The Parable of the Code Review

Last week’s events, with Linus Torvalds pledging to stop behaving like an asshole, instituting a code of conduct in Linux kernel development, and all but running off to join a monastery, have made a lot of waves. The last bastion of meritocracy has fallen! Linus, the man with five middle fingers on each hand, was going to save free software from ruin by tellin’ it like it is to all those writers of bad patches. Now he has gone over to the Dark Side, etc., etc.

There is one thing that struck me when reading the arguments last week, that I never realized before (as I guess I tend to avoid reading this type of material): the folks who argue against, are convinced that the inevitable end result of respectful behaviour is a weakening of technical skill in free software. I’ve read from many sources last week the “meritocracy or bust” argument that meritocracy means three things: the acceptance of patches on no other grounds than technical excellence, the promotion of no other than technically excellent people to maintainer positions within projects, and finally the freedom to disrespect people who are not technically excellent. As I understand these people’s arguments, the meritocracy system works, so removing any of these three pillars is therefore bound to produce worse results than meritocracy. Some go so far as to say that treating people respectfully, would mean taking technically excellent maintainers and replacing them with less proficient people chosen for how nice¹ they are.

I never considered the motivations that way; maybe I didn’t give much thought to why on earth someone would argue in favour of behaving like an asshole. But it reminded me of a culture shift that happened a number of years ago, and that’s what this post is about.

Back in the bad old days…

It used to be that we didn’t have any code review in the free software world.

Well, of course we have always had code review; you would post patches to something like Bugzilla or a mailing list and the maintainer would review them and commit them, ask for a revision, or reject them (or, if the maintainer was Linus Torvalds, reject them and tell you to kill yourself.)

But maintainers just wrote patches and committed them, and didn’t have to review them! They were maintainers because we trusted them absolutely to write bug-free code, right?² Sure, it may be that maintainers committed patches with mistakes sometimes, but those could hardly have been avoided. If you made avoidable mistakes in your patches, you didn’t get to be a maintainer, or if you did somehow get to be a maintainer then you were a bad one and you would probably run your project into the ground.

Somewhere along the line we got this idea that every patch should be reviewed, even if it was written by a maintainer. The reason is not because we want to enable maintainers who make mistakes all the time! Rather, because we recognize that even the most excellent maintainers do make mistakes, it’s just part of being human. And even if your patch doesn’t have a mistake, another pair of eyes can sometimes help you take it to the next level of elegance.

Some people complained: it’s bureaucratic! it’s for Agile weenies! really excellent developers will not tolerate it and will leave! etc. Some even still believe this. But even our tools have evolved over time to expect code review — you could argue that the foundational premise of the GitHub UI is code review! — and the perspective has shifted in our community so that code review is now a best practice, and what do you know, our code has gotten better, not worse. Maintainers who can’t handle having their code reviewed by others are rare these days.

By the way, it may not seem like such a big deal now that it’s been around for a while, but code review can be really threatening if you aren’t used to it. It’s not easy to watch your work be critiqued, and it brings out a fight-or-flight response in the best of us, until it becomes part of our routine. Even Albert Einstein famously wrote scornfully to a journal editor after a reviewer had pointed out a mistake in his paper, that he had sent the manuscript for publication, not for review.

And now imagine a future where we could say…

It used to be that we treated each other like crap in the free software world.

Well, of course we didn’t always treat each other like crap; you would submit patches and sometimes they would be gratefully accepted, but other times Linus Torvalds would tell you to kill yourself.

But maintainers did it all in the name of technical excellence! They were maintainers because we trusted them absolutely to be objective, right? Sure, it may be that patches by people who didn’t fit the “programmer” stereotype were flamed more often, and it may be that people got sick of the disrespect and left free software entirely, but the maintainers were purely objectively looking at technical excellence. If you weren’t purely objective, you didn’t get to be a maintainer, or if you somehow did get to be a maintainer then you were a bad one and you would probably run your project into the ground.

