SegFault with in `~qSlicerApplicationPrivate` only with SlicerCAT

Development
1

Hi,

When I updated the Slicer commit in my SlicerCAT I started to get Segmentation Fault in qSlicerApplicationPrivate destructor

This happens only with SlicerCAT (clean Slicer app works fine) even when all the modules are disabled ie SlicerCAT is launched with --disable-modules

Here are the steps that leads to this:

  1. launch SlicerCAT
  2. open Application Settings
  3. close Application Settings
  4. close SlicerCAT

It seems that this->SettingsDialog is already somehow unavailable by the time setting setParent(nullptr)
I’ve tried to rebuild it, debug but without success. Even though the idea behind creating/deleting SettingsDialog is pretty clear.

If somebody uses SlicerCAT with recent commits (after 26 february) I would appreciate for testing that.

2

Oh it seems I understand the root of a problem:

At first Settings has no parent at the initilization time

When we click on Application Settings the Settings object gets MainWindow parent. That means MainWindow destructor will delete Settings.

Then in ~qSlicerApplicationPrivate() destructor we are trying to set Settings parent to nullptr and explicitely delete Settings.

But what if ~MainWindow destructor is called before ~qSlicerApplicationPrivate destructor? Then in ~qSlicerApplicationPrivate we will try to access deleted Settings object.

I added cout to these destructors to see who is deleted first and the output is:

$ ./Colada --disable-modules
QXcbConnection: XCB error: 3 (BadWindow), sequence: 1157, resource id: 14779307, major code: 40 (TranslateCoords), minor code: 0
MainWindow destructor is called
Switch to module:  ""
qSlicerApplicationPrivate destructor is called
error: [~/Documents/Colada/d/Slicer-build/bin/./ColadaApp-real] exit abnormally - Report the problem.

That means in my SlicerCAT (I suspect in others too) ~MainWindow is deleted first so there is no need to explicitely delete Settings in ~qSlicerApplicationPrivate destructor.

Please take a look at this

3

The same issue is solved for the Python console, by using a QPointer. It would be great if you could submit a pull request that passes the ownership of the settings dialog similarly to how it is done for the Python console.

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4

Could please show where can I find Python console QPointer solution?
I have an idea how to solve this with QPointer but don’t know anything about python console implementation yet.

5

Search for QPointer and PythonConsole in the source and header files of the Slicer application classes.

1 Like
6

The PR is ready

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