[pdfPlugin] Multithreading does not work properly on ARM SoC

[Stefano Verzegnassi]

While loading a PDF document, the number of image providers is set based on the value returned by QThread::idealThreadCount()[1].
On the latest ARM architectures, some of the cores of a SoC may be temporarily turned off, in order to improved the power consumption.
This may cause a wrong number of initialized image providers (e.g. only 2 image providers on a quad-core CPU).

[1]: http://doc.qt.io/qt-4.8/qthread.html#idealThreadCount

[Ubuntu Phone Apps Jenkins Bot (ubuntu-phone-apps-jenkins-bot)]

Fix committed into lp:ubuntu-docviewer-app at revision 107, scheduled for release in ubuntu-docviewer-app, milestone 2014-10-30

[Stefano Verzegnassi (verzegnassi-stefano)]

Alan Pope's comment during the review of lp:~verzegnassi-stefano/ubuntu-docviewer-app/workaround-fix-1432412 branch:

"Tested on bq device and works fine. We may need to re-visit on meizu device (which runs vivid, and a newer kernel) because it seems to never spin more than 1 core even under heavy load in this app."

I re-mark this report as "triaged", so we can track any progress/discussion about the meizu issue.