1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
12 use core
::heap
::{Alloc, Layout}
;
15 use core
::ptr
::{self, Unique}
;
18 use super::boxed
::Box
;
19 use super::allocator
::CollectionAllocErr
;
20 use super::allocator
::CollectionAllocErr
::*;
22 /// A low-level utility for more ergonomically allocating, reallocating, and deallocating
23 /// a buffer of memory on the heap without having to worry about all the corner cases
24 /// involved. This type is excellent for building your own data structures like Vec and VecDeque.
27 /// * Produces Unique::empty() on zero-sized types
28 /// * Produces Unique::empty() on zero-length allocations
29 /// * Catches all overflows in capacity computations (promotes them to "capacity overflow" panics)
30 /// * Guards against 32-bit systems allocating more than isize::MAX bytes
31 /// * Guards against overflowing your length
33 /// * Avoids freeing Unique::empty()
34 /// * Contains a ptr::Unique and thus endows the user with all related benefits
36 /// This type does not in anyway inspect the memory that it manages. When dropped it *will*
37 /// free its memory, but it *won't* try to Drop its contents. It is up to the user of RawVec
38 /// to handle the actual things *stored* inside of a RawVec.
40 /// Note that a RawVec always forces its capacity to be usize::MAX for zero-sized types.
41 /// This enables you to use capacity growing logic catch the overflows in your length
42 /// that might occur with zero-sized types.
44 /// However this means that you need to be careful when roundtripping this type
45 /// with a `Box<[T]>`: `cap()` won't yield the len. However `with_capacity`,
46 /// `shrink_to_fit`, and `from_box` will actually set RawVec's private capacity
47 /// field. This allows zero-sized types to not be special-cased by consumers of
49 #[allow(missing_debug_implementations)]
50 pub struct RawVec
<T
, A
: Alloc
= Heap
> {
56 impl<T
, A
: Alloc
> RawVec
<T
, A
> {
57 /// Like `new` but parameterized over the choice of allocator for
58 /// the returned RawVec.
59 pub fn new_in(a
: A
) -> Self {
60 // !0 is usize::MAX. This branch should be stripped at compile time.
61 let cap
= if mem
::size_of
::<T
>() == 0 { !0 }
else { 0 }
;
63 // Unique::empty() doubles as "unallocated" and "zero-sized allocation"
71 /// Like `with_capacity` but parameterized over the choice of
72 /// allocator for the returned RawVec.
74 pub fn with_capacity_in(cap
: usize, a
: A
) -> Self {
75 RawVec
::allocate_in(cap
, false, a
)
78 /// Like `with_capacity_zeroed` but parameterized over the choice
79 /// of allocator for the returned RawVec.
81 pub fn with_capacity_zeroed_in(cap
: usize, a
: A
) -> Self {
82 RawVec
::allocate_in(cap
, true, a
)
85 fn allocate_in(cap
: usize, zeroed
: bool
, mut a
: A
) -> Self {
87 let elem_size
= mem
::size_of
::<T
>();
89 let alloc_size
= cap
.checked_mul(elem_size
).expect("capacity overflow");
90 alloc_guard(alloc_size
).expect("capacity overflow");
92 // handles ZSTs and `cap = 0` alike
93 let ptr
= if alloc_size
== 0 {
94 mem
::align_of
::<T
>() as *mut u8
96 let align
= mem
::align_of
::<T
>();
97 let result
= if zeroed
{
98 a
.alloc_zeroed(Layout
::from_size_align(alloc_size
, align
).unwrap())
100 a
.alloc(Layout
::from_size_align(alloc_size
, align
).unwrap())
104 Err(err
) => a
.oom(err
),
109 ptr
: Unique
::new_unchecked(ptr
as *mut _
),
117 impl<T
> RawVec
<T
, Heap
> {
118 /// Creates the biggest possible RawVec (on the system heap)
119 /// without allocating. If T has positive size, then this makes a
120 /// RawVec with capacity 0. If T has 0 size, then it makes a
121 /// RawVec with capacity `usize::MAX`. Useful for implementing
122 /// delayed allocation.
