      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
    283
    284
    285
    286
    287
    288
    289
    290
    291
    292
    293
    294
    295
    296
    297
    298
    299
    300
    301
    302
    303
    304
    305
    306
    307
    308
    309
    310
    311
    312
    313
    314
    315
    316
    317
    318
    319
    320
    321
    322
    323
    324
    325
    326
    327
    328
    329
    330
    331
    332
    333
    334
    335
    336
    337
    338
    339
    340
    341
    342
    343
    344
    345
    346
    347
    348
    349
    350
    351
    352
    353
    354
    355
    356
    357
    358
    359
    360
    361
    362
    363
    364
    365
    366
    367
    368
    369
    370
    371
    372
    373
    374
    375
    376
    377
    378
    379
    380
    381
    382
    383
    384
    385
    386
    387
    388
    389
    390
    391
    392
    393
    394
    395
    396
    397
    398
    399
    400
    401
    402
    403
    404
    405
    406
    407
    408
    409
    410
    411
    412
    413
    414
    415
    416

    //! Memory allocation APIs

    #![stable(feature = "alloc_module", since = "1.28.0")]

    mod global;
    mod layout;

    #[stable(feature = "global_alloc", since = "1.28.0")]
    pub use self::global::GlobalAlloc;
    #[stable(feature = "alloc_layout", since = "1.28.0")]
    pub use self::layout::{Layout, LayoutErr};

    use crate::fmt;
    use crate::ptr::{self, NonNull};

    /// The `AllocErr` error indicates an allocation failure
    /// that may be due to resource exhaustion or to
    /// something wrong when combining the given input arguments with this
    /// allocator.
    #[unstable(feature = "allocator_api", issue = "32838")]
    #[derive(Copy, Clone, PartialEq, Eq, Debug)]
    pub struct AllocErr;

    // (we need this for downstream impl of trait Error)
    #[unstable(feature = "allocator_api", issue = "32838")]
    impl fmt::Display for AllocErr {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            f.write_str("memory allocation failed")
        }
    }

    /// An implementation of `AllocRef` can allocate, grow, shrink, and deallocate arbitrary blocks of
    /// data described via [`Layout`][].
    ///
    /// `AllocRef` is designed to be implemented on ZSTs, references, or smart pointers because having
    /// an allocator like `MyAlloc([u8; N])` cannot be moved, without updating the pointers to the
    /// allocated memory.
    ///
    /// Unlike [`GlobalAlloc`][], zero-sized allocations are allowed in `AllocRef`. If an underlying
    /// allocator does not support this (like jemalloc) or return a null pointer (such as
    /// `libc::malloc`), this must be caught by the implementation.
    ///
    /// ### Currently allocated memory
    ///
    /// Some of the methods require that a memory block be *currently allocated* via an allocator. This
    /// means that:
    ///
    /// * the starting address for that memory block was previously returned by [`alloc`], [`grow`], or
    ///   [`shrink`], and
    ///
    /// * the memory block has not been subsequently deallocated, where blocks are either deallocated
    ///   directly by being passed to [`dealloc`] or were changed by being passed to [`grow`] or
    ///   [`shrink`] that returns `Ok`. If `grow` or `shrink` have returned `Err`, the passed pointer
    ///   remains valid.
    ///
    /// [`alloc`]: AllocRef::alloc
    /// [`grow`]: AllocRef::grow
    /// [`shrink`]: AllocRef::shrink
    /// [`dealloc`]: AllocRef::dealloc
    ///
    /// ### Memory fitting
    ///
    /// Some of the methods require that a layout *fit* a memory block. What it means for a layout to
    /// "fit" a memory block means (or equivalently, for a memory block to "fit" a layout) is that the
    /// following conditions must hold:
    ///
    /// * The block must be allocated with the same alignment as [`layout.align()`], and
    ///
    /// * The provided [`layout.size()`] must fall in the range `min ..= max`, where:
    ///   - `min` is the size of the layout most recently used to allocate the block, and
    ///   - `max` is the latest actual size returned from [`alloc`], [`grow`], or [`shrink`].
    ///
    /// [`layout.align()`]: Layout::align
    /// [`layout.size()`]: Layout::size
    ///
    /// # Safety
    ///
    /// * Memory blocks returned from an allocator must point to valid memory and retain their validity
    ///   until the instance and all of its clones are dropped,
    ///
    /// * cloning or moving the allocator must not invalidate memory blocks returned from this
    ///   allocator. A cloned allocator must behave like the same allocator, and
    ///
    /// * any pointer to a memory block which is [*currently allocated*] may be passed to any other
    ///   method of the allocator.
    ///
    /// [*currently allocated*]: #currently-allocated-memory
    #[unstable(feature = "allocator_api", issue = "32838")]
    pub unsafe trait AllocRef {
        /// Attempts to allocate a block of memory.
        ///
        /// On success, returns a [`NonNull<[u8]>`] 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.
        ///
        /// [`NonNull<[u8]>`]: NonNull
        ///
        /// # 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 alloc(&mut self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr>;

