1#![unstable(feature = "raw_vec_internals", reason = "unstable const warnings", issue = "none")]
2
3use core::alloc::LayoutError;
4use core::cmp;
5use core::hint;
6use core::mem::{self, ManuallyDrop, MaybeUninit, SizedTypeProperties};
7use core::ptr::{self, NonNull, Unique};
8
9#[cfg(not(no_global_oom_handling))]
10use crate::alloc::handle_alloc_error;
11use crate::alloc::{Allocator, Global, Layout};
12use crate::boxed::Box;
13use crate::collections::TryReserveError;
14use crate::collections::TryReserveErrorKind::*;
15
16#[cfg(test)]
17mod tests;
18
19// One central function responsible for reporting capacity overflows. This'll
20// ensure that the code generation related to these panics is minimal as there's
21// only one location which panics rather than a bunch throughout the module.
22#[cfg(not(no_global_oom_handling))]
23#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
24fn capacity_overflow() -> ! {
25 panic!("capacity overflow");
26}
27
28enum AllocInit {
29 /// The contents of the new memory are uninitialized.
30 Uninitialized,
31 #[cfg(not(no_global_oom_handling))]
32 /// The new memory is guaranteed to be zeroed.
33 Zeroed,
34}
35
36#[repr(transparent)]
37#[cfg_attr(target_pointer_width = "16", rustc_layout_scalar_valid_range_end(0x7fff))]
38#[cfg_attr(target_pointer_width = "32", rustc_layout_scalar_valid_range_end(0x7fff_ffff))]
39#[cfg_attr(target_pointer_width = "64", rustc_layout_scalar_valid_range_end(0x7fff_ffff_ffff_ffff))]
40struct Cap(usize);
41
42impl Cap {
43 const ZERO: Cap = unsafe { Cap(0) };
44}
45
46/// A low-level utility for more ergonomically allocating, reallocating, and deallocating
47/// a buffer of memory on the heap without having to worry about all the corner cases
48/// involved. This type is excellent for building your own data structures like Vec and VecDeque.
49/// In particular:
50///
51/// * Produces `Unique::dangling()` on zero-sized types.
52/// * Produces `Unique::dangling()` on zero-length allocations.
53/// * Avoids freeing `Unique::dangling()`.
54/// * Catches all overflows in capacity computations (promotes them to "capacity overflow" panics).
55/// * Guards against 32-bit systems allocating more than isize::MAX bytes.
56/// * Guards against overflowing your length.
57/// * Calls `handle_alloc_error` for fallible allocations.
58/// * Contains a `ptr::Unique` and thus endows the user with all related benefits.
59/// * Uses the excess returned from the allocator to use the largest available capacity.
60///
61/// This type does not in anyway inspect the memory that it manages. When dropped it *will*
62/// free its memory, but it *won't* try to drop its contents. It is up to the user of `RawVec`
63/// to handle the actual things *stored* inside of a `RawVec`.
64///
65/// Note that the excess of a zero-sized types is always infinite, so `capacity()` always returns
66/// `usize::MAX`. This means that you need to be careful when round-tripping this type with a
67/// `Box<[T]>`, since `capacity()` won't yield the length.
68#[allow(missing_debug_implementations)]
69pub(crate) struct RawVec<T, A: Allocator = Global> {
70 ptr: Unique<T>,
71 /// Never used for ZSTs; it's `capacity()`'s responsibility to return usize::MAX in that case.
72 ///
73 /// # Safety
74 ///
75 /// `cap` must be in the `0..=isize::MAX` range.
76 cap: Cap,
77 alloc: A,
78}
79
80impl<T> RawVec<T, Global> {
81 /// HACK(Centril): This exists because stable `const fn` can only call stable `const fn`, so
82 /// they cannot call `Self::new()`.
83 ///
84 /// If you change `RawVec<T>::new` or dependencies, please take care to not introduce anything
85 /// that would truly const-call something unstable.
86 pub const NEW: Self = Self::new();
87
88 /// Creates the biggest possible `RawVec` (on the system heap)
89 /// without allocating. If `T` has positive size, then this makes a
90 /// `RawVec` with capacity `0`. If `T` is zero-sized, then it makes a
91 /// `RawVec` with capacity `usize::MAX`. Useful for implementing
92 /// delayed allocation.
