Pushing through a straw

Recently, a user reported a noticeable delay between sending a command in-game to multiple users and the result of that command appearing to everyone. You didn't notice this when testing alone but I could confirm there was almost a second delay sometimes between entering the command and some users seeing the result. A second is very long for stuff like this. Processing time for a single command is usually in the milliseconds. What was going on?

Some background 

Evennia has two components, the Portal and the Server, running as two separate processes. The basic principle is that players connecting to an Evennia instance connects to the Portal side - this is the outward facing part of Evennia. The connection data and any other input and output will be piped from the Portal to the Server and back again.

The main reason for this setup is that it allows us to completely reset the Server component (reloading module data in memory is otherwise error-prone or at least very tricky to make generically work in Python) without anyone getting disconnected from the Portal. On the whole it works very well.

Debugging

Tracing of timings throughout the entire Server<->Portal pipeline quickly led me to rule out the command handler or any of the core systems being responsible - including both sides of the process divide was a few milliseconds. But in the transfer between Portal and Server, an additional 900 miliseconds were suddenly added! This was clearly the cause for the delay.

Turns out that it all came down to faulty optimization. At some point I built a batch-send algorithm between the Server and Portal. The idea was to group command data together if they arrived too fast - bunch them together and send them as a single batch. In theory this would be more efficient once the rate of command sending increased. It was partly a DoS protection, partly a way to optimize transfer handling.

The (faulty) idea was to drop incoming data into a queue and if the rate was too high, wait to empty that queue until a certain "command/per second" rate was fullfilled. There was also a timed routine that every second force-emptied the queue to make sure it would be cleaned up also if noone made any further commands.

In retrospect it sounds silly but the "rate of command" was based on a simple two-time-points derivative;

rate = 1 / (now - last_command_time)

If this rate exceeded a set value, the batch queuing mechanism would kick in. The issue with this (which is easy to see now) is that if you set your limit at (say) 100 commands / second, two commands can happen to enter so close to each other time that their rate far exceed that limit just based on the time passed between them. But there are not actually 100 commands coming in every second which is really what the mechanism was meant to react to.

So basically using a moment-to-moment rate like this is just too noisy to be useful; the value will jump all over the place. The slowdown seen was basically the DoS protection kicking in because when you are relaying data to other users, each of them will receive "commands" in quick succession - fast enough to trigger the limiter. These would be routed to the queue and the sometimes-delay simply depended on  when the queue cleanup mechanism happened to kick in.

Resolution

Once having identfied the rate measuring bug, the obvious solution to this would be to gather command rates over a longer time period and take an average - you will then filter out the moment-to-moment noise and get an actually useful rate.

Instead I ended up going with an even simpler solution: Every command that comes in ups a counter. If I want a command rate limit of 100 commands/second, I wait until that counter reaches 100. At that point I check when the time difference between now and when the counter was last reset. If this value is below 1, well then our command rate is higher than 100/second and I can kick in whatever queuing or limiter is needed. The drawback is that until you have 100 commands you won't know the rate. In practice though, once the rate is high enough to be of interest, this simple solution leads to an automatic check with minimal overhead.

In the end I actually removed the batch-sending component completely and instead added command DoS protection higher up on the Portal side. The Command-input is now rate limited using the same count-until-limit mechanism. Seems to work fine. People have no artificial slowdowns anymore and the DoS limiter will only kick in at loads that are actually relevant. And so all was again well in Evennia world.

A wagon-load of post-summer updates

Summer vacations are over and work resumes in Evennia land! Here's a wagon-load of small updates on what's going on.
 

Ainneve

The Ainneve project, the creation of an official, open-source Evennia demo game, has gotten going. The lead devs of the project are keen to make this a collaborative effort and there is a lot of good discussion and code being written. After some slowdown at the end of summer it's bound to pick up again. 

Ainneve's a rare chance to see a full MUD getting developed from scratch out in the open. The current issue list includes tags for difficulty and allows also newbie Python coders to jump in. Not to mention you have a chance to get valuable feedback on your work by seasoned coders!

So if you are at all interested in making a MUD, try out Python/Evennia or just get involved in a semi-big programming project, this is a great chance to do so.