Somewhere along the line we got this idea that contributors should be treated with respect and not driven away from projects, even if the maintainer didn’t agree with their patches. The reason is not because we want to force maintainers to be less objective about technical excellence! Rather, because we recognize that even the most objective maintainers do suffer from biases, it’s just part of being human. And even if someone’s patch is objectively bad, treating them nonetheless with respect can help ensure they will stick around, contribute their perspectives which may be different from yours, and rise to a maintainer’s level of competence in the future.

Some people complained: it’s dishonest! it’s for politically correct weenies! really excellent developers will not tolerate it and will leave! etc. Some even still believe this. But the perspective has shifted in our community so that respect is now a best practice, and what do you know, our code (and our communities) have gotten better, not worse. Maintainers who can’t handle treating people respectfully are rare these days.

By the way, it may not seem like such a big deal now that it’s been around for a while, but confronting and acknowledging your own biases can be really threatening if you aren’t used to it… I think by now you get the idea.

Conclusion, and a note for the choir

I generally try not to preach to the choir anymore, and leave that instead to others. So if you are in the choir, you are not the audience for this post. I’m hoping, possibly vainly, that this actually might convince someone to think differently about meritocracy, and consider this a bug report.

But here’s a small note for us in the choir: I believe we are not doing ourselves any favours by framing respectful behaviour as the opposite of meritocracy, and I think that’s part of why the pro-disrespect camp have such a strong reaction against it. I understand why the jargon developed that way: those driven away by the current, flawed, implementation of meritocracy are understandably sick of hearing about how meritocracy works so well, and the term itself has become a bit poisoned.

If anything, we are simply trying to fix a bug in meritocracy³, so that we get an environment where we really do get the code written by the most technically excellent people, including those who in the current system get driven away by abusive language and behaviour.

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[1] To be clear, I strive to be both nice and technically excellent, and the number of times I’ve been forced to make a tradeoff between those two things is literally zero. But that’s really the whole point of this essay ↩

[2] A remnant of these bad old days of absolute trust in maintainers, that still persists in GNOME to this day, is that committer privileges are for the whole GNOME project. I can literally commit anything I like, to any repository in gitlab.gnome.org/GNOME, even repositories that I have no idea what they do, or are written in a programming language that I don’t know! ↩

[3] A point made eloquently by Matthew Garrett several years ago ↩

JavaScript news from GNOME 3.30

Welcome back to the latest news on GJS, the Javascript engine that powers GNOME Shell, Endless OS, and many GNOME apps.

I haven’t done one of these posts for several versions now, but I think it’s a good tradition to continue. GNOME 3.30 has been released for several weeks now, and while writing this post I just released the first bugfix update, GJS 1.54.1. Here’s what’s new!

If you prefer to watch videos rather than read, see my GUADEC talk on the subject.

JavaScript upgrade!

GJS is based on SpiderMonkey, which is the name of the JavaScript engine from Mozilla Firefox. We now use the version of SpiderMonkey from Firefox 60. (The way it goes is that we upgrade whenever Firefox makes an extended support release (ESR), which happens about once a year.)

This brings a few language improvements: not as many as in 2017 when we zipped through a backlog of four ESRs in one year, but here’s a short list:

• Asynchronous iterators (for await (... in ...))
• Rest operator in object destructuring (var {a, b, ...cd} = ...)
• Spread operator in object literals (obj3 = {...obj1, ...obj2})
• Anonymous catch (catch {...} instead of catch (e) {...})
• Promise.prototype.finally()

There are also some removals from the language, of Mozilla-specific extensions that never made it into the web standards.

• Conditional catch (catch (e if ...))
• For-each-in loops (for each (... in ...))
• Legacy lambda syntax (function (x) x * x)
• Legacy iterator protocol
• Array and generator comprehensions ([for (x of iterable) expr(x)])

Hopefully you weren’t using any of these, because they will not even parse anymore! I wrote a tool called moz60tool that will scan your source files and hopefully flag any uses of the removed syntax. It’s also available as a shell extension by Andy Holmes.’