        /// Behaves like `alloc`, 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 alloc_zeroed(&mut self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
            let ptr = self.alloc(layout)?;
            // SAFETY: `alloc` returns a valid memory block
            unsafe { ptr.as_non_null_ptr().as_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 dealloc(&mut self, ptr: NonNull<u8>, layout: Layout);

        /// Attempts to extend the memory block.
        ///
        /// Returns a new [`NonNull<[u8]>`] containing a pointer and the actual size of the allocated
        /// memory. The pointer is suitable for holding data described by a new layout with `layout`’s
        /// alignment and a size given by `new_size`. 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. The memory may or may not have been freed, and should be
        /// considered unusable unless it was transferred back to the caller again via the return value
        /// of this method.
        ///
        /// 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.
        ///
        /// [`NonNull<[u8]>`]: NonNull
        ///
        /// # Safety
        ///
        /// * `ptr` must denote a block of memory [*currently allocated*] via this allocator,
        /// * `layout` must [*fit*] that block of memory (The `new_size` argument need not fit it.),
        /// * `new_size` must be greater than or equal to `layout.size()`, and
        /// * `new_size`, when rounded up to the nearest multiple of `layout.align()`, must not overflow
        ///   (i.e., the rounded value must be less than or equal to `usize::MAX`).
        ///
        /// [*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(
            &mut self,
            ptr: NonNull<u8>,
            layout: Layout,
            new_size: usize,
        ) -> Result<NonNull<[u8]>, AllocErr> {
            let size = layout.size();
            debug_assert!(
                new_size >= size,
                "`new_size` must be greater than or equal to `layout.size()`"
            );

            // SAFETY: the caller must ensure that the `new_size` does not overflow.
            // `layout.align()` comes from a `Layout` and is thus guaranteed to be valid for a Layout.
            let new_layout = unsafe { Layout::from_size_align_unchecked(new_size, layout.align()) };
            let new_ptr = self.alloc(new_layout)?;

            // SAFETY: because `new_size` must be greater than or equal to `size`, both the old and new
            // memory allocation are valid for reads and writes for `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_ptr.as_mut_ptr(), size);
                self.dealloc(ptr, 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..layout.size()` are preserved from the original allocation.
        ///   * Bytes `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` call.
        ///
        /// # Safety
        ///
        /// * `ptr` must denote a block of memory [*currently allocated*] via this allocator,
        /// * `layout` must [*fit*] that block of memory (The `new_size` argument need not fit it.),
        /// * `new_size` must be greater than or equal to `layout.size()`, and
        /// * `new_size`, when rounded up to the nearest multiple of `layout.align()`, must not overflow
        ///   (i.e., the rounded value must be less than or equal to `usize::MAX`).
        ///
        /// [*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(
            &mut self,
            ptr: NonNull<u8>,
            layout: Layout,
            new_size: usize,
        ) -> Result<NonNull<[u8]>, AllocErr> {
            let size = layout.size();
            debug_assert!(
                new_size >= size,
                "`new_size` must be greater than or equal to `layout.size()`"
            );

