Review Request 128473: Avoid recursive calls to QPlatformTheme::createPlatformSystemTrayIcon()

David Edmundson david at davidedmundson.co.uk
Mon Aug 8 11:24:25 UTC 2016 


> On July 19, 2016, 4:02 a.m., David Edmundson wrote:
> > KStatusNotifierItemPrivate::setLegacySystemTrayEnabled(bool enabled)
> > already has a recursion check added in b45544f3d4dd9cb1873b92a609f45a68f5f6e471  (in knotifications) - which basically checks if we're using the KDE platform theme (albeit in a slightly weird way)
> > 
> > Not saying yours is "worse" but we don't want two fixes in two places.
> > 
> > Could you check you have that patch? and why it doesn't work?
> 
> Martin Tobias Holmedahl Sandsmark wrote:
>     firstly, as you said, it checks in a weird way, which doesn't work, that's why I thought it made more sense to fix it in the platform theme itself which already knows that it is loaded and whether an SNI host is available.
>     
>     (fwiw, qApp->platformName() is not correct either, that's what I thought was the "proper" way to do it)
> 
> Martin Tobias Holmedahl Sandsmark wrote:
>     patching around that also leads to no legacy tray icon being created at all, which is obviously wrong.
> 
> David Edmundson wrote:
>     Is it wrong?
>     
>     If you're logged in to a plasma session with the plasma integration running it's a valid assumption that people will run Plasmashell. 
>     
>     Without plasmashell you won't get the legacy tray icons appearing either. 
>     
>     And if you're running a different shell..you shouldn't be using the plasma integration in the first place.
> 
> Martin Tobias Holmedahl Sandsmark wrote:
>     The legacy tray icons will work in cases where SNI won't, so breaking that fallback is wrong in my opinion, but I agree it is better than the alternative.
>     
>     Anyhow, this is a mess and the interdependencies on behaviour is bad. IMHO it should be "fixed" in both places, the plasma-integration plugin shouldn't rely on some shaky string magic logic in KSNI not to hang applications.
>     
>     So if the only objection to this patch is that some applications a) under X11 get a legacy tray icon instead of a SNI one if started too early instead of hanging, b) under Wayland might not get a tray icon at all instead of just hanging if started too early, I think this should go in.
> 
> David Edmundson wrote:
>     >The legacy tray icons will work in cases where SNI won't
>     
>     How? If Plasmashell is running you get the SNIs. If plasmashell is not running you don't get the legacy icons anyway.
>     
>     It's not going in until you can explain:
>     1) why this is needed
>     2) why the other patch doesn't work.
> 
> Martin Tobias Holmedahl Sandsmark wrote:
>     > How? If Plasmashell is running you get the SNIs. If plasmashell is not running you don't get the legacy icons anyway.
>     
>     Because they're very different technologies with very different kinds of bugs? There's a reason the fallback is there already.
>     
>     and that's just the unintended ways it can fail, then you have users that for some reasons intentionally don't run plasma-shell with the default settings, use another tray solution, etc.
>     
>     
>     > 2) why the other patch doesn't work.
>     
>     The other patch won't work because it doesn't know if the plasma integration plugin is loaded. it's also the wrong place to put those kinds of checks, even if you would find a 100% bulletproof bug free way to detect that. hardcoding in fixes for bugs in platform plugins (e. g. if another platform plugin decides to do the same) is wrong.
>     
>     and as already demonstrated, it doesn't work well in practice.
>     
>     
>     > 1) why this is needed
>     
>     to avoid applications hanging/crashing, approach the zen of failing gracefully, and in general make this a bit more robust.
>     
>     imho, this shouldn't even be using the same KSNI classes that applications are supposed to use, it's a design error that leads to these kinds of problems, but this makes it a bit more sane.
>     
>     
>     but this discussion was absurd several posts ago, and it's not getting better...
> 
> Martin Gräßlin wrote:
>     So could you please explain why the existing solution doesn't work and why this is needed in addition? We just try to understand and whether there are things we need to change in KNotifications.
>     
>     Btw. the fact that this will break SNIs during startup in a racy way on Wayland is a reason for me to not make it go in. We need to start thinking about the "can break in Wayland" cases more, after all there are people using it productivly ;-)
> 
> Martin Tobias Holmedahl Sandsmark wrote:
>     Sorry for the late reply, dayjob started up again. :-)
>     
>     
>     > So could you please explain why the existing solution doesn't work [...]
>     
>     I'll try to summarize:
>     
>     * It has the same race condition problem that you say this patch has, only worse, as far as I can tell. If a SNI is unavailable on startup of the application, the application won't even get a legacy tray icon on X11, and nothing on Wayland.
>     * A fundemental problem is that KNotifications does not have a (robust) way of knowing whether plasma-integration is used. The current hack to try to do this seems to break for various users. I tried with a patch to use «qgetenv("QT_QPA_PLATFORMTHEME") == "kde"» in addition to the existing checks, but it didn't seem to be enough.
>     * An "ideological" reason is that putting hacks in a framework like KNotifications for plasma-integration is wrong.
>     * People might run a plasma session without SNI. I'm not sure how realistic this is, though, but I don't think applications should crash and burn even in this case.
>     
>     
>     > [...] and why this is needed in addition?
>     
>     The hack in KNotifications should be removed eventually, IMHO, this is a replacement not an addition to the existing fix/solution.
>     
>     
>     > We need to start thinking about the "can break in Wayland" cases more, after all there are people using it productivly ;-)
>     
>     I agree, I'd like to move to wayland soon myself. :-)
>     
>     But this patch won't break anything on Wayland that isn't broken already.
>     
>     
>     I don't really have any good ideas for how to fix it properly. Maybe using dbus activation somehow? Or a proxy SNI "host" that allows applications to connect even if the full plasma session isn't up and running yet?

