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.
11 #![unstable(feature = "allocator_api",
12 reason = "the precise API and guarantees it provides may be tweaked \
13 slightly, especially to possibly take into account the \
14 types being stored to make room for a future \
15 tracing garbage collector",
22 use core::ptr::{self, NonNull};
24 /// Represents the combination of a starting address and
25 /// a total capacity of the returned block.
27 pub struct Excess(pub *mut u8, pub usize);
29 fn size_align<T>() -> (usize, usize) {
30 (mem::size_of::<T>(), mem::align_of::<T>())
33 /// Layout of a block of memory.
35 /// An instance of `Layout` describes a particular layout of memory.
36 /// You build a `Layout` up as an input to give to an allocator.
38 /// All layouts have an associated non-negative size and a
39 /// power-of-two alignment.
41 /// (Note however that layouts are *not* required to have positive
42 /// size, even though many allocators require that all memory
43 /// requests have positive size. A caller to the `Alloc::alloc`
44 /// method must either ensure that conditions like this are met, or
45 /// use specific allocators with looser requirements.)
46 #[derive(Clone, Debug, PartialEq, Eq)]
48 // size of the requested block of memory, measured in bytes.
51 // alignment of the requested block of memory, measured in bytes.
52 // we ensure that this is always a power-of-two, because API's
53 // like `posix_memalign` require it and it is a reasonable
54 // constraint to impose on Layout constructors.
56 // (However, we do not analogously require `align >= sizeof(void*)`,
57 // even though that is *also* a requirement of `posix_memalign`.)
62 // FIXME: audit default implementations for overflow errors,
63 // (potentially switching to overflowing_add and
64 // overflowing_mul as necessary).
67 /// Constructs a `Layout` from a given `size` and `align`,
68 /// or returns `None` if any of the following conditions
71 /// * `align` must be a power of two,
73 /// * `align` must not exceed 2<sup>31</sup> (i.e. `1 << 31`),
75 /// * `size`, when rounded up to the nearest multiple of `align`,
76 /// must not overflow (i.e. the rounded value must be less than
79 pub fn from_size_align(size: usize, align: usize) -> Option<Layout> {
80 if !align.is_power_of_two() {
84 if align > (1 << 31) {
88 // (power-of-two implies align != 0.)
90 // Rounded up size is:
91 // size_rounded_up = (size + align - 1) & !(align - 1);
93 // We know from above that align != 0. If adding (align - 1)
94 // does not overflow, then rounding up will be fine.
96 // Conversely, &-masking with !(align - 1) will subtract off
97 // only low-order-bits. Thus if overflow occurs with the sum,
98 // the &-mask cannot subtract enough to undo that overflow.
100 // Above implies that checking for summation overflow is both
101 // necessary and sufficient.
102 if size > usize::MAX - (align - 1) {
107 Some(Layout::from_size_align_unchecked(size, align))
111 /// Creates a layout, bypassing all checks.
115 /// This function is unsafe as it does not verify that `align` is
116 /// a power-of-two that is also less than or equal to 2<sup>31</sup>, nor
117 /// that `size` aligned to `align` fits within the address space
118 /// (i.e. the `Layout::from_size_align` preconditions).
120 pub unsafe fn from_size_align_unchecked(size: usize, align: usize) -> Layout {
121 Layout { size: size, align: align }
124 /// The minimum size in bytes for a memory block of this layout.
126 pub fn size(&self) -> usize { self.size }
128 /// The minimum byte alignment for a memory block of this layout.
130 pub fn align(&self) -> usize { self.align }
132 /// Constructs a `Layout` suitable for holding a value of type `T`.
133 pub fn new<T>() -> Self {
134 let (size, align) = size_align::<T>();
135 Layout::from_size_align(size, align).unwrap()
138 /// Produces layout describing a record that could be used to
139 /// allocate backing structure for `T` (which could be a trait
140 /// or other unsized type like a slice).
141 pub fn for_value<T: ?Sized>(t: &T) -> Self {
142 let (size, align) = (mem::size_of_val(t), mem::align_of_val(t));
143 Layout::from_size_align(size, align).unwrap()
146 /// Creates a layout describing the record that can hold a value
147 /// of the same layout as `self`, but that also is aligned to
148 /// alignment `align` (measured in bytes).
150 /// If `self` already meets the prescribed alignment, then returns
153 /// Note that this method does not add any padding to the overall
154 /// size, regardless of whether the returned layout has a different
155 /// alignment. In other words, if `K` has size 16, `K.align_to(32)`
156 /// will *still* have size 16.
160 /// Panics if the combination of `self.size` and the given `align`
161 /// violates the conditions listed in `from_size_align`.
163 pub fn align_to(&self, align: usize) -> Self {
164 Layout::from_size_align(self.size, cmp::max(self.align, align)).unwrap()
167 /// Returns the amount of padding we must insert after `self`
168 /// to ensure that the following address will satisfy `align`
169 /// (measured in bytes).