123 pub fn new() -> Self {
127 /// Creates a RawVec (on the system heap) with exactly the
128 /// capacity and alignment requirements for a `[T; cap]`. This is
129 /// equivalent to calling RawVec::new when `cap` is 0 or T is
130 /// zero-sized. Note that if `T` is zero-sized this means you will
131 /// *not* get a RawVec with the requested capacity!
135 /// * Panics if the requested capacity exceeds `usize::MAX` bytes.
136 /// * Panics on 32-bit platforms if the requested capacity exceeds
137 /// `isize::MAX` bytes.
143 pub fn with_capacity(cap
: usize) -> Self {
144 RawVec
::allocate_in(cap
, false, Heap
)
147 /// Like `with_capacity` but guarantees the buffer is zeroed.
149 pub fn with_capacity_zeroed(cap
: usize) -> Self {
150 RawVec
::allocate_in(cap
, true, Heap
)
154 impl<T
, A
: Alloc
> RawVec
<T
, A
> {
155 /// Reconstitutes a RawVec from a pointer, capacity, and allocator.
157 /// # Undefined Behavior
159 /// The ptr must be allocated (via the given allocator `a`), and with the given capacity. The
160 /// capacity cannot exceed `isize::MAX` (only a concern on 32-bit systems).
161 /// If the ptr and capacity come from a RawVec created via `a`, then this is guaranteed.
162 pub unsafe fn from_raw_parts_in(ptr
: *mut T
, cap
: usize, a
: A
) -> Self {
164 ptr
: Unique
::new_unchecked(ptr
),
171 impl<T
> RawVec
<T
, Heap
> {
172 /// Reconstitutes a RawVec from a pointer, capacity.
174 /// # Undefined Behavior
176 /// The ptr must be allocated (on the system heap), and with the given capacity. The
177 /// capacity cannot exceed `isize::MAX` (only a concern on 32-bit systems).
178 /// If the ptr and capacity come from a RawVec, then this is guaranteed.
179 pub unsafe fn from_raw_parts(ptr
: *mut T
, cap
: usize) -> Self {
181 ptr
: Unique
::new_unchecked(ptr
),
187 /// Converts a `Box<[T]>` into a `RawVec<T>`.
188 pub fn from_box(mut slice
: Box
<[T
]>) -> Self {
190 let result
= RawVec
::from_raw_parts(slice
.as_mut_ptr(), slice
.len());
197 impl<T
, A
: Alloc
> RawVec
<T
, A
> {
198 /// Gets a raw pointer to the start of the allocation. Note that this is
199 /// Unique::empty() if `cap = 0` or T is zero-sized. In the former case, you must
201 pub fn ptr(&self) -> *mut T
{
205 /// Gets the capacity of the allocation.
207 /// This will always be `usize::MAX` if `T` is zero-sized.
209 pub fn cap(&self) -> usize {
210 if mem
::size_of
::<T
>() == 0 {
217 /// Returns a shared reference to the allocator backing this RawVec.
218 pub fn alloc(&self) -> &A
{
222 /// Returns a mutable reference to the allocator backing this RawVec.
223 pub fn alloc_mut(&mut self) -> &mut A
{
227 fn current_layout(&self) -> Option
<Layout
> {
231 // We have an allocated chunk of memory, so we can bypass runtime
232 // checks to get our current layout.
234 let align
= mem
::align_of
::<T
>();
235 let size
= mem
::size_of
::<T
>() * self.cap
;
236 Some(Layout
::from_size_align_unchecked(size
, align
))
241 /// Doubles the size of the type's backing allocation. This is common enough
242 /// to want to do that it's easiest to just have a dedicated method. Slightly
243 /// more efficient logic can be provided for this than the general case.
