Blog Archives

Data about people’s contribution to the Mozilla code base

Tonight I was talking to Josh and he mentioned how he’s interested in getting data on people’s recent contributions to different parts of the Mozilla code base.  He basically wanted to get a list of people who have contributed patches

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Renaming directories in Mercurial by just changing the case

Today we experienced a new way in which Mercurial can fail you.  I’m not talking about performance, twisted workflows, etc.  This time we’re talking about Mercurial being unable to handle things that you can put into your repository in one

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mozilla-central git mirror back up again

When the IonMonkey project merged their history to mozilla-central on Tuesday, my scripts responsible for updating the mozilla-central git mirror happily picked up that huge merge of more than 2000 changesets, and started converting them to the git commit.  And

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So long Drupal, hello WordPress

About four years ago, I made a decision to start a blog.  I researched the various CMS solutions available back in the day, and I chose to use Drupal.  That was a huge mistake, and today I finally fixed it!

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Git mirror of mozilla-central

 A while ago I spent some time in order to generate the perfect git mirror of mozilla-central, and it’s now up on github.  Here’s the story behind the repository.  If you’re not interested in history lessons, scroll down to the "What does this mean for me" section.


Jeff spent quite some time in order to convince me that git is superior to mercurial.  He was right.  And I’m glad I listened to him.  So I decided that I want to use git for most of my Mozilla development.  Some time before that, Chris Double had gone through the trouble of creating a git mirror of mozilla-central using hg-git, so I started to use that repository.  All was well until one day Jeff taught me about grafting two git repositories.  What grafting means is to replace the parent of a commit in one repository to point to a commit in another local repository.  Jeff had created a git mirror of the old Mozilla CVS repository.  The curious reader may realize what this meant: you could graft the git mirror of mozilla-central against the old CVS mirror, and you would get yourself a repository containing all of Mozilla’s history.  That’s right!  No more cross-blaming stuff on hg and bonsai.  You would just do git log or git blame in the grafted repository, and things would work as if we had never abandoned multiple years of the project’s history when we migrated from CVS to mercurial.  Beautiful!

Now, grafting two repositories has some problems.  The graft support has been added as an after-thought, which means that you cannot publish the grafted repositories so that others can consume them, and you might occasionally find that some git commands do not properly handle grafted repositories.  So, I took it upon myself of sharing the joy of the full history with everyone else in the project.  That, was easier said than done!

We discovered that git’s history rewriting tool, the filter-branch command, doesn’t really know about grafts, which has this exciting side-effect that if you issue a filter-branch command in your grafted repository starting at the parent of the graft point, filter-branch will create a full alternate history of your repository, with different commit SHA1’s (since the parent SHA1 has changed), which is a real non-grafted git repository.  So I took Chris’ and Jeff’s repository, grafted them together, and started running filter-branch to convert the grafted repository into a regular repository.  After about a day or so (yes, git filter-branch is that slow), I had a nice error message complaining that I have a commit with an invalid author line.  What the heck, the reader might ask?  It turns out that mercurial is a hipster when it comes to author lines for commits, and git is bipolar.

Mercurial treats the author information for a given changeset as basically a free-form text field.  You can put anything you want in there, and Mercurial would store it for you, and display it as is.  What you see is what you put into it (although, not necessarily what you intended.)  Git, however, has a stricter notion of what an author line could be.  To put it roughly, git expects the author information to be in the form of "Name <>" (yes, it won’t even allow multiple people take credit for a commit!).  And the author lines that hg-git produces from mercurial changesets were sort of sanitized to conform to that format, but not quite.  And weird things that we have in our mercurial history such as this changeset from Ms2ger confused hg-git.  At this point, it was very easy to blame hg-git, or at least Ms2ger, but being the responsible person that I am(!), I decided to delve a little bit deeper into this.  Having looked into git’s source code, it turns out that most of its high-level tools enforce this author line format, but some of its internal tools don’t, and readers who know anything about git’s source code know that looking for anything remotely similar to consistency in its code is like looking for a needle in a pile of haystack where you know there’s no needle to be found.  Hence the bipolarity diagnosis for git.  Now, it was time to get practical and address the problem somehow.