93 #[must_use]
94 pub const fn new() -> Self {
95 Self::new_in(Global)
96 }
97
98 /// Creates a `RawVec` (on the system heap) with exactly the
99 /// capacity and alignment requirements for a `[T; capacity]`. This is
100 /// equivalent to calling `RawVec::new` when `capacity` is `0` or `T` is
101 /// zero-sized. Note that if `T` is zero-sized this means you will
102 /// *not* get a `RawVec` with the requested capacity.
103 ///
104 /// Non-fallible version of `try_with_capacity`
105 ///
106 /// # Panics
107 ///
108 /// Panics if the requested capacity exceeds `isize::MAX` bytes.
109 ///
110 /// # Aborts
111 ///
112 /// Aborts on OOM.
113 #[cfg(not(any(no_global_oom_handling, test)))]
114 #[must_use]
115 #[inline]
116 pub fn with_capacity(capacity: usize) -> Self {
117 match Self::try_allocate_in(capacity, AllocInit::Uninitialized, Global) {
118 Ok(res) => res,
119 Err(err) => handle_error(err),
120 }
121 }
122
123 /// Like `with_capacity`, but guarantees the buffer is zeroed.
124 #[cfg(not(any(no_global_oom_handling, test)))]
125 #[must_use]
126 #[inline]
127 pub fn with_capacity_zeroed(capacity: usize) -> Self {
128 Self::with_capacity_zeroed_in(capacity, Global)
129 }
130}
131
132impl<T, A: Allocator> RawVec<T, A> {
133 // Tiny Vecs are dumb. Skip to:
134 // - 8 if the element size is 1, because any heap allocators is likely
135 // to round up a request of less than 8 bytes to at least 8 bytes.
136 // - 4 if elements are moderate-sized (<= 1 KiB).
137 // - 1 otherwise, to avoid wasting too much space for very short Vecs.
138 pub(crate) const MIN_NON_ZERO_CAP: usize = if mem::size_of::<T>() == 1 {
139 8
140 } else if mem::size_of::<T>() <= 1024 {
141 4
142 } else {
143 1
144 };
145
146 /// Like `new`, but parameterized over the choice of allocator for
147 /// the returned `RawVec`.
148 pub const fn new_in(alloc: A) -> Self {
149 // `cap: 0` means "unallocated". zero-sized types are ignored.
150 Self { ptr: Unique::dangling(), cap: Cap::ZERO, alloc }
151 }
152
153 /// Like `with_capacity`, but parameterized over the choice of
154 /// allocator for the returned `RawVec`.
155 #[cfg(not(no_global_oom_handling))]
156 #[inline]
157 pub fn with_capacity_in(capacity: usize, alloc: A) -> Self {
158 match Self::try_allocate_in(capacity, AllocInit::Uninitialized, alloc) {
159 Ok(res) => res,
160 Err(err) => handle_error(err),
161 }
162 }
163
164 /// Like `try_with_capacity`, but parameterized over the choice of
165 /// allocator for the returned `RawVec`.
166 #[inline]
167 pub fn try_with_capacity_in(capacity: usize, alloc: A) -> Result<Self, TryReserveError> {
168 Self::try_allocate_in(capacity, AllocInit::Uninitialized, alloc)
169 }
170
171 /// Like `with_capacity_zeroed`, but parameterized over the choice
172 /// of allocator for the returned `RawVec`.
173 #[cfg(not(no_global_oom_handling))]
174 #[inline]
175 pub fn with_capacity_zeroed_in(capacity: usize, alloc: A) -> Self {
176 match Self::try_allocate_in(capacity, AllocInit::Zeroed, alloc) {
177 Ok(res) => res,
178 Err(err) => handle_error(err),
179 }
180 }
181
182 /// Converts the entire buffer into `Box<[MaybeUninit<T>]>` with the specified `len`.
183 ///
184 /// Note that this will correctly reconstitute any `cap` changes
185 /// that may have been performed. (See description of type for details.)
186 ///
187 /// # Safety
188 ///
189 /// * `len` must be greater than or equal to the most recently requested capacity, and
190 /// * `len` must be less than or equal to `self.capacity()`.
191 ///
192 /// Note, that the requested capacity and `self.capacity()` could differ, as
193 /// an allocator could overallocate and return a greater memory block than requested.
194 pub unsafe fn into_box(self, len: usize) -> Box<[MaybeUninit<T>], A> {
195 // Sanity-check one half of the safety requirement (we cannot check the other half).
