1 //! Memory allocation APIs
3 #![stable(feature = "alloc_module", since = "1.28.0")]
8 #[stable(feature = "global_alloc", since = "1.28.0")]
9 pub use self::global::GlobalAlloc;
10 #[stable(feature = "alloc_layout", since = "1.28.0")]
11 pub use self::layout::{Layout, LayoutErr};
14 use crate::ptr::{self, NonNull};
16 /// The `AllocErr` error indicates an allocation failure
17 /// that may be due to resource exhaustion or to
18 /// something wrong when combining the given input arguments with this
20 #[unstable(feature = "allocator_api", issue = "32838")]
21 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
24 // (we need this for downstream impl of trait Error)
25 #[unstable(feature = "allocator_api", issue = "32838")]
26 impl fmt::Display for AllocErr {
27 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
28 f.write_str("memory allocation failed")
32 /// An implementation of `AllocRef` can allocate, grow, shrink, and deallocate arbitrary blocks of
33 /// data described via [`Layout`][].
35 /// `AllocRef` is designed to be implemented on ZSTs, references, or smart pointers because having
36 /// an allocator like `MyAlloc([u8; N])` cannot be moved, without updating the pointers to the
39 /// Unlike [`GlobalAlloc`][], zero-sized allocations are allowed in `AllocRef`. If an underlying
40 /// allocator does not support this (like jemalloc) or return a null pointer (such as
41 /// `libc::malloc`), this must be caught by the implementation.
43 /// ### Currently allocated memory
45 /// Some of the methods require that a memory block be *currently allocated* via an allocator. This
48 /// * the starting address for that memory block was previously returned by [`alloc`], [`grow`], or
51 /// * the memory block has not been subsequently deallocated, where blocks are either deallocated
52 /// directly by being passed to [`dealloc`] or were changed by being passed to [`grow`] or
53 /// [`shrink`] that returns `Ok`. If `grow` or `shrink` have returned `Err`, the passed pointer
56 /// [`alloc`]: AllocRef::alloc
57 /// [`grow`]: AllocRef::grow
58 /// [`shrink`]: AllocRef::shrink
59 /// [`dealloc`]: AllocRef::dealloc
61 /// ### Memory fitting
63 /// Some of the methods require that a layout *fit* a memory block. What it means for a layout to
64 /// "fit" a memory block means (or equivalently, for a memory block to "fit" a layout) is that the
65 /// following conditions must hold:
67 /// * The block must be allocated with the same alignment as [`layout.align()`], and
69 /// * The provided [`layout.size()`] must fall in the range `min ..= max`, where:
70 /// - `min` is the size of the layout most recently used to allocate the block, and
71 /// - `max` is the latest actual size returned from [`alloc`], [`grow`], or [`shrink`].
73 /// [`layout.align()`]: Layout::align
74 /// [`layout.size()`]: Layout::size
78 /// * Memory blocks returned from an allocator must point to valid memory and retain their validity
79 /// until the instance and all of its clones are dropped,
81 /// * cloning or moving the allocator must not invalidate memory blocks returned from this
82 /// allocator. A cloned allocator must behave like the same allocator, and
84 /// * any pointer to a memory block which is [*currently allocated*] may be passed to any other
85 /// method of the allocator.
87 /// [*currently allocated*]: #currently-allocated-memory
88 #[unstable(feature = "allocator_api", issue = "32838")]
89 pub unsafe trait AllocRef {
90 /// Attempts to allocate a block of memory.
92 /// On success, returns a [`NonNull<[u8]>`] meeting the size and alignment guarantees of `layout`.
94 /// The returned block may have a larger size than specified by `layout.size()`, and may or may
95 /// not have its contents initialized.
97 /// [`NonNull<[u8]>`]: NonNull
101 /// Returning `Err` indicates that either memory is exhausted or `layout` does not meet
102 /// allocator's size or alignment constraints.
104 /// Implementations are encouraged to return `Err` on memory exhaustion rather than panicking or
105 /// aborting, but this is not a strict requirement. (Specifically: it is *legal* to implement
106 /// this trait atop an underlying native allocation library that aborts on memory exhaustion.)
108 /// Clients wishing to abort computation in response to an allocation error are encouraged to
109 /// call the [`handle_alloc_error`] function, rather than directly invoking `panic!` or similar.
111 /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
112 fn alloc(&mut self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr>;
114 /// Behaves like `alloc`, but also ensures that the returned memory is zero-initialized.
118 /// Returning `Err` indicates that either memory is exhausted or `layout` does not meet
119 /// allocator's size or alignment constraints.
121 /// Implementations are encouraged to return `Err` on memory exhaustion rather than panicking or
122 /// aborting, but this is not a strict requirement. (Specifically: it is *legal* to implement
123 /// this trait atop an underlying native allocation library that aborts on memory exhaustion.)
