I am a software architect at CCP Games. Work on the launcher, Wine support, graphics engine and other random stuff for EVE Online, usually low level. This blog details some interesting things I run into at work, as well as new things I'm trying out in my spare time. Lately I've been picking up new programming languages - Erlang/Elixir, Go, Swift whereas most of my work in the past is in C++ and Python.
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Expiring records in Erlang
I'm continuing my experiments with Erlang - this time trying out gen_server with a simple key/value store with a twist - the values have an expiration date.
As a first iteration I'm simply using a dictionary to store the values, and only expiring records when they are looked up. My plan is to extend this later on so that this can be a global key/value store across multiple Erlang nodes but for now I'm focusing on two things - get something going using gen_server, and try out the common_test testing framework.
I should probably wrap the gen_server:call calls to make this more readable - I'm just realizing that now as I write this, but I want this blog to reflect my progress on learning Erlang, rather than just presenting some final result.
Coming from a long background of writing in C++ and Python, the notion of having no object with a state still feels a bit weird. The gen_server process replaces that by passing the state around so it kind of boils down to the same thing. I just have to remember to return the new state when changing the dict.
I kept running into problems with eunit when trying to set up a fixture for running the various tests, all starting with a fresh instance of the expiring_records server. Looking at Common Test it seemed it might be more suitable so I've set up my tests with it this time around. I recommend this section of the Learn You Some Erlang for Great Good tutorial for getting started with Common Test.
Note that Travis CI by default runs eunit when testing Erlang projects - I had to add the following to my .travis.ymlfile:
rebar3 ct --suite app_test
This is still very much a work in progress - I want to look at Mnesia for storing the data, rather than a simple dict. I figure that is the easiest way to achieve my goal of having this a global store across multiple nodes.
I also want to add a way to prune expired records without looking them up, to prevent the accumulation of expired records.
Learning new things is important for every developer. I've mentioned this before, and in the spirit of doing just that, I've started a somewhat ambitious project. I want to do a large-scale simulation, using Elixir and Go , coupled with a physics simulation in C++. I've never done anything in Elixir before, and only played a little bit with Go, but I figure, how hard can it be ? Exsim I've dubbed this project exsim - it's a simulation done in Elixir. Someday I'll think about a more catchy name - for now I'm just focusing on the technical bits. Here's an overview of the system as I see it today: exsim sits at the heart of it - this is the main server, implemented in Elixir. exsim-physics is the physics simulation. It is implemented in C++, using the Bullet physics library. exsim-physics-viewer is a simple viewer for the state of the physics simulation, written in Go. exsim-bot is a bot for testing exsim, written in Go.
Xmpp is an open standard for messaging and presence, used for instant messaging systems. It is also used for chat systems in several games, most notably League of Legends made by Riot Games. Xmpp is an xml based protocol. Normally you work with xml documents - with Xmpp you work with a stream of xml elements, or stanzas - see https://tools.ietf.org/html/rfc3920 for the full definitions of these concepts. This has some implications on how best to work with the xml. To experiment with Xmpp, let's start by installing a chat server based on Xmpp and start interacting with it. For my purposes I've chosen Prosody - it's nice and simple to install, especially on macOS with Homebrew : brew tap prosody/prosody brew install prosody Start the server with prosodyctl - you may need to edit the configuration file (/usr/local/etc/prosody/prosody.cfg.lua on the Mac), adding entries for prosody_user and pidfile. Once the server is up and running we can start poking at it
From now on I will be posting on https://snorristurluson.github.io/ Most of my postings have code snippets in them and I've been using markdown, checking into a GitHub repo, then copying and pasting the contents. Using a static site generated with Jekyll just seems easier. Thanks, Blogger - I have moved on...