Blog Archives

Blog entries related to the Mozilla project

Running Microsoft Visual C++ 2013 under Wine on Linux

The Wine project lets you run Windows programs on other operating systems, such as Linux.  I spent some time recently trying to see what it would take to run Visual C++ 2013 Update 4 under Linux using Wine. The first

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Pushing to Mozilla hg servers directly from git

I’ve been using git for a few years for doing Mozilla work, which has caused me to have to go through a painful workflow every single time that I push code to inbound.  Now, glandium has written this awesome tool

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Per-window private browsing ready for testing now!

One of the most often requested features in the private browsing support for Firefox has been the ability to open a private window without needing to close the entire session. Over the past 19 months, we have been working on

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How I started reviewing patches faster

The discussion about whether and how we should do patch reviews faster has been brought up for a few years now.  Here is the story of how I decided to stop being lazy start to actually review patches faster.  It’s

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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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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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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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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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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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Updating Firefox in the Background

The dialog below should look familiar. It displays while Firefox completes the update process after a new version is installed and the browser is restarted.

Firefox Update Dialog

In order to update itself, Firefox first starts to download an update in the background. When the update is downloaded, Firefox stages it in a directory ready to be applied. The next time that Firefox is about to start up, it checks out the staging directory. If an update ready to be applied is found, Firefox launches the updater program, and applies the update on top of the existing installation (showing that progress bar as it’s doing its job). When the update process is finished, the updater program restarts Firefox. All of this happens as you’re waiting for your browser to start up in order to do what you wanted to do. This is clearly less than ideal.

For the past few weeks, I have been working on a project to improve this process. The goal of my project is to minimize the amount of time it takes for Firefox to launch after downloading an update. The technical details of how I’m fixing this problem can be found this document. Here’s a short version of how the fix works. When Firefox finishes downloading an update, it launches the updater application in the background without displaying any UI, and applies the update in a new directory that is completely separate from the existing installation directory. Instead of staging the update itself, an entire updated version of Firefox is staged. The next time that Firefox starts up, the existing installation is swapped with the new updated installation which is ready to be used. In this scenario, you likely won’t notice that Firefox has applied an update as no UI is shown.

Now, the reason that this approach fixes the problem is that swapping the directories, unlike the actual process of applying the update, is really fast. We are effectively moving the cost of applying the update to right after the update has been downloaded while the browser is running. This leaves only the really fast copy operation to be performed the next time that the browser starts up.

I have some experimental builds with this feature ready in a temporary channel called Ash. The implementation is now at a stage where it can benefit testing from the community. You can download the latest builds here. I will trigger a few nightly builds on this branch every day so that you would get updates if you’re running an Ash build.

In order to help with testing this new update process, all you need to do is to download the latest build from Ash, then wait a few hours so that a new nightly build becomes available, and then update to that build. Updating can be triggered manually by opening the About dialog, or by the background update checker if you leave the build running for a few hours. If everything works correctly, when you restart Firefox, you should get a new build without seeing any progress bar as Firefox is starting up. In order to verify that you have indeed been updated to a new build, you can go to about:buildconfig, copy its contents, and then compare it with the contents of about:buildconfig when Firefox starts up after an update.

It would be extremely useful if you can test this with different types of security and anti-virus software running. If you observe any problems or warning, or if you see that the update did not change the contents of about:buildconfig, then please let me know so that I can try to fix those problems.

For people who are curious to see the code, I’m doing my development on this branch, and I’m regularly posting patches on bug 307181.

Please note that this is still in the testing stage, and at this point, we’re not quite sure which version of Firefox this will land in (we’re working to land it as soon as is safely possible). No matter which version of Firefox includes this feature for the first time, we believe that this will be a very positive change in making the Firefox update experience more streamlined for all of our users.

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