245 /// This function is ideal for when pushing elements one-at-a-time because
246 /// you don't need to incur the costs of the more general computations
247 /// reserve needs to do to guard against overflow. You do however need to
248 /// manually check if your `len == cap`.
252 /// * Panics if T is zero-sized on the assumption that you managed to exhaust
253 /// all `usize::MAX` slots in your imaginary buffer.
254 /// * Panics on 32-bit platforms if the requested capacity exceeds
255 /// `isize::MAX` bytes.
264 /// # #![feature(alloc)]
265 /// # extern crate alloc;
267 /// # use alloc::raw_vec::RawVec;
268 /// struct MyVec<T> {
273 /// impl<T> MyVec<T> {
274 /// pub fn push(&mut self, elem: T) {
275 /// if self.len == self.buf.cap() { self.buf.double(); }
276 /// // double would have aborted or panicked if the len exceeded
277 /// // `isize::MAX` so this is safe to do unchecked now.
279 /// ptr::write(self.buf.ptr().offset(self.len as isize), elem);
285 /// # let mut vec = MyVec { buf: RawVec::new(), len: 0 };
291 pub fn double(&mut self) {
293 let elem_size
= mem
::size_of
::<T
>();
295 // since we set the capacity to usize::MAX when elem_size is
296 // 0, getting to here necessarily means the RawVec is overfull.
297 assert
!(elem_size
!= 0, "capacity overflow");
299 let (new_cap
, uniq
) = match self.current_layout() {
301 // Since we guarantee that we never allocate more than
302 // isize::MAX bytes, `elem_size * self.cap <= isize::MAX` as
303 // a precondition, so this can't overflow. Additionally the
304 // alignment will never be too large as to "not be
305 // satisfiable", so `Layout::from_size_align` will always
308 // tl;dr; we bypass runtime checks due to dynamic assertions
309 // in this module, allowing us to use
310 // `from_size_align_unchecked`.
311 let new_cap
= 2 * self.cap
;
312 let new_size
= new_cap
* elem_size
;
313 let new_layout
= Layout
::from_size_align_unchecked(new_size
, cur
.align());
314 alloc_guard(new_size
).expect("capacity overflow");
315 let ptr_res
= self.a
.realloc(self.ptr
.as_ptr() as *mut u8,
319 Ok(ptr
) => (new_cap
, Unique
::new_unchecked(ptr
as *mut T
)),
320 Err(e
) => self.a
.oom(e
),
324 // skip to 4 because tiny Vec's are dumb; but not if that
325 // would cause overflow
326 let new_cap
= if elem_size
> (!0) / 8 { 1 }
else { 4 }
;
327 match self.a
.alloc_array
::<T
>(new_cap
) {
328 Ok(ptr
) => (new_cap
, ptr
.into()),
329 Err(e
) => self.a
.oom(e
),
338 /// Attempts to double the size of the type's backing allocation in place. This is common
339 /// enough to want to do that it's easiest to just have a dedicated method. Slightly
340 /// more efficient logic can be provided for this than the general case.
342 /// Returns true if the reallocation attempt has succeeded, or false otherwise.
346 /// * Panics if T is zero-sized on the assumption that you managed to exhaust
347 /// all `usize::MAX` slots in your imaginary buffer.
348 /// * Panics on 32-bit platforms if the requested capacity exceeds
349 /// `isize::MAX` bytes.
352 pub fn double_in_place(&mut self) -> bool
{
354 let elem_size
= mem
::size_of
::<T
>();
355 let old_layout
= match self.current_layout() {
356 Some(layout
) => layout
,
357 None
=> return false, // nothing to double
360 // since we set the capacity to usize::MAX when elem_size is
361 // 0, getting to here necessarily means the RawVec is overfull.
362 assert
!(elem_size
!= 0, "capacity overflow");
364 // Since we guarantee that we never allocate more than isize::MAX
365 // bytes, `elem_size * self.cap <= isize::MAX` as a precondition, so
366 // this can't overflow.
