Tag Archives: GSoC2011

Progress report and a happy surprise

Since the last blog post most of my work has been less milestone oriented.

  • Full multilingual support for human readable nodes, nodes which show up in UIs
  • Preliminary support for Option XMLs
  • Two fixes for the XML schema to bring it upto date
  • Creation of a script wrapping XMLint and foomatics XML schema XSDes
  • Clean up of the OpenPrinting front page

I felt the the XML schema was important because my Perl module, the one replacing the C programs, is very forgiving. Robustness is of course a desirable trait in production software but Foomatic still needs something to enforce consistency. I knew we had XML XSDes but we were missing a simply script to run them. Once I had my new script in place two bugs in the printer schema came up. After I fixed that a rerun uncovered four XMLs that needed fixing.

When I started writing support for overviews (a massive data structure containing every printer and its drivers) I uncovered a bug, see if you can spot it:

# This variable holds the current time #
my $now = time;
my $Parser = xmlParse->new('en','0');
my @allPrinters
foreach my $xml (<../printer/*.xml>) {
   my$perlData = $Parser->parsePrinter($xml);
   print Dumper($perlData);

# Calculate runtime
$runtime = time - $now;

I hope you didn’t look too hard, the bug is way too easy to be obvious. This is from scaffolding.pl, a script I use to run xmlParse.pl through its paces. Its a throw away script that exists only for testing. Part of this testing is keeping an eye on runtime, and this is where the bug was.

Notice that our runtime calculation includes Dumper(A helper function that outputs Perl data structures in human readable form), when I wrote the script my assumption was that dumping the data structure was trivial. I was very wrong about this. We can read and parse an XML in one third the time it takes Dumper to print it. Every single printer XML can be read and parsed in under four seconds. Parsing every single Driver we get a runtime of 0:00, the one second resolution of the crude runtime calculator is insufficient! Fixing this bug also reduces the runtime of the C programs, but because the data structures are the same the cost of dumping is constant between the two parsing implementations. Thus the Perl implementation’s relative runtime advantage is even greater than I originally thought.

Definitely good news to report for the next OpenPrinting teleconn.

Prototype completed

The first week of my project was scheduled as  “April 25: Write a perl script capable of parsing a specific XML, extrapolate results to determine relativity to our performance requirements.”.

That week is over and the original goals of the prototype have been completed. In fact I sort of got carried away and the prototype is now nearly feature complete, for printer xml parsing. It turned out to be so fast that I simply have it parse ALL of the printer xmls when ever I want to test it. How fast? About twice as fast as the C program. Since this is a prototype the results are only preliminary, but I expect the final implementation to be at least on par with the C program. This speed was unexpected, my expectation was for the Perl to be linearly slower than the C, and  hoped it wasn’t exponentially slower, yet it is actually faster! This bodes well for the other three fourths of this portion of the project; driver xml, options xml, and overview.

Thanks to this unexpected computational speed I will be focusing on simplicitly in the implementation, since maintainability was the primarly goal of this portion of the project. I will keep an eye out for improvements but now primarily for the opportunity to simplify the code base.

All ready, let GSoC begin!

I’ve now officially finished setting up my workstation, and I have to show it off.

Muhahaha, although the third monitor is waiting until I can get to the store and buy a displayPort cable. =\ I bought an ATI graphics card because in theory they can now drive three monitors with the one card, unfortunately a displayPort connection is required for it to do so.

On a related yet more useful note I set up a launchPad repository for my development work. I’m using Bazaar because that’s what The Linux Foundation repositories are, and launchPad because bzr has mature support for the site. The path of least resistance.