171 /// E.g. if `self.size` is 9, then `self.padding_needed_for(4)`
172 /// returns 3, because that is the minimum number of bytes of
173 /// padding required to get a 4-aligned address (assuming that the
174 /// corresponding memory block starts at a 4-aligned address).
176 /// The return value of this function has no meaning if `align` is
177 /// not a power-of-two.
179 /// Note that the utility of the returned value requires `align`
180 /// to be less than or equal to the alignment of the starting
181 /// address for the whole allocated block of memory. One way to
182 /// satisfy this constraint is to ensure `align <= self.align`.
184 pub fn padding_needed_for(&self, align: usize) -> usize {
185 let len = self.size();
187 // Rounded up value is:
188 // len_rounded_up = (len + align - 1) & !(align - 1);
189 // and then we return the padding difference: `len_rounded_up - len`.
191 // We use modular arithmetic throughout:
193 // 1. align is guaranteed to be > 0, so align - 1 is always
196 // 2. `len + align - 1` can overflow by at most `align - 1`,
197 // so the &-mask wth `!(align - 1)` will ensure that in the
198 // case of overflow, `len_rounded_up` will itself be 0.
199 // Thus the returned padding, when added to `len`, yields 0,
200 // which trivially satisfies the alignment `align`.
202 // (Of course, attempts to allocate blocks of memory whose
203 // size and padding overflow in the above manner should cause
204 // the allocator to yield an error anyway.)
206 let len_rounded_up = len.wrapping_add(align).wrapping_sub(1) & !align.wrapping_sub(1);
207 return len_rounded_up.wrapping_sub(len);
210 /// Creates a layout describing the record for `n` instances of
211 /// `self`, with a suitable amount of padding between each to
212 /// ensure that each instance is given its requested size and
213 /// alignment. On success, returns `(k, offs)` where `k` is the
214 /// layout of the array and `offs` is the distance between the start
215 /// of each element in the array.
217 /// On arithmetic overflow, returns `None`.
219 pub fn repeat(&self, n: usize) -> Option<(Self, usize)> {
220 let padded_size = self.size.checked_add(self.padding_needed_for(self.align))?;
221 let alloc_size = padded_size.checked_mul(n)?;
223 // We can assume that `self.align` is a power-of-two that does
224 // not exceed 2<sup>31</sup>. Furthermore, `alloc_size` has already been
225 // rounded up to a multiple of `self.align`; therefore, the
226 // call to `Layout::from_size_align` below should never panic.
227 Some((Layout::from_size_align(alloc_size, self.align).unwrap(), padded_size))
230 /// Creates a layout describing the record for `self` followed by
231 /// `next`, including any necessary padding to ensure that `next`
232 /// will be properly aligned. Note that the result layout will
233 /// satisfy the alignment properties of both `self` and `next`.
235 /// Returns `Some((k, offset))`, where `k` is layout of the concatenated
236 /// record and `offset` is the relative location, in bytes, of the
237 /// start of the `next` embedded within the concatenated record
238 /// (assuming that the record itself starts at offset 0).
240 /// On arithmetic overflow, returns `None`.
241 pub fn extend(&self, next: Self) -> Option<(Self, usize)> {
242 let new_align = cmp::max(self.align, next.align);
243 let realigned = Layout::from_size_align(self.size, new_align)?;
245 let pad = realigned.padding_needed_for(next.align);
247 let offset = self.size.checked_add(pad)?;
248 let new_size = offset.checked_add(next.size)?;
250 let layout = Layout::from_size_align(new_size, new_align)?;
251 Some((layout, offset))
254 /// Creates a layout describing the record for `n` instances of
255 /// `self`, with no padding between each instance.
257 /// Note that, unlike `repeat`, `repeat_packed` does not guarantee
258 /// that the repeated instances of `self` will be properly
259 /// aligned, even if a given instance of `self` is properly
260 /// aligned. In other words, if the layout returned by
261 /// `repeat_packed` is used to allocate an array, it is not
262 /// guaranteed that all elements in the array will be properly
265 /// On arithmetic overflow, returns `None`.
266 pub fn repeat_packed(&self, n: usize) -> Option<Self> {
267 let size = self.size().checked_mul(n)?;
268 Layout::from_size_align(size, self.align)
271 /// Creates a layout describing the record for `self` followed by
272 /// `next` with no additional padding between the two. Since no
273 /// padding is inserted, the alignment of `next` is irrelevant,
274 /// and is not incorporated *at all* into the resulting layout.
276 /// Returns `(k, offset)`, where `k` is layout of the concatenated
277 /// record and `offset` is the relative location, in bytes, of the
278 /// start of the `next` embedded within the concatenated record
279 /// (assuming that the record itself starts at offset 0).
