1 //! Memory allocation APIs
3 #![stable(feature = "alloc_module", since = "1.28.0")]
6 intrinsics::{min_align_of_val, size_of_val},
7 ptr::{NonNull, Unique},
11 #[stable(feature = "alloc_module", since = "1.28.0")]
13 pub use core::alloc::*;
16 // These are the magic symbols to call the global allocator. rustc generates
17 // them from the `#[global_allocator]` attribute if there is one, or uses the
18 // default implementations in libstd (`__rdl_alloc` etc in `src/libstd/alloc.rs`)
21 #[rustc_allocator_nounwind]
22 fn __rust_alloc(size: usize, align: usize) -> *mut u8;
23 #[rustc_allocator_nounwind]
24 fn __rust_dealloc(ptr: *mut u8, size: usize, align: usize);
25 #[rustc_allocator_nounwind]
26 fn __rust_realloc(ptr: *mut u8,
29 new_size: usize) -> *mut u8;
30 #[rustc_allocator_nounwind]
31 fn __rust_alloc_zeroed(size: usize, align: usize) -> *mut u8;
34 /// The global memory allocator.
36 /// This type implements the [`Alloc`] trait by forwarding calls
37 /// to the allocator registered with the `#[global_allocator]` attribute
38 /// if there is one, or the `std` crate’s default.
39 #[unstable(feature = "allocator_api", issue = "32838")]
40 #[derive(Copy, Clone, Default, Debug)]
43 /// Allocate memory with the global allocator.
45 /// This function forwards calls to the [`GlobalAlloc::alloc`] method
46 /// of the allocator registered with the `#[global_allocator]` attribute
47 /// if there is one, or the `std` crate’s default.
49 /// This function is expected to be deprecated in favor of the `alloc` method
50 /// of the [`Global`] type when it and the [`Alloc`] trait become stable.
54 /// See [`GlobalAlloc::alloc`].
59 /// use std::alloc::{alloc, dealloc, Layout};
62 /// let layout = Layout::new::<u16>();
63 /// let ptr = alloc(layout);
65 /// *(ptr as *mut u16) = 42;
66 /// assert_eq!(*(ptr as *mut u16), 42);
68 /// dealloc(ptr, layout);
71 #[stable(feature = "global_alloc", since = "1.28.0")]
73 pub unsafe fn alloc(layout: Layout) -> *mut u8 {
74 __rust_alloc(layout.size(), layout.align())
77 /// Deallocate memory with the global allocator.
79 /// This function forwards calls to the [`GlobalAlloc::dealloc`] method
80 /// of the allocator registered with the `#[global_allocator]` attribute
81 /// if there is one, or the `std` crate’s default.
83 /// This function is expected to be deprecated in favor of the `dealloc` method
84 /// of the [`Global`] type when it and the [`Alloc`] trait become stable.
88 /// See [`GlobalAlloc::dealloc`].
89 #[stable(feature = "global_alloc", since = "1.28.0")]
91 pub unsafe fn dealloc(ptr: *mut u8, layout: Layout) {
92 __rust_dealloc(ptr, layout.size(), layout.align())
95 /// Reallocate memory with the global allocator.
97 /// This function forwards calls to the [`GlobalAlloc::realloc`] method
98 /// of the allocator registered with the `#[global_allocator]` attribute
99 /// if there is one, or the `std` crate’s default.
101 /// This function is expected to be deprecated in favor of the `realloc` method
102 /// of the [`Global`] type when it and the [`Alloc`] trait become stable.
106 /// See [`GlobalAlloc::realloc`].
107 #[stable(feature = "global_alloc", since = "1.28.0")]
109 pub unsafe fn realloc(ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
110 __rust_realloc(ptr, layout.size(), layout.align(), new_size)
113 /// Allocate zero-initialized memory with the global allocator.
115 /// This function forwards calls to the [`GlobalAlloc::alloc_zeroed`] method
116 /// of the allocator registered with the `#[global_allocator]` attribute
117 /// if there is one, or the `std` crate’s default.
