alloc.rs.html -- source
Description: Source to the Rust file `liballoc/alloc.rs`.
Keywords: rust, rustlang, rust-lang

      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

    // Copyright 2014-2015 The Rust Project Developers. See the COPYRIGHT
    // file at the top-level directory of this distribution and at
    // http://rust-lang.org/COPYRIGHT.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.

    //! Memory allocation APIs

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

    use core::intrinsics::{min_align_of_val, size_of_val};
    use core::ptr::{NonNull, Unique};
    use core::usize;

    #[stable(feature = "alloc_module", since = "1.28.0")]
    #[doc(inline)]
    pub use core::alloc::*;

    extern "Rust" {
        #[allocator]
        #[rustc_allocator_nounwind]
        fn __rust_alloc(size: usize, align: usize) -> *mut u8;
        #[rustc_allocator_nounwind]
        fn __rust_dealloc(ptr: *mut u8, size: usize, align: usize);
        #[rustc_allocator_nounwind]
        fn __rust_realloc(ptr: *mut u8,
                          old_size: usize,
                          align: usize,
                          new_size: usize) -> *mut u8;
        #[rustc_allocator_nounwind]
        fn __rust_alloc_zeroed(size: usize, align: usize) -> *mut u8;
    }

    /// The global memory allocator.
    ///
    /// This type implements the [`Alloc`] trait by forwarding calls
    /// to the allocator registered with the `#[global_allocator]` attribute
    /// if there is one, or the `std` crate’s default.
    #[unstable(feature = "allocator_api", issue = "32838")]
    #[derive(Copy, Clone, Default, Debug)]
    pub struct Global;

    /// Allocate memory with the global allocator.
    ///
    /// This function forwards calls to the [`GlobalAlloc::alloc`] method
    /// of the allocator registered with the `#[global_allocator]` attribute
    /// if there is one, or the `std` crate’s default.
    ///
    /// This function is expected to be deprecated in favor of the `alloc` method
    /// of the [`Global`] type when it and the [`Alloc`] trait become stable.
    ///
    /// # Safety
    ///
    /// See [`GlobalAlloc::alloc`].
    ///
    /// # Examples
    ///
    /// ```
    /// use std::alloc::{alloc, dealloc, Layout};
    ///
    /// unsafe {
    ///     let layout = Layout::new::<u16>();
    ///     let ptr = alloc(layout);
    ///
    ///     *(ptr as *mut u16) = 42;
    ///     assert_eq!(*(ptr as *mut u16), 42);
    ///
    ///     dealloc(ptr, layout);
    /// }
    /// ```
    #[stable(feature = "global_alloc", since = "1.28.0")]
    #[inline]
    pub unsafe fn alloc(layout: Layout) -> *mut u8 {
        __rust_alloc(layout.size(), layout.align())
    }

    /// Deallocate memory with the global allocator.
    ///
    /// This function forwards calls to the [`GlobalAlloc::dealloc`] method
    /// of the allocator registered with the `#[global_allocator]` attribute
    /// if there is one, or the `std` crate’s default.
    ///
    /// This function is expected to be deprecated in favor of the `dealloc` method
    /// of the [`Global`] type when it and the [`Alloc`] trait become stable.
    ///
    /// # Safety
    ///
    /// See [`GlobalAlloc::dealloc`].
    #[stable(feature = "global_alloc", since = "1.28.0")]
    #[inline]
    pub unsafe fn dealloc(ptr: *mut u8, layout: Layout) {
        __rust_dealloc(ptr, layout.size(), layout.align())
    }

    /// Reallocate memory with the global allocator.
    ///
    /// This function forwards calls to the [`GlobalAlloc::realloc`] method
    /// of the allocator registered with the `#[global_allocator]` attribute
    /// if there is one, or the `std` crate’s default.
    ///
    /// This function is expected to be deprecated in favor of the `realloc` method
    /// of the [`Global`] type when it and the [`Alloc`] trait become stable.
    ///
    /// # Safety
    ///
    /// See [`GlobalAlloc::realloc`].
    #[stable(feature = "global_alloc", since = "1.28.0")]
    #[inline]
    pub unsafe fn realloc(ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
        __rust_realloc(ptr, layout.size(), layout.align(), new_size)
    }

    /// Allocate zero-initialized memory with the global allocator.
    ///
    /// This function forwards calls to the [`GlobalAlloc::alloc_zeroed`] method
    /// of the allocator registered with the `#[global_allocator]` attribute
    /// if there is one, or the `std` crate’s default.
    ///
    /// This function is expected to be deprecated in favor of the `alloc_zeroed` method
    /// of the [`Global`] type when it and the [`Alloc`] trait become stable.
    ///
    /// # Safety
    ///
    /// See [`GlobalAlloc::alloc_zeroed`].
    ///
    /// # Examples
    ///
    /// ```
    /// use std::alloc::{alloc_zeroed, dealloc, Layout};
    ///
    /// unsafe {
    ///     let layout = Layout::new::<u16>();
    ///     let ptr = alloc_zeroed(layout);
    ///
    ///     assert_eq!(*(ptr as *mut u16), 0);
    ///
    ///     dealloc(ptr, layout);
    /// }
    /// ```
    #[stable(feature = "global_alloc", since = "1.28.0")]
    #[inline]
    pub unsafe fn alloc_zeroed(layout: Layout) -> *mut u8 {
        __rust_alloc_zeroed(layout.size(), layout.align())
    }

