Category Archives: _Twitter Archive 🐤

Find your own bugs

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: _Micropost 🍪, _Tech 💻, _Twitter Archive 🐤, Open Source, Software Development

Audio version: https://podcasters.spotify.com/offlinemark/episodes/Find-your-own-bugs-e2i15vc

Contributing to open source is a popular recommendation for junior developers, but what do you actually do?

Fixing bugs is a natural first step, and people might say to look a the bug tracker and find a simple bug to fix. However, my advice would be to find your own bugs.

In 2019, I had some free time and really wanted to contribute to the LLVM project in some way. Working on the actual compiler seemed scary, but LLDB, the debugger, seemed more approachable.

I went to the LLVM Dev Meeting, met some LLDB devs, and got super excited to contribute. I went home, found a random bug on the bug trackers, took a look for all of 30 minutes, then … gave up. Fixing some one else’s random string formatting bug simply wasn’t interesting enough to motivate me to contribute.

3 months later I was doing some C++ dev for fun. I was debugging my code and ran into a really, really strange crash in the debugger. It was so strange that I looked into it further and it turned out to be a bug in LLDB’s handling of the “return” command for returning back to the caller of the current function. The command didn’t correctly handle returning from assembly stubs that don’t follow the standard stack layout/ABI, and caused memory corruption in the debugged process which eventually led to a crash.

This was totally different. I had found a super juicy bug and dedicated a couple weeks to doing a root cause analysis and working with the LLDB devs to create a patch, which was accepted.

So if you want to contribute to open source, I would agree with the common advice to fix some bug, but would recommend finding your own — it will be way more rewarding, fulfilling, and a better story to tell.

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https://twitter.com/offlinemark/status/1778483168611610940
https://twitter.com/offlinemark/status/1208491737099882496

Removing dates from post URLs

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: _Micropost 🍪, _Twitter Archive 🐤, Blogging

Originally I used a YYYY/MM/DD/<slug> url scheme for my blog, which felt nice since it creates namespacing and one can also get some date context about a blog post simply from the URL.

However, I eventually removed all date context from the URLs entirely. Namespacing isn’t a real benefit in practice (name collisions are rare) and neither is date context. I also found it annoying that I couldn’t type post URLS from memory, which is occasionally useful. Plus shorter URLs is also often a plus.

To migrate to this new URL scheme without breaking links, I used the “Redirection” WordPress plugin. Yet another reason why I like WordPress.

This simple no-date naming scheme is also inspired by bloggers like Paul Graham, Patrick Collison, and Sam Altman.

The astonishing cost/benefit asymmetry of a four-day work week

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: _Essay 📝, _Twitter Archive 🐤, Life

Work update: I reduced to working 4 days/week and the cost/benefit asymmetry is astonishing.

Just one extra free day might not sound like much, but I feel like I gain >100% more high quality free time (Friday off is even better than Saturday; Sunday is not high quality free time for me – too much adulting to do).

And I lose only 20% of my productive work capacity (Well a bit more; Friday would be a more productive day than average for me b/c it’s quieter & less meetings).

I’ve constantly felt squashed the last few years, but always convinced myself it was a me problem, rather than a possibility that even “normal” working hours didn’t actually leave me with enough free time for everything I had to do*. (Maybe some of both)

But my energy and mood are way better than in a long time, so maybe it goes to show that the latter was the case, and one extra day can go a long way. (But that’s less surprising when you frame it as 100% more time).

I do need to be a bit more conscious of how I use my work week, and I have noticed a tendency to try to fit 5 days of work into 4… but overall it’s going well. I’m curious if I end up filling up the extra personal capacity and end up just as stressed, but I somehow doubt that will happen.

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*You might ask, well why are you so busy anyway? Are you just piling on voluntary responsibilities?

I’ve thought about this at length and I think my answer is glibly, “expat life”.