368 // Similarly like with `double` above we can go straight to
369 // `Layout::from_size_align_unchecked` as we know this won't
370 // overflow and the alignment is sufficiently small.
371 let new_cap
= 2 * self.cap
;
372 let new_size
= new_cap
* elem_size
;
373 alloc_guard(new_size
).expect("capacity overflow");
374 let ptr
= self.ptr() as *mut _
;
375 let new_layout
= Layout
::from_size_align_unchecked(new_size
, old_layout
.align());
376 match self.a
.grow_in_place(ptr
, old_layout
, new_layout
) {
378 // We can't directly divide `size`.
389 /// Ensures that the buffer contains at least enough space to hold
390 /// `used_cap + needed_extra_cap` elements. If it doesn't already,
391 /// will reallocate the minimum possible amount of memory necessary.
392 /// Generally this will be exactly the amount of memory necessary,
393 /// but in principle the allocator is free to give back more than
396 /// If `used_cap` exceeds `self.cap()`, this may fail to actually allocate
397 /// the requested space. This is not really unsafe, but the unsafe
398 /// code *you* write that relies on the behavior of this function may break.
402 /// * Panics if the requested capacity exceeds `usize::MAX` bytes.
403 /// * Panics on 32-bit platforms if the requested capacity exceeds
404 /// `isize::MAX` bytes.
409 pub fn try_reserve_exact(&mut self, used_cap
: usize, needed_extra_cap
: usize)
410 -> Result
<(), CollectionAllocErr
> {
413 // NOTE: we don't early branch on ZSTs here because we want this
414 // to actually catch "asking for more than usize::MAX" in that case.
415 // If we make it past the first branch then we are guaranteed to
418 // Don't actually need any more capacity.
419 // Wrapping in case they gave a bad `used_cap`.
420 if self.cap().wrapping_sub(used_cap
) >= needed_extra_cap
{
424 // Nothing we can really do about these checks :(
425 let new_cap
= used_cap
.checked_add(needed_extra_cap
).ok_or(CapacityOverflow
)?
;
426 let new_layout
= Layout
::array
::<T
>(new_cap
).ok_or(CapacityOverflow
)?
;
428 alloc_guard(new_layout
.size())?
;
430 let res
= match self.current_layout() {
432 let old_ptr
= self.ptr
.as_ptr() as *mut u8;
433 self.a
.realloc(old_ptr
, layout
, new_layout
)
435 None
=> self.a
.alloc(new_layout
),
438 self.ptr
= Unique
::new_unchecked(res?
as *mut T
);
445 pub fn reserve_exact(&mut self, used_cap
: usize, needed_extra_cap
: usize) {
446 match self.try_reserve_exact(used_cap
, needed_extra_cap
) {
447 Err(CapacityOverflow
) => panic
!("capacity overflow"),
448 Err(AllocErr(e
)) => self.a
.oom(e
),
449 Ok(()) => { /* yay */ }
453 /// Calculates the buffer's new size given that it'll hold `used_cap +
454 /// needed_extra_cap` elements. This logic is used in amortized reserve methods.
455 /// Returns `(new_capacity, new_alloc_size)`.
456 fn amortized_new_size(&self, used_cap
: usize, needed_extra_cap
: usize)
457 -> Result
<usize, CollectionAllocErr
> {
459 // Nothing we can really do about these checks :(
460 let required_cap
= used_cap
.checked_add(needed_extra_cap
).ok_or(CapacityOverflow
)?
;
461 // Cannot overflow, because `cap <= isize::MAX`, and type of `cap` is `usize`.
462 let double_cap
= self.cap
* 2;
463 // `double_cap` guarantees exponential growth.
