1 | //! Memory allocation APIs |
2 | |
3 | #![stable (feature = "alloc_module" , since = "1.28.0" )] |
4 | |
5 | mod global; |
6 | mod layout; |
7 | |
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; |
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)] |
19 | pub use self::layout::LayoutErr; |
20 | |
21 | #[stable (feature = "alloc_layout_error" , since = "1.50.0" )] |
22 | pub use self::layout::LayoutError; |
23 | |
24 | use crate::error::Error; |
25 | use crate::fmt; |
26 | use 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)] |
34 | pub 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 | )] |
41 | impl Error for AllocError {} |
42 | |
43 | // (we need this for downstream impl of trait Error) |
44 | #[unstable (feature = "allocator_api" , issue = "32838" )] |
45 | impl 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" )] |
109 | pub 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" )] |
369 | unsafe impl<A> Allocator for &A |
370 | where |
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 | |