1 #![unstable(feature = "raw_vec_internals", reason = "unstable const warnings", issue = "none")]
2
3 use core::alloc::LayoutError;
4 use core::cmp;
5 use core::intrinsics;
6 use core::mem::{self, ManuallyDrop, MaybeUninit};
7 use core::ops::Drop;
8 use core::ptr::{self, NonNull, Unique};
9 use core::slice;
10
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::*;
17
18 #[cfg(test)]
19 mod tests;
20
21 #[cfg(not(no_global_oom_handling))]
22 enum AllocInit {
23 /// The contents of the new memory are uninitialized.
24 Uninitialized,
25 /// The new memory is guaranteed to be zeroed.
26 Zeroed,
27 }
28
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.
32 /// In particular:
33 ///
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.
43 ///
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`.
47 ///
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> {
53 ptr: Unique<T>,
54 cap: usize,
55 alloc: A,
56 }
57
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()`.
61 ///
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();
65
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 #[must_use]
new() -> Self72 pub const fn new() -> Self {
73 Self::new_in(Global)
74 }
75
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.
81 ///
82 /// # Panics
83 ///
84 /// Panics if the requested capacity exceeds `isize::MAX` bytes.
85 ///
86 /// # Aborts
87 ///
88 /// Aborts on OOM.
89 #[cfg(not(any(no_global_oom_handling, test)))]
90 #[must_use]
91 #[inline]
with_capacity(capacity: usize) -> Self92 pub fn with_capacity(capacity: usize) -> Self {
93 Self::with_capacity_in(capacity, Global)
94 }
95
96 /// Like `with_capacity`, but guarantees the buffer is zeroed.
97 #[cfg(not(any(no_global_oom_handling, test)))]
98 #[must_use]
99 #[inline]
with_capacity_zeroed(capacity: usize) -> Self100 pub fn with_capacity_zeroed(capacity: usize) -> Self {
101 Self::with_capacity_zeroed_in(capacity, Global)
102 }
103 }
104
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 const MIN_NON_ZERO_CAP: usize = if mem::size_of::<T>() == 1 {
112 8
113 } else if mem::size_of::<T>() <= 1024 {
114 4
115 } else {
116 1
117 };
118
119 /// Like `new`, but parameterized over the choice of allocator for
120 /// the returned `RawVec`.
121 #[rustc_allow_const_fn_unstable(const_fn)]
new_in(alloc: A) -> Self122 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 }
125 }
126
127 /// Like `with_capacity`, but parameterized over the choice of
128 /// allocator for the returned `RawVec`.
129 #[cfg(not(no_global_oom_handling))]
130 #[inline]
with_capacity_in(capacity: usize, alloc: A) -> Self131 pub fn with_capacity_in(capacity: usize, alloc: A) -> Self {
132 Self::allocate_in(capacity, AllocInit::Uninitialized, alloc)
133 }
134
135 /// Like `with_capacity_zeroed`, but parameterized over the choice
136 /// of allocator for the returned `RawVec`.
137 #[cfg(not(no_global_oom_handling))]
138 #[inline]
with_capacity_zeroed_in(capacity: usize, alloc: A) -> Self139 pub fn with_capacity_zeroed_in(capacity: usize, alloc: A) -> Self {
140 Self::allocate_in(capacity, AllocInit::Zeroed, alloc)
141 }
142
143 /// Converts the entire buffer into `Box<[MaybeUninit<T>]>` with the specified `len`.
144 ///
145 /// Note that this will correctly reconstitute any `cap` changes
146 /// that may have been performed. (See description of type for details.)
147 ///
148 /// # Safety
149 ///
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()`.
152 ///
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.
into_box(self, len: usize) -> Box<[MaybeUninit<T>], A>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).
