Document Viewer app freezes/crashes on clicking back from pdf files

[Kristijan Žic ]

Device: mako
Channel: rc-proposed

App freezes every time on clicking back arrow when trying to close pdf files and go back to the documents list.
The only solution seems to be closing the app every time I want to open other pdf.
On some occasions, the app will crash by itself when getting out of an pdf.

[EDIT]:
Former DocViewer contributor Stefano Verzegnassi took a look at this bug so I'll just paste his response here:

I've found a few minutes for having a look at this issue, and I guess this has nothing to do with Document Viewer. The component which causes the issue hasn't received any update since an year.

The issue in the DocViewer seems to be the same described in bug #1568016, which sounds to me as a regression in the UI Toolkit.

During the last months a lot of regressions have been introduced with any UITK update, because critical changes are directly committed to a stable target.
As long as core apps should always target the latest version of the toolkit, it should also be granted that a new toolkit update does not break any core app functionality.

Anyway, since the UITK team is actually rewriting many components, I suspect the faulty component of the PDF viewer should be entirely rewritten too, since there's a small chance the issue gets fixed upstream (and that's what they did with the issue at the link below).

I'm no more an active contributor of the Ubuntu Document Viewer, and whoever will join the team should also take care of fixing this.

https://bugs.launchpad.net/ubuntu/+source/ubuntu-ui-toolkit/+bug/1568016

[Kristijan Žic  (kristijan-zic)]

Adding a video that shows the bug.

[Anupam (anupam207)]

In case of my E5 phone, the app actually closes after pressing back.

[Pat McGowan (pat-mcgowan)]

The referenced UITK fix was landed and the crash is still happening. I assume the hang is while apport is writing the crash file, as subsequent tests crash immediately.

[Pat McGowan (pat-mcgowan)]

@timp any idea whats happening here?

[adam plaice (adam.plaice)]

I'm not sure if it's relevant, but the crash also occurs when importing a pdf from elsewhere (e.g. the web browser).

To reproduce:
Open a pdf in the Document viewer
Switch to the web browser (without closing the Document viewer)
Navigate to a pdf on the web
Select "Choose an application" -> "Document viewer"
Upon "Download complete" -> "Open"

Document viewer briefly appears (with the previous document visible) and crashes

The crash does not occur when the Document viewer is closed before switching or the screen in the Document viewer, that one switches away from, is the document list, suggesting that this is the same bug as above.

(FWIW I'm also affected by the bug when simply pressing the back button within the Document viewer.)

(Device: BQ E5 (vegetahd))

[Tim Peeters (tpeeters)]

Confirmed in image r562 on Krillin.

[Tim Peeters (tpeeters)]

Something strange is happening with VerticalView of poppler-qml-plugin. When destroying the page displaying the PDF, the VerticalView in QML reports that it is being destroyed (I added Component.onDestruction: print("destroying VerticalView"), but it is not yet being fully destroyed, and in C++ when calling .isNull() on the VerticalView, it appears to return false.

In ucheader.cpp we detect a change in the header visibility (it is made invisible because it is also being destroyed) which triggers an update in the flickable margins. We always first check there that the flickable is still valide using m_flickable.isNull(), which reports that the flickable is still valid. However, when calling functions on m_flickable, we get a segfault.

This is weird and requires further investigation. But I will attach a branch with a workaround for the document viewer.

[Tim Peeters (tpeeters)]

The workaround is here https://code.launchpad.net/~tpeeters/ubuntu-docviewer-app/bug1577277-workaround/+merge/304561

I did not mark it yet as fixing the bug because the cause needs further investigation. But the workaround will do it now if we need a quick fix.

[Jenkins Bot (ubuntu-core-apps-jenkins-bot)]

Fix committed into lp:ubuntu-docviewer-app at revision 350, scheduled for release in ubuntu-docviewer-app, milestone ww02-2016