EVE Online Stackless Python Upgrade Q&A

Questions by Cody “Micajah” Bye

Questions by Cody
“Micajah” Bye

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“porkbelly” Jónsson, Senior Software
Engineer for CCP, during one of the company's "Formal Wednesdays".

A few weeks ago, CCP Games issued a press release that
announced their successful upgrade of href="http://www.stackless.com/">Stackless Python
and that this
upgrade would increase the speed of the gameplay for EVE Online
players. Many players of EVE Online probably shrugged their shoulders
and continued playing their game, noticing the performance increase but
generally not thinking twice about the upgrade.

However, the staff at Ten Ton Hammer (we were in San Diego at
the time) found the press release to be interesting, albeit a bit short
for our tastes. We wanted to know more, what had actually occurred in
this update and why was it necessary? What is Stackless Python? Does
anyone else use it besides CCP?

These were our questions, and (thanks to Valerie Massey) we
were able to send those questions to Kristján
“porkbelly” Jónsson, Senior Software
Engineer for CCP. After you read the Q&A, you’ll know
that Kristján knows his tech and all of his answers are both
informative and honest.

style="font-weight: bold;">Ten Ton Hammer: To start,
could you summarize what your high-level programming language,
Stackless Python, accomplishes within the EVE Online world? How does
thread-based programming work? In your press releases you
don’t offer much of an explanation on Stackless Python and
I’m sure the community would be interested in hearing a
simplified version of what Stackless Python is all about.

Kristján: Python is by now a well-established
programming language. Being an interpreted dynamic language, it allows
for great expressivity to the programmer and rapid development. This
makes it easier to focus on the software architecture and the problems
at hand rather than having to deal with the infrastructure of languages
such as C++.  In addition, the dynamic nature allows a very
high turnaround rate. We can make changes to the code and see the
effects in the running client or server without restarting them. It
turns out that performance in terms of programming output by developers
is just as important as the performance of the product they are

Stackless adds a further twist to this by allowing tasks to be
separated into smaller tasks, Tasklets, which can then be split off the
main program to execute on their own. This can be used for
fire-and-forget tasks, like sending off an email, or dispatching an
event, or for IO operations, e.g. sending and receiving network
packets. One tasklet waits for a packet from the network while others
continue running the game loop.

It is in some ways like threads, but is non-preemptive and
explicitly scheduled, so there are fewer issues with synchronization.
Also, switching between tasklets is much faster than thread switching,
and you can have a huge number of active tasklets whereas the number of
threads is severely limited by the computer hardware.

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EVE Online runs well
on many different types of machines, but upgrading Stackless Python
made it even faster.

Ten Ton Hammer: What sort of
factors helped push you towards the decision to upgrade Stackless
Python? You mentioned some upgrades to Python and the NeedForSpeed
sprint, but why choose to upgrade the client now rather than before
Revelations II or farther down the road?

Kristján: Due to various issues, mostly being
swamped with day-to-day development and maintenance of EVE, we
didn’t pay enough attention with keeping the Python part of
the engine up-to-date. At various points we have attempted to catch up
but we never had the breathing space to do so. This time we had the
core technology ready and decided to go for it. It was a question of
reserving a space in the release schedule for it. We wanted to apply
the change in the breathing room after Revelations II when the initial
flurry of hotfixes had subsided. The patch went out without any other
change so that we could monitor the effects of this change in

Ten Ton Hammer: Honestly,
the performance improvements with Stackless Python seem to be pretty
substantial and certainly frees up some resources from the users that
you could take advantage of. Might we see some upgrades to the EVE
client down the line, like improved graphics, more intensive AI, and
other enhancements that would not have been possible without Stackless
Python 2.5?

Kristján: Improvements to our graphics are
something we’ve been working on for quite a while now and
players will begin seeing those this fall. However, some of the slack
that is generated by improvements such as these is usually taken up
somewhat by something else. On the client, for instance, the frame rate
may go up to compensate. On the server side, we have found that
increased responsiveness reduces lag, which again stimulates the users
to place additional load on the servers. People may be hesitant to give
up the improved responsiveness for more features. It’s a
question of balance, I suppose.

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