157 debug_assert!(
158 len <= self.capacity(),
159 "`len` must be smaller than or equal to `self.capacity()`"
160 );
161
162 let me = ManuallyDrop::new(self);
163 unsafe {
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))
166 }
167 }
168
169 #[cfg(not(no_global_oom_handling))]
allocate_in(capacity: usize, init: AllocInit, alloc: A) -> Self170 fn allocate_in(capacity: usize, init: AllocInit, alloc: A) -> Self {
171 if mem::size_of::<T>() == 0 {
172 Self::new_in(alloc)
173 } else {
174 // We avoid `unwrap_or_else` here because it bloats the amount of
175 // LLVM IR generated.
176 let layout = match Layout::array::<T>(capacity) {
177 Ok(layout) => layout,
178 Err(_) => capacity_overflow(),
179 };
180 match alloc_guard(layout.size()) {
181 Ok(_) => {}
182 Err(_) => capacity_overflow(),
183 }
184 let result = match init {
185 AllocInit::Uninitialized => alloc.allocate(layout),
186 AllocInit::Zeroed => alloc.allocate_zeroed(layout),
187 };
188 let ptr = match result {
189 Ok(ptr) => ptr,
190 Err(_) => handle_alloc_error(layout),
191 };
192
193 Self {
194 ptr: unsafe { Unique::new_unchecked(ptr.cast().as_ptr()) },
195 cap: Self::capacity_from_bytes(ptr.len()),
196 alloc,
197 }
198 }
199 }
200
201 /// Reconstitutes a `RawVec` from a pointer, capacity, and allocator.
202 ///
203 /// # Safety
204 ///
205 /// The `ptr` must be allocated (via the given allocator `alloc`), and with the given
206 /// `capacity`.
207 /// The `capacity` cannot exceed `isize::MAX` for sized types. (only a concern on 32-bit
208 /// systems). ZST vectors may have a capacity up to `usize::MAX`.
209 /// If the `ptr` and `capacity` come from a `RawVec` created via `alloc`, then this is
210 /// guaranteed.
211 #[inline]
from_raw_parts_in(ptr: *mut T, capacity: usize, alloc: A) -> Self212 pub unsafe fn from_raw_parts_in(ptr: *mut T, capacity: usize, alloc: A) -> Self {
213 Self { ptr: unsafe { Unique::new_unchecked(ptr) }, cap: capacity, alloc }
214 }
215
216 /// Gets a raw pointer to the start of the allocation. Note that this is
217 /// `Unique::dangling()` if `capacity == 0` or `T` is zero-sized. In the former case, you must
218 /// be careful.
219 #[inline]
ptr(&self) -> *mut T220 pub fn ptr(&self) -> *mut T {
221 self.ptr.as_ptr()
222 }
223
224 /// Gets the capacity of the allocation.
225 ///
226 /// This will always be `usize::MAX` if `T` is zero-sized.
227 #[inline(always)]
capacity(&self) -> usize228 pub fn capacity(&self) -> usize {
229 if mem::size_of::<T>() == 0 { usize::MAX } else { self.cap }
230 }
231
232 /// Returns a shared reference to the allocator backing this `RawVec`.
allocator(&self) -> &A233 pub fn allocator(&self) -> &A {
234 &self.alloc
235 }
236
current_memory(&self) -> Option<(NonNull<u8>, Layout)>237 fn current_memory(&self) -> Option<(NonNull<u8>, Layout)> {
238 if mem::size_of::<T>() == 0 || self.cap == 0 {
239 None
240 } else {
241 // We have an allocated chunk of memory, so we can bypass runtime
242 // checks to get our current layout.
243 unsafe {
244 let align = mem::align_of::<T>();
245 let size = mem::size_of::<T>() * self.cap;
246 let layout = Layout::from_size_align_unchecked(size, align);
247 Some((self.ptr.cast().into(), layout))
248 }
249 }
250 }
251
252 /// Ensures that the buffer contains at least enough space to hold `len +
253 /// additional` elements. If it doesn't already have enough capacity, will
254 /// reallocate enough space plus comfortable slack space to get amortized
255 /// *O*(1) behavior. Will limit this behavior if it would needlessly cause
256 /// itself to panic.
