IDAaaS Freeze and crash when Browsing to Directory with lots of files

[robertapplin]

Original reporter: Sarah Rogers, Adhip Rahman

Describe the bug
Browsing to a directory from the Manage User Directories dialog on IDAaaS can sometimes freeze Mantid. Then clicking on the X of the dialog causes Mantid to crash. This seems to happen when browsing to directories that contain a large number of files.

To Reproduce

For example

1. Create a Mantid workspace on IDAaaS here https://dev.analysis.stfc.ac.uk/
2. Open ISIS SANS interface
3. Click Manage User Directories
4. Click Browse To Directory
5. Browse to the following directory /archive/NDXLARMOR/Instrument/data/cycle_22_3/. Or another directory containing a large number of files
6. Mantid should freeze.
7. Click on the X for the Browse dialog and Mantid will crash

Expected behavior
There should be no freeze if possible, and no crash.

Platform/Version (please complete the following information):

• IDAaaS

[thomashampson]

Can we confirm that this is a linux only problem and also that it's not specific to IDAaaS?

[MialLewis]

I'm sure this is a not very good test, but I copied the /archive/NDXLARMOR/Instrument/data/cycle_22_3/ folder onto my hard drive and can access it without hang using WSL. If anyone can check with an actual linux machine that would be great.

[thomashampson]

Things to investigate:

• compare 6.4 conda and non-conda version on IDAaaS
• try accessing the same archive directories on linux and IDAaaS
• manid imaging appear to not suffer from the same problem - why not?

[thomashampson]

Thanks to @samtygier-stfc for helping track down a fix for this, see here:
mantidproject/mantidimaging#1742
To summarise:
Mantid imaging's nightly suffers from the same issue since they moved the pyqt5 package installing from pypi to conda-forge. This is because the conda pacakges do no include the GTK integration. See these:
conda-forge/pyqt-feedstock#87
conda-forge/qt-main-feedstock#120
We should be able to fix it by installing the qt-gtk-platformtheme package:
https://github.com/conda-forge/qt-gtk-platformtheme-feedstock

This requires us upgrading qt-core to 5.15.8, which we had pinned back to 5.15.4 due to QTabWidget rendering issues in the instrument viewer and some scientific interfaces (#35013)