Rust - Implement Custom Allocator

In this article, we are going to learn about implement Custom Allocator in Rust with examples and details.

Rust’s default memory allocator is designed to be efficient and general-purpose but sometimes you may need more fine-grained control over memory allocation to optimize performance or minimize memory usage in your applications. Here, we’ll dive into implement Custom Allocator in Rust .

Table of Contents:

Rust Memory Management Basics
The Global Allocator Trait
Implementing a Custom Allocator
Using a Custom Allocator in Your Rust Project
Example: A Simple Custom Allocator
When to Use Custom Allocators

Rust Memory Management Basics:

Rust uses a two-tiered memory management system:

Stack: Memory for local variables and function calls is managed on the stack which provides fast and deterministic allocation and deallocation.
Heap: Memory for data with a dynamic size or unknown lifetime is managed on the heap which requires manual allocation and deallocation.

By default, Rust uses a global allocator to manage heap memory which is typically based on the system’s memory allocator or an allocator like jemalloc.

The Global Allocator Trait:

In Rust, the std::alloc::GlobalAlloc trait defines the interface for custom allocators. To create a custom allocator, you need to implement this trait and provide implementations for the alloc and dealloc methods.

Implementing a Custom Allocator:

To implement a custom allocator, follow these steps:

Import the necessary items from std::alloc.
Create a new struct for your custom allocator.
Implement the GlobalAlloc trait for your allocator struct, providing custom alloc and dealloc methods.

Using a Custom Allocator in Your Rust Project:

To use a custom allocator in your Rust project:

Import your custom allocator and std::alloc::Layout.
Apply the #[global_allocator] attribute to a static instance of your custom allocator.

Example:

Here’s an example of a simple custom allocator that wraps the default system allocator:

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


struct MyCustomAllocator;


unsafe impl GlobalAlloc for MyCustomAllocator {

    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {

        // Custom allocation logic can be added here

        System.alloc(layout)

    }


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

        // Custom deallocation logic can be added here

        System.dealloc(ptr, layout)

    }

}


#[global_allocator]

static GLOBAL: MyCustomAllocator = MyCustomAllocator;


fn main() {

    let data = Box::new(42);

    println!("Data: {}", data);

}

When to Use Custom Allocators:

Custom allocators are useful when:

You need to optimize memory allocation for specific use cases.
You want to track memory usage and detect leaks.
You need to implement custom allocation strategies like pooling or caching.

Relevant Rust topics:

Rust tutorial

References:

https://en.wikipedia.org/wiki/Rust_(programming_language)

Rust – Implement Custom Allocator