So I decided to fix hg-git, because, "what could possibly go wrong?".  The fix itself was fairly easy, even for somebody like me who only pretends to know Python (and really just looks up all of the language constructs and library functions on Google and just types them in his text editor.)  And I did that, and I tested my fix, and it avoided the Ms2ger problem!  So I went ahead and attempted to convert mozilla-central’s mercurial repository using my patched hg-git.  Little did I know that hg-git is the slowest piece of software ever written!  After 3-4 days, it finally finished converting the seventy something thousand changesets in the source Mercurial repository.  And after a day of running git filter-branch (remember what the workflow looks like?), I came in to the office one morning to find out that filter-branch has died on another commit, further down the history line, again, because of a bad author line.

To keep this blog post short enough so that you can actually download it on a fast connection, I had to do this whole round a few more times, each time fixing more problems that the hg-git authors did not anticipate.  With a turn-around time of about a business week for every single time, you can probably guess why I grin why people complain these days about waiting for 4-5 hours for their try server results.

Finally I had fixed all of the hg-git bugs that the mozilla-central history helped me catch.  And being a good open source citizen and all of that, I upstreamed my hg-git patches (well, really here‘s where I upstreamed them, since I was confused on the patch submission process for hg-git!).

So, I finally had a full git mirror of mozilla-central containing all of Mozilla’s history.  This was maybe a couple of months after I started this project (which I was working on in my free time!), and I had shed enough blood and tears and I thought that it’s useful enough for people that I sneaked it in under mozilla’s github account.

Then, I decided that a git mirror that does not update based on the main repository is not worth much.  So I spent a little time to show off my lack of shell scripting skills to create a cron script which would update the git mirror based on the stuff pushed to mozilla-central.  A few months later somebody (sorry, don’t remember who… maybe jlebar?) pinged me and asked me whether my mirror has an inbound branch.  I said no, and I wanted to explain why I don’t really have time to add that, but I realized that it would take me less time to modify the mozilla-central update script to also include mozilla-inbound, so I sat down and did that, and now I had a branch tracking mozilla-inbound!

I didn’t really talk a lot about the existence of the repository so much to people, mostly because I wanted to write this blog post first (and it took me only about a year to do that) until some time ago when Andreas Gal told me that the b2g project is based on my repository, and there’s apparently tons of people who are using this repository for their day to day development.  This was both nice to hear and frightening at the same time (scroll down to the Fun Facts section to know why!), and this motivated me to finally sit down and write this blog post (about a couple of months after talking to Andreas… I know, I know!).

What does this mean for me?

If you’re a Mozilla developer who’s fed up^H^H^H^H^H^H prefers to use git as opposed to mercurial, just clone the git mirror and start using git.  There’s even an inbound branch in that repository if you really want to live on the bleeding edge.

If you’re a Mozilla developer who has been using Chris’ git mirror, you should switch to this mirror instead, since Chris has stopped updating his mirror.  The update should be fairly painless if you pull my mirror’s master branch and rebase your local branches on top of it.  Once you have rebased all of your branches, git gc will kick in at some point and clean out the old history that you’re no longer using.

If you’re interested in having a repository with the full history of the Mozilla project, including the CVS history, either clone the git mirror and run git log and git blame locally, or use the github UI for blames (here’s a demo).  But be warned that github is sort of slow for large projects, so you will be much better off with a local clone and running git blame (or fugitive.vim, if you’re a vim user.)

If you’re interested in following my steps to do your own conversion, I have good news for you.  I have documented the detailed steps for this conversion from the bare CVS and mercurial repositories to the final git repository.  That directory also includes all of the files and resources that you will need for the conversion.