281 /// (The `offset` is always the same as `self.size()`; we use this
282 /// signature out of convenience in matching the signature of
285 /// On arithmetic overflow, returns `None`.
286 pub fn extend_packed(&self, next: Self) -> Option<(Self, usize)> {
287 let new_size = self.size().checked_add(next.size())?;
288 let layout = Layout::from_size_align(new_size, self.align)?;
289 Some((layout, self.size()))
292 /// Creates a layout describing the record for a `[T; n]`.
294 /// On arithmetic overflow, returns `None`.
295 pub fn array<T>(n: usize) -> Option<Self> {
299 debug_assert!(offs == mem::size_of::<T>());
305 /// The `AllocErr` error specifies whether an allocation failure is
306 /// specifically due to resource exhaustion or if it is due to
307 /// something wrong when combining the given input arguments with this
309 #[derive(Clone, PartialEq, Eq, Debug)]
311 /// Error due to hitting some resource limit or otherwise running
312 /// out of memory. This condition strongly implies that *some*
313 /// series of deallocations would allow a subsequent reissuing of
314 /// the original allocation request to succeed.
315 Exhausted { request: Layout },
317 /// Error due to allocator being fundamentally incapable of
318 /// satisfying the original request. This condition implies that
319 /// such an allocation request will never succeed on the given
320 /// allocator, regardless of environment, memory pressure, or
321 /// other contextual conditions.
323 /// For example, an allocator that does not support requests for
324 /// large memory blocks might return this error variant.
325 Unsupported { details: &'static str },
330 pub fn invalid_input(details: &'static str) -> Self {
331 AllocErr::Unsupported { details: details }
334 pub fn is_memory_exhausted(&self) -> bool {
335 if let AllocErr::Exhausted { .. } = *self { true } else { false }
338 pub fn is_request_unsupported(&self) -> bool {
339 if let AllocErr::Unsupported { .. } = *self { true } else { false }
342 pub fn description(&self) -> &str {
344 AllocErr::Exhausted { .. } => "allocator memory exhausted",
345 AllocErr::Unsupported { .. } => "unsupported allocator request",
350 // (we need this for downstream impl of trait Error)
351 impl fmt::Display for AllocErr {
352 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
353 write!(f, "{}", self.description())
357 /// The `CannotReallocInPlace` error is used when `grow_in_place` or
358 /// `shrink_in_place` were unable to reuse the given memory block for
359 /// a requested layout.
360 #[derive(Clone, PartialEq, Eq, Debug)]
361 pub struct CannotReallocInPlace;
363 impl CannotReallocInPlace {
364 pub fn description(&self) -> &str {
365 "cannot reallocate allocator's memory in place"
369 // (we need this for downstream impl of trait Error)
370 impl fmt::Display for CannotReallocInPlace {
371 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
372 write!(f, "{}", self.description())
376 /// Augments `AllocErr` with a CapacityOverflow variant.
377 #[derive(Clone, PartialEq, Eq, Debug)]
378 #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
379 pub enum CollectionAllocErr {
380 /// Error due to the computed capacity exceeding the collection's maximum
381 /// (usually `isize::MAX` bytes).
383 /// Error due to the allocator (see the `AllocErr` type's docs).
387 #[unstable(feature = "try_reserve", reason = "new API", issue="48043")]
388 impl From<AllocErr> for CollectionAllocErr {
389 fn from(err: AllocErr) -> Self {
390 CollectionAllocErr::AllocErr(err)
394 /// An implementation of `Alloc` can allocate, reallocate, and
395 /// deallocate arbitrary blocks of data described via `Layout`.
397 /// Some of the methods require that a memory block be *currently
398 /// allocated* via an allocator. This means that:
400 /// * the starting address for that memory block was previously
401 /// returned by a previous call to an allocation method (`alloc`,
402 /// `alloc_zeroed`, `alloc_excess`, `alloc_one`, `alloc_array`) or
403 /// reallocation method (`realloc`, `realloc_excess`, or
404 /// `realloc_array`), and
406 /// * the memory block has not been subsequently deallocated, where
407 /// blocks are deallocated either by being passed to a deallocation
408 /// method (`dealloc`, `dealloc_one`, `dealloc_array`) or by being
409 /// passed to a reallocation method (see above) that returns `Ok`.
411 /// A note regarding zero-sized types and zero-sized layouts: many
412 /// methods in the `Alloc` trait state that allocation requests
413 /// must be non-zero size, or else undefined behavior can result.
415 /// * However, some higher-level allocation methods (`alloc_one`,
416 /// `alloc_array`) are well-defined on zero-sized types and can
417 /// optionally support them: it is left up to the implementor
418 /// whether to return `Err`, or to return `Ok` with some pointer.
