Bug 256709 - KDevelop freezes when stopping project build
Summary: KDevelop freezes when stopping project build
Alias: None
Product: kdevplatform
Classification: Developer tools
Component: project (show other bugs)
Version: 0.9.94
Platform: openSUSE Linux
: HI major
Target Milestone: 1.2.0
Assignee: kdevelop-bugs-null
Depends on:
Reported: 2010-11-12 15:54 UTC by Valerio Pilo
Modified: 2011-07-04 05:44 UTC (History)
1 user (show)

See Also:
Latest Commit:
Version Fixed In:

First time the freeze happened (14.70 KB, text/x-log)
2010-11-12 15:54 UTC, Valerio Pilo
Second time the freeze happened (12.78 KB, text/x-log)
2010-11-12 15:54 UTC, Valerio Pilo

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Description Valerio Pilo 2010-11-12 15:54:17 UTC
Created attachment 53363 [details]
First time the freeze happened

Version:           4.1.0 (using KDE 4.5.3) 
OS:                Linux

Pressing Esc or clicking the Stop button while a CMake+Qt4 project is building makes KDev to freeze.

The problem is reproducible with my project; I tried creating a new CMake+Qt4 project and restarting KDev, but with that project I couldn't make it to freeze.

Reproducible: Always

Steps to Reproduce:
1) Open a complex CMake+Qt4 project (mine has 3 targets each linking a common static library).
2) Remove/empty the builddir so it'll rebuild from scratch.
3) Start building the whole project.
4) Press Esc or activate the Stop All Processes QAction.

Actual Results:  
KDevelop hangs.

Expected Results:  
The build process gets stopped.

I've reproduced the issue a number of times and debugged it in GDB. I'm attaching two backtraces.

I cannot link you the project I'm getting the bug on (closed development for work) but I'm available on IRC to help you better pinpoint the issue. I'm vpilo on IRC@freenode.
Comment 1 Valerio Pilo 2010-11-12 15:54:41 UTC
Created attachment 53364 [details]
Second time the freeze happened
Comment 2 Olivier.jg 2010-12-16 08:39:43 UTC
This actually isn't related to the biuld job.

Easy reproduction:
Open or Reload KDevelop (or other largish project)
Press stop

Thread #1 hangs after importProjectJob.cpp:104 (d->m_watcher->waitForFinished();)
That call to waitForFinished() happens after the requisite d->m_watcher->cancel();

Qt Docs for that cancel() function say:
"Be aware that not all asynchronous computations can be canceled. For example, the future returned by QtConcurrent::run() cannot be canceled;"
That watcher is indeed watching a QFuture that is started by QtConcurrent::run(). 

Presumably an import job, when created, should not be created with "setCapabilities(Killable)" (importProjectJob.cpp:66). This fixes it for me.
Or perhaps it should be run in such a way that it can be safely canceled.

Not sure which is preferable, so passing this on to whoever knows this code.
Comment 3 Olivier.jg 2010-12-16 08:43:19 UTC
Confirmed, and not a crash bug, but an easy to hit deadlock.
Comment 4 Milian Wolff 2010-12-16 17:03:13 UTC
see also: http://lists.kde.org/?l=kdevelop-devel&m=129027254932711&w=2
Comment 5 Olivier.jg 2011-06-13 11:16:32 UTC
More information on this:
When you stop a project import, the main thread will wait for the project reload to finish. Unfortunately, in the case of a project import, there's often a bit of projectModel work being done, this involves signals being sent to the model using a BlockingQueuedConnection (in particular, this happens in ProjectBaseItem::setText). So, deadlock.

Changing that to a QueuedConnection fixes that, but often CMakeManager will end up crashing with an assert instead (most probably unrelated to the QueuedConnection change, from what I can see).

So, once again, why are ProjectImportJobs killable?

Even when it works, the best you have is a useless half-open project. The fact that it doesn't work at all for at least two unrelated reasons means it should at least be disabled until it works, I think.
Comment 6 Milian Wolff 2011-06-17 23:12:55 UTC
if making it un-killable workarounds the bug please commit that hotfix.
Comment 7 Olivier.jg 2011-07-04 05:44:09 UTC
Git commit 30fb0611a497ed69ff90c9bee9c84f281223817b by Olivier JG.
Committed on 04/07/2011 at 07:32.
Pushed by olivierjg into branch 'master'.

ProjectImportJob killing causes deadlocks/crashes.
Until it works properly, don't make it killable.
BUG: 256709

M  +0    -2    project/importprojectjob.cpp