125 /// Clients wishing to abort computation in response to an allocation error are encouraged to
126 /// call the [`handle_alloc_error`] function, rather than directly invoking `panic!` or similar.
128 /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
129 fn alloc_zeroed(&mut self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
130 let ptr = self.alloc(layout)?;
131 // SAFETY: `alloc` returns a valid memory block
132 unsafe { ptr.as_non_null_ptr().as_ptr().write_bytes(0, ptr.len()) }
136 /// Deallocates the memory referenced by `ptr`.
140 /// * `ptr` must denote a block of memory [*currently allocated*] via this allocator, and
141 /// * `layout` must [*fit*] that block of memory.
143 /// [*currently allocated*]: #currently-allocated-memory
144 /// [*fit*]: #memory-fitting
145 unsafe fn dealloc(&mut self, ptr: NonNull<u8>, layout: Layout);
147 /// Attempts to extend the memory block.
149 /// Returns a new [`NonNull<[u8]>`] containing a pointer and the actual size of the allocated
150 /// memory. The pointer is suitable for holding data described by `new_layout`. To accomplish
151 /// this, the allocator may extend the allocation referenced by `ptr` to fit the new layout.
153 /// If this returns `Ok`, then ownership of the memory block referenced by `ptr` has been
154 /// transferred to this allocator. The memory may or may not have been freed, and should be
155 /// considered unusable unless it was transferred back to the caller again via the return value
158 /// If this method returns `Err`, then ownership of the memory block has not been transferred to
159 /// this allocator, and the contents of the memory block are unaltered.
161 /// [`NonNull<[u8]>`]: NonNull
165 /// * `ptr` must denote a block of memory [*currently allocated*] via this allocator.
166 /// * `old_layout` must [*fit*] that block of memory (The `new_layout` argument need not fit it.).
167 /// * `new_layout.size()` must be greater than or equal to `old_layout.size()`.
169 /// [*currently allocated*]: #currently-allocated-memory
170 /// [*fit*]: #memory-fitting
174 /// Returns `Err` if the new layout does not meet the allocator's size and alignment
175 /// constraints of the allocator, or if growing otherwise fails.
177 /// Implementations are encouraged to return `Err` on memory exhaustion rather than panicking or
178 /// aborting, but this is not a strict requirement. (Specifically: it is *legal* to implement
179 /// this trait atop an underlying native allocation library that aborts on memory exhaustion.)
181 /// Clients wishing to abort computation in response to an allocation error are encouraged to
182 /// call the [`handle_alloc_error`] function, rather than directly invoking `panic!` or similar.
184 /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
190 ) -> Result<NonNull<[u8]>, AllocErr> {
192 new_layout.size() >= old_layout.size(),
193 "`new_layout.size()` must be greater than or equal to `old_layout.size()`"
196 let new_ptr = self.alloc(new_layout)?;
198 // SAFETY: because `new_layout.size()` must be greater than or equal to
199 // `old_layout.size()`, both the old and new memory allocation are valid for reads and
200 // writes for `old_layout.size()` bytes. Also, because the old allocation wasn't yet
201 // deallocated, it cannot overlap `new_ptr`. Thus, the call to `copy_nonoverlapping` is
202 // safe. The safety contract for `dealloc` must be upheld by the caller.
204 ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), old_layout.size());
205 self.dealloc(ptr, old_layout);
211 /// Behaves like `grow`, but also ensures that the new contents are set to zero before being
214 /// The memory block will contain the following contents after a successful call to
216 /// * Bytes `0..old_layout.size()` are preserved from the original allocation.
217 /// * Bytes `old_layout.size()..old_size` will either be preserved or zeroed, depending on
218 /// the allocator implementation. `old_size` refers to the size of the memory block prior
219 /// to the `grow_zeroed` call, which may be larger than the size that was originally
220 /// requested when it was allocated.
221 /// * Bytes `old_size..new_size` are zeroed. `new_size` refers to the size of the memory
222 /// block returned by the `grow_zeroed` call.
226 /// * `ptr` must denote a block of memory [*currently allocated*] via this allocator.
227 /// * `old_layout` must [*fit*] that block of memory (The `new_layout` argument need not fit it.).
228 /// * `new_layout.size()` must be greater than or equal to `old_layout.size()`.
230 /// [*currently allocated*]: #currently-allocated-memory
231 /// [*fit*]: #memory-fitting
235 /// Returns `Err` if the new layout does not meet the allocator's size and alignment
236 /// constraints of the allocator, or if growing otherwise fails.
238 /// Implementations are encouraged to return `Err` on memory exhaustion rather than panicking or
239 /// aborting, but this is not a strict requirement. (Specifically: it is *legal* to implement
240 /// this trait atop an underlying native allocation library that aborts on memory exhaustion.)
242 /// Clients wishing to abort computation in response to an allocation error are encouraged to
243 /// call the [`handle_alloc_error`] function, rather than directly invoking `panic!` or similar.
