lol_alloc 0.1.3

lol_alloc: A laughably simple wasm global_allocator.
Documentation

lol_alloc

A laughably simple wasm global_allocator.

Like wee_alloc, but smaller since I used skinnier letters in the name.

lol_alloc is a experimental wasm global_allocator.

I wrote lol_alloc to learn about allocators (I hadn't written one before) and because wee_alloc seems unmaintained and has a leak. After looking at wee_alloc's implementation (which I failed to understand or fix), I wanted to find out how hard it really is to make a wasm global_allocator, and it seemed like providing one could be useful to the rust wasm community.

Status

Not production ready.

Current a few allocators are provided with minimal testing. If you use it, please report any bugs: I expect there are some. If it actually works for you, also let me know (you can post an issue with your report).

Currently only FailAllocator and LeakingPageAllocator are thread-safe safe.

Sizes of allocators include overhead from example:

  • FailAllocator: 195 bytes: errors on allocations. Operations are O(1),
  • LeakingPageAllocator: 230 bytes: Allocates pages for each allocation. Operations are O(1).
  • LeakingAllocator: 356 bytes: Bump pointer allocator, growing the heap as needed and does not reuse/free memory. Operations are O(1).
  • FreeListAllocator: 656 bytes: Free list based allocator. Operations (both allocation and freeing) are O(length of free list), but it does coalesce adjacent free list nodes.

LeakingAllocator should have no allocating space overhead other than for alignment.

FreeListAllocator rounds allocations up to at least 2 words in size, but otherwise should use all the space. Even gaps from high alignment allocations end up in its free list for use by smaller allocations.

Builtin rust allocator is 5053 bytes in this same test. If you can afford the extra code size, use it: its a much better allocator.

Supports only wasm32: other targets may build, but the allocators will not work on them (except: FailAllocator, it errors on all platforms just fine).

Usage

You can replace the global_allocator in wasm32 with FreeListAllocator builds using:

#[cfg(target_arch = "wasm32")]
use lol_alloc::FreeListAllocator;

#[cfg(target_arch = "wasm32")]
#[global_allocator]
static ALLOCATOR: FreeListAllocator = FreeListAllocator::new();

Testing

There are some normal rust unit tests (run with cargo run test), which use a test implementation of MemoryGrower.

There are also some wasm-pack tests (run with wasm-pack test --node lol_alloc)

Size testing:

wasm-pack build --release example && ls -l example/pkg/lol_alloc_example_bg.wasm