Archive for July 14, 2016

Thursday, July 14, 2016

Facebook’s Mobile Device Testing Lab

Frederic Lardinois (via Peter Steinberger):

The mobile device lab currently occupies 60 racks in the data center. Each rack holds 32 phones, for a total of almost 2,000 devices, but, as Facebook’s Antoine Reversat told us, the plan is to bring this number to 64 devices per rack.

Each rack features its own Wi-Fi signal and is also an EMI enclosure to make sure that neighboring racks can’t pick up the Wi-Fi signals from its neighbors.

Every time an engineer makes changes to one of Facebook’s main mobile apps, that new version of the app is automatically tested on these devices to ensure that there are no crashes or performance issues.


All of the phones also need to be connected to a PC or Mac in order to receive the latest code. Because of this, there are PCs and Mac Mini’s under every rack. Facebook uses eight Mac Minis per rack for iOS testing (because each one can only talk to four iPhones) or four OCP Leopard servers for testing Android devices.

Legal Decisions

Orin Kerr:

The U.S. Court of Appeals for the 9th Circuit has handed down a very important decision on the Computer Fraud and Abuse Act, Facebook v. Vachani, which I flagged just last week. For those of us worried about broad readings of the Computer Fraud and Abuse Act, the decision is quite troubling. Its reasoning appears to be very broad. If I’m reading it correctly, it says that if you tell people not to visit your website, and they do it anyway knowing you disapprove, they’re committing a federal crime of accessing your computer without authorization.


At this point you may be thinking: Hey, wait, didn’t the en banc 9th Circuit rule in Nosal I that using a computer in violation of its terms of use is not a CFAA violation? If intentionally using a computer in violation of the terms of use is legal authorized access, as the en banc 9th Circuit held in Nosal I, why is intentionally using a computer after receiving a cease-and-desist letter criminal access “without authorization”? In one case, the user goes to the website and sees the terms; in the other, the website owner contacts the user and shows the terms to them. But it’s the same thing, right?

Bruce Schneier:

In a truly terrible ruling, the US 9th Circuit Court ruled that using someone else’s password with their permission but without the permission of the site owner is a federal crime.

Mark Rumold:

In a dangerously flawed decision unsealed today, a federal district court in Virginia ruled that a criminal defendant has no “reasonable expectation of privacy” in his personal computer, located inside his home. According to the court, the federal government does not need a warrant to hack into an individual’s computer.

MathML Improvements in WebKit

Frédéric Wang:

This new feature is obvious: You can now create a hyperlink for any part of a mathematical formula!


In the following screenshot, you can see that the letters f, x and y are now drawn with this special mathematical italic glyphs and that WebKit uses the conventional fraktur style for the Lie algebra g. Note that the prime is still too small because WebKit does not make use of the ssty feature yet.


As said in my previous blog post, the rendering of large and stretchy operators have been rewritten a lot and as a consequence the rendering has improved. Also, I mentioned that the width of operators may depend on their height. This may cause accumulated approximations during the computation of preferred widths. The old flexbox-based implementation incorrectly forced layout during preferred computation to avoid that but a quick workaround for that security concern caused the approximate preferred widths to be used for the logical widths. With our new implementation, the logical width is now correctly calculated. Finally, we added partial support for the mpadded element which is often used to tweak spacing in mathematical formulas.

Update (2016-07-24): See also:

Pinboard Turns Seven

Maciej Cegłowski (via Manton Reece):

I’ve added revenue this year because I’m no longer afraid of competitors, and I’d like to encourage people who are considering doing their own one- or zero-person business. The site costs something like $17K/year to run, so you can make a good living at this artisanal SaaS stuff.

As you can see, most everything has been steady year-to-year for a while now. Revenue dropped a bit in 2015 (as I moved to an annual subscription system), then picked up substantially this year as the first wave of subscription renewals came due, and people had the option of renewing for multiple years.