1 //! Memory allocation APIs
3 #![stable(feature = "alloc_module", since = "1.28.0")]
5 use core::intrinsics::{self, min_align_of_val, size_of_val};
6 use core::ptr::{NonNull, Unique};
8 #[stable(feature = "alloc_module", since = "1.28.0")]
10 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, old_size: usize, align: usize, new_size: usize) -> *mut u8;
27 #[rustc_allocator_nounwind]
28 fn __rust_alloc_zeroed(size: usize, align: usize) -> *mut u8;
31 /// The global memory allocator.
33 /// This type implements the [`AllocRef`] trait by forwarding calls
34 /// to the allocator registered with the `#[global_allocator]` attribute
35 /// if there is one, or the `std` crate’s default.
37 /// Note: while this type is unstable, the functionality it provides can be
38 /// accessed through the [free functions in `alloc`](index.html#functions).
40 /// [`AllocRef`]: trait.AllocRef.html
41 #[unstable(feature = "allocator_api", issue = "32838")]
42 #[derive(Copy, Clone, Default, Debug)]
45 /// Allocate memory with the global allocator.
47 /// This function forwards calls to the [`GlobalAlloc::alloc`] method
48 /// of the allocator registered with the `#[global_allocator]` attribute
49 /// if there is one, or the `std` crate’s default.
51 /// This function is expected to be deprecated in favor of the `alloc` method
52 /// of the [`Global`] type when it and the [`AllocRef`] trait become stable.
56 /// See [`GlobalAlloc::alloc`].
58 /// [`Global`]: struct.Global.html
59 /// [`AllocRef`]: trait.AllocRef.html
60 /// [`GlobalAlloc::alloc`]: trait.GlobalAlloc.html#tymethod.alloc
65 /// use std::alloc::{alloc, dealloc, Layout};
68 /// let layout = Layout::new::<u16>();
69 /// let ptr = alloc(layout);
71 /// *(ptr as *mut u16) = 42;
72 /// assert_eq!(*(ptr as *mut u16), 42);
74 /// dealloc(ptr, layout);
77 #[stable(feature = "global_alloc", since = "1.28.0")]
79 pub unsafe fn alloc(layout: Layout) -> *mut u8 {
80 unsafe { __rust_alloc(layout.size(), layout.align()) }
83 /// Deallocate memory with the global allocator.
85 /// This function forwards calls to the [`GlobalAlloc::dealloc`] method
86 /// of the allocator registered with the `#[global_allocator]` attribute
87 /// if there is one, or the `std` crate’s default.
89 /// This function is expected to be deprecated in favor of the `dealloc` method
90 /// of the [`Global`] type when it and the [`AllocRef`] trait become stable.
94 /// See [`GlobalAlloc::dealloc`].
96 /// [`Global`]: struct.Global.html
97 /// [`AllocRef`]: trait.AllocRef.html
98 /// [`GlobalAlloc::dealloc`]: trait.GlobalAlloc.html#tymethod.dealloc
99 #[stable(feature = "global_alloc", since = "1.28.0")]
101 pub unsafe fn dealloc(ptr: *mut u8, layout: Layout) {
102 unsafe { __rust_dealloc(ptr, layout.size(), layout.align()) }
105 /// Reallocate memory with the global allocator.
107 /// This function forwards calls to the [`GlobalAlloc::realloc`] method
108 /// of the allocator registered with the `#[global_allocator]` attribute
109 /// if there is one, or the `std` crate’s default.
111 /// This function is expected to be deprecated in favor of the `realloc` method
112 /// of the [`Global`] type when it and the [`AllocRef`] trait become stable.
116 /// See [`GlobalAlloc::realloc`].
118 /// [`Global`]: struct.Global.html
119 /// [`AllocRef`]: trait.AllocRef.html
120 /// [`GlobalAlloc::realloc`]: trait.GlobalAlloc.html#method.realloc
121 #[stable(feature = "global_alloc", since = "1.28.0")]
123 pub unsafe fn realloc(ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
124 unsafe { __rust_realloc(ptr, layout.size(), layout.align(), new_size) }
127 /// Allocate zero-initialized memory with the global allocator.
129 /// This function forwards calls to the [`GlobalAlloc::alloc_zeroed`] method
130 /// of the allocator registered with the `#[global_allocator]` attribute
131 /// if there is one, or the `std` crate’s default.
133 /// This function is expected to be deprecated in favor of the `alloc_zeroed` method
134 /// of the [`Global`] type when it and the [`AllocRef`] trait become stable.
138 /// See [`GlobalAlloc::alloc_zeroed`].
140 /// [`Global`]: struct.Global.html
141 /// [`AllocRef`]: trait.AllocRef.html
142 /// [`GlobalAlloc::alloc_zeroed`]: trait.GlobalAlloc.html#method.alloc_zeroed
147 /// use std::alloc::{alloc_zeroed, dealloc, Layout};
150 /// let layout = Layout::new::<u16>();
151 /// let ptr = alloc_zeroed(layout);
153 /// assert_eq!(*(ptr as *mut u16), 0);
155 /// dealloc(ptr, layout);
158 #[stable(feature = "global_alloc", since = "1.28.0")]
160 pub unsafe fn alloc_zeroed(layout: Layout) -> *mut u8 {
161 unsafe { __rust_alloc_zeroed(layout.size(), layout.align()) }
166 fn alloc_impl(&mut self, layout: Layout, zeroed: bool) -> Result<NonNull<[u8]>, AllocErr> {
167 match layout.size() {
168 0 => Ok(NonNull::slice_from_raw_parts(layout.dangling(), 0)),
169 // SAFETY: `layout` is non-zero in size,
171 let raw_ptr = if zeroed { alloc_zeroed(layout) } else { alloc(layout) };
172 let ptr = NonNull::new(raw_ptr).ok_or(AllocErr)?;
173 Ok(NonNull::slice_from_raw_parts(ptr, size))
178 // Safety: Same as `AllocRef::grow`
186 ) -> Result<NonNull<[u8]>, AllocErr> {
188 new_size >= layout.size(),
189 "`new_size` must be greater than or equal to `layout.size()`"
192 match layout.size() {
193 // SAFETY: the caller must ensure that the `new_size` does not overflow.
