The Old New Thing

Code - The Old New Thing

GUIDs are designed to be unique, not random

May 23, 2012 May 23, 2012 05/23/12
Raymond Chen
A customer liaison asked, "My customer is looking for information on the GUID generation algorithm. They need to select N items randomly from a pool of M (jury selection), and their proposed algorithm is to assign each item a GUID, then sort the items by GUID and take the first N." (I've seen similar questions regarding using ...

When you crash on a mov ebx, eax instruction, there aren't too many obvious explanations, so just try what you can

May 11, 2012 May 11, 2012 05/11/12
Raymond Chen
A computer running some tests encountered a mysterious crash: A colleague of mine quickly diagnosed the proximate cause. *Something* marked the code page PAGE_READWRITE, instead of PAGE_EXECUTE_READ. I suspect a bug in a driver. FOO is just a victim here. This diagnosis was met with astonishment. "Wow! What made you think to check ...

How do I hide a window without blocking on it?

May 9, 2012 May 9, 2012 05/9/12
Raymond Chen
A customer was working on improving their application startup performance. They found that if their application was launched immediately after a fresh boot, the act of dismissing their splash screen was taking over 5% of their boot time. Their code removed the splash screen by calling . They suspect that the splash screen thread has, for some ...

How does the MultiByteToWideChar function treat invalid characters?

May 4, 2012 May 4, 2012 05/4/12
Raymond Chen
The flag controls how the function treats invalid characters. Some people claim that the following sentences in the documentation are contradictory: "Starting with Windows Vista, the function does not drop illegal code points if the application does not set the flag." "Windows XP: If this flag is not set, the function silently ...

A process shutdown puzzle, Episode 2

April 27, 2012 Apr 27, 2012 04/27/12
Raymond Chen
A customer reported that their program would very sporadically crash in the function . The customer was kind enough to provide a stack trace at the point of the crash: The customer wondered, "Could the problem be that my cleanup group does not have a callback? MSDN seems to suggest that this is okay." The exception being thrown is , but...

What does INIT_ONCE_CTX_RESERVED_BITS mean?

April 20, 2012 Apr 20, 2012 04/20/12
Raymond Chen
Windows Vista adds the One-Time Initialization family of functions which address a common coding pattern: I want a specific chunk of code to run exactly once, even in the face of multiple calls from different threads. There are many implementations of this pattern, such as the infamous double-checked lock. The double-checked lock is very ...

Why do we need IsDialogMessage at all?

April 16, 2012 Apr 16, 2012 04/16/12
Raymond Chen
alv wonders why we need the function at all. "All its activity could take place inside the window procedure of the modeless dialog itself", since when it doesn't have focus, it shouldn't be responding to messages anyway. Sure, that works great if the modeless dialog has focus. But it almost never does. What has focus is a control inside the...

You already know the answer since you do it yourself

April 13, 2012 Apr 13, 2012 04/13/12
Raymond Chen
A customer was writing a program that performed virtual drag/drop. They were using the technique but found that many applications don't support drag/drop of virtual content. They support only . What's more, often these applications query for on not because they want to access the file, but just because they want to get the file names (for ...