Imaginary Realities

Since a few weeks, there is a new issue of Imaginary realities (vol 7, issue 3) is out. As usual I have an article in it. This venerable e-zine was revitalized to include articles on both MU* as well as roguelikes, Interactive fiction and others. Not only is this issue the most content-rich since the reboot, with this issue they have also spruced up their interface to make past issues easier to navigate.

• "A text MUD with a working ecology system" - in this article Molly O'Hara  details the concepts behind simulating a functioning ecologic network in a game. Interesting stuff and some parts of this is certainly worth considering for any open-world game design. I wonder at which level of detail the system become more complex than the players can appreciate though.
• "Dispelling the gloom" by Tomasz Gruca is an interesting essay on the author's history growing up in the former Soviet Union and eventually finding text adventure games and interactive fiction, a passion he has apparently lately re-kindled. He makes the observation that the current "retro" trend of games have not really reached back to the text-based game world when it comes to mainstream acceptance.
• "How integral are letters and text to ASCII gaming?"by Mark R. Johnson goes into the practical use of ASCII in traditional rogue-like games (beyond nostalgia). This is a meaty article that goes into both text-as-graphics as well as the use of text for aiding imagination and suggest subtle puzzles in some classic rogue-likes. 
• "Legend and the lore" (Hugo Zombiestalker) proclaims the death of the traditional point-and-click adventure game and but then moves on to try to distill just why those games nevertheless was so appealing to him and how it can be applied in modern game designs like zombie-survival MUD Epitath which he is a senior developer for. Plenty of good observations here!
• "The bonds of mudding" by Clint Itan Kuranes Knapp writes about the community that can spring up on a long-running MUD, the interactions the friends and the relationships that could persist already long before "social media" became a buzz word. A warm text with plenty of anecdotes and examples and things to ponder for both designers and staff when wanting to cater for this type of player bonding. 
• "The mercurial temperament at the end of the world" (Drakkos) discusses NPCs and how they rarely are as interactive as one would want (the term "vend a chat" is a good one I think). He then goes on to how they have implemented their "Mercurial" system for NPCs in Epitath. This seems to be a state-AI system where NPCs have moods that affects what they say based on their circumstance and relation to other actors in the world. Sounds really cool and since he goes into some details on the implementation there is a lot to ponder here. 
• "Where do I begin?" by me, Griatch, discusses one of the more common questions we get in the Evennia chat - 'I want to make a MUD, but how do I begin?' This article starts before Evennia's Game planning wiki page - it discusses assessing your capabilities and resources in the form of programming skills, code bases and motivations to help you figure out what you can realistically accomplish. 

 

Evennia Web client

In the pipeline I have some updates to Evennia's websocket/JSON MUD-web client component. These are changes that are intended to make the webclient easier to customize and hook into Evennia output using only HTML/CSS. More details on this will be forthcoming when I have more solid stuff to show.

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Image: The troll here a-cometh by Griatch

Announcing the Evennia example-game project "Ainneve"

The Evennia example-game project is underway!

I was quite impressed with the response I got on the mailing list to my call for developing an Evennia example game (see my Need your Help blog post).

The nature of the responses varied, many were from interested people with little to no experience in Evennia or Python whereas others had the experience but not the time to lead it. It was however clear that the interest to work on an "official" Evennia game is quite big.

I'm happy to announce, however, that after only a week we now have a solid lead developer/manager, George Oliver. Helping him on the technical/architecture side is Whitenoise (who, despite a barren github profile, is a professional developer).

George put together a game proposal based on the OpenAdventure rpg, an open-source (CC-SA) ruleset that is also found on github. The example game is to be named "Ainneve" and its development is found in a in a separate repository under the github Evennia organisation.

All the relevant links and future discussion can be found on the mailing list.

George and whitenoise have already made it clear that they aim to not only make Ainneve a good example Evennia game for others to learn from and build on, but to make the development itself a possibility for people of all skill levels to get involved. So get in touch with them if you are at all interested in Python, Evennia and mud development!

So thanks to George and whitenoise for taking this on, looking forward to see where it leads!


image from loveintoblender.

Need your help

This for all you developers out there who want to make a game with Evennia but are not sure about what game to make or where to start off.