Time for your code to get a checkup… Photo by rawpixel.com on Pexels.com

ByteArray

A special note about ByteArray: the SpiderMonkey upgrade made it necessary to rewrite the ByteArray class, since support for intercepting property accesses in C++-native JS objects was removed, and that was what ByteArray used internally to implement expressions like bytearray[5].

The replacement API I think would have made performance worse, and ByteArray is pretty performance critical; so I took the opportunity to replace ByteArray with JavaScript’s built-in Uint8Array. (Uint8Array didn’t exist when GJS was invented.) For this, I implemented a feature in SpiderMonkey that allows you to store a GBytes inside a JavaScript ArrayBuffer object.

The result is not 100% backwards compatible. Some functions now return a Uint8Array object instead of a ByteArray and there’s not really a way around that. The two are not really unifiable; Uint8Array’s length is immutable, for one thing. If you want the old behaviour back, you can call new ByteArray.ByteArray() on the returned Uint8Array and all the rest of your code should work as before. However, the legacy ByteArray will have worse performance than the Uint8Array, so instead you should port your code.

Technical Preview: Async Operations

The subject of Avi Zajac’s summer internship was integrating Promises and async functions with GIO’s asynchronous operations. That is, instead of this,

file.load_contents_async(null, (obj, res) => {
    const [, contentsBytes, etag] = obj.load_contents_finish(res);
    print(ByteArray.toString(contentsBytes));
});

you should be able to do this:

file.load_contents_async(null)
.then((contentsBytes, etag) => print(ByteArray.toString(contentsBytes)));

or this:

const [contentsBytes, etag] = await file.load_contents_async(null);
print(ByteArray.toString(contentsBytes));

If you don’t pass in a callback to the operation, it assumes you want a Promise instead of a callback, and will return one so that you can call .then() on it, or use it in an await expression.

This feature is a technology preview in GNOME 3.30 meaning, you must opt in for each method that you want to use it with. Opt in by executing this code at the startup of your program:

Gio._promisify(classPrototype, asyncMethodName, finishMethodName);

This is made a bit extra complicated for file operations, because Gio.File is actually an interface, not a class, and because of a bug where JS methods on interface prototypes are ignored. We also provide a workaround API for this, which unfortunately only works on local (disk) files. So the call to enable the above load_contents_async() code would look like this:

Gio._promisify(Gio._LocalFilePrototype, 'load_contents_async', 'load_contents_finish');

And, of course, if you are using an older GNOME version than 3.30 but you still want to use this feature, you can just copy the Promisify code into your own program, if the license is suitable. I’ve already been writing some code for Endless Hack in this way and it is so convenient that I never want to go back.

Debugger

At long last, there is a debugger. Run it with gjs -d yourscript.js!

The debugger commands should be familiar if you’ve ever used GDB. It is a bit bare-bones right now; if you want to help improve it, I’ve opened issues #207 and #208 for some improvements that shouldn’t be too hard to do.

The debugger is based on Jorendb, a toy debugger by Jason Orendorff which is included in the SpiderMonkey source repository as an example of the Debugger API.

Performance improvements

We’ve made some good improvements in performance, which should be especially apparent in GNOME Shell. The biggest improvement is the Big Hammer patch by Georges Stavracas, which should stop your GNOME Shell session from holding on to hundreds of megabytes at a time. It’s a mitigation of the Tardy Sweep problem which is explained in detail by Georges here. Unfortunately, it makes a tradeoff of worse CPU usage in exchange for better memory usage. We are still trying to find a more permanent solution. Carlos Garnacho also made some further improvements to this patch during the 3.30 cycle.

The other prominent improvement is better memory usage for GObjects in general. A typical GNOME Shell run contains thousands or maybe ten-thousands of GObjects, so shaving even a few bytes off per object has a noticeable effect. Carlos Garnacho started some work in this direction and I continued it. In the end we went from 128 bytes per GObject to 88 bytes. In both cases there is an extra 32 byte penalty if the object has any state set on it from JavaScript code. With these changes, GNOME Shell uses several tens of megabytes less memory before you even do anything.