196 debug_assert!(
197 len <= self.capacity(),
198 "`len` must be smaller than or equal to `self.capacity()`"
199 );
200
201 let me = ManuallyDrop::new(self);
202 unsafe {
203 let slice = ptr::slice_from_raw_parts_mut(me.ptr() as *mut MaybeUninit<T>, len);
204 Box::from_raw_in(slice, ptr::read(&me.alloc))
205 }
206 }
207
208 fn try_allocate_in(
209 capacity: usize,
210 init: AllocInit,
211 alloc: A,
212 ) -> Result<Self, TryReserveError> {
213 // Don't allocate here because `Drop` will not deallocate when `capacity` is 0.
214
215 if T::IS_ZST || capacity == 0 {
216 Ok(Self::new_in(alloc))
217 } else {
218 // We avoid `unwrap_or_else` here because it bloats the amount of
219 // LLVM IR generated.
220 let layout = match Layout::array::<T>(capacity) {
221 Ok(layout) => layout,
222 Err(_) => return Err(CapacityOverflow.into()),
223 };
224
225 if let Err(err) = alloc_guard(layout.size()) {
226 return Err(err);
227 }
228
229 let result = match init {
230 AllocInit::Uninitialized => alloc.allocate(layout),
231 #[cfg(not(no_global_oom_handling))]
232 AllocInit::Zeroed => alloc.allocate_zeroed(layout),
233 };
234 let ptr = match result {
235 Ok(ptr) => ptr,
236 Err(_) => return Err(AllocError { layout, non_exhaustive: () }.into()),
237 };
238
239 // Allocators currently return a `NonNull<[u8]>` whose length
240 // matches the size requested. If that ever changes, the capacity
241 // here should change to `ptr.len() / mem::size_of::<T>()`.
242 Ok(Self { ptr: Unique::from(ptr.cast()), cap: unsafe { Cap(capacity) }, alloc })
243 }
244 }
245
246 /// Reconstitutes a `RawVec` from a pointer, capacity, and allocator.
247 ///
248 /// # Safety
249 ///
250 /// The `ptr` must be allocated (via the given allocator `alloc`), and with the given
251 /// `capacity`.
252 /// The `capacity` cannot exceed `isize::MAX` for sized types. (only a concern on 32-bit
253 /// systems). For ZSTs capacity is ignored.
254 /// If the `ptr` and `capacity` come from a `RawVec` created via `alloc`, then this is
255 /// guaranteed.
256 #[inline]
257 pub unsafe fn from_raw_parts_in(ptr: *mut T, capacity: usize, alloc: A) -> Self {
258 let cap = if T::IS_ZST { Cap::ZERO } else { unsafe { Cap(capacity) } };
259 Self { ptr: unsafe { Unique::new_unchecked(ptr) }, cap, alloc }
260 }
261
262 /// A convenience method for hoisting the non-null precondition out of [`RawVec::from_raw_parts_in`].
263 ///
264 /// # Safety
265 ///
266 /// See [`RawVec::from_raw_parts_in`].
267 #[inline]
268 pub(crate) unsafe fn from_nonnull_in(ptr: NonNull<T>, capacity: usize, alloc: A) -> Self {
269 let cap = if T::IS_ZST { Cap::ZERO } else { unsafe { Cap(capacity) } };
270 Self { ptr: Unique::from(ptr), cap, alloc }
271 }
272
273 /// Gets a raw pointer to the start of the allocation. Note that this is
274 /// `Unique::dangling()` if `capacity == 0` or `T` is zero-sized. In the former case, you must
275 /// be careful.
276 #[inline]
277 pub fn ptr(&self) -> *mut T {
278 self.ptr.as_ptr()
279 }
280
281 #[inline]
282 pub fn non_null(&self) -> NonNull<T> {
283 NonNull::from(self.ptr)
284 }
285
286 /// Gets the capacity of the allocation.
287 ///
288 /// This will always be `usize::MAX` if `T` is zero-sized.
289 #[inline(always)]
290 pub fn capacity(&self) -> usize {
291 if T::IS_ZST { usize::MAX } else { self.cap.0 }
292 }
293
294 /// Returns a shared reference to the allocator backing this `RawVec`.