257 ///
258 /// If `len` exceeds `self.capacity()`, this may fail to actually allocate
259 /// the requested space. This is not really unsafe, but the unsafe
260 /// code *you* write that relies on the behavior of this function may break.
261 ///
262 /// This is ideal for implementing a bulk-push operation like `extend`.
263 ///
264 /// # Panics
265 ///
266 /// Panics if the new capacity exceeds `isize::MAX` bytes.
267 ///
268 /// # Aborts
269 ///
270 /// Aborts on OOM.
271 #[cfg(not(no_global_oom_handling))]
272 #[inline]
reserve(&mut self, len: usize, additional: usize)273 pub fn reserve(&mut self, len: usize, additional: usize) {
274 // Callers expect this function to be very cheap when there is already sufficient capacity.
275 // Therefore, we move all the resizing and error-handling logic from grow_amortized and
276 // handle_reserve behind a call, while making sure that this function is likely to be
277 // inlined as just a comparison and a call if the comparison fails.
278 #[cold]
279 fn do_reserve_and_handle<T, A: Allocator>(
280 slf: &mut RawVec<T, A>,
281 len: usize,
282 additional: usize,
283 ) {
284 handle_reserve(slf.grow_amortized(len, additional));
285 }
286
287 if self.needs_to_grow(len, additional) {
288 do_reserve_and_handle(self, len, additional);
289 }
290 }
291
292 /// The same as `reserve`, but returns on errors instead of panicking or aborting.
try_reserve(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError>293 pub fn try_reserve(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
294 if self.needs_to_grow(len, additional) {
295 self.grow_amortized(len, additional)
296 } else {
297 Ok(())
298 }
299 }
300
301 /// Ensures that the buffer contains at least enough space to hold `len +
302 /// additional` elements. If it doesn't already, will reallocate the
303 /// minimum possible amount of memory necessary. Generally this will be
304 /// exactly the amount of memory necessary, but in principle the allocator
305 /// is free to give back more than we asked for.
306 ///
307 /// If `len` exceeds `self.capacity()`, this may fail to actually allocate
308 /// the requested space. This is not really unsafe, but the unsafe code
309 /// *you* write that relies on the behavior of this function may break.
310 ///
311 /// # Panics
312 ///
313 /// Panics if the new capacity exceeds `isize::MAX` bytes.
314 ///
315 /// # Aborts
316 ///
317 /// Aborts on OOM.
318 #[cfg(not(no_global_oom_handling))]
reserve_exact(&mut self, len: usize, additional: usize)319 pub fn reserve_exact(&mut self, len: usize, additional: usize) {
320 handle_reserve(self.try_reserve_exact(len, additional));
321 }
322
323 /// The same as `reserve_exact`, but returns on errors instead of panicking or aborting.
try_reserve_exact( &mut self, len: usize, additional: usize, ) -> Result<(), TryReserveError>324 pub fn try_reserve_exact(
325 &mut self,
326 len: usize,
327 additional: usize,
328 ) -> Result<(), TryReserveError> {
329 if self.needs_to_grow(len, additional) { self.grow_exact(len, additional) } else { Ok(()) }
330 }
331
332 /// Shrinks the allocation down to the specified amount. If the given amount
333 /// is 0, actually completely deallocates.
334 ///
335 /// # Panics
336 ///
337 /// Panics if the given amount is *larger* than the current capacity.
338 ///
339 /// # Aborts
340 ///
341 /// Aborts on OOM.
342 #[cfg(not(no_global_oom_handling))]
shrink_to_fit(&mut self, amount: usize)343 pub fn shrink_to_fit(&mut self, amount: usize) {
344 handle_reserve(self.shrink(amount));
345 }
346 }
347
348 impl<T, A: Allocator> RawVec<T, A> {
349 /// Returns if the buffer needs to grow to fulfill the needed extra capacity.
