Some time back while I was working on getting the Javascript Windows Store app platform running on Windows Phone (now available on the last Windows Phone release!) I had an interesting bug that in retrospect is amusing.
I had just finished a work item to get accessibility working for JS WinPhone apps when I got a new bug: With some set of JS apps, accessibility appeared to be totally broken. At that time in development the only mechanism we had to test accessibility was a test tool that runs on the PC, connects to the phone, and dumps out the accessibility tree of whatever app is running on the phone. In this bug, the tool would spin for a while and then timeout with an error and no accessibility information.
My first thought was this was an issue in my new accessibility code. However, debugging with breakpoints on my code I could see none of my code was run nor the code that should call it. The code that called that code was a more generic messaging system that hit my breakpoints constantly.
Rather than trying to work backward from the failure point, I decided to try and narrow down the repro and work forwards from there. One thing all the apps with the bug had in common was their usage of WinJS, but not all WinJS apps demonstrated the issue. Using a binary search approach on one such app I removed unrelated app code until all that was left was the app's usage of the WinJS AppBar and the bug still occurred. I replaced the WinJS AppBar usage with direct usage of the underlying AppBar WinRT APIs and continued.
Only some calls to the AppBar WinRT object produced the issue:
var appBar = Windows.UI.WebUI.Core.WebUICommandBar.getForCurrentView();
// appBar.opacity = 1;
// appBar.closeDisplayMode = Windows.UI.WebUI.Core.WebUICommandBarClosedDisplayMode.default;
appBar.backgroundColor = Windows.UI.Colors.white; // Bug!
I eventually realized that predefined WinRT color values like Windows.UI.Colors.aqua would cause the issue while JS literal based colors didn't cause the issue (Windows.UI.Color is a WinRT struct which projects in JS as a JS literal object with the struct members as JS
object properties so its easy to write something like {r: 0, g: 0, b: 0, a: 0} to make a color) and I had been mixing both in my tests without realizing there would be a difference.
I debugged into the backgroundColor property setter that consumed the WinRT color struct to see what was different between Windows.UI.Colors.black and {a: 1, r: 0, g: 0, b: 0} and
found the two structs to be byte wise exactly the same.
On a hunch I tried my test app with only a reference to the color and otherwise no interaction with the AppBar and not doing anything with the actual reference to the color:
Windows.UI.Colors.black;. This too caused the issue. I knew that the implementation for these WinRT const values live in a DLL and guessed that something in the code to create these
predefined colors was causing the issue. I debugged in and no luck. Now I also have experienced crusty code that would do exciting things in its DllMain, the function that's called when a DLL is loaded into the process so I tried modifying my
C++ code to simply LoadLibrary the DLL containing the WinRT color definition, windows.ui.xaml.dll and found the bug still occurred! A short lived moment of relief as the world seemed to make
sense again.
Debugging into DllMain nothing interesting happened. There were interesting calls in there to be sure, but all of them behind conditions that were false. I was again stumped. On another hunch I tried renaming the DLL and only LoadLibrary'ing it and the bug went away. I took a different DLL renamed it windows.ui.xaml.dll and tried LoadLibrary'ing that and the bug came back. Just the name of the DLL was causing the issue.
I searched for the DLL name in our source code index and found hits in the accessibility tool. Grinning I opened the source to find that the accessibility tool's phone side service was trying to determine if a process belonged to a XAML app or not because XAML apps had a different accessibility contract. It did this by checking to see if windows.ui.xaml.dll was loaded in the target process.
At this point I got to fix my main issue and open several new bugs for the variety of problems I had just run into. This is a how to on writing software that is difficult to debug.
A reminder that those Doritos you love are trash:
Shortly after Disneyland opened in 1955, the founder of Frito-Lay got permission from Walt Disney to open a restaurant in Frontierland with a Mexican-ish theme. “Casa de Fritos” was, unsurprisingly, all about the Fritos. Customers got free Fritos, and Fritos were incorporated into many of the dishes. Fritos were dispensed by an animatronic vending machine that featured the terrifying “Frito Kid”asking his assistant “Klondike” to bring the bag up from a mineshaft. I guess the conceit is that Fritos were mined by Forty-Niners?
Casa de Fritos contracted their tortilla production to a company called Alex Foods. One of the salesmen from Alex Foods, making a delivery to Casa de Fritos, noticed stale tortillas in the garbage and gave the cook a little tip: fry them and sell them as chips instead of throwing them away. Casa de Fritos began making these fried, seasoned chips to enormous success, but didn’t report this new menu item to the Frito-Lay company.
Eventually Frito-Lay found out what they were doing with the chips, packaged them, and sold them by the truckload. See, dumpster diving works out sometimes!
Ringleader claimed to be an IT contractor, got access to bank computers.
Using social engineering to install a remote-controlled keyboard-video-mouse (KVM) switch on bank PCs, the gang managed to transfer millions to outside accounts in two separate jobs in April and July of 2013. They were caught attempting to rob a third bank in September.
IE8, the software I've been working on for some time now, has finally been released at MIX09.
Sarah and I met up with Jon, Scott, Jesse, and Grib in Las Vegas last weekend and we had a fun time.
We started at Home Depot because I didn't know better. The screws are all listed in metric sizes which is apparently uncommon and a helpful senior worker forwarded us to McLendons whose stock was better but we were again redirected this time to Tacoma Screw Products.
Tacoma Screw Products is great! See them for your hardware needs first! The store has a back area with every kind of screw ever. I felt a little out of place as as all the customers looked like contractors. The employee who helped me explained the various options I had in screws as the bike instructions weren't as explicit as they could have been. In the end I bought all my screws for only one dollar (much better than $30!) and they all fit correctly.
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