Segfault on shutdown due to thread building meta data cache still running

[agx]

Symptoms: phosh test case the involves building the meta data cache segfaults sporadically when built with clang.

Details: https://gitlab.gnome.org/World/Phosh/phosh/-/issues/1240

Backtrace: https://gitlab.gnome.org/-/project/16747/uploads/bcccb0e53f4315a7b0027b7e1adf1130/backtrace-all-threads-2.txt

As far as I can tell we're cancelling correctly but it seems as_pool_update_desktop_entries_table is not being terminated. I think
as_pool_load_thread needs to call g_task_set_return_on_cancel`. @ximion if that makes sense I could look at a fix.

[ximion]

Hmm... It does make some sense, however, I wonder if this isn't actually the bug fixed in d4fbd56 instead. Which version of AppStream are you using? Anything >= 1.0.4 should have this fixed.

[agx]

No idea which version but from what @CyberTailor usually reports I'd assume pretty recent.

I've asked the reporter in the corresponding phosh issue to follow up here.

[ximion]

That makes sense, thank you! :-)

I have not been able to reproduce this, but given that it's intermittent, that may not mean much (I also have only tried with the most recent version of AppStream).