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Posts tagged with 'guadec'

pitti

Yesterday, GUADEC hosted a PyGObject hackfest. I was really happy to see so many participants, and a lot of whom who are rather new to the project. I originally feared that it would just be the core crew of four people, as this is not exactly the shiniest part of GNOME development.

So I did not work on the stuff I was planning for, but instead walked around and provided mentoring, help, and patch review. Unfortunately I do not know all the results from the participants, hopefully they will blog some details themselves. But this is what I was involved in:

  • Manuel Quiñones added an gtk_tree_view_column_set_attributes() override (the original C function uses varargs and thus is not introspectable). Most time was spent figuring out an appropriate test case.
  • I showed Didier Roche some tricks about porting a pygtk application to PyGI/GTK3. He gave a shot to porting Meld, but unfortunately it uses a lot of pygtk hacks/tricks, most of which are obsolete now. So this proved too big a project for one day eventually :-(
  • Paolo and I guided Marta Maria Casetti, one of this year’s GNOME GSoC students, through her first pygobject patch. The test case still needs some love (again, nothing regarding GtkTreeView is easy), but the actual patch is good. Thanks Marta for participating, and not getting intimidated by all the new stuff!
  • While working on above patch, Marta encountered a rather curious TypeError: Expected Gtk.TreeViewColumn, but got GObjectMeta when writing the override. What seemed to be a trivial problem at first quickly turned into an one-hour debugging session involving grandmaster John Palmieri and me, with others chipping in as well. In the end it (of course!) turned out to be a trivial four-character change in Marta’s patch, but it was fun to get to understand the problem (a loong-forgotten special case of overrides resolution in overrides code). Now pygobject gives a proper error message which is actually helpful, i. e. which argument causes the problem and which module/class/method is provided, which should prevent us from being misguided into the totally wrong direction the next time this happens.
  • John Stowers got the Windows build working again, and showed off the gtk-demo under Windows. This is really amazing, I hope we can get that into trunk soon and not let it bitrot again for so long. Thanks!
  • Simon and Manuel worked on porting some Sugar extensions. Together with Paolo we also discussed the GStreamer 1.0 API a bit, which parts can become API additions and which need to become overrides.
  • Michal Hruby debugged a leak in the handling of GVariant arrays when using libdee.

Thanks everyone for participating! I hope everyone enjoyed it and got to learn a new thing or two. See you at the next one!

PyGObject hackfest at GUADEC 2012

PyGObject hackfest at GUADEC 2012

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pitti

I have had the pleasure of attending GUADEC in full this year. TL;DR: A lot of great presentations + lots of hall conversations about QA stuff + the obligatory be{er,ach} = ?.

Last year I just went to the hackfest, and I never made it to any previous one, so GUADEC 2012 was a kind of first-time experience for me. It was great to put some faces and personal impressions to a lot of the people I have worked with for many years, as well as catching up with others that I did meet before.

I discussed various hardware/software testing stuff with Colin Walters, Matthias Clasen, Lennart Poettering, Bertrand Lorentz, and others, so I have a better idea how to proceed with automated testing in plumbing and GNOME now. It was also really nice to meet my fellow PyGObject co-maintainer Paolo Borelli, as well as seeing Simon Schampier and Ignacio Casal Quinteiro again.

No need to replicate the whole schedule here (see for yourself on the interwebs), so I just want to point out some personal highlights in the presentations:

  • Jacob Appelbaum’s keynote about Tor brought up some surprising facts about how the project has outgrown its past performance problems and how useful it was during e. g. the Arab revolution
  • .

