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 the shorter |
99 | /// of: |
100 | /// - the borrow-checker lifetime of the allocator type itself. |
101 | /// - as long as at least one of the instance and all of its clones has not been dropped. |
102 | /// |
103 | /// * copying, cloning, or moving the allocator must not invalidate memory blocks returned from this |
104 | /// allocator. A copied or cloned allocator must behave like the same allocator, and |
105 | /// |
106 | /// * any pointer to a memory block which is [*currently allocated*] may be passed to any other |
107 | /// method of the allocator. |
108 | /// |
109 | /// [*currently allocated*]: #currently-allocated-memory |
110 | #[unstable (feature = "allocator_api" , issue = "32838" )] |
111 | pub unsafe trait Allocator { |
112 | /// Attempts to allocate a block of memory. |
113 | /// |
114 | /// On success, returns a [`NonNull<[u8]>`][NonNull] meeting the size and alignment guarantees of `layout`. |
115 | /// |
116 | /// The returned block may have a larger size than specified by `layout.size()`, and may or may |
117 | /// not have its contents initialized. |
118 | /// |
119 | /// The returned block of memory remains valid as long as it is [*currently allocated*] and the shorter of: |
120 | /// - the borrow-checker lifetime of the allocator type itself. |
121 | /// - as long as at the allocator and all its clones has not been dropped. |
122 | /// |
123 | /// # Errors |
124 | /// |
125 | /// Returning `Err` indicates that either memory is exhausted or `layout` does not meet |
126 | /// allocator's size or alignment constraints. |
127 | /// |
128 | /// Implementations are encouraged to return `Err` on memory exhaustion rather than panicking or |
129 | /// aborting, but this is not a strict requirement. (Specifically: it is *legal* to implement |
130 | /// this trait atop an underlying native allocation library that aborts on memory exhaustion.) |
131 | /// |
132 | /// Clients wishing to abort computation in response to an allocation error are encouraged to |
133 | /// call the [`handle_alloc_error`] function, rather than directly invoking `panic!` or similar. |
134 | /// |
135 | /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html |
136 | fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError>; |
137 | |
138 | /// Behaves like `allocate`, but also ensures that the returned memory is zero-initialized. |
139 | /// |
140 | /// # Errors |
141 | /// |
142 | /// Returning `Err` indicates that either memory is exhausted or `layout` does not meet |
143 | /// allocator's size or alignment constraints. |
144 | /// |
145 | /// Implementations are encouraged to return `Err` on memory exhaustion rather than panicking or |
146 | /// aborting, but this is not a strict requirement. (Specifically: it is *legal* to implement |
147 | /// this trait atop an underlying native allocation library that aborts on memory exhaustion.) |
148 | /// |
149 | /// Clients wishing to abort computation in response to an allocation error are encouraged to |
150 | /// call the [`handle_alloc_error`] function, rather than directly invoking `panic!` or similar. |
151 | /// |
152 | /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html |
153 | fn allocate_zeroed(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> { |
154 | let ptr = self.allocate(layout)?; |
155 | // SAFETY: `alloc` returns a valid memory block |
156 | unsafe { ptr.as_non_null_ptr().as_ptr().write_bytes(0, ptr.len()) } |
157 | Ok(ptr) |
158 | } |
159 | |
160 | /// Deallocates the memory referenced by `ptr`. |
161 | /// |
162 | /// # Safety |
163 | /// |
164 | /// * `ptr` must denote a block of memory [*currently allocated*] via this allocator, and |
165 | /// * `layout` must [*fit*] that block of memory. |
166 | /// |
167 | /// [*currently allocated*]: #currently-allocated-memory |
168 | /// [*fit*]: #memory-fitting |
169 | unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout); |
170 | |