Tip: When you’re learning a new programming language, look up prominent open source projects and copy their style

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: _Twitter Archive 🐤, Software Development

Tip: When you’re learning a new programming language, look up prominent open source projects and copy their style.

Aside from the core language, there are many conventions & little details to learn: naming (variables, classes, files), file structuring, literal code formatting

These are things few blogs talk about because it’s highly opinionated. But nevertheless when you’re learning, you’ll benefit from at least some reference for these.

Find a few “professional” open source projects and browse to see what various interpretations of “professional style” are. Then pick one you like most.

Be careful of picking projects that are too old — they might use older style for consistency with legacy, even though they might ideally wish to modernize it.

And ideally pick projects whose contributors are experienced engineers who work on it full-time. Since they “live in” the codebase, they’re less likely to tolerate sloppiness – or are at least more invested in cleaning it up.

The last idea is influenced by @awesomekling, who talks about similar things in his classic “My top advice for programmers looking to improve” car-talk video =]

Personal projects are like free weights

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: _Micropost 🍪, _Twitter Archive 🐤, Career

I thought of this 7 years ago and I still think it rings true. In my experience, school projects were tightly scoped and had things like a basic build system and boilerplate runnable code (e.g. main) already provided. Maybe even some tests. It trains a specific muscle in a certain way.

With personal projects, you do all of this yourself and incidentally also train the equivalent “stabilizer” muscles. Things like: making the repo, writing the main and boilerplate code, setting up unit tests, setting up CI, setting up dependencies and their management.

And in my experience, it’s all these “stabilizer” activities that define what it means to be a senior engineer. Junior engineers work within an existing project; senior engineers own the entire thing, including these “little” (critical) parts.

The point here isn’t to necessarily criticize CS education; there are good, practical reasons for setting up such project structure to ensure all students have a good experience, given the time constraints. The point is that students should be wary of not doing any personal projects at all throughout a CS education. Maybe it would be possible so students don’t have to do this in their free time, and build it into some kind of flexible course. I suppose this is the point of final capstone projects, but I think senior year is far too late to be doing this for the first time.

SerenityOS Day 1: Debugging the piano app

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: _Tech 💻, _Twitter Archive 🐤

I love spelunking into unknown codebases with nothing but find and grep. It’s one of the most valuable skills one can develop as a programmer imo and in this video you can see how I approach it.

This video focuses on debugging GUI event handling. At first the bug seemed related to the app’s waveform selection, but I then realized it was a more general topic with the SerenityOS GUI UX — selecting a dropdown entry retains focus, and requires an explicit escape key.

Ultimately I made progress accidentally by hitting the keyboard while the selection was still active, revealing to me that fact (which I hadn’t noticed before).

You can see my general debugging flow:

  • Get things building
  • How to run app from command line (to see stdout)?
  • How to print to stdout?
  • Using debug prints to understand the GUI event handling

Overall I’m quite impressed with SerenityOS. I only realized after looking into the code exactly how much code they had written and how fully featured the system is. Well done to the team.

Do you need to learn how to implement a red-black tree?

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: _Twitter Archive 🐤, Career, Other

Pitfalls with fork() in real-time contexts

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: _Twitter Archive 🐤, Linux Kernel

This thread went viral. The main takeaways:

  • After calling fork(), a parent process gets its entire address space write protected to facilitate COW. This causes page faults.
  • This makes fork() unsafe to call from anywhere in a process with realtime deadlines — including non realtime threads! Usually non RT can do what they want, but that is an interesting exception.
  • On modern glibc, system() doesn’t use fork(), it uses posix_spawn(). But is posix_spawn() safe from a non RT thread?
  • posix_spawn() doesn’t COW — the parent/child literally share memory — so the page fault issue doesn’t apply. However the parent is suspended to prevent races between the child and parent. This seems RT unsafe…
  • However, only the caller thread of the parent is suspended, meaning the RT threads are not suspended and continue running with no page faults.
  • So it is safe to use system() or posix_spawn() from a non RT thread.