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:

#![feature(allocator_api)]

use core::{alloc::Allocator, mem::size_of};
use std::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.by_ref());
let mut vec2 = Vec::with_capacity_in(32, linear_allocator.by_ref());

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:

#![feature(allocator_api)]

use core::{alloc::Allocator, mem::size_of};
use std::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.by_ref());
let mut vec2 = Vec::with_capacity_in(32, chain_allocator.by_ref());

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());