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Blog has moved

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...

Popular posts from this blog

Mnesia queries

I've added search and trim to my expiring records module in Erlang. This started out as an in-memory key/value store, that I then migrated over to using Mnesia and eventually to a replicated Mnesia table. The fetch/1 function is already doing a simple query, with match_object. Result=mnesia:match_object(expiring_records, #record{key=Key, value='_', expires_at='_'}, read) The three parameters there are the name of the table - expiring_records, the matching pattern and the lock type (read lock). The fetch/1 function looks up the key as it was added to the table with store/3. If the key is a tuple, we can also do a partial match: Result=mnesia:match_object(expiring_records, #record{key= {'_', "bongo"}, value='_', expires_at='_'}, read) I've added a search/1 function the module that takes in a matching pattern and returns a list of items where the key matches the pattern. Here's the test for the search/1 function: search_partial_…

Waiting for an answer

I want to describe my first iteration of exsim, the core server for the large scale simulation I described in my last blog post. A Listener module opens a socket for listening to incoming connections. Once a connection is made, a process is spawned for handling the login and the listener continues listening for new connections. Once logged in, a Player is created, and a Solarsystem is started (if it hasn't already). The solar system also starts a PhysicsProxy, and the player starts a Ship. These are all GenServer processes. The source for this is up on GitHub: https://github.com/snorristurluson/exsim Player The player takes ownership of the TCP connection and handles communication with the game client (or bot). Incoming messages are parsed in handle_info/2 and handled by the player or routed to the ship, as appropriate. The player creates the ship in its init/1 function. The state for the player holds the ship and the name of the player. Ship The ship holds the state of the ship - …

Replicated Mnesia

I'm still working on my expiring records module in Erlang (see here and here for my previous posts on this). Previously, I had started using Mnesia, but only a RAM based table. I've now switched it over to a replicated disc based table. That was easy enough, but it took a while to figure out how to do, nonetheless. I had assumed that simply adding ... {disc_copies, [node()]} ... to the arguments to mnesia:create_table would be enough. This resulted in an error: {app_test,init_per_testcase, {{badmatch, {aborted, {bad_type,expiring_records,disc_copies,nonode@nohost}}}, ... After some head-scratching and lots of Googling I realized that I was missing a call to mnesia:create_schema to allow it to create disc based tables. My tests for this module are done with common_test so I set up a per suite initialization function like this: init_per_suite(Config) ->mnesia:create_schema([node()]), mnesia:start(…