January 2016 | The Old New Thing

Does the thread pool have different handle access privileges? Why am I getting ERROR_INVALID_HANDLE?

Raymond ChenJanuary 29, 2016Jan 29, 201601/29/16

A customer was observing strange behavior in their application with handles and the thread pool. We have a service that spawns a child process, and under certain conditions, we need to terminate that child process. If I try to terminate the process immediately upon the condition being met, then everything works. But now we want to wait a ...

Why is getting the HP_HASHSIZE so weird?

Raymond ChenJanuary 28, 2016Jan 28, 201601/28/16

A comment on the documentation page for CryptGetHashParam notes that the "obvious" way to get the HP_HASHSIZE is incorrect. What's going on here? I mean, the documentation says that if you want to get the size of a parameter, you pass nullptr for the buffer, and the DWORD* parameter gets the size of the buffer. So if I ...

Why does CryptDestroyHash crash, but only sometimes?

Raymond ChenJanuary 27, 2016Jan 27, 201601/27/16

A customer was having a problem with the cryptographic hashing functions. They reported that their function ran successfully most of the time, but once in a while, it crashed at the call to CryptDestroyHash: The reason for the crash is straightforward. As noted in the documentation, you must call CryptDestroyHash before ...

Some senior executives are afraid to provide feedback, because they know that their feedback will be given too much weight

Raymond ChenJanuary 26, 2016Jan 26, 201601/26/16

I recall a conversation I had with Steve Sinofsky, back when he was in charge of Windows. As you might expect, he gets to see early versions of a lot of things, his laptop is running dogfood everything, and everybody is asking for feedback. And he rarely gives any.¹ Not because he's a jerk, but because he understands that if he provides...

How can I tell whether my console program was launched from Explorer or from a command prompt?

Raymond ChenJanuary 25, 2016Jan 25, 201601/25/16

So you have a console program. This console program could be run by typing its name at the command prompt, or it could be run by the user double-clicking it from Explorer. And you want to know which case you're in. This is another case of digging into the question to find the problem. In this case, the problem is "Well, if I'm run directly ...

If I’m going to store a SID in a file, should I store the string form or the binary form?

Raymond ChenJanuary 22, 2016Jan 22, 201601/22/16

A customer needed to save some user SIDs into a file and wanted guidance on whether to use string format or binary format. Here are some pros and cons. String format: To save the SID, use the ConvertSidToStringSid function, then save the string to the file. To load the SID, read the string from the file, then call Convert...

What does the /V (verify) flag to XCOPY mean, and how did it get that way?

Raymond ChenJanuary 21, 2016Jan 21, 201601/21/16

The XCOPY command has a flag called /V, which stands for verify. Sort of. First, the easy question: What does this flag do? Answer: If this flag is set, then after a file is copied, the XCOPY program will verify that the source and destination files are the same size. As you might surmise, this doesn't really get you much. On top of that, ...

So how bad is it that I’m calling RegOpenKey instead of RegOpenKeyEx?

Raymond ChenJanuary 20, 2016Jan 20, 201601/20/16

A customer had some code that called the RegOpenKey function and was concerned by the remark in MSDN: Note This function is provided only for compatibility with 16-bit versions of Windows. Applications should use the RegOpenKeyEx function. What are the dire consequences of using this old function instead of the new one? In ...

What makes XCOPY so X?

Raymond ChenJanuary 19, 2016Jan 19, 201601/19/16

There's COPY and there's XCOPY. First things first: I don't know what the X stands for. Extra? Exorbitant? Excellent? My guess is Extended, but it's just a guess. The built-in MS-DOS COPY command copied one file at a time. This was a real pain if you wanted to copy a bunch of files from one floppy disk to another, and you had a single-floppy ...

Some notes about the blog migration

Raymond ChenJanuary 18, 2016Jan 18, 201601/18/16

I've opened a number of tickets with the blog migration team. Some of the issues have been fixed. The most significant remaining one is that many redirects from the old site are still broken. In particular, the old URL http://blogs.msdn.com/b/oldnewthing/archive/yyyy/mm/dd/nnnn.aspx redirects to https://blogs.msdn.microsoft.com/oldnewthing/...

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