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).
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 [`AllocRef`] 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 unsafe { __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 [`AllocRef`] 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 unsafe { __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 [`AllocRef`] 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 unsafe { __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 [`AllocRef`] 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 unsafe { __rust_alloc_zeroed(layout.size(), layout.align()) }
148 fn alloc_impl(&mut self, layout: Layout, zeroed: bool) -> Result<NonNull<[u8]>, AllocErr> {
149 match layout.size() {
150 0 => Ok(NonNull::slice_from_raw_parts(layout.dangling(), 0)),
151 // SAFETY: `layout` is non-zero in size,
153 let raw_ptr = if zeroed { alloc_zeroed(layout) } else { alloc(layout) };
154 let ptr = NonNull::new(raw_ptr).ok_or(AllocErr)?;
155 Ok(NonNull::slice_from_raw_parts(ptr, size))
160 // Safety: Same as `AllocRef::grow`
168 ) -> Result<NonNull<[u8]>, AllocErr> {
170 new_size >= layout.size(),
171 "`new_size` must be greater than or equal to `layout.size()`"
174 match layout.size() {
175 // SAFETY: the caller must ensure that the `new_size` does not overflow.
176 // `layout.align()` comes from a `Layout` and is thus guaranteed to be valid for a Layout.
178 let new_layout = Layout::from_size_align_unchecked(new_size, layout.align());
179 self.alloc_impl(new_layout, zeroed)
182 // SAFETY: `new_size` is non-zero as `old_size` is greater than or equal to `new_size`
183 // as required by safety conditions. Other conditions must be upheld by the caller
185 // `realloc` probably checks for `new_size >= size` or something similar.
186 intrinsics::assume(new_size >= layout.size());
188 let raw_ptr = realloc(ptr.as_ptr(), layout, new_size);
189 let ptr = NonNull::new(raw_ptr).ok_or(AllocErr)?;
191 raw_ptr.add(old_size).write_bytes(0, new_size - old_size);
193 Ok(NonNull::slice_from_raw_parts(ptr, new_size))
199 #[unstable(feature = "allocator_api", issue = "32838")]
200 unsafe impl AllocRef for Global {
202 fn alloc(&mut self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
203 self.alloc_impl(layout, false)
207 fn alloc_zeroed(&mut self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
208 self.alloc_impl(layout, true)
212 unsafe fn dealloc(&mut self, ptr: NonNull<u8>, layout: Layout) {
213 if layout.size() != 0 {
214 // SAFETY: `layout` is non-zero in size,
215 // other conditions must be upheld by the caller
216 unsafe { dealloc(ptr.as_ptr(), layout) }
226 ) -> Result<NonNull<[u8]>, AllocErr> {
227 // SAFETY: all conditions must be upheld by the caller
228 unsafe { self.grow_impl(ptr, layout, new_size, false) }
232 unsafe fn grow_zeroed(
237 ) -> Result<NonNull<[u8]>, AllocErr> {
238 // SAFETY: all conditions must be upheld by the caller
239 unsafe { self.grow_impl(ptr, layout, new_size, true) }
248 ) -> Result<NonNull<[u8]>, AllocErr> {
250 new_size <= layout.size(),
251 "`new_size` must be smaller than or equal to `layout.size()`"
255 // SAFETY: conditions must be upheld by the caller
257 self.dealloc(ptr, layout);
258 Ok(NonNull::slice_from_raw_parts(layout.dangling(), 0))
261 // SAFETY: `new_size` is non-zero. Other conditions must be upheld by the caller
263 // `realloc` probably checks for `new_size <= size` or something similar.
264 intrinsics::assume(new_size <= layout.size());
266 let raw_ptr = realloc(ptr.as_ptr(), layout, new_size);
267 let ptr = NonNull::new(raw_ptr).ok_or(AllocErr)?;
268 Ok(NonNull::slice_from_raw_parts(ptr, new_size))
274 /// The allocator for unique pointers.
275 // This function must not unwind. If it does, MIR codegen will fail.
277 #[lang = "exchange_malloc"]
279 unsafe fn exchange_malloc(size: usize, align: usize) -> *mut u8 {
280 let layout = unsafe { Layout::from_size_align_unchecked(size, align) };
281 match Global.alloc(layout) {
282 Ok(ptr) => ptr.as_non_null_ptr().as_ptr(),
283 Err(_) => handle_alloc_error(layout),
287 #[cfg_attr(not(test), lang = "box_free")]
289 // This signature has to be the same as `Box`, otherwise an ICE will happen.
290 // When an additional parameter to `Box` is added (like `A: AllocRef`), this has to be added here as
292 // For example if `Box` is changed to `struct Box<T: ?Sized, A: AllocRef>(Unique<T>, A)`,
293 // this function has to be changed to `fn box_free<T: ?Sized, A: AllocRef>(Unique<T>, A)` as well.
294 pub(crate) unsafe fn box_free<T: ?Sized>(ptr: Unique<T>) {
296 let size = size_of_val(ptr.as_ref());
297 let align = min_align_of_val(ptr.as_ref());
298 let layout = Layout::from_size_align_unchecked(size, align);
299 Global.dealloc(ptr.cast().into(), layout)
303 /// Abort on memory allocation error or failure.
305 /// Callers of memory allocation APIs wishing to abort computation
306 /// in response to an allocation error are encouraged to call this function,
307 /// rather than directly invoking `panic!` or similar.
309 /// The default behavior of this function is to print a message to standard error
310 /// and abort the process.
311 /// It can be replaced with [`set_alloc_error_hook`] and [`take_alloc_error_hook`].
313 /// [`set_alloc_error_hook`]: ../../std/alloc/fn.set_alloc_error_hook.html
314 /// [`take_alloc_error_hook`]: ../../std/alloc/fn.take_alloc_error_hook.html
315 #[stable(feature = "global_alloc", since = "1.28.0")]
316 #[rustc_allocator_nounwind]
317 pub fn handle_alloc_error(layout: Layout) -> ! {
320 fn oom_impl(layout: Layout) -> !;
322 unsafe { oom_impl(layout) }