  • Philip Whitnall’s presented Bendy Bus, a tool to mock D-Bus services for both unit and fuzz testing. He successfully used it to find and replicate bugs in Evolution (by mocking evolution-data-server) as well as libfolks (by mocking the telepathy daemons). It should work just as well to mock system services like upower or NetworkManager to test the UI bits that use it. This is a topic which has been on my wishlist for a long time already, so I’m happy that there is already an existing solution out there. We might have to add some small features to it, but it’s by and large what I had in mind, and in the discussion afterwards Philip said he’d appreciate patches against it.
  • Christophe Fergeau showed how to easily do Windows builds and installers from GNOME tarballs with MinGW-w64, without having to actually touch/use Windows (using cross-building and running tests etc. under wine). I found it surprising how easy that actually is, and it should not be hard to integrate that in a jhbuild-like setup, so that it does not keep breaking every time.
  • Colin Walters gave an introduction to OSTree, a project to build bootable images from kernel/plumbing/desktop upstream git heads on a daily basis. This is mostly to avoid the long delays that we otherwise have with doing upstream releases, packaging them, and getting them into a form that can safely be tested by users. In an afterwards discussion we threw some ideas around how we can integrate existing and future tests into this (something in spirit like our autopkgtest). This will be the area where I’ll put most focus on in the next time.
  • Adam Dingle of yorba fame shared his thoughts about how we can crowdfunding of Free Software Projects work in practice, comparing efforts like codefoundry and kickstarter. Of course he does not have a solution for this yet, but he raised some interesting concerns and it spun off lots of good discussions over lunchtime.
  • Last but not least, the sport event on Saturday evening was awesome! In hindsight I was happy to not have signed up for soccer, as people like Bastian or Jordi played this really seriously. I participated in the Basketball competition instead, which was the right mix of fun and competition without seriously trying to hurt each other. :-)

There were a lot of other good ones, some of them technical and some amusing and enlightening, such as Frederico’s review of the history of GNOME.

On Monday I prepared and participated in a PyGObject hackfest, but I’ll blog about this separately.

I want to thank all presenters for the excellent program, as well as the tireless GUADEC organizer team for making everything so smooth and working flawlessly! Great Job, and see you again in Strasbourg or Brno!

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pitti

I started to collect some easy PyGObject bugs which are appropriate for the PyGObject hackfest at GUADEC on July 30th. These are bugs which do not need a lot of previous knowlege and are excellent starters for new contributors, such as adding overrides, fixing build system issues, etc.

I also created an initial idea pool/agenda/coordination page, where participants can add or signup for things to work on.

Feel free to add your own topics! I’m really looking forward to GUADEC and the hackfest, see you there!

GUADEC 2012

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pitti

I just received confirmation that my request for a PyGObject hackfest has been approved by the GUADEC organizers.

If you are developing GObject-introspection based Python applications and have some problems with PyGObject, this is the time and place to get to know each other, getting bugs fixed, learn about pygobject’s innards, or update libraries to become introspectable. I will prepare a list of easy things to look into if you are interested in learning about and getting involved in PyGObject’s development.

See you on July 30th in A Coruña!

GUADEC Badge

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Tim Penhey (thumper)

Bazaar has the model right

Some people in the GNOME community have suggested that if Bazaar has nice usability, then GNOME can just use Git on the back-end, and Bazaar lovers can just use the Git back-end via Bazaar. It's true that Bazaar could support this — an experimental plug-in exists to do this right now. But this suggestion betrays several wrong assumptions.

People assume Git and Bazaar are the same. They're not. People assume that if Git and Bazaar have technical differences, then Git must have it right.

The problem with these assumptions is that usability begins at the ground level. Bazaar started with a focus on usability. Git began with a focus on speed. The data models of both Bazaar and Git reflect their initial focus. But Bazaar's model can also be fast. In fact, the Bazaar developers are currently optimising a number of key operations for speed.

Data retrieval

Git and Bazaar are both key/value mapping systems. When bytes are needed, they are requested with that key.

The big difference is that Git's keys are also the hashes of the bytes. This is why it's called a content-addressable file system. This allows git to offer a guarantee that if the value hashes to the key, it has not been modified, whether deliberately or by accident. The Bazaar team considered adopting this approach, but decided it was too constricting. Bazaar uses UUIDs instead.

Authenticating revisions

For detecting malicious modification of revisions, Git uses its cryptographic hashes.

Bazaar uses revision-signing. All revisions can be PGP-signed. No signed revision can be forged. And the hashed representation can easily be generated and passed around to ensure that exactly the same content is used.

If SHA-1 is broken, both Bazaar and Git will lose their ability to detect malicious modification. But since Bazaar uses UUIDs to identify revisions, users can re-sign their old revisions with whatever method proves to be secure. Changing the hash used by Git would make it incompatible with all existing repositories.