295 pub fn allocator(&self) -> &A {
296 &self.alloc
297 }
298
299 fn current_memory(&self) -> Option<(NonNull<u8>, Layout)> {
300 if T::IS_ZST || self.cap.0 == 0 {
301 None
302 } else {
303 // We could use Layout::array here which ensures the absence of isize and usize overflows
304 // and could hypothetically handle differences between stride and size, but this memory
305 // has already been allocated so we know it can't overflow and currently Rust does not
306 // support such types. So we can do better by skipping some checks and avoid an unwrap.
307 const { assert!(mem::size_of::<T>() % mem::align_of::<T>() == 0) };
308 unsafe {
309 let align = mem::align_of::<T>();
310 let size = mem::size_of::<T>().unchecked_mul(self.cap.0);
311 let layout = Layout::from_size_align_unchecked(size, align);
312 Some((self.ptr.cast().into(), layout))
313 }
314 }
315 }
316
317 /// Ensures that the buffer contains at least enough space to hold `len +
318 /// additional` elements. If it doesn't already have enough capacity, will
319 /// reallocate enough space plus comfortable slack space to get amortized
320 /// *O*(1) behavior. Will limit this behavior if it would needlessly cause
321 /// itself to panic.
322 ///
323 /// If `len` exceeds `self.capacity()`, this may fail to actually allocate
324 /// the requested space. This is not really unsafe, but the unsafe
325 /// code *you* write that relies on the behavior of this function may break.
326 ///
327 /// This is ideal for implementing a bulk-push operation like `extend`.
328 ///
329 /// # Panics
330 ///
331 /// Panics if the new capacity exceeds `isize::MAX` _bytes_.
332 ///
333 /// # Aborts
334 ///
335 /// Aborts on OOM.
336 #[cfg(not(no_global_oom_handling))]
337 #[inline]
338 pub fn reserve(&mut self, len: usize, additional: usize) {
339 // Callers expect this function to be very cheap when there is already sufficient capacity.
340 // Therefore, we move all the resizing and error-handling logic from grow_amortized and
341 // handle_reserve behind a call, while making sure that this function is likely to be
342 // inlined as just a comparison and a call if the comparison fails.
343 #[cold]
344 fn do_reserve_and_handle<T, A: Allocator>(
345 slf: &mut RawVec<T, A>,
346 len: usize,
347 additional: usize,
348 ) {
349 if let Err(err) = slf.grow_amortized(len, additional) {
350 handle_error(err);
351 }
352 }
353
354 if self.needs_to_grow(len, additional) {
355 do_reserve_and_handle(self, len, additional);
356 }
357 }
358
359 /// A specialized version of `self.reserve(len, 1)` which requires the
360 /// caller to ensure `len == self.capacity()`.
361 #[cfg(not(no_global_oom_handling))]
362 #[inline(never)]
363 pub fn grow_one(&mut self) {
364 if let Err(err) = self.grow_amortized(self.cap.0, 1) {
365 handle_error(err);
366 }
367 }
368
369 /// The same as `reserve`, but returns on errors instead of panicking or aborting.
370 pub fn try_reserve(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
371 if self.needs_to_grow(len, additional) {
372 self.grow_amortized(len, additional)?;
373 }
374 unsafe {
375 // Inform the optimizer that the reservation has succeeded or wasn't needed
376 hint::assert_unchecked(!self.needs_to_grow(len, additional));
377 }
378 Ok(())
379 }
380
381 /// Ensures that the buffer contains at least enough space to hold `len +
382 /// additional` elements. If it doesn't already, will reallocate the
383 /// minimum possible amount of memory necessary. Generally this will be
384 /// exactly the amount of memory necessary, but in principle the allocator
385 /// is free to give back more than we asked for.
386 ///
387 /// If `len` exceeds `self.capacity()`, this may fail to actually allocate
388 /// the requested space. This is not really unsafe, but the unsafe code
389 /// *you* write that relies on the behavior of this function may break.
390 ///
391 /// # Panics
392 ///
393 /// Panics if the new capacity exceeds `isize::MAX` _bytes_.
394 ///
395 /// # Aborts
396 ///
397 /// Aborts on OOM.
398 #[cfg(not(no_global_oom_handling))]
399 pub fn reserve_exact(&mut self, len: usize, additional: usize) {
400 if let Err(err) = self.try_reserve_exact(len, additional) {
401 handle_error(err);
402 }
403 }
404
405 /// The same as `reserve_exact`, but returns on errors instead of panicking or aborting.
