Piece

Piece is a collection of composable allocators for rust.

Allocators

Currently this crate contains two allocators, piece::LinearAllocator and piece::ChainAllocator.

Linear allocator

piece::LinearAllocator is an allocator that keeps a fixed-sized buffer internally and use it to make allocations. Once the buffer is full, all next allocations fails.

This allocator is useful when you want a "scratch space" for multiple tiny allocations that share the same lifetime.

Usage:

#![cfg_attr(not(feature = "stable"), feature(allocator_api))]
#[cfg(feature = "vec")]
{
    use core::mem::size_of;

    use piece::vec::Vec;
    use piece::LinearAllocator;

    let linear_allocator = LinearAllocator::with_capacity(64 * size_of::<i32>());

    let mut vec1 = Vec::with_capacity_in(32, &linear_allocator);
    let mut vec2 = Vec::with_capacity_in(32, &linear_allocator);

    vec1.extend_from_slice(&[1, 2, 3, 4, 5]);
    vec2.extend_from_slice(&[6, 7, 8, 9, 10]);

    assert_eq!(vec1, &[1, 2, 3, 4, 5]);
    assert_eq!(vec2, &[6, 7, 8, 9, 10]);
}

Chain allocator

A piece::ChainAllocator create a new allocator of type A when the existing allocators of this

It can be useful when used with a piece::LinearAllocator for example. When all of its memory is used, the ChainAllocator will create a new one. This is useful when you want to use fixed-sized allocators but you're worried that your program will run out of memory.

Usage:

#![cfg_attr(not(feature = "stable"), feature(allocator_api))]
#[cfg(feature="vec")]
{
    use core::mem::size_of;

    use piece::vec::Vec;
    use piece::LinearAllocator;
    use piece::ChainAllocator;

    // Make room for the allocator pointer
    let chain_allocator = ChainAllocator::new(|| {
        LinearAllocator::with_capacity(32 * size_of::<i32>() + size_of::<*const ()>())
    });

    // Create two vectors that fills the whole `LinearAllocator` so
    // each `Vec` creates a new allocator
    let mut vec1 = Vec::with_capacity_in(32, &chain_allocator);
    let mut vec2 = Vec::with_capacity_in(32, &chain_allocator);

    vec1.extend_from_slice(&[1, 2, 3, 4, 5]);
    vec2.extend_from_slice(&[6, 7, 8, 9, 10]);

    assert_eq!(vec1, &[1, 2, 3, 4, 5]);
    assert_eq!(vec2, &[6, 7, 8, 9, 10]);

    assert_eq!(2, chain_allocator.allocator_count());
}

Nightly channel

You should enable the Rust feature_api on nightly builds adding #![feature(allocator_api)] to the root of your crate.

Stable channel

To use this library on stable channels, you should enable the feature stable. It will enable piece to use allocator_api2, that contains a mirror of the unstable nightly Allocator trait. You should be able to use any collections that are generic over allocator_api2::Allocator.