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::{self, 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(&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_layout.size() >= old_layout.size(),
171 "`new_layout.size()` must be greater than or equal to `old_layout.size()`"
174 match old_layout.size() {
175 0 => self.alloc_impl(new_layout, zeroed),
177 // SAFETY: `new_size` is non-zero as `old_size` is greater than or equal to `new_size`
178 // as required by safety conditions. Other conditions must be upheld by the caller
179 old_size if old_layout.align() == new_layout.align() => unsafe {
180 let new_size = new_layout.size();
182 // `realloc` probably checks for `new_size >= old_layout.size()` or something similar.
183 intrinsics::assume(new_size >= old_layout.size());
185 let raw_ptr = realloc(ptr.as_ptr(), old_layout, new_size);
186 let ptr = NonNull::new(raw_ptr).ok_or(AllocErr)?;
188 raw_ptr.add(old_size).write_bytes(0, new_size - old_size);
190 Ok(NonNull::slice_from_raw_parts(ptr, new_size))
193 // SAFETY: because `new_layout.size()` must be greater than or equal to `old_size`,
194 // both the old and new memory allocation are valid for reads and writes for `old_size`
195 // bytes. Also, because the old allocation wasn't yet deallocated, it cannot overlap
196 // `new_ptr`. Thus, the call to `copy_nonoverlapping` is safe. The safety contract
197 // for `dealloc` must be upheld by the caller.
199 let new_ptr = self.alloc_impl(new_layout, zeroed)?;
200 ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), old_size);
201 self.dealloc(ptr, old_layout);
208 #[unstable(feature = "allocator_api", issue = "32838")]
209 unsafe impl AllocRef for Global {
211 fn alloc(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
212 self.alloc_impl(layout, false)
216 fn alloc_zeroed(&mut self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
217 self.alloc_impl(layout, true)
221 unsafe fn dealloc(&mut self, ptr: NonNull<u8>, layout: Layout) {
222 if layout.size() != 0 {
223 // SAFETY: `layout` is non-zero in size,
224 // other conditions must be upheld by the caller
225 unsafe { dealloc(ptr.as_ptr(), layout) }
235 ) -> Result<NonNull<[u8]>, AllocErr> {
236 // SAFETY: all conditions must be upheld by the caller
237 unsafe { self.grow_impl(ptr, old_layout, new_layout, false) }
241 unsafe fn grow_zeroed(
246 ) -> Result<NonNull<[u8]>, AllocErr> {
247 // SAFETY: all conditions must be upheld by the caller
248 unsafe { self.grow_impl(ptr, old_layout, new_layout, true) }
257 ) -> Result<NonNull<[u8]>, AllocErr> {
259 new_layout.size() <= old_layout.size(),
260 "`new_layout.size()` must be smaller than or equal to `old_layout.size()`"
263 match new_layout.size() {
264 // SAFETY: conditions must be upheld by the caller
266 self.dealloc(ptr, old_layout);
267 Ok(NonNull::slice_from_raw_parts(new_layout.dangling(), 0))
270 // SAFETY: `new_size` is non-zero. Other conditions must be upheld by the caller
271 new_size if old_layout.align() == new_layout.align() => unsafe {
272 // `realloc` probably checks for `new_size <= old_layout.size()` or something similar.
273 intrinsics::assume(new_size <= old_layout.size());
275 let raw_ptr = realloc(ptr.as_ptr(), old_layout, new_size);
276 let ptr = NonNull::new(raw_ptr).ok_or(AllocErr)?;
277 Ok(NonNull::slice_from_raw_parts(ptr, new_size))
280 // SAFETY: because `new_size` must be smaller than or equal to `old_layout.size()`,
281 // both the old and new memory allocation are valid for reads and writes for `new_size`
282 // bytes. Also, because the old allocation wasn't yet deallocated, it cannot overlap
283 // `new_ptr`. Thus, the call to `copy_nonoverlapping` is safe. The safety contract
284 // for `dealloc` must be upheld by the caller.
286 let new_ptr = self.alloc(new_layout)?;
287 ptr::copy_nonoverlapping(ptr.as_ptr(), new_ptr.as_mut_ptr(), new_size);
288 self.dealloc(ptr, old_layout);
295 /// The allocator for unique pointers.
296 // This function must not unwind. If it does, MIR codegen will fail.
298 #[lang = "exchange_malloc"]
300 unsafe fn exchange_malloc(size: usize, align: usize) -> *mut u8 {
301 let layout = unsafe { Layout::from_size_align_unchecked(size, align) };
302 match Global.alloc(layout) {
303 Ok(ptr) => ptr.as_mut_ptr(),
304 Err(_) => handle_alloc_error(layout),
308 #[cfg_attr(not(test), lang = "box_free")]
310 // This signature has to be the same as `Box`, otherwise an ICE will happen.
311 // When an additional parameter to `Box` is added (like `A: AllocRef`), this has to be added here as
313 // For example if `Box` is changed to `struct Box<T: ?Sized, A: AllocRef>(Unique<T>, A)`,
314 // this function has to be changed to `fn box_free<T: ?Sized, A: AllocRef>(Unique<T>, A)` as well.
315 pub(crate) unsafe fn box_free<T: ?Sized>(ptr: Unique<T>) {
317 let size = size_of_val(ptr.as_ref());
318 let align = min_align_of_val(ptr.as_ref());
319 let layout = Layout::from_size_align_unchecked(size, align);
320 Global.dealloc(ptr.cast().into(), layout)
324 /// Abort on memory allocation error or failure.
326 /// Callers of memory allocation APIs wishing to abort computation
327 /// in response to an allocation error are encouraged to call this function,
328 /// rather than directly invoking `panic!` or similar.
330 /// The default behavior of this function is to print a message to standard error
331 /// and abort the process.
332 /// It can be replaced with [`set_alloc_error_hook`] and [`take_alloc_error_hook`].
334 /// [`set_alloc_error_hook`]: ../../std/alloc/fn.set_alloc_error_hook.html
335 /// [`take_alloc_error_hook`]: ../../std/alloc/fn.take_alloc_error_hook.html
336 #[stable(feature = "global_alloc", since = "1.28.0")]
337 #[rustc_allocator_nounwind]
338 pub fn handle_alloc_error(layout: Layout) -> ! {
341 fn oom_impl(layout: Layout) -> !;
343 unsafe { oom_impl(layout) }