Jon Gjengset
@jonhoo.eu
Rust live-coder and OSS tinkerer who loves teaching. I try to maintain a high SNR. Wrote Rust for Rustaceans. At Helsing.ai. Formerly AWS. Co-founded ReadySet. @jonhoo elsewhere. he/him/they
Recording of yesterday's open source maintenance stream is now up! We got through left-right (a concurrency primitive), HdrHistogram (a fun data structure), rust-imap (you guessed it), and inferno (the Rust port of flamegraph) in about 5 hours — OSS is no joke 😅 youtu.be/bAINppA0BSU
Open Source Maintenance, 2026-07-18
YouTube video by Jon Gjengset
youtu.be
Haven't done an open source maintenance stream in a while, and by now I have a few open open-source issues and pull requests I'm behind on, so let's rectify that! Stream will be this Saturday at 1pm UTC on youtube.com/live/7h7ciBk... — see you there!
Open source maintenance
YouTube video by Jon Gjengset
youtube.com
After the AI Engineer conference, which was full of useful criticism, I remembered that the most confident takes on AI often came from the least exposure. Rejection is easy, trial and error is expensive. I wrote about it. lucumr.pocoo.org/2026/4/11/th...
The Center Has a Bias
Why a measured position on AI tends to lean towards actually trying it.
lucumr.pocoo.org
Recording of yesterday's stream implementing a WAV noise file generator in #rust is now up on YouTube! We managed to get white, pink, brownian, blue, violet, and grey (psychoacoustic!) noise all implemented, so I'll count that as a success 🔊 youtu.be/zOTE4BN59u4
impl Rust: WAV noise generator
YouTube video by Jon Gjengset
youtu.be
A few weeks ago I was interviewed by Daniel from Rock the JVM, a channel (unsurprisingly) for folks in the JVM ecosystem. It was fun to chat about Rust with someone "from the outside", and if you want to hear it, it's now up on his YouTube channel! youtu.be/Cg8gASzqqOs?...
Jon Gjengset on Rust Internals, Vibe Coding, and Teaching by Streaming
YouTube video by Rock the JVM
youtu.be
The past few streams have been pretty high level, but not this time! Friday at 4p UTC (everytimezone.com?t=69cf0300,3c0), we're going back down to "what bits go where". We'll try to write an audio generator that produces WAV files with white/pink/brown noise by hand 🔊 youtube.com/live/BKHE7st...
impl Rust: WAV noise generator
YouTube video by Jon Gjengset
youtube.com
Back in January I gave a talk at Jane Street titled "Are Mutexes Slow?" (I gave a lightning version of it at @rustikon.dev last week!). And it's now up on YouTube if you're interested in wonky details about CPU cache coherence and the cost of coordination! www.youtube.com/watch?v=tND-...
The Cost of Concurrency Coordination with Jon Gjengset
YouTube video by Jane Street
youtube.com
Sadly I can't make it to the inaugural TokioConf (Portland, Apr 20-22), but I do have a 15% off code I've been told to hand out to people excited to go! So, if you've been on the fence, ping me and I'll see what I can do! More on the conf & who it's for (most people!) here: tokio.rs/blog/2026-03...
TokioConf Update: What to Expect | Tokio - An asynchronous Rust runtime
Tokio is a runtime for writing reliable asynchronous applications with Rust. It provides async I/O, networking, scheduling, timers, and more.
tokio.rs
In January, @anishathalye.bsky.social, @josejg.bsky.social, and I returned to @csail.mit.edu to teach Missing Semester, a class on topics we miss from most CS programs—tools and techniques that everyone should know, like Bash, Git, CI, and AI tools. Today, we’re releasing the course for free online!
