Tag Archives: cocoa

The Joy of Coding (Ep. 15): OS X Printing Returns

In Episode 15, we kept working on the same bug as the last two episodes – proxying the printing dialog on OS X to the parent process from the content process. At the end of Episode 14, we’d finished the serialization bits, and put in the infrastructure for deserialization. In this episode, we did the rest of the deserialization work.

And then we attempted to print a test page. And it worked!

We did it!

Then, we cleaned up the patches and posted them up for review. I had a lot of questions about my Objective-C++ stuff, specifically with regards to memory management (it seems as if some things in Objective-C++ are memory managed, and it’s not immediately obvious what that applies to). So I’ve requested review, and I hope to hear back from someone more experienced soon!

I also plugged a new show that’s starting up! If you’re a designer, and want to see how a designer at Mozilla does their work, you’ll love The Design Hour, by Ricardo Vazquez. His design chops are formidable, and he shows you exactly how he operates. It’s great!

Finally, I failed to mention that I’m on holiday next week, so I can’t stream live. I have, however, pre-recorded a shorter Episode 16, which should air at the right time slot next week. The show must go on!

Episode Agenda


Bug 1091112 – Print dialog doesn’t get focus automatically, if e10s is enabled – Notes

The Joy of Coding (Ep. 14): More OS X Printing

In this episode, I kept working on the same bug as last week – proxying the print dialog from the content process on OS X. We actually finished the serialization bit, and started doing deserialization!

Hopefully, next episode we can polish off the deserialization and we’l be done. Fingers crossed!

Note that this episode was about 2 hours and 10 minutes, but the standard-definition recording up on Air Mozilla only plays for about 13 minutes and 5 seconds. Not too sure what’s going on there – we’ve filed a bug with the people who’ve encoded it. Hopefully, we’ll have the full episode up for standard-definition soon.

In the meantime, if you’d like to watch the whole episode, you can go to the Air Mozilla page and watch it in HD, or you can go to the YouTube mirror.

Episode Agenda


Bug 1091112 – Print dialog doesn’t get focus automatically, if e10s is enabled – Notes

The Joy of Coding (Ep. 13): Printing. Again!

Had to deal with some network issues during this video – sorry if people were getting dropped frames during the live show! I have personally checked this recording, and almost all frames are there.

The only frames that are missing are the ones where I scramble around to connect to the wired network, which was boring anyhow.

In this episode, I worked on proxying the print dialog from the content process on OS X. It was a wild ride, and I learned quite a bit about Cocoa stuff. It was also a throwback to my very first episode, where I essentially did the same thing for Linux!

We’ll probably polish this off in the next episode, or in the episode after.

Episode Agenda


Bug 1091112 – Print dialog doesn’t get focus automatically, if e10s is enabled – Notes

Things I’ve Learned This Week (May 4 – May 8, 2015)

How to convert an NSString to a Gecko nsAString

I actually discovered this during my most recent Joy of Coding episode – there is a static utility method to convert between native Cocoa NSStrings and Gecko nsAStrings – nsCocoaUtils::GetStringForNSString. Very handy, and works exactly as advertised.

An “Attach to Process by pid” Keyboard Shortcut for XCode

I actually have colleague Garvan Keeley to thank for this one, and technically I learned this on April 24th. It was only this week that I remembered I had learned it!

When I’m debugging Firefox on OS X, I tend to use XCode, and I usually attach to Firefox after it has started running. I have to navigate some menus in order to bring up the dialog to attach to a process by pid, and I was getting tired of doing that over and over again.

So, as usual, I tweeted my frustration:


It seems small, but the savings in time for something that I do so frequently quickly adds up. And it always feels good to go faster!

Things I’ve Learned This Week (April 13 – April 17, 2015)

When you send a sync message from a frame script to the parent, the return value is always an array


// Some contrived code in the browser
let browser = gBrowser.selectedBrowser;
browser.messageManager.addMessageListener("GIMMEFUE,GIMMEFAI", function onMessage(message) {

// Frame script that runs in the browser
let result = sendSendMessage("GIMMEFUE,GIMMEFAI");
// Writes to the console: GIMMEDABAJABAZA

From the documentation:

Because a single message can be received by more than one listener, the return value of sendSyncMessage() is an array of all the values returned from every listener, even if it only contains a single value.

I don’t use sync messages from frame scripts a lot, so this was news to me.

You can use [cocoaEvent hasPreciciseScrollingDeltas] to differentiate between scrollWheel events from a mouse and a trackpad

scrollWheel events can come from a standard mouse or a trackpad1. According to this Stack Overflow post, one potential way of differentiating between the scrollWheel events coming from a mouse, and the scrollWheel events coming from a trackpad is by calling:

bool isTrackpad = [theEvent hasPreciseScrollingDeltas];

since mouse scrollWheel is usually line-scroll, whereas trackpads (and Magic Mouse) are pixel scroll.

The srcdoc attribute for iframes lets you easily load content into an iframe via a string

It’s been a while since I’ve done web development, so I hadn’t heard of srcdoc before. It was introduced as part of the HTML5 standard, and is defined as:

The content of the page that the embedded context is to contain. This attribute
is expected to be used together with the sandbox and seamless attributes. If a
browser supports the srcdoc attribute, it will override the content specified in
the src attribute (if present). If a browser does NOT support the srcdoc
attribute, it will show the file specified in the src attribute instead (if

So that’s an easy way to inject some string-ified HTML content into an iframe.

Primitives on IPDL structs are not initialized automatically

I believe this is true for structs in C and C++ (and probably some other languages) in general, but primitives on IPDL structs do not get initialized automatically when the struct is instantiated. That means that things like booleans carry random memory values in them until they’re set. Having spent most of my time in JavaScript, I found that a bit surprising, but I’ve gotten used to it. I’m slowly getting more comfortable working lower-level.

This was the ultimate cause of this crasher bug that dbaron was running into while exercising the e10s printing code on a debug Nightly build on Linux.

This bug was opened to investigate initializing the primitives on IPDL structs automatically.

Networking is ultimately done in the parent process in multi-process Firefox

All network requests are proxied to the parent, which serializes the results back down to the child. Here’s the IPDL protocol for the proxy.

On bi-directional text and RTL

gw280 and I noticed that in single-process Firefox, a <select> dropdown set with dir=”rtl”, containing an <option> with the value “A)” would render the option as “(A”.

If the value was “A) Something else”, the string would come out unchanged.

We were curious to know why this flipping around was happening. It turned out that this is called “BiDi”, and some documentation for it is here.

If you want to see an interesting demonstration of BiDi, click this link, and then resize the browser window to reflow the text. Interesting to see where the period on that last line goes, no?

It might look strange to someone coming from a LTR language, but apparently it makes sense if you’re used to RTL.

I had not known that.

Some terminal spew

Some terminal spew

Now what’s all this?

My friend and colleague Mike Hoye showed me the above screenshot upon coming into work earlier this week. He had apparently launched Nightly from the terminal, and at some point, all that stuff just showed up.

“What is all of that?”, he had asked me.

I hadn’t the foggiest idea – but a quick DXR showed basic_code_modules.cc inside Breakpad, the tool used to generate crash reports when things go wrong.

I referred him to bsmedberg, since that fellow knows tons about crash reporting.

Later that day, mhoye got back to me, and told me that apparently this was output spew from Firefox’s plugin hang detection code. Mystery solved!

So if you’re running Firefox from the terminal, and suddenly see some basic_code_modules.cc stuff show up… a plugin you’re running probably locked up, and Firefox shanked it.

  1. And probably a bunch of other peripherals as well