cursor interactions cause lockup with pocket desktop

not quite sure if its a mir problem or a qtmir+u8 problem, so will tag both.

Steps for pocked desktop setup:
https://docs.google.com/document/d/1gfLy7cBHHwZXD0t74tqYpHvw60W5nc_qJoYUiU4A6mo/edit#

Package versions of qtmir+u8+mirserver, as well as the system-image-cli. (installed on frieza)

I noticed this first during mir 0.23.0 release testing... so wanted to see if it was a the race was any better or worse with 0.23.0 vs 0.22.1.

So, did a quick manual check of time to failure on 0.23.0 and 0.22.1. (attached). Seems its just about as prevalent on each version of mir. This doesn't exonerate mir altogether, but IMO, should let us proceed with the 0.23.0 release.

There is a known bug where libmirclient crashes on Xmir cursor updates -> bug 1506358
Please check your Xmir has not crashed (so this bug is not a duplicate of that one)

If this was bug 1506358 though I would expect Unity8 to keep working and not freeze the whole desktop. But Unity8 might not be able to survive bug 1506358 as well as the Mir demo servers(?).

Please also check Unity8 lockup bug 1588534

Xmir does not appear to have crashed. I don't think this is bug 1506358, as that exception isn't seen, and it appears to be the Qt renderloop/renderthread that is locked up.

Cause seems to be a busy loop in QQuickSpriteEngine::assembledImage() triggered by changing between bitmap cursors (as opposed to named cursors).

It's a but in Qt triggered by the peculiar way unity8 uses AnimatedSprite QML Type

s/but/bug

Qt bug:
https://bugreports.qt.io/browse/QTBUG-53937

Fix for bug in qtdeclarative:
https://codereview.qt-project.org/#/c/161896/

This bug was fixed in the package unity8 - 8.12+16.10.20160617-0ubuntu1

---------------
unity8 (8.12+16.10.20160617-0ubuntu1) yakkety; urgency=medium

  [ Michael Terry ]
  * Do not create Label/Icon if we don't need it
  * Fix Z-ordering of prompt surfaces (LP: #1586219)
  * Drop bottom edge tutorials completely and small fixes for other
    edges. (LP: #1565103)
  * Redo visuals for greeter prompt box. (LP: #1435923)
  * Make tutorial qmltests more robust. (LP: #1590810)
  * Stop showing an extra lockscreen in desktop unity8 sessions. (LP:
    #1582987)

  [ Albert Astals Cid ]
  * Improve dash plugin mock
  * Stabilize PreviewExpandableTest::test_all_widgets_height
  * Workaround QTBUG-53460
  * Split artShape code for cardTool card and regular card
  * Simplify the code since fixedArtSize code is mandatory for regular
    cards
  * Desktop stage: Support rotatesWindowContents (LP: #1547481)
  * Turn if if else into if elseif else
  * Fix leaks in QInputDeviceManagerPrivate::addDevice
  * Do not call |= on uninitialized sigterm.sa_flags
  * initialize udevMonitor
  * Make notifier and notifierFd function local variables
  * Fix crash if a component that is not an Item is given to
    sectionDelegate
  * Tests: Do not use dynamic_cast if we're not going to test it anyway
  * Minor coverity fixes
  * Fix warning about anchors.fill in ProportionalShape (LP: #1590963)
  * Make wait in cleanup() wait for snapTo animation to have finished

  [ Alexandros Frantzis ]
  * Improve the way notifications interact with power management (LP:
    #1570922)

  [ Andrea Cimitan ]
  * Correctly refresh cardcreator cache on artshapestyle changes (LP:
    #1588335)
  * Same tweaks we have for click scope now for libertine
  * add a timer to pull to refresh to work on small windows (LP:
    #1589060)

  [ Daniel d'Andrada ]
  * Clean up debug leftovers
  * Ensure mouse and window movement are pixel-aligned (LP: #1510382)
  * Fix SpreadDelegate rotation animations
  * No point in version-controlling files that are automatically
    generated
  * Center cursor on screen when it's first shown
  * Custom cursor name just have to start with "custom"
  * Work around AnimatedSprite infinite loop bug (LP: #1588929)

  [ Josh Arenson ]
  * Disable showDash when it is already shown. (LP: #1506708)
  * Add a timestamp to the dash log (LP: #1580074)
  * Add timestamp to unity8 log (LP: #1498169)

  [ Lukáš Tinkl ]
  * Implement keyboard shortcuts info panel
  * Implement window controls overlay activatable with 3 fingers tap
    (LP: #1489020)
  * Select correct Chinese input method for OSK in the wizard (LP:
    #1588633)

  [ Michael Zanetti ]
  * Add support for the launcher surface pips displaying the correct
    number of surfaces
  * Add support for the persistent alert state. (LP: #1575147, #1584348,
    #1586621)
  * send a Alt-release event on alt+tab instead of delaying it
    completely and invoking it later (LP: #1565236)

  [ Stephen M. Webb ]
  * added a new upstart $SESSION for unity8-desktop-session (LP:
    #1376715)

 -- Michael Terry <email address hidden> Fri, 17 Jun 2016 01:22:57 +0000