406 pub fn try_reserve_exact(
407 &mut self,
408 len: usize,
409 additional: usize,
410 ) -> Result<(), TryReserveError> {
411 if self.needs_to_grow(len, additional) {
412 self.grow_exact(len, additional)?;
413 }
414 unsafe {
415 // Inform the optimizer that the reservation has succeeded or wasn't needed
416 hint::assert_unchecked(!self.needs_to_grow(len, additional));
417 }
418 Ok(())
419 }
420
421 /// Shrinks the buffer down to the specified capacity. If the given amount
422 /// is 0, actually completely deallocates.
423 ///
424 /// # Panics
425 ///
426 /// Panics if the given amount is *larger* than the current capacity.
427 ///
428 /// # Aborts
429 ///
430 /// Aborts on OOM.
431 #[cfg(not(no_global_oom_handling))]
432 pub fn shrink_to_fit(&mut self, cap: usize) {
433 if let Err(err) = self.shrink(cap) {
434 handle_error(err);
435 }
436 }
437}
438
439impl<T, A: Allocator> RawVec<T, A> {
440 /// Returns if the buffer needs to grow to fulfill the needed extra capacity.
441 /// Mainly used to make inlining reserve-calls possible without inlining `grow`.
442 fn needs_to_grow(&self, len: usize, additional: usize) -> bool {
443 additional > self.capacity().wrapping_sub(len)
444 }
445
446 /// # Safety:
447 ///
448 /// `cap` must not exceed `isize::MAX`.
449 unsafe fn set_ptr_and_cap(&mut self, ptr: NonNull<[u8]>, cap: usize) {
450 // Allocators currently return a `NonNull<[u8]>` whose length matches
451 // the size requested. If that ever changes, the capacity here should
452 // change to `ptr.len() / mem::size_of::<T>()`.
453 self.ptr = Unique::from(ptr.cast());
454 self.cap = unsafe { Cap(cap) };
455 }
456
457 // This method is usually instantiated many times. So we want it to be as
458 // small as possible, to improve compile times. But we also want as much of
459 // its contents to be statically computable as possible, to make the
460 // generated code run faster. Therefore, this method is carefully written
461 // so that all of the code that depends on `T` is within it, while as much
462 // of the code that doesn't depend on `T` as possible is in functions that
463 // are non-generic over `T`.
464 fn grow_amortized(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
465 // This is ensured by the calling contexts.
466 debug_assert!(additional > 0);
467
468 if T::IS_ZST {
469 // Since we return a capacity of `usize::MAX` when `elem_size` is
470 // 0, getting to here necessarily means the `RawVec` is overfull.
471 return Err(CapacityOverflow.into());
472 }
473
474 // Nothing we can really do about these checks, sadly.
475 let required_cap = len.checked_add(additional).ok_or(CapacityOverflow)?;
476
477 // This guarantees exponential growth. The doubling cannot overflow
478 // because `cap <= isize::MAX` and the type of `cap` is `usize`.
479 let cap = cmp::max(self.cap.0 * 2, required_cap);
480 let cap = cmp::max(Self::MIN_NON_ZERO_CAP, cap);
481
482 let new_layout = Layout::array::<T>(cap);
483
484 // `finish_grow` is non-generic over `T`.
485 let ptr = finish_grow(new_layout, self.current_memory(), &mut self.alloc)?;
486 // SAFETY: finish_grow would have resulted in a capacity overflow if we tried to allocate more than isize::MAX items
487 unsafe { self.set_ptr_and_cap(ptr, cap) };
488 Ok(())
489 }
490
491 // The constraints on this method are much the same as those on
492 // `grow_amortized`, but this method is usually instantiated less often so
493 // it's less critical.
494 fn grow_exact(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
495 if T::IS_ZST {
496 // Since we return a capacity of `usize::MAX` when the type size is
497 // 0, getting to here necessarily means the `RawVec` is overfull.
498 return Err(CapacityOverflow.into());
499 }
500
501 let cap = len.checked_add(additional).ok_or(CapacityOverflow)?;
502 let new_layout = Layout::array::<T>(cap);
503
504 // `finish_grow` is non-generic over `T`.
