bucket_vec 0.1.1

An efficient vector-like data structure that consists of fixed-capacity buckets in order to store elements without moving them arround upon reallocations allowing safe pinned references to internal elements if the outer bucket vector is pinned.
Documentation

Bucket Vector

⚠️ Caution

USE WITH CAUTION

As of now this crate has not yet been battle tested or benchmarked to an extend where the author would recommend general production usage. Please file bugs, suggestions or enhancements to the issue tracker of this repository.

Description

A vector-like data structure that organizes its elements into a set of buckets of fixed-capacity in order to guarantee that mutations to the bucket vector never moves elements and thus invalidates references to them.

This is comparable to a Vec<Box<T>> but a lot more efficient.

Configs

The BucketVecConfig trait allows to customize the internal structure of your BucketVec. This allows users to fine-tune their BucketVec for particular use cases.

The trait mainly controls the capacity of the first bucket and the growth rate of the capacity of new buckets.

The default DefaultConfig tries to balance out the different interests between start capacity and growth rate.

Under the Hood

The BucketVec is really just a vector of Bucket instances. Whenever an element is pushed to the BucketVec the element is pushed onto the last Bucket if it isn't filled, yet. If the last Bucket is filled a new Bucket is pushed onto the BucketVec with a new capacity determined by the used bucket vector configuration.

This way the BucketVec never moves elements around upon inserting new elements in order to preserve references. When a normal Vec is modified it can potentially invalidate references because of reallocation of the internal buffer which might cause severe bugs if references to the internal elements are stored outside the Vec. Note that normally Rust prevents such situations so the BucketVec is mainly used in the area of unsafe Rust where a developer actively decides that they want or need pinned references into another data structure.

For the same reasons as stated above the BucketVec does not allow to remove or swap elements.

Example

Looking at an example BucketVec<i32> with the following configuration:

  • start_capacity := 1
  • growth_rate := 2

We have already pushed the elements A,.., K onto it.

[ [A], [B, C], [D, E, F, G], [H, I, J, K, _, _, _, _] ]

Where _ refers to a vacant bucket entry.

Pushing another L,.., O onto the same BucketVec results in:

[ [A], [B, C], [D, E, F, G], [H, I, J, K, L, M, N, O] ]

So we are full on capacity for all buckets. The next time we push another element onto the BucketVec it will create a new Bucket with a capacity of 16 since growth_rate == 2 and our current latest bucket already has a capacity of 8.

[ [A], [B, C], [D, E, F, G], [H, I, J, K, L, M, N, O], [P, 15 x _] ]

Where 15 x _ denotes 15 consecutive vacant entries.

Authors & Credits

Author: Robin Freyler (github.com/Robbepop)

Special thanks to Niklas Tittjung (github.com/lugino-emeritus) who helped me a lot with some internal formulae.

License

Licensed under either of

at your option.

Dual licence: badge badge