The Old New Thing

Code - The Old New Thing

In pursuit of the message queue

February 21, 2006 Feb 21, 2006 02/21/06
Raymond Chen
In 16-bit Windows, every thread (or "task" as it was called then) had a message queue, end of story. In the transition to 32-bit Windows, this model broke down because Win32 introduced the concepts of "worker threads" and "console applications", neither of which had much need for messaging. Creating a queue for every thread in the system would...

Why does my program run faster if I click and hold the caption bar?

February 20, 2006 Feb 20, 2006 02/20/06
Raymond Chen
Sometimes, people discover that a long-running task runs faster if you hold down the mouse. How can that be? This strange state of affairs typically results when a program is spending too much time updating its progress status and not enough time actually doing work. (In other words, the programmer messed up badly.) When you click and hold ...

Because programmers were trusted to do the right thing, part 2

February 16, 2006 Feb 16, 2006 02/16/06
Raymond Chen
Some time ago, I discussed briefly the philosophy of API design that prevailed in the early days. One of the places this manifested itself was in the area of power management. As originally designed, power management was a cooperative affair (as was nearly everything in Windows in the early days). When the user attempted to put the computer ...

The dangers of sleeping on a UI thread

February 10, 2006 Feb 10, 2006 02/10/06
Raymond Chen
If you have a thread that owns a window, you should not be using the function, because that causes your thread to stop responding to messages for the duration of the sleep. This is true even for sleeps of short duration, such as sleeping for a few seconds and waking up in order to poll the state of something in the system. As we noted ...

Viewing function composition as transformation of the domain

February 7, 2006 Feb 7, 2006 02/7/06
Raymond Chen
A lot of formulas you encounter in computer science can be viewed as function composition. Let's start with the simple problem of rounding integers down to the nearest multiple of some positive constant. The formula for this should be relatively easy for you to produce: round_down(n, m) = floor_div(n, m) * m where returns the largest ...

Beware of redirected folders, too

February 6, 2006 Feb 6, 2006 02/6/06
Raymond Chen
Earlier, we learned about roaming user profiles, wherein the master copy of the user's profile is kept on a central server (which for the purpose of discussion I will call the "profile server") and is copied around to follow the user as she logs onto computers throughout an organization. In the comments, many people said that what they really...

You can't even trust the identity of the calling executable

February 3, 2006 Feb 3, 2006 02/3/06
Raymond Chen
A while back, I demonstrated that you can't trust the return address. What's more, you can't even trust the identity of the calling executable. I've seen requests from people who say, "I want to check whether I'm being called from MYAPP.EXE. I'm going to make a security decision based on the result." Although you can do this, all it does is ...

Be careful when interpreting security descriptors across machine boundaries

February 2, 2006 Feb 2, 2006 02/2/06
Raymond Chen
While it's true the function can be used to check whether a particular security descriptor grants access to a token, you need to be aware of where that security descriptor came from. If the security descriptor came from another machine (for example, if you got it by calling and passing the path to a file on a network share), calling the ...

The per-class window styles and things really are per-class

February 1, 2006 Feb 1, 2006 02/1/06
Raymond Chen
Earlier, I discussed which window style bits belong to whom. One detail of this that I neglected to emphasize is that since the lower 16 bits of the window style are defined by the class, you can't just take styles from one class and apply them to another. For example, you can't create a button control and pass the style expecting to have ...