505 let ptr = finish_grow(new_layout, self.current_memory(), &mut self.alloc)?;
506 // SAFETY: finish_grow would have resulted in a capacity overflow if we tried to allocate more than isize::MAX items
507 unsafe {
508 self.set_ptr_and_cap(ptr, cap);
509 }
510 Ok(())
511 }
512
513 #[cfg(not(no_global_oom_handling))]
514 fn shrink(&mut self, cap: usize) -> Result<(), TryReserveError> {
515 assert!(cap <= self.capacity(), "Tried to shrink to a larger capacity");
516
517 let (ptr, layout) = if let Some(mem) = self.current_memory() { mem } else { return Ok(()) };
518 // See current_memory() why this assert is here
519 const { assert!(mem::size_of::<T>() % mem::align_of::<T>() == 0) };
520
521 // If shrinking to 0, deallocate the buffer. We don't reach this point
522 // for the T::IS_ZST case since current_memory() will have returned
523 // None.
524 if cap == 0 {
525 unsafe { self.alloc.deallocate(ptr, layout) };
526 self.ptr = Unique::dangling();
527 self.cap = Cap::ZERO;
528 } else {
529 let ptr = unsafe {
530 // `Layout::array` cannot overflow here because it would have
531 // overflowed earlier when capacity was larger.
532 let new_size = mem::size_of::<T>().unchecked_mul(cap);
533 let new_layout = Layout::from_size_align_unchecked(new_size, layout.align());
534 self.alloc
535 .shrink(ptr, layout, new_layout)
536 .map_err(|_| AllocError { layout: new_layout, non_exhaustive: () })?
537 };
538 // SAFETY: if the allocation is valid, then the capacity is too
539 unsafe {
540 self.set_ptr_and_cap(ptr, cap);
541 }
542 }
543 Ok(())
544 }
545}
546
547// This function is outside `RawVec` to minimize compile times. See the comment
548// above `RawVec::grow_amortized` for details. (The `A` parameter isn't
549// significant, because the number of different `A` types seen in practice is
550// much smaller than the number of `T` types.)
551#[inline(never)]
552fn finish_grow<A>(
553 new_layout: Result<Layout, LayoutError>,
554 current_memory: Option<(NonNull<u8>, Layout)>,
555 alloc: &mut A,
556) -> Result<NonNull<[u8]>, TryReserveError>
557where
558 A: Allocator,
559{
560 // Check for the error here to minimize the size of `RawVec::grow_*`.
561 let new_layout: Layout = new_layout.map_err(|_| CapacityOverflow)?;
562
563 alloc_guard(alloc_size:new_layout.size())?;
564
565 let memory: Result, AllocError> = if let Some((ptr: NonNull, old_layout: Layout)) = current_memory {
566 debug_assert_eq!(old_layout.align(), new_layout.align());
567 unsafe {
568 // The allocator checks for alignment equality
569 hint::assert_unchecked(cond:old_layout.align() == new_layout.align());
570 alloc.grow(ptr, old_layout, new_layout)
571 }
572 } else {
573 alloc.allocate(new_layout)
574 };
575
576 memory.map_err(|_| AllocError { layout: new_layout, non_exhaustive: () }.into())
577}
578
579unsafe impl<#[may_dangle] T, A: Allocator> Drop for RawVec<T, A> {
580 /// Frees the memory owned by the `RawVec` *without* trying to drop its contents.
581 fn drop(&mut self) {
582 if let Some((ptr: NonNull, layout: Layout)) = self.current_memory() {
583 unsafe { self.alloc.deallocate(ptr, layout) }
584 }
585 }
586}
587
588// Central function for reserve error handling.
589#[cfg(not(no_global_oom_handling))]
590#[cold]
591fn handle_error(e: TryReserveError) -> ! {
592 match e.kind() {
593 CapacityOverflow => capacity_overflow(),
594 AllocError { layout: Layout, .. } => handle_alloc_error(layout),
595 }
596}
597
598// We need to guarantee the following:
599// * We don't ever allocate `> isize::MAX` byte-size objects.
600// * We don't overflow `usize::MAX` and actually allocate too little.
601//
602// On 64-bit we just need to check for overflow since trying to allocate
603// `> isize::MAX` bytes will surely fail. On 32-bit and 16-bit we need to add
604// an extra guard for this in case we're running on a platform which can use
605// all 4GB in user-space, e.g., PAE or x32.
606#[inline]
607fn alloc_guard(alloc_size: usize) -> Result<(), TryReserveError> {
608 if usize::BITS < 64 && alloc_size > isize::MAX as usize {
609 Err(CapacityOverflow.into())
610 } else {
611 Ok(())
612 }
613}
614