Data Integrity and Serialization formats

Bazaar stores hashes of every value, so it equally capable of detecting accidental modification. It can be useful to have different representations of a tree in different repositories. For example, when Git lists files, it divides this data by directory. This is a good approach, but not necessarily the best approach. An alternative approach would be to use a radix tree. This would ensure that Git performed quickly even if users put unreasonable numbers of files in a single directory. But Git's keys are hashes, upgrading Git's format to use radix trees would change the keys, which means that people could not use the commit-id from one repository to refer to the same tree in an other form.

Bazaar doesn't assume it has the perfect format. It provides an upgrade path, and does't change the commit-id of a revision if you change your format. What's more, Bazaar can even reference data it has never seen. This allows partial imports from other VCSes to be fully compatible with more complete imports. And if a VCS provides UUIDs (content hashes certainly qualify as UUIDs), Bazaar can refer to those UUIDs directly.

File and directory representation

Git refers to files by path. It makes no attempt to track renames in its data store.

Bazaar has an inode abstraction; files and directories both have ids. When a file is renamed, its id stays the same. Bazaar's core code refers to files by their id, so merging a renamed file requires no special effort.

Git's approach means that users are warned not to rename files while changing their content. But when files are renamed, those files that refer to the renamed files must have their contents changed as well. For example, if you rename foo.h and foo.c to bar.h and bar.c, you should update the contents of bar.c, or else you will break the build. With Bazaar, users can do whatever they want, and the VCS just works. While Git must always use heuristics to deduce renames, Bazaar does not have to. Of course, it can if it wants to. This is an example of why it is important to design a model for usability from the beginning.

Bazaar can import rename data losslessly from foreign VCSes. Some other VCSes support file-ids, and Bazaar can reuse those without change. For VCSes that support renames, but not file-ids, Bazaar's representation is also non-lossy. When data imports are deterministic and non-lossy, it's easy to export them back to their source VCS. Bazaar's Subversion integration is a great example of how this can work.

Choose the back-end with the right model

In any situation it makes sense to use a back-end that stores the richer dataset. It makes more sense to have a front end client that doesn't use all the functionality or data representation of the back-end than it does to have a richer client that isn't able to store the required information as the back-end is not able to represent it.

If a single back-end storage is going to be used, it makes more sense to use a Bazaar back-end as Bazaar is able to represent everything that Git does, but the reverse is not true.

Conclusion

The Bazaar developers focused on usability, which requires having a model that supports usability. Bazaar has improved its model to increase the usability of the system. We believe that Bazaar has the right model.

co-written by Aaron Bentley and Tim Penhey

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Tim Penhey (thumper)

J5 mentioned in his post his interpretation of the number of users for GIT, Bazaar and Hg (Mercurial). He also finishes with "Converse amongst yourselves".

I guess I should first point out that I am a Bazaar user, and that I work for Canonical. I felt somewhat enraged at the post from J5, and have spent some time trying to work out some response.

John Carr mentioned that 83% of statistics are made up on the spot, and that cannot be more true here. I had been waiting for someone else to post the numbers that they saw at the BOF, but so far I have not seen one.

Here is my take on it.

Yes there were more GIT users than Bazaar users at the BOF, but the numbers were more like 50% of the audience were GIT users, and about 40% were Bazaar users. Someone piped up and said "What about Mercurial?" and so the question was asked, and there were about five or six people. There was an overlap of the GIT and Bazaar groups, and there was by far the larger majority of the audience that had not used any DVCS.

What conclusions can we draw from this? Not much. Many people attending the pre-conference work for larger companies, like Red Hat, Novell, and Nokia, and many of those people work on some hard core linux stuff, many of which have chosen GIT. Many have chosen GIT because that is what the linux kernel is using. Is that a good reason to chose a DVCS? I don't feel that we can really answer that question as I am sure there are strong advocates for both sides.

An interesting question is "Which DVCS is easier for the casual contributor to use?" Surely one of the reasons that a project chooses a DVCS is to allow for more community contributions in an easy to merge way that has a clear contribution history. Bazaar just works. It works for the hard-core developers, but is also easy for those soft-core (?).

From the people I talk to, and I've tried to talk to many here, is that of those that use Bazaar it just works. Bazaar doesn't get in your way of developing the software that you are working on. It is just a tool that works.

One final point. The questions were "Who uses <insert DVCS>?", not "Who likes/loves using <insert DVCS>?".

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