o1heap-rs

Rust bindings for o1heap - a constant-time deterministic memory allocator for hard real-time systems.

Features

• Constant-time O(1) allocation and deallocation
• Deterministic behavior suitable for real-time systems
• No-std compatible - designed for embedded systems
• Bounded fragmentation - predictable memory usage

Installation

[dependencies]
o1heap = "0.0.2"

Usage

As Global Allocator (STM32)

#![no_std]
#![no_main]

extern crate alloc;

use alloc::vec::Vec;
use core::mem::{size_of, MaybeUninit};
use core::ptr::addr_of_mut;
use cortex_m_rt::entry;
use o1heap::O1Heap;
use panic_halt as _;

#[repr(C, align(16))]
struct Arena([MaybeUninit<u8>; 8192]);
static mut ARENA: Arena = Arena([MaybeUninit::uninit(); 8192]);

#[global_allocator]
static HEAP: O1Heap = O1Heap::empty();

#[entry]
fn main() -> ! {
    unsafe {
        HEAP.init(addr_of_mut!(ARENA).cast(), size_of::<Arena>())
            .expect("heap init failed");
    }

    let mut xs = Vec::new();
    xs.push(1);

    loop { }
}

Alignment

o1heap guarantees that all allocated memory is aligned to:

• 32-bit systems: 16 bytes
• 64-bit systems: 32 bytes

This alignment is available as o1heap::ALIGNMENT.

Diagnostics

let diag = heap.diagnostics();
println!("Capacity: {}", diag.capacity);
println!("Allocated: {}", diag.allocated);
println!("Peak allocated: {}", diag.peak_allocated);
println!("OOM count: {}", diag.oom_count);

assert!(heap.invariants_hold());

Thread Safety

o1heap is not thread-safe. If you need to use it from multiple threads or interrupt contexts, you must provide external synchronization (e.g., critical sections, mutexes).

License

MIT license. The underlying o1heap C library is also MIT licensed.