We need an example game

One of the main critiques Evennia get from newbies is the lack of an (optional) full game implementation to use as an example and base to build from. So, Evennia needs a full, BSD-licensed example game. I'm talking "diku-like", something you could in principle hook up and allow players into within minutes of installing Evennia. The Tutorial world we already have is a start but it is more of a solo quest, it's not designed to be a full multiplayer game. Whereas Evennia supports other forms of MU* too, the idea is that the systems from a more "code-heavy" MUD could easily be extracted and adopted to a more freeform-style game whereas the reverse is not generally true.

The exact structure of such a game would be up to the person or team taking this on, but it should be making use of Evennia's api and come distributed as a custom game folder (the folder you get with evennia --init). We will set this up as a separate repository under the Evennia github organisation - a spin-off from the main evennia project, and maintained separately.

We need you!

Thing is, while I am (and, I'm sure other Evennia core devs) certainly willing to give considerable help and input on such a project, it's not something I have time to take the lead on myself. So I'm looking for enthusiastic coders who would be willing to step up to both help and take the lead on this; both designing and (especially) coding such an example game. Even if you have your own game in mind for the future, you still need to build most of these systems, so starting with a generic system will still help you towards that final goal - plus you get to be immortalized in the code credits, of course.

Suggestion for game

Being an example game, it should be well-documented and following good code practices (this is something we can always fix and adjust as we go though). The systems should be designed as stand-alone/modular as possible to make them easy to rip out and re-purpose (you know people will do so anyway). These are the general features I would imagine are needed (they are open to discussion):

• Generic fantasy theme (lore is not the focus here, but it can still be made interesting)
• Character creation module
• Races (say, 2-3)
• Classes (say 2-3)
• Attributes and Skills (based on D&D? Limit number of skills to the minimal set)
• Rule module for making skill checks, rolls etc (D&D rules?)
• Combat system (twitch? Turn-based?)
• Mobs, both friendly and aggressive, with AI
• Trade with NPC / other players (money system)
• Quest system
• Eventual new GM/admin tools as needed
• Small game world (batch-built) to demonstrate all features (of good quality to show off)
• More? Less?

I'm interested!

Great! We are as a first step looking for a driven lead dev for this project, a person who has the enthusiasm, coding experience and drive to see the project through and manage it. You will (hopefully) get plenty of collaborators willing to help out but It is my experience that a successful hobby project really needs at least one person taking responsibility to "lead the charge" and having the final say on features: Collaborative development can otherwise easily mean that everyone does their own thing or cannot agree on a common course. This would be a spin-off from the main Evennia project and maintained separately as mentioned above.

Reply to this thread if you are willing to participate at any level to the project, including chipping in with code from your already ongoing development. I don't know if there'd be any "competition" over the lead-dev position but if multiple really enthusiastic and willing devs step forward we'll handle that then.

So get in touch!

Dreaming big?

Optional Reality's Dreaming Big Challenge has come to an end. This was a challenge about designing a "sales pitch" in 600 words or less for a text-based online roleplaying game. This is the kind of pitch you'd tease knowledgeable investors with -  if investors cared about multiplayer text games and you ended up in an elevator with one, that is.

There were 10 entries to the competition and as the results are now in (including very elaborate judge feedback!), I encourage you to go read all the entries. The focus was on originality and fresh ideas and maybe these short pitches represent a cross-section of the current trends or a whiff of where the wind is blowing for future games. Or maybe it will help inspire you to make a sales pitch of your own.

You can find all the entries linked from the second post of this thread. Enjoy!

Things going on

We are currently in a maintenance and cleanup phase of Evennia, where bugs are found and reported and things are getting more and more stable as people learn and use the new features we merged a few months back.

Overall though I must say the relatively big changes we did to the infrastructure (making Evennia into a full library and making a complete overhaul of the typeclass system behind the scenes) went over with surprising smoothness. There were a flurry of things to fix immediately after the devel-branch merger but no more than expected. For the big changes it really worked very well I think, with no big disaster stories. We have a few bugs lingering in the issue tracker that need to be addressed but nothing show-stopping.

I have been a bit busy with various projects off-MUD so to speak. I was contracted for making the cover and illustration for a book (this is not hobby art for once, but a professional commission which I was quite excited to be asked to do). I also author and draw a fantasy comic as part of another project.

I've not been slacking off on on the MUD side though: I have written and submitted an article for the revived Imaginary Realities e-zine (next issue should be out end of May/early June?) and another article (on Evennia) for the new Optional Realities MUD community website. I also contributed a game-design blurb for the latter's Dreaming Big contest, where you compete (for cash prizes, actually!) by submitting a game sale's pitch under 600 words.