350 /// Mainly used to make inlining reserve-calls possible without inlining `grow`.
needs_to_grow(&self, len: usize, additional: usize) -> bool351 fn needs_to_grow(&self, len: usize, additional: usize) -> bool {
352 additional > self.capacity().wrapping_sub(len)
353 }
354
capacity_from_bytes(excess: usize) -> usize355 fn capacity_from_bytes(excess: usize) -> usize {
356 debug_assert_ne!(mem::size_of::<T>(), 0);
357 excess / mem::size_of::<T>()
358 }
359
set_ptr(&mut self, ptr: NonNull<[u8]>)360 fn set_ptr(&mut self, ptr: NonNull<[u8]>) {
361 self.ptr = unsafe { Unique::new_unchecked(ptr.cast().as_ptr()) };
362 self.cap = Self::capacity_from_bytes(ptr.len());
363 }
364
365 // This method is usually instantiated many times. So we want it to be as
366 // small as possible, to improve compile times. But we also want as much of
367 // its contents to be statically computable as possible, to make the
368 // generated code run faster. Therefore, this method is carefully written
369 // so that all of the code that depends on `T` is within it, while as much
370 // of the code that doesn't depend on `T` as possible is in functions that
371 // are non-generic over `T`.
grow_amortized(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError>372 fn grow_amortized(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
373 // This is ensured by the calling contexts.
374 debug_assert!(additional > 0);
375
376 if mem::size_of::<T>() == 0 {
377 // Since we return a capacity of `usize::MAX` when `elem_size` is
378 // 0, getting to here necessarily means the `RawVec` is overfull.
379 return Err(CapacityOverflow.into());
380 }
381
382 // Nothing we can really do about these checks, sadly.
383 let required_cap = len.checked_add(additional).ok_or(CapacityOverflow)?;
384
385 // This guarantees exponential growth. The doubling cannot overflow
386 // because `cap <= isize::MAX` and the type of `cap` is `usize`.
387 let cap = cmp::max(self.cap * 2, required_cap);
388 let cap = cmp::max(Self::MIN_NON_ZERO_CAP, cap);
389
390 let new_layout = Layout::array::<T>(cap);
391
392 // `finish_grow` is non-generic over `T`.
393 let ptr = finish_grow(new_layout, self.current_memory(), &mut self.alloc)?;
394 self.set_ptr(ptr);
395 Ok(())
396 }
397
398 // The constraints on this method are much the same as those on
399 // `grow_amortized`, but this method is usually instantiated less often so
400 // it's less critical.
grow_exact(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError>401 fn grow_exact(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
402 if mem::size_of::<T>() == 0 {
403 // Since we return a capacity of `usize::MAX` when the type size is
404 // 0, getting to here necessarily means the `RawVec` is overfull.
405 return Err(CapacityOverflow.into());
406 }
407
408 let cap = len.checked_add(additional).ok_or(CapacityOverflow)?;
409 let new_layout = Layout::array::<T>(cap);
410
411 // `finish_grow` is non-generic over `T`.
412 let ptr = finish_grow(new_layout, self.current_memory(), &mut self.alloc)?;
413 self.set_ptr(ptr);
414 Ok(())
415 }
416
shrink(&mut self, amount: usize) -> Result<(), TryReserveError>417 fn shrink(&mut self, amount: usize) -> Result<(), TryReserveError> {
418 assert!(amount <= self.capacity(), "Tried to shrink to a larger capacity");
419
420 let (ptr, layout) = if let Some(mem) = self.current_memory() { mem } else { return Ok(()) };
421 let new_size = amount * mem::size_of::<T>();
422
423 let ptr = unsafe {
424 let new_layout = Layout::from_size_align_unchecked(new_size, layout.align());
425 self.alloc
426 .shrink(ptr, layout, new_layout)
427 .map_err(|_| AllocError { layout: new_layout, non_exhaustive: () })?