>It has the same race condition problem that you say this patch has, only worse.

That's not the case.

Currently with the race condition case the app will get a KSNI object. That will go into legacy mode, fail the env check and do nothing. Plasma will load, then it will call checkForRegisteredHosts, setLegacyMode(false) and create a 100% working SNI.

With ths modification the user will end up with either:
  - a half-working icon via xembedsniproxy
  - a floating window with an icon in
  - absolutley nothing.

>From our position, that's obviously an unnaceptable step backwards. 

That assumes a working Plasma setup and for apps to correct have the env vars set by startkde.
(obviously, that's not the case on *your* system - though I still don't know what, which is what we've tried asking multiple times.)

> Or a proxy SNI "host" that allows applications to connect even if the full plasma session isn't up and running yet?

This sort of exists, there is the SNI watcher which is a KDED module which is what clients register to.
A host (Plasma) talks to the watcher, which tells it where clients are. 
>From a pure SNI API point of view, clients can register to the watcher before a host exists.

Or:
We could just add a setAllowLegacyFallBack(bool) to kstatusnotifier item which our QPT can then use.
Or even a qApp->setProperty("") in the QPT constructor and check in the KSNI code.
Or we can copy/paste the DBus code from KSNI into here. It's not too much code.


- David


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On July 17, 2016, 8:14 p.m., Martin Tobias Holmedahl Sandsmark wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://git.reviewboard.kde.org/r/128473/
> -----------------------------------------------------------
> 
> (Updated July 17, 2016, 8:14 p.m.)
> 
> 
> Review request for Plasma.
> 
> 
> Repository: plasma-integration
> 
> 
> Description
> -------
> 
> If the status notifier item host is not available, KSNI tries to create a normal QSystemTrayIcon.
> 
> The plasma platform plugin uses KSNI when it is called to create a QPlatformSystemTrayIcon.
> 
> So if the status notifier item host for any reason was unavailable, this would recursively run forever (assuming a turing machine with infinite memory).
> 
> 
> Diffs
> -----
> 
>   src/platformtheme/kdeplatformsystemtrayicon.h 6825b4d 
>   src/platformtheme/kdeplatformsystemtrayicon.cpp 0e82385 
>   src/platformtheme/kdeplatformtheme.cpp 5f0407c 
> 
> Diff: https://git.reviewboard.kde.org/r/128473/diff/
> 
> 
> Testing
> -------
> 
> Now it is possible to run applications that have tray icons with the plasma platform plugin even when the status notifier item host is down or unavailable.
> 
> 
> Thanks,
> 
> Martin Tobias Holmedahl Sandsmark
> 
>

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