171 | /// Attempts to extend the memory block. |
172 | /// |
173 | /// Returns a new [`NonNull<[u8]>`][NonNull] containing a pointer and the actual size of the allocated |
174 | /// memory. The pointer is suitable for holding data described by `new_layout`. To accomplish |
175 | /// this, the allocator may extend the allocation referenced by `ptr` to fit the new layout. |
176 | /// |
177 | /// If this returns `Ok`, then ownership of the memory block referenced by `ptr` has been |
178 | /// transferred to this allocator. Any access to the old `ptr` is Undefined Behavior, even if the |
179 | /// allocation was grown in-place. The newly returned pointer is the only valid pointer |
180 | /// for accessing this memory now. |
181 | /// |
182 | /// If this method returns `Err`, then ownership of the memory block has not been transferred to |
183 | /// this allocator, and the contents of the memory block are unaltered. |
184 | /// |
185 | /// # Safety |
186 | /// |
187 | /// * `ptr` must denote a block of memory [*currently allocated*] via this allocator. |
188 | /// * `old_layout` must [*fit*] that block of memory (The `new_layout` argument need not fit it.). |
189 | /// * `new_layout.size()` must be greater than or equal to `old_layout.size()`. |
190 | /// |
191 | /// Note that `new_layout.align()` need not be the same as `old_layout.align()`. |
192 | /// |
193 | /// [*currently allocated*]: #currently-allocated-memory |
194 | /// [*fit*]: #memory-fitting |
195 | /// |
196 | /// # Errors |
197 | /// |
198 | /// Returns `Err` if the new layout does not meet the allocator's size and alignment |
199 | /// constraints of the allocator, or if growing otherwise fails. |
200 | /// |
201 | /// Implementations are encouraged to return `Err` on memory exhaustion rather than panicking or |
202 | /// aborting, but this is not a strict requirement. (Specifically: it is *legal* to implement |
203 | /// this trait atop an underlying native allocation library that aborts on memory exhaustion.) |
204 | /// |
205 | /// Clients wishing to abort computation in response to an allocation error are encouraged to |
206 | /// call the [`handle_alloc_error`] function, rather than directly invoking `panic!` or similar. |
207 | /// |
208 | /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html |
209 | unsafe fn grow( |
210 | &self, |
211 | ptr: NonNull<u8>, |
212 | old_layout: Layout, |
213 | new_layout: Layout, |
214 | ) -> Result<NonNull<[u8]>, AllocError> { |
215 | debug_assert!( |
216 | new_layout.size() >= old_layout.size(), |
217 | "`new_layout.size()` must be greater than or equal to `old_layout.size()`" |
218 | ); |
219 | |
220 | let new_ptr = self.allocate(new_layout)?; |
221 | |
222 | // SAFETY: because `new_layout.size()` must be greater than or equal to |
223 | // `old_layout.size()`, both the old and new memory allocation are valid for reads and |
224 | // writes for `old_layout.size()` bytes. Also, because the old allocation wasn't yet |
225 | // deallocated, it cannot overlap `new_ptr`. Thus, the call to `copy_nonoverlapping` is |
226 | // safe. The safety contract for `dealloc` must be upheld by the caller. |
227 | unsafe { |
228 | ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), old_layout.size()); |
229 | self.deallocate(ptr, old_layout); |
230 | } |
231 | |
232 | Ok(new_ptr) |
233 | } |
234 | |
235 | /// Behaves like `grow`, but also ensures that the new contents are set to zero before being |
236 | /// returned. |
237 | /// |
238 | /// The memory block will contain the following contents after a successful call to |
239 | /// `grow_zeroed`: |
240 | /// * Bytes `0..old_layout.size()` are preserved from the original allocation. |
241 | /// * Bytes `old_layout.size()..old_size` will either be preserved or zeroed, depending on |
242 | /// the allocator implementation. `old_size` refers to the size of the memory block prior |
243 | /// to the `grow_zeroed` call, which may be larger than the size that was originally |
244 | /// requested when it was allocated. |