119 /// This function is expected to be deprecated in favor of the `alloc_zeroed` method
120 /// of the [`Global`] type when it and the [`Alloc`] trait become stable.
124 /// See [`GlobalAlloc::alloc_zeroed`].
129 /// use std::alloc::{alloc_zeroed, dealloc, Layout};
132 /// let layout = Layout::new::<u16>();
133 /// let ptr = alloc_zeroed(layout);
135 /// assert_eq!(*(ptr as *mut u16), 0);
137 /// dealloc(ptr, layout);
140 #[stable(feature = "global_alloc", since = "1.28.0")]
142 pub unsafe fn alloc_zeroed(layout: Layout) -> *mut u8 {
143 __rust_alloc_zeroed(layout.size(), layout.align())
146 #[unstable(feature = "allocator_api", issue = "32838")]
147 unsafe impl Alloc for Global {
149 unsafe fn alloc(&mut self, layout: Layout) -> Result<NonNull<u8>, AllocErr> {
150 NonNull::new(alloc(layout)).ok_or(AllocErr)
154 unsafe fn dealloc(&mut self, ptr: NonNull<u8>, layout: Layout) {
155 dealloc(ptr.as_ptr(), layout)
159 unsafe fn realloc(&mut self,
163 -> Result<NonNull<u8>, AllocErr>
165 NonNull::new(realloc(ptr.as_ptr(), layout, new_size)).ok_or(AllocErr)
169 unsafe fn alloc_zeroed(&mut self, layout: Layout) -> Result<NonNull<u8>, AllocErr> {
170 NonNull::new(alloc_zeroed(layout)).ok_or(AllocErr)
174 /// The allocator for unique pointers.
175 // This function must not unwind. If it does, MIR codegen will fail.
177 #[lang = "exchange_malloc"]
179 unsafe fn exchange_malloc(size: usize, align: usize) -> *mut u8 {
183 let layout = Layout::from_size_align_unchecked(size, align);
184 let ptr = alloc(layout);
188 handle_alloc_error(layout)
193 #[cfg_attr(not(test), lang = "box_free")]
195 pub(crate) unsafe fn box_free<T: ?Sized>(ptr: Unique<T>) {
196 let ptr = ptr.as_ptr();
197 let size = size_of_val(&*ptr);
198 let align = min_align_of_val(&*ptr);
199 // We do not allocate for Box<T> when T is ZST, so deallocation is also not necessary.
201 let layout = Layout::from_size_align_unchecked(size, align);
202 dealloc(ptr as *mut u8, layout);
206 /// Abort on memory allocation error or failure.
208 /// Callers of memory allocation APIs wishing to abort computation
209 /// in response to an allocation error are encouraged to call this function,
210 /// rather than directly invoking `panic!` or similar.
212 /// The default behavior of this function is to print a message to standard error
213 /// and abort the process.
214 /// It can be replaced with [`set_alloc_error_hook`] and [`take_alloc_error_hook`].
216 /// [`set_alloc_error_hook`]: ../../std/alloc/fn.set_alloc_error_hook.html
217 /// [`take_alloc_error_hook`]: ../../std/alloc/fn.take_alloc_error_hook.html
218 #[stable(feature = "global_alloc", since = "1.28.0")]
219 #[rustc_allocator_nounwind]
220 pub fn handle_alloc_error(layout: Layout) -> ! {
221 #[allow(improper_ctypes)]
224 fn oom_impl(layout: Layout) -> !;
226 unsafe { oom_impl(layout) }
232 use self::test::Bencher;
235 alloc::{Global, Alloc, Layout, handle_alloc_error},
239 fn allocate_zeroed() {
241 let layout = Layout::from_size_align(1024, 1).unwrap();
242 let ptr = Global.alloc_zeroed(layout.clone())
243 .unwrap_or_else(|_| handle_alloc_error(layout));
245 let mut i = ptr.cast::<u8>().as_ptr();
246 let end = i.add(layout.size());
251 Global.dealloc(ptr, layout);
256 fn alloc_owned_small(b: &mut Bencher) {
258 let _: Box<_> = box 10;