1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
use core::alloc::Layout;
use core::fmt;
use core::ptr::{self, NonNull};
use std::error::Error;
mod fixed_buf;
pub use fixed_buf::FixedBufferAllocator;
mod vec;
pub use vec::Vec;
#[derive(Debug)]
pub struct AllocError;
impl Error for AllocError {}
impl fmt::Display for AllocError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.write_str("memory allocation failed")
}
}
pub unsafe trait Allocator {
/// Attempts to allocate a block of memory.
///
/// On success, returns a [`NonNull<[u8]>`][NonNull] meeting the size and alignment guarantees of `layout`.
///
/// The returned block may have a larger size than specified by `layout.size()`, and may or may
/// not have its contents initialized.
///
/// # Errors
///
/// Returning `Err` indicates that either memory is exhausted or `layout` does not meet
/// allocator's size or alignment constraints.
///
/// Implementations are encouraged to return `Err` on memory exhaustion rather than panicking or
/// aborting, but this is not a strict requirement. (Specifically: it is *legal* to implement
/// this trait atop an underlying native allocation library that aborts on memory exhaustion.)
///
/// Clients wishing to abort computation in response to an allocation error are encouraged to
/// call the [`handle_alloc_error`] function, rather than directly invoking `panic!` or similar.
///
/// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError>;
/// Behaves like `allocate`, but also ensures that the returned memory is zero-initialized.
///
/// # Errors
///
/// Returning `Err` indicates that either memory is exhausted or `layout` does not meet
/// allocator's size or alignment constraints.
///
/// Implementations are encouraged to return `Err` on memory exhaustion rather than panicking or
/// aborting, but this is not a strict requirement. (Specifically: it is *legal* to implement
/// this trait atop an underlying native allocation library that aborts on memory exhaustion.)
///
/// Clients wishing to abort computation in response to an allocation error are encouraged to
/// call the [`handle_alloc_error`] function, rather than directly invoking `panic!` or similar.
///
/// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
fn allocate_zeroed(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
let ptr = self.allocate(layout)?;
// SAFETY: `alloc` returns a valid memory block
let raw_ptr = ptr.as_ptr() as *mut u8;
unsafe { raw_ptr.write_bytes(0, ptr.len()) };
Ok(ptr)
}
/// Deallocates the memory referenced by `ptr`.
///
/// # Safety
///
/// * `ptr` must denote a block of memory [*currently allocated*] via this allocator, and
/// * `layout` must [*fit*] that block of memory.
///
/// [*currently allocated*]: #currently-allocated-memory
/// [*fit*]: #memory-fitting
unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout);
/// Attempts to extend the memory block.
///
/// Returns a new [`NonNull<[u8]>`][NonNull] containing a pointer and the actual size of the allocated
/// memory. The pointer is suitable for holding data described by `new_layout`. To accomplish
/// this, the allocator may extend the allocation referenced by `ptr` to fit the new layout.
///
/// If this returns `Ok`, then ownership of the memory block referenced by `ptr` has been
/// transferred to this allocator. Any access to the old `ptr` is Undefined Behavior, even if the
/// allocation was grown in-place. The newly returned pointer is the only valid pointer
/// for accessing this memory now.
///
/// If this method returns `Err`, then ownership of the memory block has not been transferred to
/// this allocator, and the contents of the memory block are unaltered.
///
/// # Safety
///
/// * `ptr` must denote a block of memory [*currently allocated*] via this allocator.
/// * `old_layout` must [*fit*] that block of memory (The `new_layout` argument need not fit it.).
/// * `new_layout.size()` must be greater than or equal to `old_layout.size()`.
///
/// Note that `new_layout.align()` need not be the same as `old_layout.align()`.
///
/// [*currently allocated*]: #currently-allocated-memory
/// [*fit*]: #memory-fitting
///
/// # Errors
///
/// Returns `Err` if the new layout does not meet the allocator's size and alignment
/// constraints of the allocator, or if growing otherwise fails.
///
/// Implementations are encouraged to return `Err` on memory exhaustion rather than panicking or
/// aborting, but this is not a strict requirement. (Specifically: it is *legal* to implement
/// this trait atop an underlying native allocation library that aborts on memory exhaustion.)
///
/// Clients wishing to abort computation in response to an allocation error are encouraged to
/// call the [`handle_alloc_error`] function, rather than directly invoking `panic!` or similar.
///
/// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
unsafe fn grow(
&self,
ptr: NonNull<u8>,
old_layout: Layout,
new_layout: Layout,
) -> Result<NonNull<[u8]>, AllocError> {
debug_assert!(
new_layout.size() >= old_layout.size(),
"`new_layout.size()` must be greater than or equal to `old_layout.size()`"
);
let new_ptr = self.allocate(new_layout)?;
let new_raw_ptr = new_ptr.as_ptr() as *mut u8;
// SAFETY: because `new_layout.size()` must be greater than or equal to
// `old_layout.size()`, both the old and new memory allocation are valid for reads and
// writes for `old_layout.size()` bytes. Also, because the old allocation wasn't yet
// deallocated, it cannot overlap `new_ptr`. Thus, the call to `copy_nonoverlapping` is
// safe. The safety contract for `dealloc` must be upheld by the caller.
unsafe {
ptr::copy_nonoverlapping(ptr.as_ptr(), new_raw_ptr, old_layout.size());
self.deallocate(ptr, old_layout);
}
Ok(new_ptr)
}
/// Behaves like `grow`, but also ensures that the new contents are set to zero before being
/// returned.
///
/// The memory block will contain the following contents after a successful call to
/// `grow_zeroed`:
/// * Bytes `0..old_layout.size()` are preserved from the original allocation.
