[Bug 22119] New: [api-break] Proxies should not emit 'invalidated' when disposing.

[bugzilla-daemon at freedesktop.org]

http://bugs.freedesktop.org/show_bug.cgi?id=22119

           Summary: [api-break] Proxies should not emit 'invalidated' when
                    disposing.
           Product: Telepathy
           Version: unspecified
          Platform: Other
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: telepathy-glib
        AssignedTo: telepathy-bugs at lists.freedesktop.org
        ReportedBy: will.thompson at collabora.co.uk


I've just run into a bug in Empathy, whose root cause is that TpProxy emits
'invalidated' when it's being disposed. The bug is as follows:

* EmpathyTpContactList keeps a ref to each of a connection's Group channels in
a hash table.
* When a Group channel is invalidated, it cleans up, and removes them from the
hash table (unreffing them).

So far, so good. Now:

* If a new Group channel appears with the same name as an existing one (this
could be argued to be the real bug in Empathy: I think this happened because
the old Idle connection didn't die before Empathy tried to reconnect, so the
old Group channel proxies were still hanging around), it replaces the old
channel in the hash table.
* Replacing the old group unrefs it.
* The old group's refcount hits zero, so it's disposed, and emits Invalidated
(raising its refcount temporarily to 1).
* Empathy's invalidated callback fires, and removes the group from the the hash
table, unreffing it (a second time!).
* The refcount hits zero again, but TpChannel's dispose() is not idempotent so
everyone dies (patch to follow).

I don't think that TpProxies should emit 'invalidated' when they're disposed.
If you care about a proxy's validity, you should own a ref to it. Conflating an
object's spiritual lifecycle (whether it's 'valid') with its C lifecycle seems
to be the root of a number of bugs (see also: the conflation in CMs between
channels being unreffed and emitting Closed, leading to hacks to break loops:
#20946). We can't change this without breaking the TpProxy API, sadly.


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