#stream #rayon #parallel #streams


Asynchronous parallel streams analogous to rayon

4 releases

0.3.1 Mar 31, 2021
0.3.0 Feb 3, 2021
0.2.1 Dec 8, 2020
0.2.0 Dec 5, 2020

#133 in Asynchronous

46 downloads per month

MIT license


par-stream: Asynchronous Parallel Stream for Rust

[ crates.io | API Docs ]

An Rust implementation of asynchronous parallel streams analogous to rayon.


You must specify one of the following features to select appropriate runtime.

  • runtime_async-std
  • runtime_tokio

Here is an example Cargo.toml.

par-stream = { version = "0.3", features = ["runtime_tokio"] }


Easy usage

Add one line and you can obtain parallel combinators on existing futures stream.

use par_stream::ParStreamExt;

Parallel combinators

  • stream.par_then(limit, map_fut) processes stream items to parallel futures.
  • stream.par_map(limit, map_fn) processes stream items to parallel closures.
  • stream.par_then_unordered(limit, map_fut) and stream.par_map_unordered(limit, map_fn) are unordered correspondings of above.
  • stream.par_then_init(limit, init_fut, map_fut) accepts an extra in-local thread initializer.
  • stream.try_par_then(limit, map_fut) is the fallible version of stream.par_then(limit, map_fut).

The limit parameter configures the worker pool size. It accepts the following values:

  • None: The worker pool size scales to the number of system CPUs.
  • 10: Scale the number of workers and buffer size by 10.
  • 2.3: Scale the number of workers by 2.3 times.
  • (10, 15): Use 10 workers and buffer size 15.

Scatter and gather combinators

The feature is convenient to work with your custom organization of parallel workers.

stream.par_scatter(buf_size) allows you to convert a stream to a scattering worker and a clonable receiver. You can distribute cloned receivers to respective workers to share a stream.

par_gather(streams, buf_size) gathers multiple streams into one stream.

let (scatter_fut, rx) = stream.par_scatter(buf_size);

let rx1 = rx.clone();
let rx2 = rx.clone();

let stream1 = worker1(rx1);
let stream2 = worker1(rx2);

let gathered_stream = par_stream::par_gather(vec![stream1, stream2], buf_size);

Control the ordering of stream items

The combination of stream.wrapping_enumerate() and stream.reorder_enumerated() enable you to control the ordering of the stream items.

It gives the way to mark items with index numbers, apply to multiple unordered parallel tasks, and reorder them back. It effectively avoids reordering after each parallel task.

    // mark items with index numbers
    // a series of unordered maps
    .par_then_unordered(limit, map_fut1)
    .par_then_unordered(limit, map_fut2)
    .par_then_unordered(limit, map_fut3)
    // reorder the items back by indexes


Please visit the example directory to see usages of the crate.


MIT License. See LICENSE file.


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