194 // `layout.align()` comes from a `Layout` and is thus guaranteed to be valid for a Layout.
196 let new_layout = Layout::from_size_align_unchecked(new_size, layout.align());
197 self.alloc_impl(new_layout, zeroed)
200 // SAFETY: `new_size` is non-zero as `old_size` is greater than or equal to `new_size`
201 // as required by safety conditions. Other conditions must be upheld by the caller
203 // `realloc` probably checks for `new_size >= size` or something similar.
204 intrinsics::assume(new_size >= layout.size());
206 let raw_ptr = realloc(ptr.as_ptr(), layout, new_size);
207 let ptr = NonNull::new(raw_ptr).ok_or(AllocErr)?;
209 raw_ptr.add(old_size).write_bytes(0, new_size - old_size);
211 Ok(NonNull::slice_from_raw_parts(ptr, new_size))
217 #[unstable(feature = "allocator_api", issue = "32838")]
218 unsafe impl AllocRef for Global {
220 fn alloc(&mut self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
221 self.alloc_impl(layout, false)
225 fn alloc_zeroed(&mut self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
226 self.alloc_impl(layout, true)
230 unsafe fn dealloc(&mut self, ptr: NonNull<u8>, layout: Layout) {
231 if layout.size() != 0 {
232 // SAFETY: `layout` is non-zero in size,
233 // other conditions must be upheld by the caller
234 unsafe { dealloc(ptr.as_ptr(), layout) }
244 ) -> Result<NonNull<[u8]>, AllocErr> {
245 // SAFETY: all conditions must be upheld by the caller
246 unsafe { self.grow_impl(ptr, layout, new_size, false) }
250 unsafe fn grow_zeroed(
255 ) -> Result<NonNull<[u8]>, AllocErr> {
256 // SAFETY: all conditions must be upheld by the caller
257 unsafe { self.grow_impl(ptr, layout, new_size, true) }
266 ) -> Result<NonNull<[u8]>, AllocErr> {
268 new_size <= layout.size(),
269 "`new_size` must be smaller than or equal to `layout.size()`"
273 // SAFETY: conditions must be upheld by the caller
275 self.dealloc(ptr, layout);
276 Ok(NonNull::slice_from_raw_parts(layout.dangling(), 0))
279 // SAFETY: `new_size` is non-zero. Other conditions must be upheld by the caller
281 // `realloc` probably checks for `new_size <= size` or something similar.
282 intrinsics::assume(new_size <= layout.size());
284 let raw_ptr = realloc(ptr.as_ptr(), layout, new_size);
285 let ptr = NonNull::new(raw_ptr).ok_or(AllocErr)?;
286 Ok(NonNull::slice_from_raw_parts(ptr, new_size))
292 /// The allocator for unique pointers.
293 // This function must not unwind. If it does, MIR codegen will fail.
295 #[lang = "exchange_malloc"]
297 unsafe fn exchange_malloc(size: usize, align: usize) -> *mut u8 {
298 let layout = unsafe { Layout::from_size_align_unchecked(size, align) };
299 match Global.alloc(layout) {
300 Ok(ptr) => ptr.as_non_null_ptr().as_ptr(),
301 Err(_) => handle_alloc_error(layout),
305 #[cfg_attr(not(test), lang = "box_free")]
307 // This signature has to be the same as `Box`, otherwise an ICE will happen.
308 // When an additional parameter to `Box` is added (like `A: AllocRef`), this has to be added here as
310 // For example if `Box` is changed to `struct Box<T: ?Sized, A: AllocRef>(Unique<T>, A)`,
311 // this function has to be changed to `fn box_free<T: ?Sized, A: AllocRef>(Unique<T>, A)` as well.
312 pub(crate) unsafe fn box_free<T: ?Sized>(ptr: Unique<T>) {
314 let size = size_of_val(ptr.as_ref());
315 let align = min_align_of_val(ptr.as_ref());
316 let layout = Layout::from_size_align_unchecked(size, align);
317 Global.dealloc(ptr.cast().into(), layout)
321 /// Abort on memory allocation error or failure.
323 /// Callers of memory allocation APIs wishing to abort computation
324 /// in response to an allocation error are encouraged to call this function,
325 /// rather than directly invoking `panic!` or similar.
327 /// The default behavior of this function is to print a message to standard error
328 /// and abort the process.
329 /// It can be replaced with [`set_alloc_error_hook`] and [`take_alloc_error_hook`].
331 /// [`set_alloc_error_hook`]: ../../std/alloc/fn.set_alloc_error_hook.html
332 /// [`take_alloc_error_hook`]: ../../std/alloc/fn.take_alloc_error_hook.html
333 #[stable(feature = "global_alloc", since = "1.28.0")]
334 #[rustc_allocator_nounwind]
335 pub fn handle_alloc_error(layout: Layout) -> ! {
338 fn oom_impl(layout: Layout) -> !;
340 unsafe { oom_impl(layout) }