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Revenge Of The Autobuilds

July 4th, 2007 by Multimedia Mike

Takis has been a busy FFmpeg hacker: He recently established an experimental server to automatically build the current source-controlled copy of FFmpeg and perform some rudimentary tests with the output. This is some great initiative on his part.

(Oh, and look what else Takis has been up to while no one is looking: a graph of FFmpeg code change over time.)

I have wanted to build an automated building and testing infrastructure for FFmpeg for a long time now. I got my first concept up and running late last November. I just realized that I never blogged about it although I did announce it on the ffmpeg-devel mailing list. The concept lives at http://builds.multimedia.cx/, though be advised that the script that updates it went offline in late December.

Predictably, people seemed to think the autobuild system was a good idea but that my implementation needed a lot of work. And they were right. The reason that I never blogged about it is likely that I figured I was about to deploy a better concept very soon.

It is now July and I have had months to brainstorm ideas for an improved autobuild and test infrastructure. Unfortunately, as can often happen with revision 2 of an unproven idea, I fear my concept has devolved into an exercise in architecture astronomy.


Architecture Astronomy

Read Joel Spolsky’s excellent essay, “Don’t Let Architecture Astronauts Scare You”. It’s about people who heavily theorize in the abstract but rarely accomplish anything useful. Personally, I consider it a clear indicator of architecture astronomy when a program’s fundamental paradigm revolves around the idea that, “Everything is an object (or module)!” It is my opinion that declaring everything in your architecture to be an object is the abstraction endgame (to be more specific, everything is a swappable, user-configurable module, even the central engine of the program that is supposed to coordinate everything between other modules).

I’ll explain the evolution of my autobuild idea: It started simply enough with a script that iterated through a bunch of compiler versions and ran the configure/make commands to build each. It logged stdout and stderr separately and logged general information about success/failure, SVN version, etc. into a rudimentary database table that could be simply queried with a PHP script.

I soon realized that this is wholly inadequate to the overall goals I wished to accomplish in this endeavor (building and testing on many platforms). Security is a major issue, which I blogged about before, and which I solved in the first iteration using the most paranoid policies of chroot’ing the configure/make steps and prohibiting network access during the process. Another problem is the eventuality of infinite loop bugs. Any build or test step could conceivably encounter such a condition.

This realization led me to redesign the autobuild/test system as a series of individual executable steps, all stored in a database, of which the primary script has no hardcoded knowledge. And this is where the “Everything is a module” philosophy comes into play. Unfortunately, the further I plot this out on paper, the harder it becomes because the execution module concept is too generic; it’s hard to do certain specific things. I realize I need to back off a bit on the abstraction.

Posted in FATE Server, Multimedia Goals And TODO, Programming | 2 Comments »

2 Responses

  1. astrange Says:

    One thing I’ve been wanting to do is set up an ffmpeg auto-build server, but instead of tracking ffmpeg progress it would track gcc’s SVN compiling it.

    Getting into SPEC is the only actual way to make compiler writers care about your program, but it might help a little!

    Too bad I haven’t got any free hardware or time.

  2. Multimedia Mike Says:

    @astrange: Can you provide more information about this SPEC stuff and how to get “into” it? This is the first I have heard of it. Perhaps I can keep it in mind while building this system.