If you’re interested in more goodies available for this git mirror, check out the latest git-mapfile, the latest git commit and the corresponding hg changeset (and the latest inbound git commit and the corrsponding mozilla-inbound hg changeset).  The mozilla-history-tools repository is being constantly updated as my update scripts pick up newer changesets from mozilla-central and mozilla-inbound to always point to the latest commits and git-mapfiles.

Fun Facts

The update scripts are running on my Linux desktop machine at the office.  The mozilla-central update script runs every 30 minutes, which is much slower than the mozilla-inbound update script which runs every 10 minutes.  The box is connected to a UPS to make sure that we have a negligible reliability for power interruptions.  I do very little monitoring on the update scripts to make sure that they continue to run smoothly.  That monitoring includes glancing over the emails that cron sends me from the stdout output of the update scripts, and fixing up the problems as they come up.  As I have fixed more and more problems, the updates are running fairly smoothly and without any major problems for the past few months.  I did the original work to get the repository in my free time, and I did it because I thought it was useful and I personally wanted better tools for my day-to-day job.  I am glad that others have found it useful.

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Firefox 15: updates are now more silent

Firefox 15 is released on August 28th.  Among many new features implemented in this release is background updates.  This feature allows Firefox to download the update in the background, apply it alongside with the existing installation, and keep the updated version around so that it can quickly switch to it the next time that the browser starts up.  This effectively eliminates the update progress dialog that appears when you start Firefox after it has downloaded an update:

I previously wrote about this project.  You can see that post for more technical details.  This feature landed a while ago on the Nightly channel, and we soon discovered a few issues which we addressed in time for this to get uplifted and enabled on the Aurora channel.  Luckily no new issues were discovered with this feature as it rode the train to get on the Beta channel, and will get in the hands of all of Firefox users on Windows, Mac and Linux as part of the Firefox 15 release.

This was one of the scariest projects that I’ve ever worked on, since messing something up in the updater component could have catastrophic consequences in case it prevents users from being able to update to newer Firefox revisions.  I’m happy that the results of this project will soon get in the hands of millions of Firefox users, and I would like to thank Robert Strong, Brian Bondy, and the wonderful members of our Release Engineering (in particular, Ben Hearsum and Chris AtLee) and QA teams (in particular, Vlad Ghetiu) who helped me a lot along the way.  You guys rock, for being extremely helpful, and for making this large project possible!

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Moving the Mozilla code base over to more modern C++

 The Mozilla code base is very old.  It dates back to before many of the common features of C++ today existed.  As a result, people need to get used to a lot of arcane patterns and idioms that don’t really feel great for those used to more modern code bases.  This has been especially difficult for new contributors as it increases the barrier to entry for them by adding to the list of new things that they need to learn before they can be effective working on the Mozilla code.

This pattern bothered a lot of people, and Michael Wu fixed the first notable example of such arcane pattern: converting the usage of the type PRBool to bool.  PRBool is a typedef to int which was used all around our code base instead of the C++ bool type.  I then followed the train by converting instances of PR_TRUE and PR_FALSE in our code base to true and false.  Aryeh Gregor then stepped up to convert our null value, nsnull, into the C++11 nullptr.  And I recently switched our usages of NSPR numeric types (such as PRInt16/PRUint32) to the stdint.h numeric types (int16_t, uint32_t).

This has been a long and hard road, and we should continue to do more of this in the future.  While this type of work may not seem that interesting as it’s not improving any of the user/web developer facing features, I believe it’s very important to the continuous growth of the Mozilla project, as it makes the code more modern and pleasant to read, and it makes the live of people contributing to the Mozilla code base for the first time much easier.

If you have ideas on more of this kind of cleanup, or are interested in helping with this effort, please contact me!

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Resizing windows in Ubuntu

If you’re an Ubuntu user, you’ve probably come across problems when resizing Windows in the recent versions of Ubuntu. Jeff made me excited today by showing me one way to fix this problem. I looked around a bit on the web, and I found an even better way.

