April 2016 | The Old New Thing

What does QueryThreadCycleTime actually count?

Raymond ChenApril 29, 2016Apr 29, 201604/29/16

A customer wanted some clarification on the QueryThreadCycleTime function. Based on the name, it suggests that it counts CPU cycles, but they observed that when the power profile is set to Balanced (which lets the CPU run at low frequencies when there is low demand), the thread cycle time increases twice as fast as when the pow

Is there an API for redrawing a specific window from another application?

Raymond ChenApril 28, 2016Apr 28, 201604/28/16

A customer had a Web-based full-screen application, and they wanted to write a companion application that did the following every second: FindWindow → InvalidateRect → UpdateWindow, or FindWindow → RedrawWindow. They wanted to know whether there was some other API for redrawing a window, because the mechanisms abov

How does Explorer calculate “Size on disk”?

Raymond ChenApril 27, 2016Apr 27, 201604/27/16

When you ask to see the size of a file, you get two values. One is the nominal file size (the value that shows up in a directory listing). The other is something called "Size on disk". What is "Size on disk"? The algorithm for "Size on disk" is as follows: If the file is sparse, then report the number of non-sparse bytes. If the file is comp

Why can’t I pin a document to the taskbar?

Raymond ChenApril 26, 2016Apr 26, 201604/26/16

Sven2 wonders why the taskbar won't let you pin a batch file or a shortcut to a log file. The idea behind pinning an item to the taskbar is that it represents something that isn't running on the taskbar right now, but when you click the pinned item, it turns into a real item in the taskbar. And items on the taskbar are identified by their ap

Getting MS-DOS games to run on Windows 95: Too much EMM memory

Raymond ChenApril 25, 2016Apr 25, 201604/25/16

A report arrived on an MS-DOS game that crashed when run on Windows 95. Mind you, the game ran for quite a while before finally keeling over. The repro steps were "Start the game, then go to City 1, then City A, then City Alpha, then City 𓀀, then City ⛄. When you go to City ⛄, the game crashes." I gotta say: Our testers

Should I be concerned that WaitForSingleObject is taking a large percentage of my performance test’s execution time

Raymond ChenApril 22, 2016Apr 22, 201604/22/16

A customer designed a client-server system where the client and the server ran on the same machine (but with different security contexts). They were doing some performance tests of the data transfer portion of the system, and one of tests consisted of the following: Client opens a unit of content on the server. Repeat 100,000 times:

It rather involved being on the other side of this airtight hatchway: Invalid parameters from one security level crashing code at the same security level (doesn’t get old)

Raymond ChenApril 21, 2016Apr 21, 201604/21/16

We received a very professional security vulnerability report from a video driver manufacturer which reported a security vulnerability in DirectX. You can tell it's a professional operation because the vulnerability report took the form of a neatly-formatted PowerPoint presentation with corporate logos in every corner. Unfortunately, you'll ha

Why are mouse wheel messages delivered to the focus window instead of the window under the mouse?

Raymond ChenApril 20, 2016Apr 20, 201604/20/16

Douglas asks, "Is there a good reason that mouse wheel messages are sent to the focused window instead of the window under the mouse?" I don't know if there's a good reason, but there's a reason. The mouse wheel turned into one of those features whose primary use is not the original intended use. The original intent of the mouse wheel was to

Why is there a screen that says “It is now safe to turn off your computer”?

Raymond ChenApril 19, 2016Apr 19, 201604/19/16

I don't know whose idea it was, but Windows 95 added a screen that appeared when you shut down Windows. This message was added because people would shut down Windows and then not know what to do next. I witnessed this first hand once. I was on an airplane flight, and the person sitting next to me was trying to turn off a laptop computer, w

Getting MS-DOS games to run on Windows 95: Too much memory!

Raymond ChenApril 18, 2016Apr 18, 201604/18/16

Piggybacking on Roger Lipscombe's story of the MS-DOS extender that didn't work if you have 64MB of RAM: There was a popular MS-DOS game from 1994 that didn't run in Windows 95. After some investigation, the conclusion was that the game didn't work if your computer had more than 16MB of memory (physical, if running under MS-DOS; virtual, if r

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