src/liballoc/alloc.rs

   1 // Copyright 2014-2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! Memory allocation APIs
  12
  13 #![stable(feature = "alloc_module", since = "1.28.0")]
  14
  15 use core::intrinsics::{min_align_of_val, size_of_val};
  16 use core::ptr::{NonNull, Unique};
  17 use core::usize;
  18
  19 #[stable(feature = "alloc_module", since = "1.28.0")]
  20 #[doc(inline)]
  21 pub use core::alloc::*;
  22
  23 extern "Rust" {
  24     #[allocator]
  25     #[rustc_allocator_nounwind]
  26     fn __rust_alloc(size: usize, align: usize) -> *mut u8;
  27     #[rustc_allocator_nounwind]
  28     fn __rust_dealloc(ptr: *mut u8, size: usize, align: usize);
  29     #[rustc_allocator_nounwind]
  30     fn __rust_realloc(ptr: *mut u8,
  31                       old_size: usize,
  32                       align: usize,
  33                       new_size: usize) -> *mut u8;
  34     #[rustc_allocator_nounwind]
  35     fn __rust_alloc_zeroed(size: usize, align: usize) -> *mut u8;
  36 }
  37
  38 /// The global memory allocator.
  39 ///
  40 /// This type implements the [`Alloc`] trait by forwarding calls
  41 /// to the allocator registered with the `#[global_allocator]` attribute
  42 /// if there is one, or the `std` crate’s default.
  43 #[unstable(feature = "allocator_api", issue = "32838")]
  44 #[derive(Copy, Clone, Default, Debug)]
  45 pub struct Global;
  46
  47 /// Allocate memory with the global allocator.
  48 ///
  49 /// This function forwards calls to the [`GlobalAlloc::alloc`] method
  50 /// of the allocator registered with the `#[global_allocator]` attribute
  51 /// if there is one, or the `std` crate’s default.
  52 ///
  53 /// This function is expected to be deprecated in favor of the `alloc` method
  54 /// of the [`Global`] type when it and the [`Alloc`] trait become stable.
  55 ///
  56 /// # Safety
  57 ///
  58 /// See [`GlobalAlloc::alloc`].
  59 #[stable(feature = "global_alloc", since = "1.28.0")]
  60 #[inline]
  61 pub unsafe fn alloc(layout: Layout) -> *mut u8 {
  62     __rust_alloc(layout.size(), layout.align())
  63 }
  64
  65 /// Deallocate memory with the global allocator.
  66 ///
  67 /// This function forwards calls to the [`GlobalAlloc::dealloc`] method
  68 /// of the allocator registered with the `#[global_allocator]` attribute
  69 /// if there is one, or the `std` crate’s default.
  70 ///
  71 /// This function is expected to be deprecated in favor of the `dealloc` method
  72 /// of the [`Global`] type when it and the [`Alloc`] trait become stable.
  73 ///
  74 /// # Safety
  75 ///
  76 /// See [`GlobalAlloc::dealloc`].
  77 #[stable(feature = "global_alloc", since = "1.28.0")]
  78 #[inline]
  79 pub unsafe fn dealloc(ptr: *mut u8, layout: Layout) {
  80     __rust_dealloc(ptr, layout.size(), layout.align())
  81 }
  82
  83 /// Reallocate memory with the global allocator.
  84 ///
  85 /// This function forwards calls to the [`GlobalAlloc::realloc`] method
  86 /// of the allocator registered with the `#[global_allocator]` attribute
  87 /// if there is one, or the `std` crate’s default.
  88 ///
  89 /// This function is expected to be deprecated in favor of the `realloc` method
  90 /// of the [`Global`] type when it and the [`Alloc`] trait become stable.
  91 ///
  92 /// # Safety
  93 ///
  94 /// See [`GlobalAlloc::realloc`].
  95 #[stable(feature = "global_alloc", since = "1.28.0")]
  96 #[inline]
  97 pub unsafe fn realloc(ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
  98     __rust_realloc(ptr, layout.size(), layout.align(), new_size)
  99 }
 100
 101 /// Allocate zero-initialized memory with the global allocator.
 102 ///
 103 /// This function forwards calls to the [`GlobalAlloc::alloc_zeroed`] method
 104 /// of the allocator registered with the `#[global_allocator]` attribute
 105 /// if there is one, or the `std` crate’s default.
 106 ///
 107 /// This function is expected to be deprecated in favor of the `alloc_zeroed` method
 108 /// of the [`Global`] type when it and the [`Alloc`] trait become stable.
 109 ///
 110 /// # Safety
 111 ///
 112 /// See [`GlobalAlloc::alloc_zeroed`].