420 /// * If an `Alloc` implementation chooses to return `Ok` in this
421 /// case (i.e. the pointer denotes a zero-sized inaccessible block)
422 /// then that returned pointer must be considered "currently
423 /// allocated". On such an allocator, *all* methods that take
424 /// currently-allocated pointers as inputs must accept these
425 /// zero-sized pointers, *without* causing undefined behavior.
427 /// * In other words, if a zero-sized pointer can flow out of an
428 /// allocator, then that allocator must likewise accept that pointer
429 /// flowing back into its deallocation and reallocation methods.
431 /// Some of the methods require that a layout *fit* a memory block.
432 /// What it means for a layout to "fit" a memory block means (or
433 /// equivalently, for a memory block to "fit" a layout) is that the
434 /// following two conditions must hold:
436 /// 1. The block's starting address must be aligned to `layout.align()`.
438 /// 2. The block's size must fall in the range `[use_min, use_max]`, where:
440 /// * `use_min` is `self.usable_size(layout).0`, and
442 /// * `use_max` is the capacity that was (or would have been)
443 /// returned when (if) the block was allocated via a call to
444 /// `alloc_excess` or `realloc_excess`.
448 /// * the size of the layout most recently used to allocate the block
449 /// is guaranteed to be in the range `[use_min, use_max]`, and
451 /// * a lower-bound on `use_max` can be safely approximated by a call to
454 /// * if a layout `k` fits a memory block (denoted by `ptr`)
455 /// currently allocated via an allocator `a`, then it is legal to
456 /// use that layout to deallocate it, i.e. `a.dealloc(ptr, k);`.
460 /// The `Alloc` trait is an `unsafe` trait for a number of reasons, and
461 /// implementors must ensure that they adhere to these contracts:
463 /// * Pointers returned from allocation functions must point to valid memory and
464 /// retain their validity until at least the instance of `Alloc` is dropped
467 /// * It's undefined behavior if global allocators unwind. This restriction may
468 /// be lifted in the future, but currently a panic from any of these
469 /// functions may lead to memory unsafety. Note that as of the time of this
470 /// writing allocators *not* intending to be global allocators can still panic
471 /// in their implementation without violating memory safety.
473 /// * `Layout` queries and calculations in general must be correct. Callers of
474 /// this trait are allowed to rely on the contracts defined on each method,
475 /// and implementors must ensure such contracts remain true.
477 /// Note that this list may get tweaked over time as clarifications are made in
478 /// the future. Additionally global allocators may gain unique requirements for
479 /// how to safely implement one in the future as well.
480 pub unsafe trait Alloc {
482 // (Note: existing allocators have unspecified but well-defined
483 // behavior in response to a zero size allocation request ;
484 // e.g. in C, `malloc` of 0 will either return a null pointer or a
485 // unique pointer, but will not have arbitrary undefined
486 // behavior. Rust should consider revising the alloc::heap crate
487 // to reflect this reality.)
489 /// Returns a pointer meeting the size and alignment guarantees of
492 /// If this method returns an `Ok(addr)`, then the `addr` returned
493 /// will be non-null address pointing to a block of storage
494 /// suitable for holding an instance of `layout`.
496 /// The returned block of storage may or may not have its contents
497 /// initialized. (Extension subtraits might restrict this
498 /// behavior, e.g. to ensure initialization to particular sets of
503 /// This function is unsafe because undefined behavior can result
504 /// if the caller does not ensure that `layout` has non-zero size.
506 /// (Extension subtraits might provide more specific bounds on
507 /// behavior, e.g. guarantee a sentinel address or a null pointer
508 /// in response to a zero-size allocation request.)
512 /// Returning `Err` indicates that either memory is exhausted or
513 /// `layout` does not meet allocator's size or alignment
516 /// Implementations are encouraged to return `Err` on memory
517 /// exhaustion rather than panicking or aborting, but this is not
518 /// a strict requirement. (Specifically: it is *legal* to
519 /// implement this trait atop an underlying native allocation
520 /// library that aborts on memory exhaustion.)
522 /// Clients wishing to abort computation in response to an
523 /// allocation error are encouraged to call the allocator's `oom`
524 /// method, rather than directly invoking `panic!` or similar.
525 unsafe fn alloc(&mut self, layout: Layout) -> Result<*mut u8, AllocErr>;
527 /// Deallocate the memory referenced by `ptr`.
531 /// This function is unsafe because undefined behavior can result
532 /// if the caller does not ensure all of the following:
534 /// * `ptr` must denote a block of memory currently allocated via
537 /// * `layout` must *fit* that block of memory,
539 /// * In addition to fitting the block of memory `layout`, the
540 /// alignment of the `layout` must match the alignment used
541 /// to allocate that block of memory.
