(needed_extra_capacity).ok_or(CapacityOverflow)?;
440 let new_layout = Layout::array::<T>(cap);
442 // `finish_grow` is non-generic over `T`.
443 let memory = finish_grow(new_layout, MayMove, self.current_memory(), &mut self.alloc)?;
444 self.set_memory(memory);
451 placement: ReallocPlacement,
452 ) -> Result<(), TryReserveError> {
453 assert!(amount <= self.capacity(), "Tried to shrink to a larger capacity");
455 let (ptr, layout) = if let Some(mem) = self.current_memory() { mem } else { return Ok(()) };
456 let new_size = amount * mem::size_of::<T>();
458 let memory = unsafe {
459 self.alloc.shrink(ptr, layout, new_size, placement).map_err(|_| {
460 TryReserveError::AllocError {
461 layout: Layout::from_size_align_unchecked(new_size, layout.align()),
466 self.set_memory(memory);
471 // This function is outside `RawVec` to minimize compile times. See the comment
472 // above `RawVec::grow_amortized` for details. (The `A` parameter isn't
473 // significant, because the number of different `A` types seen in practice is
474 // much smaller than the number of `T` types.)
476 new_layout: Result<Layout, LayoutErr>,
477 placement: ReallocPlacement,
478 current_memory: Option<(NonNull<u8>, Layout)>,
480 ) -> Result<MemoryBlock, TryReserveError>
484 // Check for the error here to minimize the size of `RawVec::grow_*`.
485 let new_layout = new_layout.map_err(|_| CapacityOverflow)?;
487 alloc_guard(new_layout.size())?;
489 let memory = if let Some((ptr, old_layout)) = current_memory {
490 debug_assert_eq!(old_layout.align(), new_layout.align());
491 unsafe { alloc.grow(ptr, old_layout, new_layout.size(), placement, Uninitialized) }
494 MayMove => alloc.alloc(new_layout, Uninitialized),
495 InPlace => Err(AllocErr),
498 .map_err(|_| AllocError { layout: new_layout, non_exhaustive: () })?;
503 impl<T> RawVec<T, Global> {
504 /// Converts the entire buffer into `Box<[MaybeUninit<T>]>` with the specified `len`.
506 /// Note that this will correctly reconstitute any `cap` changes
507 /// that may have been performed. (See description of type for details.)
511 /// * `len` must be greater than or equal to the most recently requested capacity, and
512 /// * `len` must be less than or equal to `self.capacity()`.
514 /// Note, that the requested capacity and `self.capacity()` could differ, as
515 /// an allocator could overallocate and return a greater memory block than requested.
516 pub unsafe fn into_box(self, len: usize) -> Box<[MaybeUninit<T>]> {
517 // Sanity-check one half of the safety requirement (we cannot check the other half).
519 len <= self.capacity(),
520 "`len` must be smaller than or equal to `self.capacity()`"
523 let me = ManuallyDrop::new(self);
524 let slice = slice::from_raw_parts_mut(me.ptr() as *mut MaybeUninit<T>, len);
529 unsafe impl<#[may_dangle] T, A: AllocRef> Drop for RawVec<T, A> {
530 /// Frees the memory owned by the `RawVec` *without* trying to drop its contents.
532 if let Some((ptr, layout)) = self.current_memory() {
533 unsafe { self.alloc.dealloc(ptr, layout) }
538 // We need to guarantee the following:
539 // * We don't ever allocate `> isize::MAX` byte-size objects.
540 // * We don't overflow `usize::MAX` and actually allocate too little.
542 // On 64-bit we just need to check for overflow since trying to allocate
543 // `> isize::MAX` bytes will surely fail. On 32-bit and 16-bit we need to add
544 // an extra guard for this in case we're running on a platform which can use
545 // all 4GB in user-space, e.g., PAE or x32.
548 fn alloc_guard(alloc_size: usize) -> Result<(), TryReserveError> {
549 if mem::size_of::<usize>() < 8 && alloc_size > isize::MAX as usize {
550 Err(CapacityOverflow)
556 // One central function responsible for reporting capacity overflows. This'll
557 // ensure that the code generation related to these panics is minimal as there's
558 // only one location which panics rather than a bunch throughout the module.
559 fn capacity_overflow() -> ! {
560 panic!("capacity overflow");