    #[unstable(feature = "allocator_api", issue = "32838")]
    unsafe impl Alloc for Global {
        #[inline]
        unsafe fn alloc(&mut self, layout: Layout) -> Result<NonNull<u8>, AllocErr> {
            NonNull::new(alloc(layout)).ok_or(AllocErr)
        }

        #[inline]
        unsafe fn dealloc(&mut self, ptr: NonNull<u8>, layout: Layout) {
            dealloc(ptr.as_ptr(), layout)
        }

        #[inline]
        unsafe fn realloc(&mut self,
                          ptr: NonNull<u8>,
                          layout: Layout,
                          new_size: usize)
                          -> Result<NonNull<u8>, AllocErr>
        {
            NonNull::new(realloc(ptr.as_ptr(), layout, new_size)).ok_or(AllocErr)
        }

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

    /// The allocator for unique pointers.
    // This function must not unwind. If it does, MIR codegen will fail.
    #[cfg(not(test))]
    #[lang = "exchange_malloc"]
    #[inline]
    unsafe fn exchange_malloc(size: usize, align: usize) -> *mut u8 {
        if size == 0 {
            align as *mut u8
        } else {
            let layout = Layout::from_size_align_unchecked(size, align);
            let ptr = alloc(layout);
            if !ptr.is_null() {
                ptr
            } else {
                handle_alloc_error(layout)
            }
        }
    }

    #[cfg_attr(not(test), lang = "box_free")]
    #[inline]
    pub(crate) unsafe fn box_free<T: ?Sized>(ptr: Unique<T>) {
        let ptr = ptr.as_ptr();
        let size = size_of_val(&*ptr);
        let align = min_align_of_val(&*ptr);
        // We do not allocate for Box<T> when T is ZST, so deallocation is also not necessary.
        if size != 0 {
            let layout = Layout::from_size_align_unchecked(size, align);
            dealloc(ptr as *mut u8, layout);
        }
    }

    /// Abort on memory allocation error or failure.
    ///
    /// Callers of memory allocation APIs wishing to abort computation
    /// in response to an allocation error are encouraged to call this function,
    /// rather than directly invoking `panic!` or similar.
    ///
    /// The default behavior of this function is to print a message to standard error
    /// and abort the process.
    /// It can be replaced with [`set_alloc_error_hook`] and [`take_alloc_error_hook`].
    ///
    /// [`set_alloc_error_hook`]: ../../std/alloc/fn.set_alloc_error_hook.html
    /// [`take_alloc_error_hook`]: ../../std/alloc/fn.take_alloc_error_hook.html
    #[stable(feature = "global_alloc", since = "1.28.0")]
    #[rustc_allocator_nounwind]
    pub fn handle_alloc_error(layout: Layout) -> ! {
        #[allow(improper_ctypes)]
        extern "Rust" {
            #[lang = "oom"]
            fn oom_impl(layout: Layout) -> !;
        }
        unsafe { oom_impl(layout) }
    }

    #[cfg(test)]
    mod tests {
        extern crate test;
        use self::test::Bencher;
        use boxed::Box;
        use alloc::{Global, Alloc, Layout, handle_alloc_error};

        #[test]
        fn allocate_zeroed() {
            unsafe {
                let layout = Layout::from_size_align(1024, 1).unwrap();
                let ptr = Global.alloc_zeroed(layout.clone())
                    .unwrap_or_else(|_| handle_alloc_error(layout));

                let mut i = ptr.cast::<u8>().as_ptr();
                let end = i.add(layout.size());
                while i < end {
                    assert_eq!(*i, 0);
                    i = i.offset(1);
                }
                Global.dealloc(ptr, layout);
            }
        }

        #[bench]
        fn alloc_owned_small(b: &mut Bencher) {
            b.iter(|| {
                let _: Box<_> = box 10;
            })
        }
    }

# Help

## Keyboard Shortcuts

`?`
  Show this help dialog
`S`
  Focus the search field
`↑`
  Move up in search results
`↓`
  Move down in search results
`↹`
  Switch tab
`⏎`
  Go to active search result
`+`
  Expand all sections
`-`
  Collapse all sections

## Search Tricks

Prefix searches with a type followed by a colon (e.g. `fn:`) to restrict the search to a given type.

Accepted types are: `fn`, `mod`, `struct`, `enum`, `trait`, `type`, `macro`, and `const`.

Search functions by type signature (e.g. `vec -> usize` or `* -> vec`)

Search multiple things at once by splitting your query with comma (e.g. `str,u8` or `String,struct:Vec,test`)