Status changed to 'Confirmed' because the bug affects multiple users.
** Changed in: thumbnailer (Ubuntu)
Status: New => Confirmed
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https://bugs.launchpad.net/bugs/1511553
Title:
Crash in queueRequest
Status in thumbnailer package in Ubuntu:
Confirmed
Bug description:
https://errors.ubuntu.com/problem/fa22f0b18ff6dc949c4cdf768f32121d64a83b8d
We hit this occasionally, but not very often. I suspect it is because
of the way we shut down: we destroy the thumbnailer instance before
the dbus interface so we don't hit the race condition where one
instance of the service still has the database lock while a second
instance of the service is activated by a new incoming request. But,
destroying the thumbnailer first means that, if a request arrives at
just the right time, the dbu sinterface fires the request at the
already-destroyed thumbnailer.
I recently hit a whole slew of issues in a test that destroyed the
thumbnailer and dbus interface (in that order) while there were still
requests sitting in the scheduler and thread pools, and fixed a bunch
of these issues (see the request-cancellation branch.) In effect, via
the handler class that calls back into the thumbnailer and the
closures that sit in the thread pools, we have created a circular
dependency between the dbus interface and thumbnailer, which makes it
impossible to shut down either without causing problems.
I think the best solution would be to add a shutdown() method to the
dbus interface that prevents new requests from firing. We also need
some way to wait for all *received* (not just scheduled) requests to
finish executing before physically shutting down.
Does DBus have a way to say "I'm in the process of shutting down. Send
the request that just arrived and that I can't process anymore to a
new instance of the service"? Ideally, I would like to "close the
gate" on incoming requests such that they are transparently re-sent,
and then wait for all currently executing requests to finish
processing.
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