qtcreator hangs when copying to and pasting from clipboard

[Rudolf Leitgeb]

Very frequently, but not every time, I get a multi second long busy hang, when I copy code snippets to or from the clip board. SO farI have observed this behavior only when I use Ctrl+C, Ctrl-X and Ctrl-V, but not when I used the right click menu to perform the exact same action. The hang leaves one CPU running at 100%, during that time qtcreator is completely unresponsive, it does, nevertheless, remember actions (both keyboard and mouse) done during that hang period and catches up when the hang is over. This bug does not happen with other applications (I also tested it with kate which is as similar as it gets).

I would welcome hints how to support the debugging of this issue and can, if needed, compile and run test versions of qtcreator or required software. dmesg and ~/.xsession_erros show nothing related to this issue.

ProblemType: Bug
DistroRelease: Ubuntu 14.10
Package: qtcreator 3.1.1-0ubuntu4
ProcVersionSignature: Ubuntu 3.16.0-28.38-generic 3.16.7-ckt1
Uname: Linux 3.16.0-28-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.14.7-0ubuntu8
Architecture: amd64
CurrentDesktop: KDE
Date: Mon Dec 22 15:05:42 2014
InstallationDate: Installed on 2012-09-25 (817 days ago)
InstallationMedia: Kubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120423)
ProcEnviron:
 LANGUAGE=en_US
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: qtcreator
UpgradeStatus: Upgraded to utopic on 2014-10-28 (55 days ago)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Rudolf Leitgeb (rudolf-leitgeb)]

Just wanted to provide some further info in case it makes tracking down the issue easier:
* The issue is still present on my desktop PC
* I work on the same qtcreator projects on a Thinkpad X220 with Intel graphics and Gnome and this issue does not happen there.
* The hang also happens when I hit Ctrl+S to save a file, therefore I thinks it's rather related to Ctrl-key than clipboard action. The hang does not appear with short cuts which do not depend on Ctrl-key, like Alt+G C for git commit.

[Helgefan (raptor)]

I've got the same problem on two linux desktops (QtCreator 3.2.1).
You just need to hold Ctrl and move the mouse over some code. For every function, variable or class, QtCreator will try to find where it is declared (has to do with the Ctrl+click shortcut to "Follow Symbol Under Cursor", Ctrl without click will already underline variables/functions and turn them blue if QtCreator can find where it is declared). For any reasonably large project, this takes too much time, especially when the declaration is "far away", e.g. in some other project. You have to take great care not to have your mouse cursor over code when using any keyboard shortcut that includes Ctrl.
This bug pretty much broke QtCreator for me...

[Rudolf Leitgeb (rudolf-leitgeb)]

Just wanted to report that this problem is still present in the qtcreator version provided by KUbuntu 15.04, but it shows up in a less annoying way now: Copy&Paste, and many similar operations no longer produce the hang, but holding down Ctrl and hovering the mouse over some code parts still causes minute long hangs (with 100% CPU load on one core).

[Rudolf Leitgeb (rudolf-leitgeb)]

Short update: my initial optimism was unfortunately unfounded, the bug exists as it has for a long time now. Helgefan's description seems to be accurate: the problem arises when one presses Ctrl and then hovers over a symbol. Ctrl+click on that symbol immediately proceeds to the declaration of this symbol, but hovering with the mouse cursor causes the symbol text to change color to blue and underlined, and the system will hang with 100% CPU load for dozens of seconds.

It would be very helpful if I could learn whether Ctrl+mouse hover should trigger some action, what this action is supposed to be, and whether this trigger can be configured out of my system somehow.

[Fabian (fmaier)]

I had the same problem with QtCreator 3.5.1.
After disabling mouse navigation, for me the problem was solved:
Tools > Options > Text Editor > Behavior > Enable mouse navigation