To modify Ambiance to have a wider margin, open /usr/share/themes/Ambiance/metacity-1/metacity-theme-1.xml and increase the values of the following properties:

Hopefully you’ll find this useful!

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How I lost access to my Google account today

After I woke up this morning, I saw a weird login prompt on my phone asking me to log in.  I tried entering my password a couple of times but it didn’t work.  I then turned on my laptop and saw that I’ve been logged out of Gmail.  After I tried logging in, this is what I saw:

Account has been disabled

"Account has been disabled."  I’m sorry, what?!  Yes, indeed, Google has disabled my account for some reason.

I tried looking around the web for solutions, and found out that there are lots of other people who have faced this same problem.  In some cases, the situation had been resolved in a few days, but in some cases people’s accounts were never recovered.  I tried contacting somebody at Google support ("Surely they should have a support department, right?" Nope, wrong!), but the only thing I could find which did not require one to be logged in to Google was a simple form which took an alternate email address from me (which Google already had), and didn’t even tell me that I will be contacted about this.  That was it.

It was around that time which I started to stress out.  I don’t use a lot of the Google services (thankfully), but the two things which I relied on were Gmail and Google Docs.  I have been a Gmail user probably since 2004, and I have tens of thousands of work-related and personal emails stored in my account, some of which being extremely important to me.  I also used Google Docs to store a bunch of very important documents which I won’t be able to recover by other means.  Fortunately I don’t use other services such as Blogger, Picasa, Google Talk or Google+, so other parts of my online life such my ability to speak my mind freely on my blog, share photos with friends, talk to them or otherwise interact with them have not been affected by this.  There are also other relatively minor nuiances happenening as a result of this (I won’t be able to use the Market to install or update applications on my Android phone, and my application purchases are in an unknwon state at this point), but given the other problems I am dealing with right now, these seem pretty minor.

Now I understand that these Google services are free, but I’ve been paying for the Gmail+Docs shared storage, but apparently that does not help me to get customer support, have any rights over the data I have stored on the Google storage for which I am paying, or at least get notified on the reason why my account has been disabled.

Now time to get to the gist of what I want to say in this post.  We’ve all (yours truly included) heard about the importance of owning your digital data, the downsides of vendor lock-in, and how if you’re being provided a free service, you’re the product, not the customer.  But I honestly never understood how deep this problem is, and how severe the consequences can be ("surely this cannot happen to me", right?!).  But starting today, I look at this problem from an entirely new angle.  The issue of user sovereignty for our data was always close to my heart, but this time it’s personal.

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Porting an OpenGL application to the web

Emscripten is a tool which compiles C/C++ applications to Javascript, which can then be run inside a web page in a browser.  I have started to work on adding an OpenGL translation layer which is based on WebGL.  The goal of this project is to make it possible to compile OpenGL C/C++ applications into Javascript which uses WebGL to draw the 3D scenes.

My first demo is a port of the es2gears application to the web.  es2gears is an OpenGL ES 2.0 port of the well-known glxgears application.  You can see the web port of es2gears in action if you’re using a WebGL enabled browser (Firefox, Chrome or Opera Next).  For some extra fun, press the arrow keys as the gears are animating!

Screenshot of the es2gears application

This port has been automatically generated from this version of es2gears.  If you want to play with this locally, you can fork the emscripten repository.

A note about the demo: this is not supposed to be a performance benchmark of any kind.  My GLUT implementation uses the requestAnimationFrame API if available which means that your rendering speed should be capped at about 60FPS.  And that is what you would get if you compile es2gears directly into a native application as well.  But this application doesn’t push either the CPU or GPU to their limits, so it is only useful as a proof-of-concept, and should not be used in order to compare the graphics/Javascript performance of browsers!

I’m very excited about this project, and this is only the beginning.  If you’re interested in this work, watch my blog for further posts about future demos!

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