245 | /// * Bytes `old_size..new_size` are zeroed. `new_size` refers to the size of the memory |
246 | /// block returned by the `grow_zeroed` call. |
247 | /// |
248 | /// # Safety |
249 | /// |
250 | /// * `ptr` must denote a block of memory [*currently allocated*] via this allocator. |
251 | /// * `old_layout` must [*fit*] that block of memory (The `new_layout` argument need not fit it.). |
252 | /// * `new_layout.size()` must be greater than or equal to `old_layout.size()`. |
253 | /// |
254 | /// Note that `new_layout.align()` need not be the same as `old_layout.align()`. |
255 | /// |
256 | /// [*currently allocated*]: #currently-allocated-memory |
257 | /// [*fit*]: #memory-fitting |
258 | /// |
259 | /// # Errors |
260 | /// |
261 | /// Returns `Err` if the new layout does not meet the allocator's size and alignment |
262 | /// constraints of the allocator, or if growing otherwise fails. |
263 | /// |
264 | /// Implementations are encouraged to return `Err` on memory exhaustion rather than panicking or |
265 | /// aborting, but this is not a strict requirement. (Specifically: it is *legal* to implement |
266 | /// this trait atop an underlying native allocation library that aborts on memory exhaustion.) |
267 | /// |
268 | /// Clients wishing to abort computation in response to an allocation error are encouraged to |
269 | /// call the [`handle_alloc_error`] function, rather than directly invoking `panic!` or similar. |
270 | /// |
271 | /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html |
272 | unsafe fn grow_zeroed( |
273 | &self, |
274 | ptr: NonNull<u8>, |
275 | old_layout: Layout, |
276 | new_layout: Layout, |
277 | ) -> Result<NonNull<[u8]>, AllocError> { |
278 | debug_assert!( |
279 | new_layout.size() >= old_layout.size(), |
280 | "`new_layout.size()` must be greater than or equal to `old_layout.size()`" |
281 | ); |
282 | |
283 | let new_ptr = self.allocate_zeroed(new_layout)?; |
284 | |
285 | // SAFETY: because `new_layout.size()` must be greater than or equal to |
286 | // `old_layout.size()`, both the old and new memory allocation are valid for reads and |
287 | // writes for `old_layout.size()` bytes. Also, because the old allocation wasn't yet |
288 | // deallocated, it cannot overlap `new_ptr`. Thus, the call to `copy_nonoverlapping` is |
289 | // safe. The safety contract for `dealloc` must be upheld by the caller. |
290 | unsafe { |
291 | ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), old_layout.size()); |
292 | self.deallocate(ptr, old_layout); |
293 | } |
294 | |
295 | Ok(new_ptr) |
296 | } |
297 | |
298 | /// Attempts to shrink the memory block. |
299 | /// |
300 | /// Returns a new [`NonNull<[u8]>`][NonNull] containing a pointer and the actual size of the allocated |
301 | /// memory. The pointer is suitable for holding data described by `new_layout`. To accomplish |
302 | /// this, the allocator may shrink the allocation referenced by `ptr` to fit the new layout. |
303 | /// |
304 | /// If this returns `Ok`, then ownership of the memory block referenced by `ptr` has been |
305 | /// transferred to this allocator. Any access to the old `ptr` is Undefined Behavior, even if the |
306 | /// allocation was shrunk in-place. The newly returned pointer is the only valid pointer |
307 | /// for accessing this memory now. |
308 | /// |
309 | /// If this method returns `Err`, then ownership of the memory block has not been transferred to |
310 | /// this allocator, and the contents of the memory block are unaltered. |
311 | /// |
312 | /// # Safety |
313 | /// |
314 | /// * `ptr` must denote a block of memory [*currently allocated*] via this allocator. |
315 | /// * `old_layout` must [*fit*] that block of memory (The `new_layout` argument need not fit it.). |
316 | /// * `new_layout.size()` must be smaller than or equal to `old_layout.size()`. |
317 | /// |
318 | /// Note that `new_layout.align()` need not be the same as `old_layout.align()`. |
319 | /// |
320 | /// [*currently allocated*]: #currently-allocated-memory |