245 /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
246 unsafe fn grow_zeroed(
251 ) -> Result<NonNull<[u8]>, AllocErr> {
253 new_layout.size() >= old_layout.size(),
254 "`new_layout.size()` must be greater than or equal to `old_layout.size()`"
257 let new_ptr = self.alloc_zeroed(new_layout)?;
259 // SAFETY: because `new_layout.size()` must be greater than or equal to
260 // `old_layout.size()`, both the old and new memory allocation are valid for reads and
261 // writes for `old_layout.size()` bytes. Also, because the old allocation wasn't yet
262 // deallocated, it cannot overlap `new_ptr`. Thus, the call to `copy_nonoverlapping` is
263 // safe. The safety contract for `dealloc` must be upheld by the caller.
265 ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), old_layout.size());
266 self.dealloc(ptr, old_layout);
272 /// Attempts to shrink the memory block.
274 /// Returns a new [`NonNull<[u8]>`] containing a pointer and the actual size of the allocated
275 /// memory. The pointer is suitable for holding data described by `new_layout`. To accomplish
276 /// this, the allocator may shrink the allocation referenced by `ptr` to fit the new layout.
278 /// If this returns `Ok`, then ownership of the memory block referenced by `ptr` has been
279 /// transferred to this allocator. The memory may or may not have been freed, and should be
280 /// considered unusable unless it was transferred back to the caller again via the return value
283 /// If this method returns `Err`, then ownership of the memory block has not been transferred to
284 /// this allocator, and the contents of the memory block are unaltered.
286 /// [`NonNull<[u8]>`]: NonNull
290 /// * `ptr` must denote a block of memory [*currently allocated*] via this allocator.
291 /// * `old_layout` must [*fit*] that block of memory (The `new_layout` argument need not fit it.).
292 /// * `new_layout.size()` must be smaller than or equal to `old_layout.size()`.
294 /// [*currently allocated*]: #currently-allocated-memory
295 /// [*fit*]: #memory-fitting
299 /// Returns `Err` if the new layout does not meet the allocator's size and alignment
300 /// constraints of the allocator, or if shrinking otherwise fails.
302 /// Implementations are encouraged to return `Err` on memory exhaustion rather than panicking or
303 /// aborting, but this is not a strict requirement. (Specifically: it is *legal* to implement
304 /// this trait atop an underlying native allocation library that aborts on memory exhaustion.)
306 /// Clients wishing to abort computation in response to an allocation error are encouraged to
307 /// call the [`handle_alloc_error`] function, rather than directly invoking `panic!` or similar.
309 /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
315 ) -> Result<NonNull<[u8]>, AllocErr> {
317 new_layout.size() <= old_layout.size(),
318 "`new_layout.size()` must be smaller than or equal to `old_layout.size()`"
321 let new_ptr = self.alloc(new_layout)?;
323 // SAFETY: because `new_layout.size()` must be lower than or equal to
324 // `old_layout.size()`, both the old and new memory allocation are valid for reads and
325 // writes for `new_layout.size()` bytes. Also, because the old allocation wasn't yet
326 // deallocated, it cannot overlap `new_ptr`. Thus, the call to `copy_nonoverlapping` is
327 // safe. The safety contract for `dealloc` must be upheld by the caller.
329 ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), new_layout.size());
330 self.dealloc(ptr, old_layout);
336 /// Creates a "by reference" adaptor for this instance of `AllocRef`.
338 /// The returned adaptor also implements `AllocRef` and will simply borrow this.
340 fn by_ref(&mut self) -> &mut Self {
345 #[unstable(feature = "allocator_api", issue = "32838")]
346 unsafe impl<A> AllocRef for &mut A
348 A: AllocRef + ?Sized,
351 fn alloc(&mut self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
352 (**self).alloc(layout)
356 fn alloc_zeroed(&mut self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
357 (**self).alloc_zeroed(layout)
361 unsafe fn dealloc(&mut self, ptr: NonNull<u8>, layout: Layout) {
362 // SAFETY: the safety contract must be upheld by the caller
363 unsafe { (**self).dealloc(ptr, layout) }
372 ) -> Result<NonNull<[u8]>, AllocErr> {
373 // SAFETY: the safety contract must be upheld by the caller
374 unsafe { (**self).grow(ptr, old_layout, new_layout) }
378 unsafe fn grow_zeroed(
383 ) -> Result<NonNull<[u8]>, AllocErr> {
384 // SAFETY: the safety contract must be upheld by the caller
385 unsafe { (**self).grow_zeroed(ptr, old_layout, new_layout) }
394 ) -> Result<NonNull<[u8]>, AllocErr> {
395 // SAFETY: the safety contract must be upheld by the caller
396 unsafe { (**self).shrink(ptr, old_layout, new_layout) }