1//! Memory allocation APIs
2
3#![stable(feature = "alloc_module", since = "1.28.0")]
4
5mod global;
6mod layout;
7
8#[stable(feature = "global_alloc", since = "1.28.0")]
9pub use self::global::GlobalAlloc;
10#[stable(feature = "alloc_layout", since = "1.28.0")]
11pub use self::layout::Layout;
12#[stable(feature = "alloc_layout", since = "1.28.0")]
13#[deprecated(
14 since = "1.52.0",
15 note = "Name does not follow std convention, use LayoutError",
16 suggestion = "LayoutError"
17)]
18#[allow(deprecated, deprecated_in_future)]
19pub use self::layout::LayoutErr;
20
21#[stable(feature = "alloc_layout_error", since = "1.50.0")]
22pub use self::layout::LayoutError;
23
24use crate::error::Error;
25use crate::fmt;
26use crate::ptr::{self, NonNull};
27
28/// The `AllocError` error indicates an allocation failure
29/// that may be due to resource exhaustion or to
30/// something wrong when combining the given input arguments with this
31/// allocator.
32#[unstable(feature = "allocator_api", issue = "32838")]
33#[derive(Copy, Clone, PartialEq, Eq, Debug)]
34pub struct AllocError;
35
36#[unstable(
37 feature = "allocator_api",
38 reason = "the precise API and guarantees it provides may be tweaked.",
39 issue = "32838"
40)]
41impl Error for AllocError {}
42
43// (we need this for downstream impl of trait Error)
44#[unstable(feature = "allocator_api", issue = "32838")]
45impl fmt::Display for AllocError {
46 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
47 f.write_str(data:"memory allocation failed")
48 }
49}
50
51/// An implementation of `Allocator` can allocate, grow, shrink, and deallocate arbitrary blocks of
52/// data described via [`Layout`][].
53///
54/// `Allocator` is designed to be implemented on ZSTs, references, or smart pointers because having
55/// an allocator like `MyAlloc([u8; N])` cannot be moved, without updating the pointers to the
56/// allocated memory.
57///
58/// Unlike [`GlobalAlloc`][], zero-sized allocations are allowed in `Allocator`. If an underlying
59/// allocator does not support this (like jemalloc) or return a null pointer (such as
60/// `libc::malloc`), this must be caught by the implementation.
61///
62/// ### Currently allocated memory
63///
64/// Some of the methods require that a memory block be *currently allocated* via an allocator. This
65/// means that:
66///
67/// * the starting address for that memory block was previously returned by [`allocate`], [`grow`], or
68/// [`shrink`], and
69///
70/// * the memory block has not been subsequently deallocated, where blocks are either deallocated
71/// directly by being passed to [`deallocate`] or were changed by being passed to [`grow`] or
72/// [`shrink`] that returns `Ok`. If `grow` or `shrink` have returned `Err`, the passed pointer
73/// remains valid.
74///
75/// [`allocate`]: Allocator::allocate
76/// [`grow`]: Allocator::grow
77/// [`shrink`]: Allocator::shrink
78/// [`deallocate`]: Allocator::deallocate
79///
80/// ### Memory fitting
81///
82/// Some of the methods require that a layout *fit* a memory block. What it means for a layout to
83/// "fit" a memory block means (or equivalently, for a memory block to "fit" a layout) is that the
84/// following conditions must hold:
85///
86/// * The block must be allocated with the same alignment as [`layout.align()`], and
87///
88/// * The provided [`layout.size()`] must fall in the range `min ..= max`, where:
89/// - `min` is the size of the layout most recently used to allocate the block, and
90/// - `max` is the latest actual size returned from [`allocate`], [`grow`], or [`shrink`].
91///
92/// [`layout.align()`]: Layout::align
93/// [`layout.size()`]: Layout::size
94///
95/// # Safety
96///
97/// * Memory blocks returned from an allocator that are [*currently allocated*] must point to
98/// valid memory and retain their validity while they are [*currently allocated*] and at
99/// least one of the instance and all of its clones has not been dropped.
100///
101/// * copying, cloning, or moving the allocator must not invalidate memory blocks returned from this
102/// allocator. A copied or cloned allocator must behave like the same allocator, and
103///
104/// * any pointer to a memory block which is [*currently allocated*] may be passed to any other
105/// method of the allocator.
106///
107/// [*currently allocated*]: #currently-allocated-memory
108#[unstable(feature = "allocator_api", issue = "32838")]
109pub unsafe trait Allocator {
110 /// Attempts to allocate a block of memory.