The above mentioned Optional Realities website is so far picking up pace with quite good discussion in its forums (the similarity of name with Imaginary Realities is unfortunate, apparently they were not aware of the former when choosing it).  While targeted at discussions of RPI-style games (a sort of sub-genre of roleplay-enforced MUDs with perma-death), it already hosts several invited articles on game design and general game development that can be interesting for any MU* dev.

People should know by now that I like to support MUD community efforts when possible, and Evennia is thus  listed as an official "affiliate" to Optional Realities (which admittedly means little more than us linking to each other but still). The team behind OR is however also using Evennia for their own "Project Redshift" Sci-fi mud, so we hope to get plenty of good feedback as their project matures.


Image: Truss from Gems NFX

Documenting Python without Sphinx

Last week Evennia merged its development branch with all the features mentioned in the last post. Post-merger we have since gone through and fixed remaining bugs and shortened the list at a good clip.

One thing I have been considering is how to make Evennia's API auto-documenting - we are after all a MUD creation library and whereas our code has always been well-documented the docs were always only accessible from the source files themselves.

Now, when you hear "Python" and "documentation" in the same sentence, the first thought usually involves Sphinx or Sphinx autodoc in some form. Sphinx produces very nice looking documentation indeed. My problem is however as follows:

• I don't want our API documentation to be written in a different format from the rest of our documentation, which is in Github's wiki using Markdown.  Our users should be able to help document Evennia without remembering which formatting language is to be used.
• I don't like reStructuredText syntax. This is a personal thing. I get that it is powerful but it is also really, really ugly to read in its raw form in the source code. I feel the sources must be easy to read on their own.
• Sphinx plugins like napoleon understands this ugliness and allows you to document your functions and classes in a saner form, such as the "Google style". One still needs reST for in-place formatting though.
• Organizing sphinx document trees is fiddly and having had a few runs with sphinx autodoc it's just a mess trying to get it to section the Evennia sources in a way that makes sense. It could probably be done if I worked a lot more with it, but it's a generic page generator and I feel that I will eventually have to get down to make those toctrees myself before I'm happy.
• I want to host the API docs as normal Wiki files on Github (this might be possible with reST too I suppose).

Long story short, rather than messing with getting Sphinx to do what I want, I ended up writing my own api-to-github-Markdown parser for the Evennia sources: api2md. Using Python's inspect module and aiming for a subset of the Google formatted docstrings, this was maybe a day's work in total - the rest was/is fine-tuning for prettiness.
 
Now whenever the source is updated, I follow the following procedure to fully update the API docs:

1. I pull the latest version of Evennia's wiki git repository from github alongside the latest version of the main Evennia repository.
2. I run api2md on the changed Evennia sources. This crawls the main repo for top-level package imports (which is a small list currently hard-coded in the crawler - this is to know which modules should create "submodule" pages rather than try to list class contents etc). Under each package I specify it then recursively gets all modules. For each module in that package, it creates a new Markdown formatted wiki page which it drops in a folder in the wiki repository. The files are named after the model's path in the library, meaning you get files like evennia.objects.models.md and can easily cross-link to subsections (aka classes and functions) on a page using page anchors.
3. I add eventual new files and commit the changes, then push the result to the Github wiki online. Done!

(I could probably automate this with a git hook. Maybe as a future project.)

The api2md program currently has some Evennia-custom elements in it (notably in which packages it imports) but it's otherwise a very generic parser of Python code into Markdown. It could maybe be broken out into its own package at some point if there's interest.   

The interesting thing is that since I already have code for converting our wiki to reST and ReadTheDocs, I should be able to get the best of both worlds and convert our API wiki pages the same way later. The result will probably not be quite as custom-stunning as a Sphinx generated autodoc (markdown is a lot simpler in what formatting options it can offer) but that is a lesser concern.
So far very few of Evennia's docstrings are actually updated for the Google style syntax (or any type of formatting, really) so the result is often not too useful. We hope that many people will help us with the doc strings in the future - it's a great and easy way to get to know Evennia while helping out.

But where the sources are updated, the auto-generated wiki page looks pretty neat.


(Image from Wikimedia commons)