542 unsafe fn dealloc(&mut self, ptr: *mut u8, layout: Layout);
544 /// Allocator-specific method for signaling an out-of-memory
547 /// `oom` aborts the thread or process, optionally performing
548 /// cleanup or logging diagnostic information before panicking or
551 /// `oom` is meant to be used by clients unable to cope with an
552 /// unsatisfied allocation request (signaled by an error such as
553 /// `AllocErr::Exhausted`), and wish to abandon computation rather
554 /// than attempt to recover locally. Such clients should pass the
555 /// signaling error value back into `oom`, where the allocator
556 /// may incorporate that error value into its diagnostic report
559 /// Implementations of the `oom` method are discouraged from
560 /// infinitely regressing in nested calls to `oom`. In
561 /// practice this means implementors should eschew allocating,
562 /// especially from `self` (directly or indirectly).
564 /// Implementations of the allocation and reallocation methods
565 /// (e.g. `alloc`, `alloc_one`, `realloc`) are discouraged from
566 /// panicking (or aborting) in the event of memory exhaustion;
567 /// instead they should return an appropriate error from the
568 /// invoked method, and let the client decide whether to invoke
569 /// this `oom` method in response.
570 fn oom(&mut self, _: AllocErr) -> ! {
571 unsafe { ::core::intrinsics::abort() }
574 // == ALLOCATOR-SPECIFIC QUANTITIES AND LIMITS ==
577 /// Returns bounds on the guaranteed usable size of a successful
578 /// allocation created with the specified `layout`.
580 /// In particular, if one has a memory block allocated via a given
581 /// allocator `a` and layout `k` where `a.usable_size(k)` returns
582 /// `(l, u)`, then one can pass that block to `a.dealloc()` with a
583 /// layout in the size range [l, u].
585 /// (All implementors of `usable_size` must ensure that
586 /// `l <= k.size() <= u`)
588 /// Both the lower- and upper-bounds (`l` and `u` respectively)
589 /// are provided, because an allocator based on size classes could
590 /// misbehave if one attempts to deallocate a block without
591 /// providing a correct value for its size (i.e., one within the
594 /// Clients who wish to make use of excess capacity are encouraged
595 /// to use the `alloc_excess` and `realloc_excess` instead, as
596 /// this method is constrained to report conservative values that
597 /// serve as valid bounds for *all possible* allocation method
600 /// However, for clients that do not wish to track the capacity
601 /// returned by `alloc_excess` locally, this method is likely to
602 /// produce useful results.
604 fn usable_size(&self, layout: &Layout) -> (usize, usize) {
605 (layout.size(), layout.size())
608 // == METHODS FOR MEMORY REUSE ==
609 // realloc. alloc_excess, realloc_excess
611 /// Returns a pointer suitable for holding data described by
612 /// `new_layout`, meeting its size and alignment guarantees. To
613 /// accomplish this, this may extend or shrink the allocation
614 /// referenced by `ptr` to fit `new_layout`.
616 /// If this returns `Ok`, then ownership of the memory block
617 /// referenced by `ptr` has been transferred to this
618 /// allocator. The memory may or may not have been freed, and
619 /// should be considered unusable (unless of course it was
620 /// transferred back to the caller again via the return value of
623 /// If this method returns `Err`, then ownership of the memory
624 /// block has not been transferred to this allocator, and the
625 /// contents of the memory block are unaltered.
627 /// For best results, `new_layout` should not impose a different
628 /// alignment constraint than `layout`. (In other words,
629 /// `new_layout.align()` should equal `layout.align()`.) However,
630 /// behavior is well-defined (though underspecified) when this
631 /// constraint is violated; further discussion below.
635 /// This function is unsafe because undefined behavior can result
636 /// if the caller does not ensure all of the following:
638 /// * `ptr` must be currently allocated via this allocator,
640 /// * `layout` must *fit* the `ptr` (see above). (The `new_layout`
641 /// argument need not fit it.)
643 /// * `new_layout` must have size greater than zero.
645 /// * the alignment of `new_layout` is non-zero.
647 /// (Extension subtraits might provide more specific bounds on
648 /// behavior, e.g. guarantee a sentinel address or a null pointer
649 /// in response to a zero-size allocation request.)
653 /// Returns `Err` only if `new_layout` does not match the
654 /// alignment of `layout`, or does not meet the allocator's size
655 /// and alignment constraints of the allocator, or if reallocation
658 /// (Note the previous sentence did not say "if and only if" -- in
659 /// particular, an implementation of this method *can* return `Ok`
660 /// if `new_layout.align() != old_layout.align()`; or it can
661 /// return `Err` in that scenario, depending on whether this
662 /// allocator can dynamically adjust the alignment constraint for
665 /// Implementations are encouraged to return `Err` on memory
666 /// exhaustion rather than panicking or aborting, but this is not
667 /// a strict requirement. (Specifically: it is *legal* to
668 /// implement this trait atop an underlying native allocation
669 /// library that aborts on memory exhaustion.)