111 ///
112 /// On success, returns a [`NonNull<[u8]>`][NonNull] meeting the size and alignment guarantees of `layout`.
113 ///
114 /// The returned block may have a larger size than specified by `layout.size()`, and may or may
115 /// not have its contents initialized.
116 ///
117 /// # Errors
118 ///
119 /// Returning `Err` indicates that either memory is exhausted or `layout` does not meet
120 /// allocator's size or alignment constraints.
121 ///
122 /// Implementations are encouraged to return `Err` on memory exhaustion rather than panicking or
123 /// aborting, but this is not a strict requirement. (Specifically: it is *legal* to implement
124 /// this trait atop an underlying native allocation library that aborts on memory exhaustion.)
125 ///
126 /// Clients wishing to abort computation in response to an allocation error are encouraged to
127 /// call the [`handle_alloc_error`] function, rather than directly invoking `panic!` or similar.
128 ///
129 /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
130 fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError>;
131
132 /// Behaves like `allocate`, but also ensures that the returned memory is zero-initialized.
133 ///
134 /// # Errors
135 ///
136 /// Returning `Err` indicates that either memory is exhausted or `layout` does not meet
137 /// allocator's size or alignment constraints.
138 ///
139 /// Implementations are encouraged to return `Err` on memory exhaustion rather than panicking or
140 /// aborting, but this is not a strict requirement. (Specifically: it is *legal* to implement
141 /// this trait atop an underlying native allocation library that aborts on memory exhaustion.)
142 ///
143 /// Clients wishing to abort computation in response to an allocation error are encouraged to
144 /// call the [`handle_alloc_error`] function, rather than directly invoking `panic!` or similar.
145 ///
146 /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
147 fn allocate_zeroed(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
148 let ptr = self.allocate(layout)?;
149 // SAFETY: `alloc` returns a valid memory block
150 unsafe { ptr.as_non_null_ptr().as_ptr().write_bytes(0, ptr.len()) }
151 Ok(ptr)
152 }
153
154 /// Deallocates the memory referenced by `ptr`.
155 ///
156 /// # Safety
157 ///
158 /// * `ptr` must denote a block of memory [*currently allocated*] via this allocator, and
159 /// * `layout` must [*fit*] that block of memory.
160 ///
161 /// [*currently allocated*]: #currently-allocated-memory
162 /// [*fit*]: #memory-fitting
163 unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout);
164
165 /// Attempts to extend the memory block.
166 ///
167 /// Returns a new [`NonNull<[u8]>`][NonNull] containing a pointer and the actual size of the allocated
168 /// memory. The pointer is suitable for holding data described by `new_layout`. To accomplish
169 /// this, the allocator may extend the allocation referenced by `ptr` to fit the new layout.
170 ///
171 /// If this returns `Ok`, then ownership of the memory block referenced by `ptr` has been
172 /// transferred to this allocator. Any access to the old `ptr` is Undefined Behavior, even if the
173 /// allocation was grown in-place. The newly returned pointer is the only valid pointer
174 /// for accessing this memory now.
175 ///
176 /// If this method returns `Err`, then ownership of the memory block has not been transferred to
177 /// this allocator, and the contents of the memory block are unaltered.
178 ///
179 /// # Safety
180 ///
181 /// * `ptr` must denote a block of memory [*currently allocated*] via this allocator.
182 /// * `old_layout` must [*fit*] that block of memory (The `new_layout` argument need not fit it.).
183 /// * `new_layout.size()` must be greater than or equal to `old_layout.size()`.
184 ///
185 /// Note that `new_layout.align()` need not be the same as `old_layout.align()`.
186 ///
187 /// [*currently allocated*]: #currently-allocated-memory
188 /// [*fit*]: #memory-fitting
189 ///
190 /// # Errors
191 ///
192 /// Returns `Err` if the new layout does not meet the allocator's size and alignment
193 /// constraints of the allocator, or if growing otherwise fails.
194 ///
195 /// Implementations are encouraged to return `Err` on memory exhaustion rather than panicking or
196 /// aborting, but this is not a strict requirement. (Specifically: it is *legal* to implement
197 /// this trait atop an underlying native allocation library that aborts on memory exhaustion.)
198 ///
199 /// Clients wishing to abort computation in response to an allocation error are encouraged to
200 /// call the [`handle_alloc_error`] function, rather than directly invoking `panic!` or similar.