/// * Bytes `old_layout.size()..old_size` will either be preserved or zeroed, depending on
/// the allocator implementation. `old_size` refers to the size of the memory block prior
/// to the `grow_zeroed` call, which may be larger than the size that was originally
/// requested when it was allocated.
/// * Bytes `old_size..new_size` are zeroed. `new_size` refers to the size of the memory
/// block returned by the `grow_zeroed` call.
///
/// # Safety
///
/// * `ptr` must denote a block of memory [*currently allocated*] via this allocator.
/// * `old_layout` must [*fit*] that block of memory (The `new_layout` argument need not fit it.).
/// * `new_layout.size()` must be greater than or equal to `old_layout.size()`.
///
/// Note that `new_layout.align()` need not be the same as `old_layout.align()`.
///
/// [*currently allocated*]: #currently-allocated-memory
/// [*fit*]: #memory-fitting
///
/// # Errors
///
/// Returns `Err` if the new layout does not meet the allocator's size and alignment
/// constraints of the allocator, or if growing otherwise fails.
///
/// Implementations are encouraged to return `Err` on memory exhaustion rather than panicking or
/// aborting, but this is not a strict requirement. (Specifically: it is *legal* to implement
/// this trait atop an underlying native allocation library that aborts on memory exhaustion.)
///
/// Clients wishing to abort computation in response to an allocation error are encouraged to
/// call the [`handle_alloc_error`] function, rather than directly invoking `panic!` or similar.
///
/// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
unsafe fn grow_zeroed(
&self,
ptr: NonNull<u8>,
old_layout: Layout,
new_layout: Layout,
) -> Result<NonNull<[u8]>, AllocError> {
debug_assert!(
new_layout.size() >= old_layout.size(),
"`new_layout.size()` must be greater than or equal to `old_layout.size()`"
);
let new_ptr = self.allocate_zeroed(new_layout)?;
let new_raw_ptr = new_ptr.as_ptr() as *mut u8;
// SAFETY: because `new_layout.size()` must be greater than or equal to
// `old_layout.size()`, both the old and new memory allocation are valid for reads and
// writes for `old_layout.size()` bytes. Also, because the old allocation wasn't yet
// deallocated, it cannot overlap `new_ptr`. Thus, the call to `copy_nonoverlapping` is
// safe. The safety contract for `dealloc` must be upheld by the caller.
unsafe {
ptr::copy_nonoverlapping(ptr.as_ptr(), new_raw_ptr, old_layout.size());
self.deallocate(ptr, old_layout);
}
Ok(new_ptr)
}
/// Attempts to shrink the memory block.
///
/// Returns a new [`NonNull<[u8]>`][NonNull] containing a pointer and the actual size of the allocated
/// memory. The pointer is suitable for holding data described by `new_layout`. To accomplish
/// this, the allocator may shrink the allocation referenced by `ptr` to fit the new layout.
///
/// If this returns `Ok`, then ownership of the memory block referenced by `ptr` has been
/// transferred to this allocator. Any access to the old `ptr` is Undefined Behavior, even if the
/// allocation was shrunk in-place. The newly returned pointer is the only valid pointer
/// for accessing this memory now.
///
/// If this method returns `Err`, then ownership of the memory block has not been transferred to
/// this allocator, and the contents of the memory block are unaltered.
///
/// # Safety
///
/// * `ptr` must denote a block of memory [*currently allocated*] via this allocator.
/// * `old_layout` must [*fit*] that block of memory (The `new_layout` argument need not fit it.).
/// * `new_layout.size()` must be smaller than or equal to `old_layout.size()`.
///
/// Note that `new_layout.align()` need not be the same as `old_layout.align()`.
///
/// [*currently allocated*]: #currently-allocated-memory
/// [*fit*]: #memory-fitting
///
/// # Errors
///
/// Returns `Err` if the new layout does not meet the allocator's size and alignment
/// constraints of the allocator, or if shrinking otherwise fails.
///
/// Implementations are encouraged to return `Err` on memory exhaustion rather than panicking or
/// aborting, but this is not a strict requirement. (Specifically: it is *legal* to implement
/// this trait atop an underlying native allocation library that aborts on memory exhaustion.)
///
/// Clients wishing to abort computation in response to an allocation error are encouraged to
/// call the [`handle_alloc_error`] function, rather than directly invoking `panic!` or similar.
///
/// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html
unsafe fn shrink(
&self,
ptr: NonNull<u8>,
old_layout: Layout,
new_layout: Layout,
) -> Result<NonNull<[u8]>, AllocError> {
debug_assert!(
new_layout.size() <= old_layout.size(),
"`new_layout.size()` must be smaller than or equal to `old_layout.size()`"
);
let new_ptr = self.allocate(new_layout)?;
let new_raw_ptr = new_ptr.as_ptr() as *mut u8;
// SAFETY: because `new_layout.size()` must be lower than or equal to
// `old_layout.size()`, both the old and new memory allocation are valid for reads and
// writes for `new_layout.size()` bytes. Also, because the old allocation wasn't yet
// deallocated, it cannot overlap `new_ptr`. Thus, the call to `copy_nonoverlapping` is
// safe. The safety contract for `dealloc` must be upheld by the caller.
unsafe {
ptr::copy_nonoverlapping(ptr.as_ptr(), new_raw_ptr, new_layout.size());
self.deallocate(ptr, old_layout);
}
Ok(new_ptr)
}
/// Creates a "by reference" adapter for this instance of `Allocator`.
///
/// The returned adapter also implements `Allocator` and will simply borrow this.
#[inline(always)]
fn by_ref(&self) -> &Self
where
Self: Sized,
{
self
}
}