#arena #constant-time #fixed-size #latency #typed-arena

no-std fixed-typed-arena

A typed arena that uses fixed-size chunks to ensure non-amortized O(1) allocations

4 releases

0.2.2 Apr 26, 2022
0.2.1 Nov 7, 2021
0.1.2 Mar 25, 2021
0.1.0 Feb 7, 2021

#122 in Memory management

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An arena that allocates values of a single type (similar to typed-arena) using chunks of memory that have a configurable fixed size. This enables it to perform allocations in non-amortized O(1) (constant) time.

Other arena implementations, like typed-arena, are optimized for throughput: they allocate chunks of memory with exponentially increasing sizes, which results in amortized constant-time allocations.

fixed-typed-arena is optimized for latency: it allocates chunks of memory with a fixed, configurable size, and individual value allocations are performed in non-amortized constant time.

This crate depends only on core and alloc, so it can be used in no_std environments that support alloc.


use fixed_typed_arena::Arena;
struct Item(u64);

let arena = Arena::<_, 128>::new();
let item1 = arena.alloc(Item(1));
let item2 = arena.alloc(Item(2));
item1.0 += item2.0;

assert_eq!(item1.0, 3);
assert_eq!(item2.0, 2);


Items allocated by an Arena can contain references to other items in the same arena, but the crate feature dropck_eyepatch must be enabled (which requires Rust nightly), as fixed-typed-arena must use the unstable feature of the same name.

Alternatively, you may be able to use a ManuallyDropArena instead.


This crate also provides ManuallyDropArena, a type like Arena that returns references of any lifetime, including 'static. The advantage of this type is that it can be used without being borrowed, but it comes with the tradeoff that it will leak memory unless the unsafe drop method is called.

No runtime deps


  • dropck_eyepatch