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Diffstat (limited to 'src/libcore/alloc/global.rs')
| -rw-r--r-- | src/libcore/alloc/global.rs | 208 |
1 files changed, 0 insertions, 208 deletions
diff --git a/src/libcore/alloc/global.rs b/src/libcore/alloc/global.rs deleted file mode 100644 index c198797e650..00000000000 --- a/src/libcore/alloc/global.rs +++ /dev/null @@ -1,208 +0,0 @@ -use crate::alloc::Layout; -use crate::cmp; -use crate::ptr; - -/// A memory allocator that can be registered as the standard library’s default -/// through the `#[global_allocator]` attribute. -/// -/// Some of the methods require that a memory block be *currently -/// allocated* via an allocator. This means that: -/// -/// * the starting address for that memory block was previously -/// returned by a previous call to an allocation method -/// such as `alloc`, and -/// -/// * the memory block has not been subsequently deallocated, where -/// blocks are deallocated either by being passed to a deallocation -/// method such as `dealloc` or by being -/// passed to a reallocation method that returns a non-null pointer. -/// -/// -/// # Example -/// -/// ```no_run -/// use std::alloc::{GlobalAlloc, Layout, alloc}; -/// use std::ptr::null_mut; -/// -/// struct MyAllocator; -/// -/// unsafe impl GlobalAlloc for MyAllocator { -/// unsafe fn alloc(&self, _layout: Layout) -> *mut u8 { null_mut() } -/// unsafe fn dealloc(&self, _ptr: *mut u8, _layout: Layout) {} -/// } -/// -/// #[global_allocator] -/// static A: MyAllocator = MyAllocator; -/// -/// fn main() { -/// unsafe { -/// assert!(alloc(Layout::new::<u32>()).is_null()) -/// } -/// } -/// ``` -/// -/// # Safety -/// -/// The `GlobalAlloc` trait is an `unsafe` trait for a number of reasons, and -/// implementors must ensure that they adhere to these contracts: -/// -/// * It's undefined behavior if global allocators unwind. This restriction may -/// be lifted in the future, but currently a panic from any of these -/// functions may lead to memory unsafety. -/// -/// * `Layout` queries and calculations in general must be correct. Callers of -/// this trait are allowed to rely on the contracts defined on each method, -/// and implementors must ensure such contracts remain true. -#[stable(feature = "global_alloc", since = "1.28.0")] -pub unsafe trait GlobalAlloc { - /// Allocate memory as described by the given `layout`. - /// - /// Returns a pointer to newly-allocated memory, - /// or null to indicate allocation failure. - /// - /// # Safety - /// - /// This function is unsafe because undefined behavior can result - /// if the caller does not ensure that `layout` has non-zero size. - /// - /// (Extension subtraits might provide more specific bounds on - /// behavior, e.g., guarantee a sentinel address or a null pointer - /// in response to a zero-size allocation request.) - /// - /// The allocated block of memory may or may not be initialized. - /// - /// # Errors - /// - /// Returning a null pointer indicates that either memory is exhausted - /// or `layout` does not meet this allocator's size or alignment constraints. - /// - /// Implementations are encouraged to return null on memory - /// exhaustion rather than aborting, but this is not - /// a strict requirement. (Specifically: it is *legal* to - /// implement this trait atop an underlying native allocation - /// library that aborts on memory exhaustion.) - /// - /// Clients wishing to abort computation in response to an - /// allocation error are encouraged to call the [`handle_alloc_error`] function, - /// rather than directly invoking `panic!` or similar. - /// - /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html - #[stable(feature = "global_alloc", since = "1.28.0")] - unsafe fn alloc(&self, layout: Layout) -> *mut u8; - - /// Deallocate the block of memory at the given `ptr` pointer with the given `layout`. - /// - /// # Safety - /// - /// This function is unsafe because undefined behavior can result - /// if the caller does not ensure all of the following: - /// - /// * `ptr` must denote a block of memory currently allocated via - /// this allocator, - /// - /// * `layout` must be the same layout that was used - /// to allocate that block of memory, - #[stable(feature = "global_alloc", since = "1.28.0")] - unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout); - - /// Behaves