![The Missing Semester of your CS education [MIT IAP 2026] - https://missing.csail.mit.edu](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:ksdsms3vq5jx3zzslkouevlp/bafkreighfwu5c3nnebavcur5n5xgr7etazrvuwnmjrydizxdq7u3hbmg7m)
@alex.wcgw.dev Hey Alex! First, thanks a lot for taking on ownership of ANTLR4 for Rust! Second, I see you made some improvements to the README over the past couple of days — was that because of my stream by any chance? 😅
Recording of our "port avro-tools' Java-based idl-to-json tool to Rust using an LLM" adventure is now on YouTube! We got to an initial working implementation in ~4hrs (though still bugs to iron out in future iterations), which isn't too shabby! Code at github.com/jonhoo/avdl. youtu.be/vmKvw73V394
impl Rust: Avro IDL tool in Rust via ANTLR
YouTube video by Jon Gjengset
youtu.be
Friday 9a UTC (everytimezone.com/s/5903cd46) sounds like a good time for a stream! This time, we'll try to port Avro's IDL-to-JSON tool from Java to Rust (with LLM help), leveraging the fact that their grammar is written using ANTLR to make our job easier. Come join me 🎉 youtube.com/live/NqV_KhD...
impl Rust: Avro IDL tool in Rust via ANTLR
YouTube video by Jon Gjengset
youtube.com
The recording of the new year's Q&A stream is now up, with all the questions annotated for easy skipping! youtu.be/S_zp82fYrGw
January 2026 Q&A
YouTube video by Jon Gjengset
youtu.be
Quick reminder that this is coming up. Lots of good questions have come in, so please take some time to go in and vote for the ones you care the most about!
Jon Gjengset@jonhoo.eu · 7mo agoWe're nearing the new year, so time for another Jan 1st Q&A! Ask questions at wewerewondering.com/event/01KDDA... — none too big or small. I'll get to as many as I can, and upload the recording after the fact. Stream starts 1/1/26 at 2:30p UTC @ youtube.com/live/g1ZgInF.... Hope to see you there ❤️
We're nearing the new year, so time for another Jan 1st Q&A! Ask questions at wewerewondering.com/event/01KDDA... — none too big or small. I'll get to as many as I can, and upload the recording after the fact. Stream starts 1/1/26 at 2:30p UTC @ youtube.com/live/g1ZgInF.... Hope to see you there ❤️
Q&A
Zero-setup, free tool for running live Q&A sessions, including question submission and voting.
wewerewondering.com
Video of the One Billion Row Challenge stream is now up at youtu.be/tCY7p6dVAGE! We got down to 1.2s without any external dependencies, and it was a fun journey down lots of performance rabbit holes (only some of which panned out 😅). It is over 10h, but hopefully the chapters in the video help!
I'm late to the party, but the One Billion Row Challenge (github.com/gunnarmorlin...) feels like an excellent way to dig into optimizing Rust code and learning somethings about assembly, SIMD, performance profiling, and just CPUs in general in the process, so let's take it on live! [1/3]
GitHub - gunnarmorling/1brc: 1️⃣🐝🏎️ The One Billion Row Challenge -- A fun exploration of how quickly 1B rows from a text file can be aggregated with Java
1️⃣🐝🏎️ The One Billion Row Challenge -- A fun exploration of how quickly 1B rows from a text file can be aggregated with Java - gunnarmorling/1brc
github.com
I've been a fan of Cory Doctorow for ages, and this episode of Adam Conover's podcast is a great synthesis of his observations on the tech industry across the board, both what's broken and how we fix it. And a slew of other great insights. Highly recommended listen! headgum.com/factually-wi...
Factually! with Adam Conover - The Ensh*ttification of Everything with Cory Doctorow
The internet is getting shittier. Hell, the whole world is getting shittier. The thing is, it’s no accident—it’s by design. The tech giants who run the internet have figured out how to make bank off o...
headgum.com
On Sunday at 2pm UTC (everytimezone.com?t=68fd6480,348), Ben and I are doing another "What's New in Rust" marathon stream for Rustacean Station! I'm guessing ~5h for part 1 😅 It'll be over at youtube.com/live/6mwVWmK.... Come join us 📺🎉
What's New in Rust 1.81-1.?? Rustacean Station marathon
YouTube video by Jon Gjengset
youtube.com
In August, I was interviewed by JetBrains about programming and Rust, ranging from the borrow checker, to agentic coding, to hiring. And it's now on YouTube! It's also general enough that it should be interesting even to those not already knee deep in Rust 😅 www.youtube.com/watch?v=nOSx...