 113 #[stable(feature = "global_alloc", since = "1.28.0")]
 114 #[inline]
 115 pub unsafe fn alloc_zeroed(layout: Layout) -> *mut u8 {
 116     __rust_alloc_zeroed(layout.size(), layout.align())
 117 }
 118
 119 #[unstable(feature = "allocator_api", issue = "32838")]
 120 unsafe impl Alloc for Global {
 121     #[inline]
 122     unsafe fn alloc(&mut self, layout: Layout) -> Result<NonNull<u8>, AllocErr> {
 123         NonNull::new(alloc(layout)).ok_or(AllocErr)
 124     }
 125
 126     #[inline]
 127     unsafe fn dealloc(&mut self, ptr: NonNull<u8>, layout: Layout) {
 128         dealloc(ptr.as_ptr(), layout)
 129     }
 130
 131     #[inline]
 132     unsafe fn realloc(&mut self,
 133                       ptr: NonNull<u8>,
 134                       layout: Layout,
 135                       new_size: usize)
 136                       -> Result<NonNull<u8>, AllocErr>
 137     {
 138         NonNull::new(realloc(ptr.as_ptr(), layout, new_size)).ok_or(AllocErr)
 139     }
 140
 141     #[inline]
 142     unsafe fn alloc_zeroed(&mut self, layout: Layout) -> Result<NonNull<u8>, AllocErr> {
 143         NonNull::new(alloc_zeroed(layout)).ok_or(AllocErr)
 144     }
 145 }
 146
 147 /// The allocator for unique pointers.
 148 // This function must not unwind. If it does, MIR codegen will fail.
 149 #[cfg(not(test))]
 150 #[lang = "exchange_malloc"]
 151 #[inline]
 152 unsafe fn exchange_malloc(size: usize, align: usize) -> *mut u8 {
 153     if size == 0 {
 154         align as *mut u8
 155     } else {
 156         let layout = Layout::from_size_align_unchecked(size, align);
 157         let ptr = alloc(layout);
 158         if !ptr.is_null() {
 159             ptr
 160         } else {
 161             handle_alloc_error(layout)
 162         }
 163     }
 164 }
 165
 166 #[cfg_attr(not(test), lang = "box_free")]
 167 #[inline]
 168 pub(crate) unsafe fn box_free<T: ?Sized>(ptr: Unique<T>) {
 169     let ptr = ptr.as_ptr();
 170     let size = size_of_val(&*ptr);
 171     let align = min_align_of_val(&*ptr);
 172     // We do not allocate for Box<T> when T is ZST, so deallocation is also not necessary.
 173     if size != 0 {
 174         let layout = Layout::from_size_align_unchecked(size, align);
 175         dealloc(ptr as *mut u8, layout);
 176     }
 177 }
 178
 179 /// Abort on memory allocation error or failure.
 180 ///
 181 /// Callers of memory allocation APIs wishing to abort computation
 182 /// in response to an allocation error are encouraged to call this function,
 183 /// rather than directly invoking `panic!` or similar.
 184 ///
 185 /// The default behavior of this function is to print a message to standard error
 186 /// and abort the process.
 187 /// It can be replaced with [`set_alloc_error_hook`] and [`take_alloc_error_hook`].
 188 ///
 189 /// [`set_alloc_error_hook`]: ../../std/alloc/fn.set_alloc_error_hook.html
 190 /// [`take_alloc_error_hook`]: ../../std/alloc/fn.take_alloc_error_hook.html
 191 #[stable(feature = "global_alloc", since = "1.28.0")]
 192 #[rustc_allocator_nounwind]
 193 pub fn handle_alloc_error(layout: Layout) -> ! {
 194     #[allow(improper_ctypes)]
 195     extern "Rust" {
 196         #[lang = "oom"]
 197         fn oom_impl(layout: Layout) -> !;
 198     }
 199     unsafe { oom_impl(layout) }
 200 }
 201
 202 #[cfg(test)]
 203 mod tests {
 204     extern crate test;
 205     use self::test::Bencher;
 206     use boxed::Box;
 207     use alloc::{Global, Alloc, Layout, handle_alloc_error};
 208
 209     #[test]
 210     fn allocate_zeroed() {
 211         unsafe {
 212             let layout = Layout::from_size_align(1024, 1).unwrap();
 213             let ptr = Global.alloc_zeroed(layout.clone())
 214                 .unwrap_or_else(|_| handle_alloc_error(layout));
 215
 216             let mut i = ptr.cast::<u8>().as_ptr();
 217             let end = i.offset(layout.size() as isize);
 218             while i < end {
 219                 assert_eq!(*i, 0);
 220                 i = i.offset(1);
 221             }
 222             Global.dealloc(ptr, layout);
 223         }
 224     }
 225
 226     #[bench]
 227     fn alloc_owned_small(b: &mut Bencher) {
 228         b.iter(|| {
 229             let _: Box<_> = box 10;
 230         })
 231     }
 232 }