like `alloc`, but also ensures that the contents - /// are set to zero before being returned. - /// - /// # Safety - /// - /// This function is unsafe for the same reasons that `alloc` is. - /// However the allocated block of memory is guaranteed to be initialized. - /// - /// # Errors - /// - /// Returning a null pointer indicates that either memory is exhausted - /// or `layout` does not meet allocator's size or alignment constraints, - /// just as in `alloc`. - /// - /// Clients wishing to abort computation in response to an - /// allocation error are encouraged to call the [`handle_alloc_error`] function, - /// rather than directly invoking `panic!` or similar. - /// - /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html - #[stable(feature = "global_alloc", since = "1.28.0")] - unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 { - let size = layout.size(); - // SAFETY: the safety contract for `alloc` must be upheld by the caller. - let ptr = unsafe { self.alloc(layout) }; - if !ptr.is_null() { - // SAFETY: as allocation succeeded, the region from `ptr` - // of size `size` is guaranteed to be valid for writes. - unsafe { ptr::write_bytes(ptr, 0, size) }; - } - ptr - } - - /// Shrink or grow a block of memory to the given `new_size`. - /// The block is described by the given `ptr` pointer and `layout`. - /// - /// If this returns a non-null pointer, then ownership of the memory block - /// referenced by `ptr` has been transferred to this allocator. - /// The memory may or may not have been deallocated, - /// and should be considered unusable (unless of course it was - /// transferred back to the caller again via the return value of - /// this method). The new memory block is allocated with `layout`, but - /// with the `size` updated to `new_size`. - /// - /// If this method returns null, then ownership of the memory - /// block has not been transferred to this allocator, and the - /// contents of the memory block are unaltered. - /// - /// # Safety - /// - /// This function is unsafe because undefined behavior can result - /// if the caller does not ensure all of the following: - /// - /// * `ptr` must be currently allocated via this allocator, - /// - /// * `layout` must be the same layout that was used - /// to allocate that block of memory, - /// - /// * `new_size` must be greater than zero. - /// - /// * `new_size`, when rounded up to the nearest multiple of `layout.align()`, - /// must not overflow (i.e., the rounded value must be less than `usize::MAX`). - /// - /// (Extension subtraits might provide more specific bounds on - /// behavior, e.g., guarantee a sentinel address or a null pointer - /// in response to a zero-size allocation request.) - /// - /// # Errors - /// - /// Returns null if the new layout does not meet the size - /// and alignment constraints of the allocator, or if reallocation - /// otherwise fails. - /// - /// Implementations are encouraged to return null on memory - /// exhaustion rather than panicking or aborting, but this is not - /// a strict requirement. (Specifically: it is *legal* to - /// implement this trait atop an underlying native allocation - /// library that aborts on memory exhaustion.) - /// - /// Clients wishing to abort computation in response to a - /// reallocation error are encouraged to call the [`handle_alloc_error`] function, - /// rather than directly invoking `panic!` or similar. - /// - /// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html - #[stable(feature = "global_alloc", since = "1.28.0")] - unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 { - // SAFETY: the caller must ensure that the `new_size` does not overflow. - // `layout.align()` comes from a `Layout` and is thus guaranteed to be valid. - let new_layout = unsafe { Layout::from_size_align_unchecked(new_size, layout.align()) }; - // SAFETY: the caller must ensure that `new_layout` is greater than zero. - let new_ptr = unsafe { self.alloc(new_layout) }; - if !new_ptr.is_null() { - // SAFETY: the previously allocated block cannot overlap the newly allocated block. - // The safety contract for `dealloc` must be upheld by the caller. - unsafe { - ptr::copy_nonoverlapping(ptr, new_ptr, cmp::min(layout.size(), new_size)); - self.dealloc(ptr, layout); - } - } - new_ptr - } -} |