std::alloc - Rust (original) (raw)

Module std::alloc

1.28.0 · source ·

Expand description

Memory allocation APIs.

In a given program, the standard library has one “global” memory allocator that is used for example by Box<T> and Vec<T>.

Currently the default global allocator is unspecified. Libraries, however, like cdylibs and staticlibs are guaranteed to use the System by default.

The #[global_allocator] attribute

This attribute allows configuring the choice of global allocator. You can use this to implement a completely custom global allocator to route all default allocation requests to a custom object.

use std::alloc::{GlobalAlloc, System, Layout};

struct MyAllocator;

unsafe impl GlobalAlloc for MyAllocator {
    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
        System.alloc(layout)
    }

    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
        System.dealloc(ptr, layout)
    }
}

#[global_allocator]
static GLOBAL: MyAllocator = MyAllocator;

fn main() {
    // This `Vec` will allocate memory through `GLOBAL` above
    let mut v = Vec::new();
    v.push(1);
}

Run

The attribute is used on a static item whose type implements theGlobalAlloc trait. This type can be provided by an external library:

ⓘ

use jemallocator::Jemalloc;

#[global_allocator]
static GLOBAL: Jemalloc = Jemalloc;

fn main() {}

Run

The #[global_allocator] can only be used once in a crate or its recursive dependencies.

• The AllocError error indicates an allocation failure that may be due to resource exhaustion or to something wrong when combining the given input arguments with this allocator.
• The global memory allocator.
• Layout of a block of memory.
• The parameters given to Layout::from_size_alignor some other Layout constructor do not satisfy its documented constraints.
• The default memory allocator provided by the operating system.
• An implementation of Allocator can allocate, grow, shrink, and deallocate arbitrary blocks of data described via Layout.
• A memory allocator that can be registered as the standard library’s default through the #[global_allocator] attribute.
• Registers a custom allocation error hook, replacing any that was previously registered.
• Unregisters the current allocation error hook, returning it.
• Allocate memory with the global allocator.
• Allocate zero-initialized memory with the global allocator.
• Deallocate memory with the global allocator.
• Signal a memory allocation error.
• Reallocate memory with the global allocator.