I have opened two issues for further investigation, #175 and #176. These are two likely avenues to reduce the memory usage even more, and it would be great if someone were interested to work on them. If they are successful, it’s likely we could get the memory usage down to 56 bytes per GObject, and eliminate the extra 32 byte penalty.

Eventually we will get to that “well-oiled machine” state… Photo by Celine Nadon on Unsplash

Developer Experience

I keep insisting it’s no coincidence, that as soon as we switched to GitLab we started seeing an uptick in contributors whom we hadn’t seen before. This trend has continued: we merged patches from 22 active contributors to GJS in this cycle, up from 13 last time.

Claudio André landed many improvements to the GitLab CI. For one thing, the program is now built and tested on more platforms and using more compile options. He also spent a lot of effort ensuring that the most common failures will fail quickly, so that developers get feedback quickly.

From my side, the maintainer tasks have gotten a lot simpler with GitLab. When I review a merge request, I can leave the questions of “does it build?” and “are all the semicolons there?” to the CI, and concentrate on the more important questions of “is this a feature we want?” and “is it implemented in the best way?” The thumbs-up votey things on issues and merge requests also provide a bit of an indication of what people would most like to see worked on, although I am not really using these systematically yet.

We have some improvements soon to be deployed to DevDocs, and GJS Guide, a site explaining some of the more basic GJS concepts. Both of these were the subject of Evan Welsh’s summer internship. Evan did a lot of work in upstream DevDocs, porting it from the current unsupported CoffeeScript version to a more modern web development stack, which will hopefully be merged upstream eventually.

It’s about time we had a signpost to point the way in GJS. Photo by Jens Johnsson on Pexels.com

We also have an auto formatter for C++ code, so if you contribute code, it’s easier to avoid your branches failing CI due to linter errors. You can set it up so that it will correct your code style every time you commit; there are instructions in the Hacking file. It uses Marco Barisione’s clang-format-hooks. The process isn’t infallible, though: the CI job uses cpplint and the auto formatter uses clang-format, and the two are not 100% compatible.

There are a few miscellaneous nice things that Claudio made. The test coverage report for the master branch is automatically published on every push. And if you want to try out the latest GJS interpreter in a Flatpak, you can manually trigger the “flatpak” CI job and download one.

What’s coming in 3.32

There are a number of efforts already underway in the 3.32 cycle.

ES6 modules should be able to land! This is an often requested feature and John Renner has a mostly-working implementation already. You can follow along on the merge request.

Avi Zajac is working on the full version of the async Promises feature, both the gobject-introspection and GJS parts, which will make it no longer opt-in; Promises will “just work” with all GIO-based async operations.

Also related to async and promises, Florian Müllner is working on a new API that will simplify calling DBus interfaces using some of the new ES6 features we have gained in recent releases.

I hope to land Giovanni Campagna’s old “argument cache” patch set, which looks like it will speed up calls from JS into C by quite a lot. Apparently there is a similar argument cache in PyGObject.

Finally, and this will be the subject of a separate blog post coming soon, I think we have a plausible solution to the Tardy Sweep problem! I’m really excited to write about this, as the solution is really ingenious (I can say that, because I did not think of it myself…)

Contributors

Thanks to everyone who participated to bring GJS to GNOME 3.30: Andy Holmes, Avi Zajac, Carlos Garnacho, Christopher Wheeldon, Claudio André, Cosimo Cecchi, Emmanuele Bassi, Evan Welsh, Florian Müllner, Georges Basile Stavracas Neto, James Cowgill, Jason Hicks, Karen Medina, Ole Jørgen Brønner, pixunil, Seth Woodworth, Simon McVittie, Tomasz Miąsko, and William Barath.

As well, this release incorporated some old patches that people contributed in the past, even up to 10 years ago, that were never merged because they needed some tweaks here or there. Thanks to those people for participating in the past, and I’m glad we were finally able to land your contributions: Giovanni Campagna, Jesus Bermudez Velazquez, Sam Spilsbury, and Tommi Komulainen.

