The Old New Thing
Practical development throughout the evolution of Windows.
Latest posts
Some light reading on lock-free programming
Today is a holiday in the United States, so I'm going to celebrate by referring you to other things to read. I'm going to start with a presentation by Bruce Dawson at GDC 2009, which is basically multiple instances of the question "Is this code correct?", and the answer is always "No!" Although the title of the talk is Lockless Programming in Games, the information is relevant to pretty much everybody. I can't find a recording of the presentation, but you can download the PowerPoint slides or view them in your browser. But I recommend downloading the PowerPoint slides and reading the notes, because the notes e...
If 16-bit Windows had a single input queue, how did you debug applications on it?
After learning about the bad things that happened if you synchronized your application's input queue with its debugger, commenter kme wonders how debugging worked in 16-bit Windows, since 16-bit Windows didn't have asynchronous input? In 16-bit Windows, all applications shared the same input queue, which means you were permanently in the situation described in the original article, where the application and its debugger (and everything else) shared an input queue and therefore would constantly deadlock. The solution to UI deadlocks is to make sure the debugger doesn't have any UI. At the most basic level, the ...
What is the difference between Full Windows Touch Support and Limited Touch Support?
In the System control panel and in the PC Info section of the PC & Devices section of PC Settings, your device's pen and touch support can be reported in a variety of ways. Here is the matrix: The meaning of No touch and Single touch are clear, but if a device supports multiple touch points, what makes the system report it as having Limited versus Full touch support? A device with Full touch support is one that has passed Touch Hardware Quality Assurance (THQA). You can read about the Windows Touch Test Lab (WTTL) to see some of the requirements for full touch support. If you have a touch device without ...
The crazy world of stripping diacritics
Today's Little Program strips diacritics from a Unicode string. Why? Hey, I said that Little Programs require little to no motivation. It might come in handy in a spam filter, since it was popular, at least for a time, to put random accent marks on spam subject lines in order to sneak past keyword filters. (It doesn't seem to be popular any more.) This is basically a C-ization of the C# code originally written by Michael Kaplan. Don't forget to read the follow-up discussion that notes that this can result in strange results. First, let's create our dialog box. Note that I intentionally give it a huge font ...
Is it wrong to call SHFileOperation from a service? Revised
My initial reaction to this question was to say, "I don't know if I'd call it wrong, but I'd call it highly inadvisable." I'd like to revise my guidance. It's flat-out wrong, at least in the case where you call it while impersonating. The registry key is bound to the current user at the time the key is first accessed by a process: The mapping between HKEY_CURRENT_USER and HKEY_USERS is per process and is established the first time the process references HKEY_CURRENT_USER. The mapping is based on the security context of the first thread to reference HKEY_CURRENT_USER. If this security context does not have a...
A library loaded via LOAD_LIBRARY_AS_DATAFILE (or similar flags) doesn't get to play in any reindeer module games
If you load a library with the flag, then it isn't really loaded in any normal sense. In fact, it's kept completely off the books. If you load a library with the , , or flag (or any similar flag added in the future), then the library gets mapped into the process address space, but it is not a true module. Functions like , , and will not see the library, because it was never entered into the database of loaded modules. These "load library as..." flags don't actually load the library in any meaningful sense. They just take the file and map it into memory manually without updating any module tracking databases...
Distinguishing between normative and positive statements to help people answer your question
Often, we get questions from a customer that use the word should in an ambiguous way: Our program creates a widget whose flux capacitor should have reverse polarity. Attached is a sample program that shows how we create the widget with . However, the resulting widget still has a flux capacitor with standard polarity. Can you help us? The phrase should have reverse polarity is ambiguous. The question could be We would like to create a widget whose flux capacitor has reverse polarity. Attached is a sample program that shows how to create a widget whose flux capacitor has standard polarity. How should we modify...
File version information does not appear in the property sheet for some files
A customer reported that file version information does not appear on the Details page of the property sheet which appears when you right-click the file and select Properties. They reported that the problem began in Windows 7. The reason that the file version information was not appearing is that the file's extension was . Older versions of Windows attempted to extract file version information for all files regardless of type. I believe it was Windows Vista that changed this behavior and extracted version information only for known file types for Win32 modules, specifically , , , , , and . If the file's ex...
How do I enumerate drives the same way that the NET USE command does?
If you use the Remote Desktop Connection client to connect to another computer, you have the option of making your local drives available to the remote computer. A customer wanted to know how to enumerate all the drives on the local machine. The were able to get the volumes mapped to drive letters, but they also wanted to get the redirected drives injected by Terminal Services. (Mind you, these aren't volumes that are assigned drive letters, so it's not clear why they are interested in them, but whatever.) With the command, they see the Terminal Services volumes in Explorer, and they can be browsed via : ...