[Kde-pim] Review Request 120999: don't handle events for systray when shutting down, avoiding null pointer dereference and crash

[René J.V. Bertin]

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https://git.reviewboard.kde.org/r/120999/
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Review request for KDEPIM.


Repository: kdepim


Description
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When quitting kontact or kmail through the quit menu action it is not impossible that the process will remain active for a certain time, or even blocked in `KMKernel::cleanup()` (for instance when stuck in the "Retrieving Folder Contents" screen). During that time, kmail's systray entry will remain accessible.
The documentation for `KJob::exec` (used in `KMKernel::cleanup()`) claims that its nested event loop does not propagate UI events, but despite this, a right-click on the systray icon will result in UI events that will ultimately lead to a null pointer dereference and a crash. See the backtrace in https://bugs.kde.org/show_bug.cgi?id=340624 .

The patch proposed here prevents this by adding an additional check on `kmkernel->shuttingDown()` in `KMSystemTray::buildPopupMenu()` which prevents the crash. It does not appear to be necessary to protect `KMSystemTray::slotActivated` in a similar way, probably because it bails when there is no main window.

Note that a similar protection *may* be required in the system tray code for the other kontact components, like akregator.


Diffs
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  kmail/kmsystemtray.cpp a960a79 

Diff: https://git.reviewboard.kde.org/r/120999/diff/


Testing
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On Kubuntu 14.04 with KDE 4.14.2 from the kubuntu-backports PPA, and my own ppa:rjvbertin/kdepim .
With this patch, kontact can still get stuck in `KMKernel::cleanup` when struck by the frozen Retrieving Folder Contents syndrome, but right-clicking the systray icon will now bring up a small menu that allows to quit the application completely.

Side-note: this 2-step exit occurs on OS X too, even when exiting without the frozen RFC screen. Only here the global menubar remains visible, with an active Quit menu item.


Thanks,

René J.V. Bertin

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