rayon-rs/rayon

idea: allow splitting that's weighted toward one side

Open

#477 opened on Nov 17, 2017

View on GitHub
 (3 comments) (0 reactions) (0 assignees)Rust (9,410 stars) (450 forks)batch import
enhancementhelp wanted

Description

Usually we just split iterators at len/2. For something like find_first, it may be better to split closer to the front of the iterator, like len/3. Likewise, find_last might prefer something like 2 * len / 3.

For find_last, it might also be a good idea to flip the join arguments, so the latter split is processed first.

I'm not sure if these ideas could be exposed generically, or if the find functions should just implement custom bridge functions to this effect. Part of the challenge is that these are also at the end of the iterator chain, so their immediate input might not a Producer at all.

Contributor guide

Tech stack
rust
Domain
performance
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
over 1 week
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
needs investigation
Prerequisites
RustRayon internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
15
Research direction
Investigate the current splitter implementation in Rayon's source code (likely in src/splitter.rs or similar). Study how `bridge` is implemented for parallel iterators and how `find first` and `find last` currently work. Consider designing a weighted splitter that takes a bias parameter (e.g., a fraction like 1/3 or 2/3) and modifies the split point accordingly. Also explore if the join order should be flipped for find last to prioritize the latter split. The goal is to propose a concrete API or custom bridge function.