chunker

Minimalistic alternative to rayon’s par_iter/par_chunks + inner iteration + reduce for parallel processing of slices with progress bar by default. Despite its name, this crate is really tiny: only 80 SLOC.

Usage

cargo add chunker

Call chunker::run or chunker::run_mut with these arguments:

• items — slice of values to process in parallel
• config — configuration:thread_count, chunk_size, progress_bar, bar_step
• init — function to initialize a worker’s intermediate result
• work — Fn accepting an individual value from items and mutating the worker’s intermediate result (and/or mutating the value itself in the case of run_mut)
• gather — FnMut accepting an mpsc::Receiver of workers’ intermediate results in random order and returns the final result (usually via reduce)

Example

Sum of squares:

chunker::run(
    &input,
    chunker::Config::default(),
    || 0,
    |thread_sum, i| *thread_sum += i * i,
    |rx| rx.iter().sum::<i64>()
)

Simple parallel implementaion of word counting:

use std::{collections::HashMap, io::{stdin, stdout, Read, Write, BufWriter}, cmp::Reverse};

fn main() {
    let mut text = String::new();
    stdin().read_to_string(&mut text).unwrap();
    let lower = text.to_ascii_lowercase();
    let lines: Vec<_> = lower.lines().collect();

    let word_counts = chunker::run(
        &lines,
        chunker::Config::default(),
        || HashMap::<&str, u32>::new(),
        |counts, line| {
            for word in line.split_whitespace() {
                *counts.entry(word).or_default() += 1;
            }
        },
        |rx| rx.into_iter().reduce(|mut word_counts, counts| {
            for (word, count) in counts {
                *word_counts.entry(word).or_default() += count;
            }

            word_counts
        }).unwrap(),
    );

    let mut sorted_word_counts: Vec<_> = word_counts.iter().collect();
    sorted_word_counts.sort_unstable_by_key(|&(_, count)| Reverse(count));
    let mut stdout = BufWriter::new(stdout().lock());

    for (word, count) in sorted_word_counts {
        writeln!(stdout, "{word} {count}").unwrap();
    }
}

$ hyperfine 'target/release/examples/count_words <kjvbible_x10.txt'
Benchmark 1: target/release/examples/count_words <kjvbible_x10.txt
  Time (mean ± σ):      84.0 ms ±   1.3 ms    [User: 314.6 ms, System: 28.2 ms]
  Range (min … max):    82.4 ms …  87.8 ms    34 runs