201 ///
202 /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
203 unsafe fn grow(
204 &self,
205 ptr: NonNull<u8>,
206 old_layout: Layout,
207 new_layout: Layout,
208 ) -> Result<NonNull<[u8]>, AllocError> {
209 debug_assert!(
210 new_layout.size() >= old_layout.size(),
211 "`new_layout.size()` must be greater than or equal to `old_layout.size()`"
212 );
213
214 let new_ptr = self.allocate(new_layout)?;
215
216 // SAFETY: because `new_layout.size()` must be greater than or equal to
217 // `old_layout.size()`, both the old and new memory allocation are valid for reads and
218 // writes for `old_layout.size()` bytes. Also, because the old allocation wasn't yet
219 // deallocated, it cannot overlap `new_ptr`. Thus, the call to `copy_nonoverlapping` is
220 // safe. The safety contract for `dealloc` must be upheld by the caller.
221 unsafe {
222 ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), old_layout.size());
223 self.deallocate(ptr, old_layout);
224 }
225
226 Ok(new_ptr)
227 }
228
229 /// Behaves like `grow`, but also ensures that the new contents are set to zero before being
230 /// returned.
231 ///
232 /// The memory block will contain the following contents after a successful call to
233 /// `grow_zeroed`:
234 /// * Bytes `0..old_layout.size()` are preserved from the original allocation.
235 /// * Bytes `old_layout.size()..old_size` will either be preserved or zeroed, depending on
236 /// the allocator implementation. `old_size` refers to the size of the memory block prior
237 /// to the `grow_zeroed` call, which may be larger than the size that was originally
238 /// requested when it was allocated.
239 /// * Bytes `old_size..new_size` are zeroed. `new_size` refers to the size of the memory
240 /// block returned by the `grow_zeroed` call.
241 ///
242 /// # Safety
243 ///
244 /// * `ptr` must denote a block of memory [*currently allocated*] via this allocator.
245 /// * `old_layout` must [*fit*] that block of memory (The `new_layout` argument need not fit it.).
246 /// * `new_layout.size()` must be greater than or equal to `old_layout.size()`.
247 ///
248 /// Note that `new_layout.align()` need not be the same as `old_layout.align()`.
249 ///
250 /// [*currently allocated*]: #currently-allocated-memory
251 /// [*fit*]: #memory-fitting
252 ///
253 /// # Errors
254 ///
255 /// Returns `Err` if the new layout does not meet the allocator's size and alignment
256 /// constraints of the allocator, or if growing otherwise fails.
257 ///
258 /// Implementations are encouraged to return `Err` on memory exhaustion rather than panicking or
259 /// aborting, but this is not a strict requirement. (Specifically: it is *legal* to implement
260 /// this trait atop an underlying native allocation library that aborts on memory exhaustion.)
261 ///
262 /// Clients wishing to abort computation in response to an allocation error are encouraged to
263 /// call the [`handle_alloc_error`] function, rather than directly invoking `panic!` or similar.
264 ///
265 /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
266 unsafe fn grow_zeroed(
267 &self,
268 ptr: NonNull<u8>,
269 old_layout: Layout,
270 new_layout: Layout,
271 ) -> Result<NonNull<[u8]>, AllocError> {
272 debug_assert!(
273 new_layout.size() >= old_layout.size(),
274 "`new_layout.size()` must be greater than or equal to `old_layout.size()`"
275 );
276
277 let new_ptr = self.allocate_zeroed(new_layout)?;
278
279 // SAFETY: because `new_layout.size()` must be greater than or equal to
280 // `old_layout.size()`, both the old and new memory allocation are valid for reads and
281 // writes for `old_layout.size()` bytes. Also, because the old allocation wasn't yet
282 // deallocated, it cannot overlap `new_ptr`. Thus, the call to `copy_nonoverlapping` is
283 // safe. The safety contract for `dealloc` must be upheld by the caller.
284 unsafe {
285 ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), old_layout.size());
286 self.deallocate(ptr, old_layout);
287 }
288
289 Ok(new_ptr)
290 }
291
292 /// Attempts to shrink the memory block.
293 ///
294 /// Returns a new [`NonNull<[u8]>`][NonNull] containing a pointer and the actual size of the allocated
295 /// memory. The pointer is suitable for holding data described by `new_layout`. To accomplish
296 /// this, the allocator may shrink the allocation referenced by `ptr` to fit the new layout.
297 ///
298 /// If this returns `Ok`, then ownership of the memory block referenced by `ptr` has been
299 /// transferred to this allocator. Any access to the old `ptr` is Undefined Behavior, even if the
300 /// allocation was shrunk in-place. The newly returned pointer is the only valid pointer
301 /// for accessing this memory now.