GUADEC 2018 Reminiscences

This year’s GUADEC in Almería, Spain, was over two months ago, and so here is a long overdue post about it. It was so long ago that I might as well call it a reminiscence! This will be a different kind of post than the ones I’ve done in past years, as plenty of other bloggers have already posted summaries about the talks.

Board of Directors

I didn’t even get to see that many talks anyway, as this was my first GUADEC after being elected to the GNOME Foundation board of directors and I found myself doing a lot of running around to complete things. The board has to prepare for a number of meetings including the GNOME Foundation’s Annual General Meeting that’s always held at GUADEC, and so there was plenty of preparation to be done.

So, except for a few sessions, I mainly followed the “hallway track” this year.

It’s an exciting time to be on the board; it’s been in the news recently that the GNOME Foundation has received two substantial donations, and is hiring some new roles. If you want more information and background, Rosanna Yuen, director of operations, explains all about it in this GUADEC talk.

Interns

Somehow I found myself mentoring two interns this summer, Avi Zajac and Evan Welsh, and both of them were able to attend GUADEC. (I co-mentored Evan with my coworker Manuel Quiñones, who unfortunately could not be there.) I had not done a good job introducing them to each other, but they connected with each other and realized that they were both working with me! If you haven’t already, make sure to read Avi’s blog post and Evan’s blog post for their perspectives on how it went. I was glad to have both of them there and really enjoyed meeting up in person.

Both internships have finished up in the meantime. Evan’s website is viewable here, as well as some improvements to DevDocs which I hope to deploy soon. Avi’s project was released as a technical preview in GNOME 3.30 and will be covered in my next blog post.

JavaScript Talk

I gave one scheduled talk, on GJS and JavaScript, and one unscheduled talk, on Endless Code.

I will cover the material from the JavaScript talk in my next post about the new features in GJS, but for now I wanted to post the slides for everyone’s reference. The video of the talk is here.

Endless Hack Talk

I was voted into one of the conference’s open talk slots with a proposal to talk about Endless Code (since then, renamed to Endless Hack). This is a new (well, it was new at the time of the conference) project at Endless. It’s a continuation of this feature which (I didn’t work on, but) my coworkers demoed about two years ago:

Want to hack on an app in @endlessglobal? Simple, just flip over the window and start coding. All code, build tools, and deps are there. pic.twitter.com/T3maWdw2eI

— Jono Bacon (@jonobacon) January 5, 2017

The Endless Hack product generalizes this idea to the whole desktop. The idea is that you should be able to tinker with everything, and there’s a narrative that guides you along the way and teaches you programming concepts. It’s aimed at children and young teenagers. Although this product hasn’t been released yet, and although some of the source code is currently open it’s not in a finished or usable state yet, I did want to talk about it at GUADEC because I think the ability to learn by tinkering is an important part of the free software experience and a direct consequence of one of the Four Software Freedoms, and it’s something the GNOME community should be aware of.

We also made a survey asking people about their experience learning how to program, or not learning how to program, and it’s still open, because I did not do a very good job in the talk of publicizing the link! You can fill it out here.

I haven’t dared to watch the video of me talking completely unrehearsed, but you can watch it here if you want.

Unconference

I had high hopes for organizing a GJS unconference session like last year, but after a certain point I was just completely tired out. We did eventually have a GJS session that consisted of people hacking on their favourite thing. Happily, I was able to convince Georges Stavracas to fix a regression that was preventing GNOME Shell from starting. I got a chance to work with Meg Ford on testing with JavaScript, and I also got some work done on the GJS debugger, a new feature in GNOME 3.30. I will talk about all this and more in my next post!

We also used some of the unconference time for a kickoff session for the GNOME Developer Center. Bastian Ilsø is leading this initiative and has a lot of material for you to read on what’s happened in the meantime.

Acknowledgements

I’d like to thank the GNOME Foundation for making it possible for me to attend the conference and the board meetings.

Thank you to my coworker Lisette Silva for convincing me to submit the open talk and giving some last-minute feedback beforehand.