464 Ok(cmp
::max(double_cap
, required_cap
))
467 /// Ensures that the buffer contains at least enough space to hold
468 /// `used_cap + needed_extra_cap` elements. If it doesn't already have
469 /// enough capacity, will reallocate enough space plus comfortable slack
470 /// space to get amortized `O(1)` behavior. Will limit this behavior
471 /// if it would needlessly cause itself to panic.
473 /// If `used_cap` exceeds `self.cap()`, this may fail to actually allocate
474 /// the requested space. This is not really unsafe, but the unsafe
475 /// code *you* write that relies on the behavior of this function may break.
477 /// This is ideal for implementing a bulk-push operation like `extend`.
481 /// * Panics if the requested capacity exceeds `usize::MAX` bytes.
482 /// * Panics on 32-bit platforms if the requested capacity exceeds
483 /// `isize::MAX` bytes.
492 /// # #![feature(alloc)]
493 /// # extern crate alloc;
495 /// # use alloc::raw_vec::RawVec;
496 /// struct MyVec<T> {
501 /// impl<T: Clone> MyVec<T> {
502 /// pub fn push_all(&mut self, elems: &[T]) {
503 /// self.buf.reserve(self.len, elems.len());
504 /// // reserve would have aborted or panicked if the len exceeded
505 /// // `isize::MAX` so this is safe to do unchecked now.
508 /// ptr::write(self.buf.ptr().offset(self.len as isize), x.clone());
515 /// # let mut vector = MyVec { buf: RawVec::new(), len: 0 };
516 /// # vector.push_all(&[1, 3, 5, 7, 9]);
519 pub fn try_reserve(&mut self, used_cap
: usize, needed_extra_cap
: usize)
520 -> Result
<(), CollectionAllocErr
> {
522 // NOTE: we don't early branch on ZSTs here because we want this
523 // to actually catch "asking for more than usize::MAX" in that case.
524 // If we make it past the first branch then we are guaranteed to
527 // Don't actually need any more capacity.
528 // Wrapping in case they give a bad `used_cap`
529 if self.cap().wrapping_sub(used_cap
) >= needed_extra_cap
{
533 let new_cap
= self.amortized_new_size(used_cap
, needed_extra_cap
)?
;
534 let new_layout
= Layout
::array
::<T
>(new_cap
).ok_or(CapacityOverflow
)?
;
536 // FIXME: may crash and burn on over-reserve
537 alloc_guard(new_layout
.size())?
;
539 let res
= match self.current_layout() {
541 let old_ptr
= self.ptr
.as_ptr() as *mut u8;
542 self.a
.realloc(old_ptr
, layout
, new_layout
)
544 None
=> self.a
.alloc(new_layout
),
547 self.ptr
= Unique
::new_unchecked(res?
as *mut T
);
554 /// The same as try_reserve, but errors are lowered to a call to oom().
555 pub fn reserve(&mut self, used_cap
: usize, needed_extra_cap
: usize) {
556 match self.try_reserve(used_cap
, needed_extra_cap
) {
557 Err(CapacityOverflow
) => panic
!("capacity overflow"),
558 Err(AllocErr(e
)) => self.a
.oom(e
),
559 Ok(()) => { /* yay */ }
562 /// Attempts to ensure that the buffer contains at least enough space to hold
563 /// `used_cap + needed_extra_cap` elements. If it doesn't already have
564 /// enough capacity, will reallocate in place enough space plus comfortable slack
565 /// space to get amortized `O(1)` behavior. Will limit this behaviour
566 /// if it would needlessly cause itself to panic.
568 /// If `used_cap` exceeds `self.cap()`, this may fail to actually allocate
569 /// the requested space. This is not really unsafe, but the unsafe
570 /// code *you* write that relies on the behavior of this function may break.
572 /// Returns true if the reallocation attempt has succeeded, or false otherwise.
576 /// * Panics if the requested capacity exceeds `usize::MAX` bytes.
577 /// * Panics on 32-bit platforms if the requested capacity exceeds
578 /// `isize::MAX` bytes.
