polazarus / rodeo

Fast dropping untyped arena for Rust

Rodeo

A dropping untyped arena based on bumpalo:

• arena: an allocator object that allows en masse deallocation
• untyped: the same allocator object may be used to allocate any type, unlike typed_arena
• dropping: any drop on the allocated data will be called, unlike bumpalo

Example

use rodeo::Rodeo;

struct S;
impl Drop for S {
    fn drop(&mut self) {
        println!("dropping S");
    }
}

{
    let rodeo = Rodeo::new();
    let n = rodeo.alloc(42);
    let r = rodeo.alloc(S);
}

prints dropping S

Features and #[no_std] Support

• bumpalo (default)

  If not selected, you will have to plug your own allocator that implements the trait ArenaAlloc.

• std (default)

  For now, rodeo is mostly a no_std crate. But std makes debugging a whole lot simpler!

You have to opt-out of bumpalo and std with default-features = false.

Safety

As a memory management library, this code uses unsafe extensively. However, the code is tested and dynamically verified with Miri.

Verification Strategy

Tests

Run the tests simply with:

$ cargo test

Miri

Miri is an interpreter for MIR (an intermediate representation of Rust) that checks Rust code and in particular unsafe code against the experimental Stacked Borrows memory model.

As of miri 0.1.0 (c1a859b 2022-11-10), Rodeo's tests show no error or warning when run with Miri.

$ rustup +nightly component add miri # if needed
$ cargo +nightly miri test
$ LEAK=1 cargo +nightly miri test # should leak two buffers

To-Do

• add generic DST allocation, hide behind feature pending stabilization of Rust RFC 2580

• investigate rodeo's use for self-referential structures

License

Rodeo is distributed under the terms of both the MIT license and the Apache License (Version 2.0). See LICENSE-MIT and LICENSE-APACHE.