Evaluation Example Dock Widgets Hangs Windows

[inflector]

I am in the process of evaulating Qt but was dismayed to have encountered a problem within five minutes of starting to use the sample application on Windows XP with the latest automatic updates from Microsoft.

Our application uses MFC which sucks so bad that I am looking for a replacement. The application requires the use of dockable windows so I launched the Dock Widgets example. Here is what I did:

1) Clicked the undock/zoom icon on the "Customers" widget.
2) Tried to drag it

This resulted in a loss of mouse responsiveness, like there is something capturing the mouse and not releasing it. Clicking on other applications does not work. Clicking on anything has no effect once this happens.

Hitting Ctrl-Alt-Delete to bring up the Task Manager does fix the problem until you try to drag that customers widget again. Sometimes after hitting Ctrl-Alt-Delete when you move the mouse over the example window it acts like the mouse is down and the Customers window will follow the cursor as if you were dragging it until you click again. The same behavior results from trying to undock and drag the "Paragraphs" widget.

Does this happen for anyone else? The previous Qt 4.1 version of the demo worked fine when I tried it about 6 months ago. I did not get this behavior.

Is this a bug in Qt or the Example code that was not updated for 4.2? One would think that the Examples would be part of the standard regression suite.

I'm looking for some reasonable explanation. I don't have the source to Qt so I have no way of debugging this issue myself.

- Curtis

[wysota]

I'm sure the examples work fine. They are tested before each release of Qt, so you must be experiencing some abnormal behaviour. Are you sure it is caused by Qt? Could you try the application on a different computer? Which exact version of Qt do you use? Does the Designer work correctly? It has dock windows as well, so you can easily check if they are working correct there. I know there are some issues with dock windows, but different from the ones you describe.

[inflector]

I am using Qt 4.2.2 Evaluation which I just downloaded today. I previously partially evaluated Qt 4.1 and did not have this problem but that was admittedly with another machine. I am running Windows XP on a Lenovo T60p laptop.

I cannot try the application on another computer at this time as I recently moved to Buenos Aires, Argentina and have only this laptop for the moment. I probably won't have access to another machine until after the first of the year.

Interestingly, the Qt Designer has exactly the same problem on my machine.

I don't see how it could be caused by anything other than Qt since I have never seen this behavior before in any other applications on this machine and every single time I try to drag on of the dockable windows I get the same exact repeatable problem.

I am running TPOSTCW* but it doesn't have this problem with any other applications.

I concede there could be something unusual about my machine, however, it does seem strange that mouse capturing would be broken in two different applications in a repeatable way. My machine is fairly new but not so new that there should be unkown mouse driver problems. Even if I had these it seems unlikely they would only show up while using Qt.

I have previously worked using MFC to handle dragging and had some similar problems in my own code when I didn't implement the mouse event capturing properly so I suspect some interaction with Qt 4.2's dock windows and Windows that was not caught in QA. This does seem like the kind of thing that others would have noticed previously however.

If you have a Windows machine running XP does this problem not happen for you?

- Curtis


* That Piece of Shit They Call Windows

[inflector]

Funny, I just read your reply to another question and noted the reference to the but database entry there. Thinking that it was likely to be a reported bug if anyone saw this before I searched for dock and mouse and found the following:

http://www.trolltech.com/developer/task-tracker/index_html?method=entry&id=135008

This appears to describe a cause which would give the symptoms I am seeing based on my previous experience having screwed this up myself before (repeat after me "I hate Windows"). It also seems to be a problem introduced in 4.2 which fits my experience.

Unfortunately, I can't evaluate 4.3.

- Curtis

[inflector]

Oh, one more possibliity.

It may be that this problem does not show up unless you are running a dual processor machine just based on the way threading works on single versus dual processor machines. This would explain why something so obvious as dragging a dockable window in the dockable window application wasn't picked up by QA.

This is something fairly new in the Core Duo laptops like the T60p.

It is possible that on a single processor machine there not enough processing for background applications for them to get to this state.

- Curtis

[Rick]

I had the exact same problem.
I've got a Thinkpad R50p (single core pentium mobile 1.6GHz) with a custom Dutch Windows XP installation.

I fixed it by reinstalling QT and rebooting after it, I don't know why it worked but it worked.

[Brandybuck]

If you have a Windows machine running XP does this problem not happen for you?

I have a Thinkpad T60, WinXP Pro, current updates, and commercial (non-eval) Qt-4.2.2, and I am not seeing this problem.