Loom - Part 0 - Rationale

Finding good introduction level articles on concurrent programming is difficult, because every post assumes some prior knowledge. You quickly find yourself into dark corners of the Web, where people talk about lock-free concurrency: you're probably not ready for this if you're reading this blog!

Part 0 in a series of articles about Project Loom.
In this part I just talk about me, me, me, me and why I wrote this.

The companion code repository is at arnaudbos/untangled

If you'd like you could head over to
Part 0 - Rationale (this page)
Part 1 - It's all about Scheduling
Part 2 - Blocking code
Part 3 - Asynchronous code
Part 4 - Non-thread-blocking async I/O

Luckily for me, a few months ago, at a client's, we've had an interesting use-case. We had to implement a scheduler for a scarce resource in our system.

We've been using a good deal of concurrency "techniques" for the past two years: simple threads, executor services, reactive (Rx) programming; we were doing fine.

However, for this service, I wasn't convinced by any of those techniques an looking for an alternative. The problem lent itself well into an actor model, so we searched for a library to help us and found Quasar.
My first introduction to Quasar was around 2014. At the time when Clojure's core.async library just came out.

I didn't understand every aspect of the value proposition or core.async, but naively started using it.
And because I was using it, I stumbled upon Pulsar (not Apache Pulsar!) which is itself built upon Quasar.
I completely missed the value propositions of Quasar and Pulsar back then, but I was interested in this concept of "lightweight concurrency" and the "actor model".
I longed for the day I would have a use case for this.

Fast forward five years, and more experience in the field, Quasar and its actor model were a great fit to solve our problem, and we used it to great effect. That's when I fell into a rabbit hole: trying to understand the underlying concepts and "how it works", I stumbled upon Project Loom.

Unfortunately, the OpenJDK wiki and the many videos by Ron Pressler take for granted a great deal of knowledge and start from there. That's when I decided to gain this fundamental knowledge in order to grok Project Loom, and share with others so they, too, can connect the dots. I ended up giving a couple of conference talks on this topic in 2019-2020, for which I've had to research a lot.

This series is about what I've learnt, and what I would have liked to read, when I began my research on concurrent programming, Reactive Streams, lightweight concurrency and Project Loom: I'm writing for the past me.

For people already familiar, I'm not promising you'll learn anything new, but hopefully you'll be interested in another point of view and kind enough to point errors.

In the next part, we talk history!