July 2016 | The Old New Thing

Further discussion of the synchronization barrier

Raymond ChenJuly 29, 2016Jul 29, 201607/29/16

The synchronization barrier is apparently more confusing than I expected. The basic idea of the synchronization barrier is that you want to each participant in some coordinated activity to wait until every participant has reached a particular state. Once the last participant reaches the desired state, all the participants are released to go ...

How can I check whether a parameter is a pointer to a stack variable?

Raymond ChenJuly 28, 2016Jul 28, 201607/28/16

A customer traced a bug in their program back to the fact that somebody passed a stack buffer to a function that operates asynchronously. Something like this: This bug led to the destination sometimes receiving corrupted data because it was a race between the stack variable being reused for something else and the data transport code copying ...

Why does setting the horizontal scroll bar range for the first time also set the vertical range, and vice versa?

Raymond ChenJuly 27, 2016Jul 27, 201607/27/16

A customer observed that if a window has never set any scroll bar parameters, then it reports its scroll bar range as nMin = nMax = 0 in both horizonal and vertical directions. But once you set the (say) horizontal scroll bar range to anything (say, nMin = 0, nMax = 999), then the vertical scroll bar range reports itself as nMin = 0, nMax = ...

Why does sharing a folder in Explorer grant full permission on the share to everyone?

Raymond ChenJuly 26, 2016Jul 26, 201607/26/16

A customer noticed that when you use Explorer to share a folder with a specific user, Explorer creates a file share with full permissions to everyone. "Why is this needed? Shouldn't it be created with permission only to the user that the folder is being shared to?" Okay, first of all, we should note that there is not a security issue here, ...

Is there a Windows API for IntelliSense?

Raymond ChenJuly 25, 2016Jul 25, 201607/25/16

A customer had a question, forwarded to the operating system group via the customer liaison. "My customer is developing an IDE and they want to implement the IntelliSense feature. We have been unable to find any documents explaining how to do this. Is there an API for this, or can you recommend a third-party SDK?" IntelliSense isn't really ...

What is the significance of changing the registration for CLSIDs to point to a private copy of MSXML3?

Raymond ChenJuly 22, 2016Jul 22, 201607/22/16

A customer reported that several of their applications stopped working after they installed a third-party program, let's call it Contoso Deluxe. They found that the Contoso Deluxe program, as part of its installation, rewrote some CLSID registrations. For example, HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{F5078F37-C551-11D3-89B9-0000F81FE221...

If you don’t want the changes to be permanent, the don’t pass the flag that says that you want the changes to be permanent

Raymond ChenJuly 21, 2016Jul 21, 201607/21/16

A customer wanted to make a change to a system setting. We advised them to use the SystemParametersInfo function, adding The SystemParametersInfo function lets you specify whether you want the change to be permanent or this-session-only. The customer wrote back, Were trying to figure out whether there is a way for the ...

Microspeak: Tick-tock

Raymond ChenJuly 20, 2016Jul 20, 201607/20/16

As you might imagine, there's a lot of stuff that needs to happen on the opening day of //build. For //build 2016, my job was to publish the new samples to the Github repo. And //build 2016 was when I was introduced to the term tick-tock: Please review your items in the tick tock from a timing perspective and send me any corrections. Visual ...

Having trouble with Windows Hello face recognition? Try a Jedi mind trick!

Raymond ChenJuly 19, 2016Jul 19, 201607/19/16

[Note: This was originally titled "Windows Hello face recognition is vulnerable to the Jedi mind trick" but many people overreacted to the the word "vulnerable".] Here's a handy tip if you use Windows Hello face recognition, which is available on the Surface Pro 4, Surface Book and a number of other devices: If the device doesn't recognize ...

When I tell Windows to compress a file, the compression is far worse than I get if I ask WinZip to compress the file; why is that?

Raymond ChenJuly 18, 2016Jul 18, 201607/18/16

A customer noted that when they took a very large (multiple gigabyte) file and went to the file's Properties and set "Compress contents to save disk space", the file shrunk by 25%. And then they needed to copy the file to a USB stick, so they used an old copy of WinZip to compress the file, and the result was half the size of the original. ...

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