About a month ago, I gave a talk at the Rust Amsterdam meetup about Sguaba (the type-safe spatial math Rust crate), and the recording of that is now online for anyone who wants their head to hurt with frames of reference and coordinate transforms 😅 youtu.be/kESBAiTYMoQ
Sguaba: Type-safe spatial math in Rust
YouTube video by Jon Gjengset
youtu.be
For those who missed the stream, you can find my chat with Maya about Rust, concurrency, left-right, Noria, career development, AI, and a whole host of other random nerdy things on YouTube now! www.youtube.com/live/kJnrbbt...
two nerds one stream w/ @jonhoo! 💜 chatting about rust/concurrency/anything you ask about!
YouTube video by Maya
youtube.com
Sunday at 6pm UTC (everytimezone.com/s/4a616697), I'll be on Maya Rainer's stream to talk about concurrency and the left-right crate. We'll take a bunch of questions from chat, so bring your burning `Send + Sync` questions :D Stream will be over at www.twitch.tv/mayarainer/s... — see you there!
mayarainer Schedule - Twitch
Check out mayarainer stream schedule, and set reminders so you don’t miss out!
twitch.tv
For those curious about the third proposed Sguaba feature, I ended up writing it myself and having Claude suggest tests. Worked quite well! Given the nuances in designing this mechanism, I suspect it would have struggled quite a lot with implementing it from scratch 😅 github.com/helsing-ai/s...
feat: make Vector generic over unit by jonhoo · Pull Request #31 · helsing-ai/sguaba
This adds support for velocity and acceleration vectors alongside the original length vectors, enabling users to store vectors that hold velocity or acceleration without losing that semantic inform...
github.com
Missing Semester has grown past 100K subscribers on YouTube. Appreciate all the engagement and support! We plan to teach another iteration of the course in January 2026, revising the curriculum and covering new topics like AI IDEs and vibe coding.
Today's "vibe-code non-trivial changes to a Rust crate" stream is up! Got to 2/4 changes and then ran out of tokens on the Claude Pro plan 😅 Still TBD if my Luddite skepticism is apt, but it was fun, interesting, and did shed light on the ups and downs of agentic Rust coding! youtu.be/EL7Au1tzNxE
Vibe coding complex changes in Rust
YouTube video by Jon Gjengset
youtu.be
Change of plans — due to the ongoing heatwave in Oslo, and Norway's general lack of A/C, my office is regularly reaching 32°C/90°F these days. This breaks my brain, and also my camera, so I'm going to move this stream to the same time next week! See you then 👋
Jon Gjengset@jonhoo.eu · last yr.Those who have followed me for a while may already know that I'm a bit of an ML Luddite. Well, it's time to challenge that. Next Friday at 17:30 UTC, I'll be attempting to vibe code complex changes to the Rust crate Sguaba (github.com/helsing-ai/s...) — come laugh at me! youtube.com/live/3NGXL_8...
Those who have followed me for a while may already know that I'm a bit of an ML Luddite. Well, it's time to challenge that. Next Friday at 17:30 UTC, I'll be attempting to vibe code complex changes to the Rust crate Sguaba (github.com/helsing-ai/s...) — come laugh at me! youtube.com/live/3NGXL_8...
Vibe coding complex changes in Rust
Those who have followed me for a while may already know that I'm a bit of an ML Luddite — it's not that I'm opposed to the use of ML-based tools, but rather that I haven't personally found much use fo...
youtube.com
The other day I was interviewed about Helsing, working in defense, and what it's like specifically to work at Helsing. We ended up covering quite a lot of questions I commonly get (and that I know people have but don't ask), so if you're curious about any aspect of it, give it a read!
filtra.io@filtra.bsky.social · last yr.