579 pub fn reserve_in_place(&mut self, used_cap
: usize, needed_extra_cap
: usize) -> bool
{
581 // NOTE: we don't early branch on ZSTs here because we want this
582 // to actually catch "asking for more than usize::MAX" in that case.
583 // If we make it past the first branch then we are guaranteed to
586 // Don't actually need any more capacity. If the current `cap` is 0, we can't
587 // reallocate in place.
588 // Wrapping in case they give a bad `used_cap`
589 let old_layout
= match self.current_layout() {
590 Some(layout
) => layout
,
591 None
=> return false,
593 if self.cap().wrapping_sub(used_cap
) >= needed_extra_cap
{
597 let new_cap
= self.amortized_new_size(used_cap
, needed_extra_cap
)
598 .expect("capacity overflow");
600 // Here, `cap < used_cap + needed_extra_cap <= new_cap`
601 // (regardless of whether `self.cap - used_cap` wrapped).
602 // Therefore we can safely call grow_in_place.
604 let ptr
= self.ptr() as *mut _
;
605 let new_layout
= Layout
::new
::<T
>().repeat(new_cap
).unwrap().0;
606 // FIXME: may crash and burn on over-reserve
607 alloc_guard(new_layout
.size()).expect("capacity overflow");
608 match self.a
.grow_in_place(ptr
, old_layout
, new_layout
) {
620 /// Shrinks the allocation down to the specified amount. If the given amount
621 /// is 0, actually completely deallocates.
625 /// Panics if the given amount is *larger* than the current capacity.
630 pub fn shrink_to_fit(&mut self, amount
: usize) {
631 let elem_size
= mem
::size_of
::<T
>();
633 // Set the `cap` because they might be about to promote to a `Box<[T]>`
639 // This check is my waterloo; it's the only thing Vec wouldn't have to do.
640 assert
!(self.cap
>= amount
, "Tried to shrink to a larger capacity");
643 // We want to create a new zero-length vector within the
644 // same allocator. We use ptr::write to avoid an
645 // erroneous attempt to drop the contents, and we use
646 // ptr::read to sidestep condition against destructuring
647 // types that implement Drop.
650 let a
= ptr
::read(&self.a
as *const A
);
651 self.dealloc_buffer();
652 ptr
::write(self, RawVec
::new_in(a
));
654 } else if self.cap
!= amount
{
656 // We know here that our `amount` is greater than zero. This
657 // implies, via the assert above, that capacity is also greater
658 // than zero, which means that we've got a current layout that
661 // We also know that `self.cap` is greater than `amount`, and
662 // consequently we don't need runtime checks for creating either
664 let old_size
= elem_size
* self.cap
;
665 let new_size
= elem_size
* amount
;
666 let align
= mem
::align_of
::<T
>();
667 let old_layout
= Layout
::from_size_align_unchecked(old_size
, align
);
668 let new_layout
= Layout
::from_size_align_unchecked(new_size
, align
);
669 match self.a
.realloc(self.ptr
.as_ptr() as *mut u8,
672 Ok(p
) => self.ptr
= Unique
::new_unchecked(p
as *mut T
),
673 Err(err
) => self.a
.oom(err
),
681 impl<T
> RawVec
<T
, Heap
> {
682 /// Converts the entire buffer into `Box<[T]>`.
684 /// While it is not *strictly* Undefined Behavior to call
685 /// this procedure while some of the RawVec is uninitialized,
686 /// it certainly makes it trivial to trigger it.
688 /// Note that this will correctly reconstitute any `cap` changes
689 /// that may have been performed. (see description of type for details)
690 pub unsafe fn into_box(self) -> Box
<[T
]> {
691 // NOTE: not calling `cap()` here, actually using the real `cap` field!
692 let slice
= slice
::from_raw_parts_mut(self.ptr(), self.cap
);
693 let output
: Box
<[T
]> = Box
::from_raw(slice
);
699 impl<T
, A
: Alloc
> RawVec
<T
, A
> {
700 /// Frees the memory owned by the RawVec *without* trying to Drop its contents.
