Recent content on Well, quite.
In the UK, it’s very common that your employer pays you once a month. When this happens, they give you a document called a payslip , that has some numbers on it, such as how much your salary is, how much they paid you this month, how much went to HMRC in tax, how much went to your pension, and a few other numbers. But they never show any workings, so you really have no way to check whether…
Since I was a child, I’ve been playing the French Horn . I still play, and I take it quite seriously. I’m lucky enough to play with some good ensembles, and I perform many concerts each year. When learning difficult music, I often practise with a metronome . A metronome is a device that clicks or beeps regularly. You can set how often it clicks; for example you might set it to click 80…
In this series: Let‘s build! Boolean operations of polygons: Part 1 - Introduction Let’s build! Boolean operations of polygons: Part 2 - Intersections In Part 1 I explained what the boolean operations on polygons are, and I gave a motivating example by way of an algorithm that traces out the intersections of a set of overlapping polygons. That algorithm uses intersection (∩), union…
In this series: Let‘s build! Boolean operations of polygons: Part 1 - Introduction Let’s build! Boolean operations of polygons: Part 2 - Intersections There are a small set of common boolean operations that you can perform on two polygons: union (a∪b), intersection (a∩b), subtraction (a−b and b−a), and exclusive-or (a xor b) (also called symmetric-difference). All apart from…
I’ve been paying some attention to serialization formats since 2014 or so. I used Cap’n Proto when I was writing GoshawkDB which dates from around 2015, and just before that I think I’d been using Protobuf . Two years ago, when working on WalkTogether , was the first time I’d used Bebop . There are dozens of different serialization formats, and a very wide range of…
Blimey, almost exactly a year since my last post. I guess that’s what happens when you have a full-time job at a start-up. I’ve run my own servers for 15 years or so. Regardless of the technologies used, servers have mutable state, and that needs backing up, ideally regularly. Whenever I have to do a lot of sysadmin work, e.g. major OS upgrades, or changing hosting provider, I always…
The software industry seems to fetishize complexity. It's extremely harmful, yet often appealing, and I don't know how we can avoid it. Follow the link to read the full post.
I've recently been doing some phone app development using Dart and Flutter. Although I've used languages with async/await before, the full consequences of that concurrency design had clearly never sunk in properly. It's much more subtle and complex than I'd realised: arguably the same as infinite threads on a single CPU core. Locking is most definitely still needed! Follow the link to read the…
After a week off, I return to the distributed editor to write some tests for the server. How to test actors? How to write randomised and deterministic soak tests? And ultimately, how to build confidence that this system works like I claim it does. Follow the link to read the full post.
I spent this week writing a new high-level binding in Go for LMDB. Follow the link to read the full post.
I have chosen to use actors to structure the server. I believe this presents a simple model to understand, in terms of concurrency and state management, whilst allowing the server to scale and make use of multiple CPU cores. This week's instalment introduces the actors model, my actors library, and explains how I have used it for the distributed editor server. Follow the link to read the full…
Back to the fun stuff: how shall I store the document and its editing history on disk? How do I calculate what the document should look like after receiving an undo or redo message? How do I get the server to make reasonable use of its CPU and disk resources so that it can scale well? These are the questions I'm exploring this week. Follow the link to read the full post.
Hugo started to annoy me, so I wrote my own static site generator. Follow the link to read the full post.
This week I focus on the client: how does it send changes to the server; how does it process updates it receives from the server; how does it synchronise with the server when it first connects and then reconnects? It turns out that most of the problems the server faces, in terms of concurrent modifications to words, can also occur at the client because of concurrent changes received from the…
In Part 1 I set the scene. Alice and Bob haven't fully specified the system, but they've certainly given me some requirements: The exact behaviour of concurrent edits is left for me to define, but I'm not allowed to solve it trivially (i.e. just do nothing), and the key requirement is that all users should end up seeing the exact same document fairly quickly, once they're connected to the server;…
The sun is bright and the sky's blue when I get to the office in London. As the lift doors ping open and I step out, a pair of heads near my desk swivel and look towards me. A sense of shame and embarrassment immediately forms in the pit of my stomach as I spot Alice and Bob sat waiting for me. I'd forgotten the meeting with them this morning that I'm late for. Follow the link to read the full…
Now I promise this isn't just a NixOS advocacy site; I do have some other content planned, honest! I just wanted to give a couple of examples of the using Nix as part of your daily workflow of building stuff. Follow the link to read the full post.
Back in 2006, for reasons that made sense to me at the time, and make no sense to anyone at all now, I decided to buy some fonts and use them when writing my final-year thesis for university. I was writing my thesis in LaTeX. What followed was a week in which I read some pretty thorough documentation and slowly figured out how to convert fonts in normal TrueType and OpenType formats into the…
I started using Linux as my main desktop OS in about the year 2000. I bought the Debian 2.1 "slink" CD-ROM set. At the time I also dabbled with other OSes too: Windows, BeOS, and also Minix. Over the last 20 years, through University and my career so far as a software engineer, Debian has been incredibly reliable, and has been my go-to choice whenever setting up a new machine. About five years ago…
Over the last year I’ve become more and more convinced that possibly the most important feature of any queuing system is the ability to take action immediately upon enqueuing of a new item, where the action can modify the queue, and is based on state of the queue itself. Most commonly, this is referred to as back-pressure. But back-pressure can have several different forms, suited to different…