The Old New Thing

September 2011 - The Old New Thing

There's also a large object heap for unmanaged code, but it's inside the regular heap

September 30, 2011 Sep 30, 2011 09/30/11
Raymond Chen
Occasionally, a customer will ask for assistance explaining some strange heap behavior, or at least heap behavior that appears to be strange if you assume that the heap behaves purely classically. I need to understand the heap behavior we're seeing. I have a sample program which allocates five blocks of memory from the process heap, each of ...

Appearing to succeed is a valid form of undefined behavior, but it's still undefined

September 29, 2011 Sep 29, 2011 09/29/11
Raymond Chen
A customer requested a clarification on the MSDN documentation for the HeapFree function. The MSDN documentation says that if the lpMem parameter is NULL, then the behavior is undefined. Is this true? As explicitly stated in MSDN, the behavior is undefined. Observe that the annotation on the lpMem parameter is __in, which means that the...
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Ah, the exciting world of cross-forest dogfood

September 27, 2011 Sep 27, 2011 09/27/11
Raymond Chen
The Windows group has its own domain (known as NTDEV for historical reasons) which operates separately from the domain forest operated by the Microsoft IT department. Various trust relationships need to be set up between them so that people on the Windows team can connect to resources managed by the Microsoft IT department and vice versa...

Sending a window a WM_DESTROY message is like prank calling somebody pretending to be the police

September 26, 2011 Sep 26, 2011 09/26/11
Raymond Chen
A customer was trying to track down a memory leak in their program. Their leak tracking tool produced the stacks which allocated memory that was never freed, and they all seemed to come from uxtheme.dll, which is a DLL that comes with Windows. The customer naturally contacted Microsoft to report what appeared to be a memory leak in Windows...
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Why does my asynchronous I/O complete synchronously?

September 23, 2011 Sep 23, 2011 09/23/11
Raymond Chen
A customer was creating a large file and found that, even though the file was opened with FILE_FLAG_OVERLAPPED and the Write­File call was being made with an OVERLAPPED structure, the I/O was nevertheless completing synchronously. Knowledge Base article 156932 covers some cases in which asynchronous I/O will be converted to synchronous I...
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Why does my single-byte write take forever?

September 22, 2011 Sep 22, 2011 09/22/11
Raymond Chen
A customer found that a single-byte write was taking several seconds, even though the write was to a file on the local hard drive that was fully spun-up. Here's the pseudocode: The customer experimented with using asynchronous I/O, but it didn't help. The write still took a long time. Even using FILE_FLAG_NO_BUFFERING (and writing full ...
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Random notes from //build/ 2011

September 20, 2011 Sep 20, 2011 09/20/11
Raymond Chen
Here are some random notes from //build/ 2011, information of no consequence whatesoever. A game we played while walking to and from the convention center was spot the geek. "Hey, there's a guy walking down the street. He's wearing a collared shirt and khakis, with a black bag over his shoulder, staring into his phone...