May 2018 | The Old New Thing

How can I obtain the heap from which a heap block was allocated?

Raymond ChenMay 31, 2018May 31, 201805/31/18

Suppose profiling reveals that heap contention is a bottleneck in your program. Furthermore, suppose that your program's heap usage pattern is that most heap blocks are allocated and freed by the same thread. One way to address this problem is to create a pool of heaps, say N of them. Each thread gets assigned one of these heaps pseudo-...

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When you call `OpenThreadToken` while impersonating, you have to say who is asking for the thread token

Raymond ChenMay 30, 2018May 30, 201805/30/18

A customer reported that OpenThreadToken was failing with the error ACCESS_DENIED and wanted help understanding why. They shared a code fragment which operates on an account name test with no special privileges. According to the documentation for OpenThreadToken: OpenAsSelf [in] TRUE if the access check is to be made ...

The alphabet, in alphabetical order, in various languages

Raymond ChenMay 29, 2018May 29, 201805/29/18

The first onstage round of the Scripps National Spelling Bee takes place today. Best of luck to all entrants! Bonus chatter: For many years, the Scripps National Spelling Bee FAQ, did not include the question "When does the spelling bee take place?"¹ As a result, every year, I have to guess when it's going to take place, and every year ...

How do I get file version information from the command line?

Raymond ChenMay 29, 2018May 29, 201805/29/18

The great thing about Windows file versions is that there are so many to choose from! For each file, you have The numeric and string versions generally match, but there is no enforcement. Often the string version incorporates the numeric version but adds some additional information, like 3.1.0.2 (alpha). Sometimes the string version ...

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How are `BitBlt` raster opcodes calculated?

Raymond ChenMay 28, 2018May 28, 201805/28/18

Commenter R P asks what the low-order 16 bits of the BitBlt raster opcodes mean. The documentation explains that the high-order 16 bits of the raster opcode are the zero-extended 8-bit value that represents the result of the raster operation given the 8 combinations of three binary inputs (pattern, source, and destination). This is the easy...

My namespace importing trick imported the same three namespaces into each top-level namespace, yet it worked?

Raymond ChenMay 25, 2018May 25, 201805/25/18

A little while ago, I noted a technique formally known as namespace composition. There was one section that appeared to confuse some people: Was this a copy/paste error? After all, the same three namespaces are being imported each time. Well, no, actually. The text is the same, but each one is interpreted differently. Let's take a simpler ...

How do I create a disabled checkbox for a listview item?

Raymond ChenMay 24, 2018May 24, 201805/24/18

A customer was using the LVS_EX_CHECKBOXES extended listview style to get checkboxes for the listview items. However, they also wanted some items to have a disabled checkbox, which is not a feature that LVS_EX_CHECKBOXES supports. They solved the problem by turning off the LVS_EX_CHECKBOXES extended style and replicating and ...

If you say that your buffer can hold 200 characters, then it had better hold 200 characters

Raymond ChenMay 23, 2018May 23, 201805/23/18

A security vulnerability report claimed that there was a vulnerability in the GetDoodadName function (not the actual function name): There is a buffer overflow bug in the GetDoodadName function. If the doodad's name is 10 characters long, and the caller provides a buffer of size 11 characters, but specifies a buffer size ...

Why does the install date and size of a program change roughly two days after I install it, even though no changes were made to the program in the meantime?

Raymond ChenMay 22, 2018May 22, 201805/22/18

A customer observed that when they install a particular company's product, and then go to the Programs and Features control panel, the program shows up with the correct installation date. But wait a few days, and then installation date jumps forward roughly two days, even though no updates for the app were installed in the meantime. (Also, the...

Maintaining Notepad is not a full-time job, but it’s not an empty job either

Raymond ChenMay 21, 2018May 21, 201805/21/18

When I mentioned that one of my now-retired colleagues was responsible for maintaining Notepad, commenter Neil noted, "I can't imagine theres much actual maintenance." You'd be surprised. For one thing, Notepad is a common guinea pig. If a team is adding a new feature, they may ask Notepad to support the feature, in order to get some ...

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