ParSeq is a framework that makes it easier to write and maintain fast, scalable applications in Java.
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ParSeq is a framework that makes it easier to write and maintain fast, scalable applications in Java.

Some of the key benefits of ParSeq include:

  • Parallelization of asynchronous operations (such as IO)
  • Serialized execution for non-blocking computation
  • Code reuse via task composition
  • Simple error propagation and recovery
  • Execution tracing and visualization

The remainder of this README provides a very basic introduction to ParSeq. We recommend looking at the ParSeq wiki for more details.

Key Concepts

In ParSeq, we have a few basic concepts:

  • Promise: like a Java Future, a Promise allows the user to get the result of an asynchronous computation. However, a Promise allows the user to wait for the result asynchronously instead of requiring a blocking get call.
  • Task: a Task is an action that can be scheduled with an Engine (see below). Tasks can be sequenced using seq and par (see below).
  • par: composes a group of Tasks that can be executed in parallel.
  • seq: composes an ordered list of Tasks that will be executed sequentially.
  • Engine: a pool of workers that executes Tasks.

Example Usage

For this example, suppose we want to get the home page for a few popular browsers in parallel and then combine them. In ParSeq, we would code this up as follows:

final Task<String> google = httpClient.fetch("");
final Task<String> bing = httpClient.fetch("");
final Task<String> yahoo = httpClient.fetch("");

final Task<String> combination = new BaseTask<String>() {
    public Promise<String> run(Context ctx) {
        String googleStr = google.get();
        String bingStr = bing.get();
        String yahooStr = yahoo.get();

        // Build some combination out of the above three strings.

        return result;

Task<String> tasks = Tasks.seq(Tasks.par(google, bing, yahoo),

This will first fetch the URL for various pages in parallel and after they have all been retrieved it will combine them using the combination task.

For many more examples, please see the example module in the source code.

What Next?

To learn more about ParSeq, please visit our Wiki.


ParSeq is licensed under the terms of the Apache License, Version 2.0.