701 pub unsafe fn dealloc_buffer(&mut self) {
702 let elem_size
= mem
::size_of
::<T
>();
704 if let Some(layout
) = self.current_layout() {
705 let ptr
= self.ptr() as *mut u8;
706 self.a
.dealloc(ptr
, layout
);
712 unsafe impl<#[may_dangle] T, A: Alloc> Drop for RawVec<T, A> {
713 /// Frees the memory owned by the RawVec *without* trying to Drop its contents.
715 unsafe { self.dealloc_buffer(); }
721 // We need to guarantee the following:
722 // * We don't ever allocate `> isize::MAX` byte-size objects
723 // * We don't overflow `usize::MAX` and actually allocate too little
725 // On 64-bit we just need to check for overflow since trying to allocate
726 // `> isize::MAX` bytes will surely fail. On 32-bit and 16-bit we need to add
727 // an extra guard for this in case we're running on a platform which can use
728 // all 4GB in user-space. e.g. PAE or x32
731 fn alloc_guard(alloc_size
: usize) -> Result
<(), CollectionAllocErr
> {
732 if mem
::size_of
::<usize>() < 8 && alloc_size
> ::core
::isize::MAX
as usize {
733 Err(CapacityOverflow
)
744 fn allocator_param() {
745 use allocator
::{Alloc, AllocErr}
;
747 // Writing a test of integration between third-party
748 // allocators and RawVec is a little tricky because the RawVec
749 // API does not expose fallible allocation methods, so we
750 // cannot check what happens when allocator is exhausted
751 // (beyond detecting a panic).
753 // Instead, this just checks that the RawVec methods do at
754 // least go through the Allocator API when it reserves
757 // A dumb allocator that consumes a fixed amount of fuel
758 // before allocation attempts start failing.
759 struct BoundedAlloc { fuel: usize }
760 unsafe impl Alloc
for BoundedAlloc
{
761 unsafe fn alloc(&mut self, layout
: Layout
) -> Result
<*mut u8, AllocErr
> {
762 let size
= layout
.size();
763 if size
> self.fuel
{
764 return Err(AllocErr
::Unsupported { details: "fuel exhausted" }
);
766 match Heap
.alloc(layout
) {
767 ok @
Ok(_
) => { self.fuel -= size; ok }
771 unsafe fn dealloc(&mut self, ptr
: *mut u8, layout
: Layout
) {
772 Heap
.dealloc(ptr
, layout
)
776 let a
= BoundedAlloc { fuel: 500 }
;
777 let mut v
: RawVec
<u8, _
> = RawVec
::with_capacity_in(50, a
);
778 assert_eq
!(v
.a
.fuel
, 450);
779 v
.reserve(50, 150); // (causes a realloc, thus using 50 + 150 = 200 units of fuel)
780 assert_eq
!(v
.a
.fuel
, 250);
784 fn reserve_does_not_overallocate() {
786 let mut v
: RawVec
<u32> = RawVec
::new();
787 // First `reserve` allocates like `reserve_exact`
789 assert_eq
!(9, v
.cap());
793 let mut v
: RawVec
<u32> = RawVec
::new();
795 assert_eq
!(7, v
.cap());
796 // 97 if more than double of 7, so `reserve` should work
797 // like `reserve_exact`.
799 assert_eq
!(97, v
.cap());
803 let mut v
: RawVec
<u32> = RawVec
::new();
805 assert_eq
!(12, v
.cap());
807 // 3 is less than half of 12, so `reserve` must grow
808 // exponentially. At the time of writing this test grow
809 // factor is 2, so new capacity is 24, however, grow factor
810 // of 1.5 is OK too. Hence `>= 18` in assert.
811 assert
!(v
.cap() >= 12 + 12 / 2);