671 /// Clients wishing to abort computation in response to an
672 /// reallocation error are encouraged to call the allocator's `oom`
673 /// method, rather than directly invoking `panic!` or similar.
674 unsafe fn realloc(&mut self,
677 new_layout: Layout) -> Result<*mut u8, AllocErr> {
678 let new_size = new_layout.size();
679 let old_size = layout.size();
680 let aligns_match = layout.align == new_layout.align;
682 if new_size >= old_size && aligns_match {
683 if let Ok(()) = self.grow_in_place(ptr, layout.clone(), new_layout.clone()) {
686 } else if new_size < old_size && aligns_match {
687 if let Ok(()) = self.shrink_in_place(ptr, layout.clone(), new_layout.clone()) {
692 // otherwise, fall back on alloc + copy + dealloc.
693 let result = self.alloc(new_layout);
694 if let Ok(new_ptr) = result {
695 ptr::copy_nonoverlapping(ptr as *const u8, new_ptr, cmp::min(old_size, new_size));
696 self.dealloc(ptr, layout);
701 /// Behaves like `alloc`, but also ensures that the contents
702 /// are set to zero before being returned.
706 /// This function is unsafe for the same reasons that `alloc` is.
710 /// Returning `Err` indicates that either memory is exhausted or
711 /// `layout` does not meet allocator's size or alignment
712 /// constraints, just as in `alloc`.
714 /// Clients wishing to abort computation in response to an
715 /// allocation error are encouraged to call the allocator's `oom`
716 /// method, rather than directly invoking `panic!` or similar.
717 unsafe fn alloc_zeroed(&mut self, layout: Layout) -> Result<*mut u8, AllocErr> {
718 let size = layout.size();
719 let p = self.alloc(layout);
721 ptr::write_bytes(p, 0, size);
726 /// Behaves like `alloc`, but also returns the whole size of
727 /// the returned block. For some `layout` inputs, like arrays, this
728 /// may include extra storage usable for additional data.
732 /// This function is unsafe for the same reasons that `alloc` is.
736 /// Returning `Err` indicates that either memory is exhausted or
737 /// `layout` does not meet allocator's size or alignment
738 /// constraints, just as in `alloc`.
740 /// Clients wishing to abort computation in response to an
741 /// allocation error are encouraged to call the allocator's `oom`
742 /// method, rather than directly invoking `panic!` or similar.
743 unsafe fn alloc_excess(&mut self, layout: Layout) -> Result<Excess, AllocErr> {
744 let usable_size = self.usable_size(&layout);
745 self.alloc(layout).map(|p| Excess(p, usable_size.1))
748 /// Behaves like `realloc`, but also returns the whole size of
749 /// the returned block. For some `layout` inputs, like arrays, this
750 /// may include extra storage usable for additional data.
754 /// This function is unsafe for the same reasons that `realloc` is.
758 /// Returning `Err` indicates that either memory is exhausted or
759 /// `layout` does not meet allocator's size or alignment
760 /// constraints, just as in `realloc`.
762 /// Clients wishing to abort computation in response to an
763 /// reallocation error are encouraged to call the allocator's `oom`
764 /// method, rather than directly invoking `panic!` or similar.
765 unsafe fn realloc_excess(&mut self,
768 new_layout: Layout) -> Result<Excess, AllocErr> {
769 let usable_size = self.usable_size(&new_layout);
770 self.realloc(ptr, layout, new_layout)
771 .map(|p| Excess(p, usable_size.1))
774 /// Attempts to extend the allocation referenced by `ptr` to fit `new_layout`.
776 /// If this returns `Ok`, then the allocator has asserted that the
777 /// memory block referenced by `ptr` now fits `new_layout`, and thus can
778 /// be used to carry data of that layout. (The allocator is allowed to
779 /// expend effort to accomplish this, such as extending the memory block to
780 /// include successor blocks, or virtual memory tricks.)
782 /// Regardless of what this method returns, ownership of the
783 /// memory block referenced by `ptr` has not been transferred, and
784 /// the contents of the memory block are unaltered.
788 /// This function is unsafe because undefined behavior can result
789 /// if the caller does not ensure all of the following:
791 /// * `ptr` must be currently allocated via this allocator,
793 /// * `layout` must *fit* the `ptr` (see above); note the
794 /// `new_layout` argument need not fit it,
796 /// * `new_layout.size()` must not be less than `layout.size()`,
798 /// * `new_layout.align()` must equal `layout.align()`.
802 /// Returns `Err(CannotReallocInPlace)` when the allocator is
803 /// unable to assert that the memory block referenced by `ptr`
804 /// could fit `layout`.
806 /// Note that one cannot pass `CannotReallocInPlace` to the `oom`
807 /// method; clients are expected either to be able to recover from
808 /// `grow_in_place` failures without aborting, or to fall back on
809 /// another reallocation method before resorting to an abort.