428 };
429 self.set_ptr(ptr);
430 Ok(())
431 }
432 }
433
434 // This function is outside `RawVec` to minimize compile times. See the comment
435 // above `RawVec::grow_amortized` for details. (The `A` parameter isn't
436 // significant, because the number of different `A` types seen in practice is
437 // much smaller than the number of `T` types.)
438 #[inline(never)]
finish_grow<A>( new_layout: Result<Layout, LayoutError>, current_memory: Option<(NonNull<u8>, Layout)>, alloc: &mut A, ) -> Result<NonNull<[u8]>, TryReserveError> where A: Allocator,439 fn finish_grow<A>(
440 new_layout: Result<Layout, LayoutError>,
441 current_memory: Option<(NonNull<u8>, Layout)>,
442 alloc: &mut A,
443 ) -> Result<NonNull<[u8]>, TryReserveError>
444 where
445 A: Allocator,
446 {
447 // Check for the error here to minimize the size of `RawVec::grow_*`.
448 let new_layout = new_layout.map_err(|_| CapacityOverflow)?;
449
450 alloc_guard(new_layout.size())?;
451
452 let memory = if let Some((ptr, old_layout)) = current_memory {
453 debug_assert_eq!(old_layout.align(), new_layout.align());
454 unsafe {
455 // The allocator checks for alignment equality
456 intrinsics::assume(old_layout.align() == new_layout.align());
457 alloc.grow(ptr, old_layout, new_layout)
458 }
459 } else {
460 alloc.allocate(new_layout)
461 };
462
463 memory.map_err(|_| AllocError { layout: new_layout, non_exhaustive: () }.into())
464 }
465
466 unsafe impl<#[may_dangle] T, A: Allocator> Drop for RawVec<T, A> {
467 /// Frees the memory owned by the `RawVec` *without* trying to drop its contents.
drop(&mut self)468 fn drop(&mut self) {
469 if let Some((ptr, layout)) = self.current_memory() {
470 unsafe { self.alloc.deallocate(ptr, layout) }
471 }
472 }
473 }
474
475 // Central function for reserve error handling.
476 #[cfg(not(no_global_oom_handling))]
477 #[inline]
handle_reserve(result: Result<(), TryReserveError>)478 fn handle_reserve(result: Result<(), TryReserveError>) {
479 match result.map_err(|e| e.kind()) {
480 Err(CapacityOverflow) => capacity_overflow(),
481 Err(AllocError { layout, .. }) => handle_alloc_error(layout),
482 Ok(()) => { /* yay */ }
483 }
484 }
485
486 // We need to guarantee the following:
487 // * We don't ever allocate `> isize::MAX` byte-size objects.
488 // * We don't overflow `usize::MAX` and actually allocate too little.
489 //
490 // On 64-bit we just need to check for overflow since trying to allocate
491 // `> isize::MAX` bytes will surely fail. On 32-bit and 16-bit we need to add
492 // an extra guard for this in case we're running on a platform which can use
493 // all 4GB in user-space, e.g., PAE or x32.
494
495 #[inline]
alloc_guard(alloc_size: usize) -> Result<(), TryReserveError>496 fn alloc_guard(alloc_size: usize) -> Result<(), TryReserveError> {
497 if usize::BITS < 64 && alloc_size > isize::MAX as usize {
498 Err(CapacityOverflow.into())
499 } else {
500 Ok(())
501 }
502 }
503
504 // One central function responsible for reporting capacity overflows. This'll
505 // ensure that the code generation related to these panics is minimal as there's
506 // only one location which panics rather than a bunch throughout the module.
507 #[cfg(not(no_global_oom_handling))]
capacity_overflow() -> !508 fn capacity_overflow() -> ! {
509 panic!("capacity overflow");
510 }
511