321 | /// [*fit*]: #memory-fitting |
322 | /// |
323 | /// # Errors |
324 | /// |
325 | /// Returns `Err` if the new layout does not meet the allocator's size and alignment |
326 | /// constraints of the allocator, or if shrinking otherwise fails. |
327 | /// |
328 | /// Implementations are encouraged to return `Err` on memory exhaustion rather than panicking or |
329 | /// aborting, but this is not a strict requirement. (Specifically: it is *legal* to implement |
330 | /// this trait atop an underlying native allocation library that aborts on memory exhaustion.) |
331 | /// |
332 | /// Clients wishing to abort computation in response to an allocation error are encouraged to |
333 | /// call the [`handle_alloc_error`] function, rather than directly invoking `panic!` or similar. |
334 | /// |
335 | /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html |
336 | unsafe fn shrink( |
337 | &self, |
338 | ptr: NonNull<u8>, |
339 | old_layout: Layout, |
340 | new_layout: Layout, |
341 | ) -> Result<NonNull<[u8]>, AllocError> { |
342 | debug_assert!( |
343 | new_layout.size() <= old_layout.size(), |
344 | "`new_layout.size()` must be smaller than or equal to `old_layout.size()`" |
345 | ); |
346 | |
347 | let new_ptr = self.allocate(new_layout)?; |
348 | |
349 | // SAFETY: because `new_layout.size()` must be lower than or equal to |
350 | // `old_layout.size()`, both the old and new memory allocation are valid for reads and |
351 | // writes for `new_layout.size()` bytes. Also, because the old allocation wasn't yet |
352 | // deallocated, it cannot overlap `new_ptr`. Thus, the call to `copy_nonoverlapping` is |
353 | // safe. The safety contract for `dealloc` must be upheld by the caller. |
354 | unsafe { |
355 | ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), new_layout.size()); |
356 | self.deallocate(ptr, old_layout); |
357 | } |
358 | |
359 | Ok(new_ptr) |
360 | } |
361 | |
362 | /// Creates a "by reference" adapter for this instance of `Allocator`. |
363 | /// |
364 | /// The returned adapter also implements `Allocator` and will simply borrow this. |
365 | #[inline (always)] |
366 | fn by_ref(&self) -> &Self |
367 | where |
368 | Self: Sized, |
369 | { |
370 | self |
371 | } |
372 | } |
373 | |
374 | #[unstable (feature = "allocator_api" , issue = "32838" )] |
375 | unsafe impl<A> Allocator for &A |
376 | where |
377 | A: Allocator + ?Sized, |
378 | { |
379 | #[inline ] |
380 | fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> { |
381 | (**self).allocate(layout) |
382 | } |
383 | |
384 | #[inline ] |
385 | fn allocate_zeroed(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> { |
386 | (**self).allocate_zeroed(layout) |
387 | } |
388 | |
389 | #[inline ] |
390 | unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout) { |
391 | // SAFETY: the safety contract must be upheld by the caller |
392 | unsafe { (**self).deallocate(ptr, layout) } |
393 | } |
394 | |
395 | #[inline ] |
396 | unsafe fn grow( |
397 | &self, |
398 | ptr: NonNull<u8>, |
399 | old_layout: Layout, |
400 | new_layout: Layout, |
401 | ) -> Result<NonNull<[u8]>, AllocError> { |
402 | // SAFETY: the safety contract must be upheld by the caller |
403 | unsafe { (**self).grow(ptr, old_layout, new_layout) } |
404 | } |
405 | |
406 | #[inline ] |
407 | unsafe fn grow_zeroed( |
408 | &self, |
409 | ptr: NonNull<u8>, |
410 | old_layout: Layout, |
411 | new_layout: Layout, |
412 | ) -> Result<NonNull<[u8]>, AllocError> { |
413 | // SAFETY: the safety contract must be upheld by the caller |
414 | unsafe { (**self).grow_zeroed(ptr, old_layout, new_layout) } |
415 | } |
416 | |
417 | #[inline ] |
418 | unsafe fn shrink( |
419 | &self, |
420 | ptr: NonNull<u8>, |
421 | old_layout: Layout, |
422 | new_layout: Layout, |
423 | ) -> Result<NonNull<[u8]>, AllocError> { |
424 | // SAFETY: the safety contract must be upheld by the caller |
425 | unsafe { (**self).shrink(ptr, old_layout, new_layout) } |
426 | } |
427 | } |
428 | |