810 unsafe fn grow_in_place(&mut self,
813 new_layout: Layout) -> Result<(), CannotReallocInPlace> {
814 let _ = ptr; // this default implementation doesn't care about the actual address.
815 debug_assert!(new_layout.size >= layout.size);
816 debug_assert!(new_layout.align == layout.align);
817 let (_l, u) = self.usable_size(&layout);
818 // _l <= layout.size() [guaranteed by usable_size()]
819 // layout.size() <= new_layout.size() [required by this method]
820 if new_layout.size <= u {
823 return Err(CannotReallocInPlace);
827 /// Attempts to shrink the allocation referenced by `ptr` to fit `new_layout`.
829 /// If this returns `Ok`, then the allocator has asserted that the
830 /// memory block referenced by `ptr` now fits `new_layout`, and
831 /// thus can only be used to carry data of that smaller
832 /// layout. (The allocator is allowed to take advantage of this,
833 /// carving off portions of the block for reuse elsewhere.) The
834 /// truncated contents of the block within the smaller layout are
835 /// unaltered, and ownership of block has not been transferred.
837 /// If this returns `Err`, then the memory block is considered to
838 /// still represent the original (larger) `layout`. None of the
839 /// block has been carved off for reuse elsewhere, ownership of
840 /// the memory block has not been transferred, and the contents of
841 /// the memory block are unaltered.
845 /// This function is unsafe because undefined behavior can result
846 /// if the caller does not ensure all of the following:
848 /// * `ptr` must be currently allocated via this allocator,
850 /// * `layout` must *fit* the `ptr` (see above); note the
851 /// `new_layout` argument need not fit it,
853 /// * `new_layout.size()` must not be greater than `layout.size()`
854 /// (and must be greater than zero),
856 /// * `new_layout.align()` must equal `layout.align()`.
860 /// Returns `Err(CannotReallocInPlace)` when the allocator is
861 /// unable to assert that the memory block referenced by `ptr`
862 /// could fit `layout`.
864 /// Note that one cannot pass `CannotReallocInPlace` to the `oom`
865 /// method; clients are expected either to be able to recover from
866 /// `shrink_in_place` failures without aborting, or to fall back
867 /// on another reallocation method before resorting to an abort.
868 unsafe fn shrink_in_place(&mut self,
871 new_layout: Layout) -> Result<(), CannotReallocInPlace> {
872 let _ = ptr; // this default implementation doesn't care about the actual address.
873 debug_assert!(new_layout.size <= layout.size);
874 debug_assert!(new_layout.align == layout.align);
875 let (l, _u) = self.usable_size(&layout);
876 // layout.size() <= _u [guaranteed by usable_size()]
877 // new_layout.size() <= layout.size() [required by this method]
878 if l <= new_layout.size {
881 return Err(CannotReallocInPlace);
886 // == COMMON USAGE PATTERNS ==
887 // alloc_one, dealloc_one, alloc_array, realloc_array. dealloc_array
889 /// Allocates a block suitable for holding an instance of `T`.
891 /// Captures a common usage pattern for allocators.
893 /// The returned block is suitable for passing to the
894 /// `alloc`/`realloc` methods of this allocator.
896 /// Note to implementors: If this returns `Ok(ptr)`, then `ptr`
897 /// must be considered "currently allocated" and must be
898 /// acceptable input to methods such as `realloc` or `dealloc`,
899 /// *even if* `T` is a zero-sized type. In other words, if your
900 /// `Alloc` implementation overrides this method in a manner
901 /// that can return a zero-sized `ptr`, then all reallocation and
902 /// deallocation methods need to be similarly overridden to accept
903 /// such values as input.
907 /// Returning `Err` indicates that either memory is exhausted or
908 /// `T` does not meet allocator's size or alignment constraints.
910 /// For zero-sized `T`, may return either of `Ok` or `Err`, but
911 /// will *not* yield undefined behavior.
913 /// Clients wishing to abort computation in response to an
914 /// allocation error are encouraged to call the allocator's `oom`
915 /// method, rather than directly invoking `panic!` or similar.
916 fn alloc_one<T>(&mut self) -> Result<NonNull<T>, AllocErr>
919 let k = Layout::new::<T>();
921 unsafe { self.alloc(k).map(|p| NonNull::new_unchecked(p as *mut T)) }
923 Err(AllocErr::invalid_input("zero-sized type invalid for alloc_one"))
927 /// Deallocates a block suitable for holding an instance of `T`.
929 /// The given block must have been produced by this allocator,
930 /// and must be suitable for storing a `T` (in terms of alignment
931 /// as well as minimum and maximum size); otherwise yields
932 /// undefined behavior.
934 /// Captures a common usage pattern for allocators.