            // SAFETY: the caller must ensure that the `new_size` does not overflow.
            // `layout.align()` comes from a `Layout` and is thus guaranteed to be valid for a Layout.
            let new_layout = unsafe { Layout::from_size_align_unchecked(new_size, layout.align()) };
            let new_ptr = self.alloc_zeroed(new_layout)?;

            // SAFETY: because `new_size` must be greater than or equal to `size`, both the old and new
            // memory allocation are valid for reads and writes for `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_ptr.as_mut_ptr(), size);
                self.dealloc(ptr, layout);
            }

            Ok(new_ptr)
        }

        /// Attempts to shrink the memory block.
        ///
        /// Returns a new [`NonNull<[u8]>`] containing a pointer and the actual size of the allocated
        /// memory. The pointer is suitable for holding data described by a new layout with `layout`’s
        /// alignment and a size given by `new_size`. 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. The memory may or may not have been freed, and should be
        /// considered unusable unless it was transferred back to the caller again via the return value
        /// of this method.
        ///
        /// 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.
        ///
        /// [`NonNull<[u8]>`]: NonNull
        ///
        /// # Safety
        ///
        /// * `ptr` must denote a block of memory [*currently allocated*] via this allocator,
        /// * `layout` must [*fit*] that block of memory (The `new_size` argument need not fit it.), and
        /// * `new_size` must be smaller than or equal to `layout.size()`.
        ///
        /// [*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(
            &mut self,
            ptr: NonNull<u8>,
            layout: Layout,
            new_size: usize,
        ) -> Result<NonNull<[u8]>, AllocErr> {
            let size = layout.size();
            debug_assert!(
                new_size <= size,
                "`new_size` must be smaller than or equal to `layout.size()`"
            );

            // SAFETY: the caller must ensure that the `new_size` does not overflow.
            // `layout.align()` comes from a `Layout` and is thus guaranteed to be valid for a Layout.
            let new_layout = unsafe { Layout::from_size_align_unchecked(new_size, layout.align()) };
            let new_ptr = self.alloc(new_layout)?;

            // SAFETY: because `new_size` must be lower than or equal to `size`, both the old and new
            // memory allocation are valid for reads and writes for `new_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_ptr.as_mut_ptr(), size);
                self.dealloc(ptr, layout);
            }

            Ok(new_ptr)
        }

        /// Creates a "by reference" adaptor for this instance of `AllocRef`.
        ///
        /// The returned adaptor also implements `AllocRef` and will simply borrow this.
        #[inline(always)]
        fn by_ref(&mut self) -> &mut Self {
            self
        }
    }

    #[unstable(feature = "allocator_api", issue = "32838")]
    unsafe impl<A> AllocRef for &mut A
    where
        A: AllocRef + ?Sized,
    {
        #[inline]
        fn alloc(&mut self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
            (**self).alloc(layout)
        }

        #[inline]
        fn alloc_zeroed(&mut self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
            (**self).alloc_zeroed(layout)
        }

        #[inline]
        unsafe fn dealloc(&mut self, ptr: NonNull<u8>, layout: Layout) {
            // SAFETY: the safety contract must be upheld by the caller
            unsafe { (**self).dealloc(ptr, layout) }
        }

        #[inline]
        unsafe fn grow(
            &mut self,
            ptr: NonNull<u8>,
            layout: Layout,
            new_size: usize,
        ) -> Result<NonNull<[u8]>, AllocErr> {
            // SAFETY: the safety contract must be upheld by the caller
            unsafe { (**self).grow(ptr, layout, new_size) }
        }

        #[inline]
        unsafe fn grow_zeroed(
            &mut self,
            ptr: NonNull<u8>,
            layout: Layout,
            new_size: usize,
        ) -> Result<NonNull<[u8]>, AllocErr> {
            // SAFETY: the safety contract must be upheld by the caller
            unsafe { (**self).grow_zeroed(ptr, layout, new_size) }
        }

        #[inline]
        unsafe fn shrink(
            &mut self,
            ptr: NonNull<u8>,
            layout: Layout,
            new_size: usize,
        ) -> Result<NonNull<[u8]>, AllocErr> {
            // SAFETY: the safety contract must be upheld by the caller
            unsafe { (**self).shrink(ptr, layout, new_size) }
        }
    }