302 ///
303 /// If this method returns `Err`, then ownership of the memory block has not been transferred to
304 /// this allocator, and the contents of the memory block are unaltered.
305 ///
306 /// # Safety
307 ///
308 /// * `ptr` must denote a block of memory [*currently allocated*] via this allocator.
309 /// * `old_layout` must [*fit*] that block of memory (The `new_layout` argument need not fit it.).
310 /// * `new_layout.size()` must be smaller than or equal to `old_layout.size()`.
311 ///
312 /// Note that `new_layout.align()` need not be the same as `old_layout.align()`.
313 ///
314 /// [*currently allocated*]: #currently-allocated-memory
315 /// [*fit*]: #memory-fitting
316 ///
317 /// # Errors
318 ///
319 /// Returns `Err` if the new layout does not meet the allocator's size and alignment
320 /// constraints of the allocator, or if shrinking otherwise fails.
321 ///
322 /// Implementations are encouraged to return `Err` on memory exhaustion rather than panicking or
323 /// aborting, but this is not a strict requirement. (Specifically: it is *legal* to implement
324 /// this trait atop an underlying native allocation library that aborts on memory exhaustion.)
325 ///
326 /// Clients wishing to abort computation in response to an allocation error are encouraged to
327 /// call the [`handle_alloc_error`] function, rather than directly invoking `panic!` or similar.
328 ///
329 /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
330 unsafe fn shrink(
331 &self,
332 ptr: NonNull<u8>,
333 old_layout: Layout,
334 new_layout: Layout,
335 ) -> Result<NonNull<[u8]>, AllocError> {
336 debug_assert!(
337 new_layout.size() <= old_layout.size(),
338 "`new_layout.size()` must be smaller than or equal to `old_layout.size()`"
339 );
340
341 let new_ptr = self.allocate(new_layout)?;
342
343 // SAFETY: because `new_layout.size()` must be lower than or equal to
344 // `old_layout.size()`, both the old and new memory allocation are valid for reads and
345 // writes for `new_layout.size()` bytes. Also, because the old allocation wasn't yet
346 // deallocated, it cannot overlap `new_ptr`. Thus, the call to `copy_nonoverlapping` is
347 // safe. The safety contract for `dealloc` must be upheld by the caller.
348 unsafe {
349 ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), new_layout.size());
350 self.deallocate(ptr, old_layout);
351 }
352
353 Ok(new_ptr)
354 }
355
356 /// Creates a "by reference" adapter for this instance of `Allocator`.
357 ///
358 /// The returned adapter also implements `Allocator` and will simply borrow this.
359 #[inline(always)]
360 fn by_ref(&self) -> &Self
361 where
362 Self: Sized,
363 {
364 self
365 }
366}
367
368#[unstable(feature = "allocator_api", issue = "32838")]
369unsafe impl<A> Allocator for &A
370where
371 A: Allocator + ?Sized,
372{
373 #[inline]
374 fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
375 (**self).allocate(layout)
376 }
377
378 #[inline]
379 fn allocate_zeroed(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
380 (**self).allocate_zeroed(layout)
381 }
382
383 #[inline]
384 unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout) {
385 // SAFETY: the safety contract must be upheld by the caller
386 unsafe { (**self).deallocate(ptr, layout) }
387 }
388
389 #[inline]
390 unsafe fn grow(
391 &self,
392 ptr: NonNull<u8>,
393 old_layout: Layout,
394 new_layout: Layout,
395 ) -> Result<NonNull<[u8]>, AllocError> {
396 // SAFETY: the safety contract must be upheld by the caller
397 unsafe { (**self).grow(ptr, old_layout, new_layout) }
398 }
399
400 #[inline]
401 unsafe fn grow_zeroed(
402 &self,
403 ptr: NonNull<u8>,
404 old_layout: Layout,
405 new_layout: Layout,
406 ) -> Result<NonNull<[u8]>, AllocError> {
407 // SAFETY: the safety contract must be upheld by the caller
408 unsafe { (**self).grow_zeroed(ptr, old_layout, new_layout) }
409 }
410
411 #[inline]
412 unsafe fn shrink(
413 &self,
414 ptr: NonNull<u8>,
415 old_layout: Layout,
416 new_layout: Layout,
417 ) -> Result<NonNull<[u8]>, AllocError> {
418 // SAFETY: the safety contract must be upheld by the caller
419 unsafe { (**self).shrink(ptr, old_layout, new_layout) }
420 }
421}
422