938 /// This function is unsafe because undefined behavior can result
939 /// if the caller does not ensure both:
941 /// * `ptr` must denote a block of memory currently allocated via this allocator
943 /// * the layout of `T` must *fit* that block of memory.
944 unsafe fn dealloc_one<T>(&mut self, ptr: NonNull<T>)
947 let raw_ptr = ptr.as_ptr() as *mut u8;
948 let k = Layout::new::<T>();
950 self.dealloc(raw_ptr, k);
954 /// Allocates a block suitable for holding `n` instances of `T`.
956 /// Captures a common usage pattern for allocators.
958 /// The returned block is suitable for passing to the
959 /// `alloc`/`realloc` methods of this allocator.
961 /// Note to implementors: If this returns `Ok(ptr)`, then `ptr`
962 /// must be considered "currently allocated" and must be
963 /// acceptable input to methods such as `realloc` or `dealloc`,
964 /// *even if* `T` is a zero-sized type. In other words, if your
965 /// `Alloc` implementation overrides this method in a manner
966 /// that can return a zero-sized `ptr`, then all reallocation and
967 /// deallocation methods need to be similarly overridden to accept
968 /// such values as input.
972 /// Returning `Err` indicates that either memory is exhausted or
973 /// `[T; n]` does not meet allocator's size or alignment
976 /// For zero-sized `T` or `n == 0`, may return either of `Ok` or
977 /// `Err`, but will *not* yield undefined behavior.
979 /// Always returns `Err` on arithmetic overflow.
981 /// Clients wishing to abort computation in response to an
982 /// allocation error are encouraged to call the allocator's `oom`
983 /// method, rather than directly invoking `panic!` or similar.
984 fn alloc_array<T>(&mut self, n: usize) -> Result<NonNull<T>, AllocErr>
987 match Layout::array::<T>(n) {
988 Some(ref layout) if layout.size() > 0 => {
990 self.alloc(layout.clone())
992 NonNull::new_unchecked(p as *mut T)
996 _ => Err(AllocErr::invalid_input("invalid layout for alloc_array")),
1000 /// Reallocates a block previously suitable for holding `n_old`
1001 /// instances of `T`, returning a block suitable for holding
1002 /// `n_new` instances of `T`.
1004 /// Captures a common usage pattern for allocators.
1006 /// The returned block is suitable for passing to the
1007 /// `alloc`/`realloc` methods of this allocator.
1011 /// This function is unsafe because undefined behavior can result
1012 /// if the caller does not ensure all of the following:
1014 /// * `ptr` must be currently allocated via this allocator,
1016 /// * the layout of `[T; n_old]` must *fit* that block of memory.
1020 /// Returning `Err` indicates that either memory is exhausted or
1021 /// `[T; n_new]` does not meet allocator's size or alignment
1024 /// For zero-sized `T` or `n_new == 0`, may return either of `Ok` or
1025 /// `Err`, but will *not* yield undefined behavior.
1027 /// Always returns `Err` on arithmetic overflow.
1029 /// Clients wishing to abort computation in response to an
1030 /// reallocation error are encouraged to call the allocator's `oom`
1031 /// method, rather than directly invoking `panic!` or similar.
1032 unsafe fn realloc_array<T>(&mut self,
1035 n_new: usize) -> Result<NonNull<T>, AllocErr>
1038 match (Layout::array::<T>(n_old), Layout::array::<T>(n_new), ptr.as_ptr()) {
1039 (Some(ref k_old), Some(ref k_new), ptr) if k_old.size() > 0 && k_new.size() > 0 => {
1040 self.realloc(ptr as *mut u8, k_old.clone(), k_new.clone())
1041 .map(|p| NonNull::new_unchecked(p as *mut T))
1044 Err(AllocErr::invalid_input("invalid layout for realloc_array"))
1049 /// Deallocates a block suitable for holding `n` instances of `T`.
1051 /// Captures a common usage pattern for allocators.
1055 /// This function is unsafe because undefined behavior can result
1056 /// if the caller does not ensure both:
1058 /// * `ptr` must denote a block of memory currently allocated via this allocator
1060 /// * the layout of `[T; n]` must *fit* that block of memory.
1064 /// Returning `Err` indicates that either `[T; n]` or the given
1065 /// memory block does not meet allocator's size or alignment
1068 /// Always returns `Err` on arithmetic overflow.
1069 unsafe fn dealloc_array<T>(&mut self, ptr: NonNull<T>, n: usize) -> Result<(), AllocErr>
1072 let raw_ptr = ptr.as_ptr() as *mut u8;
1073 match Layout::array::<T>(n) {
1074 Some(ref k) if k.size() > 0 => {
1075 Ok(self.dealloc(raw_ptr, k.clone()))
1078 Err(AllocErr::invalid_input("invalid layout for dealloc_array"))