For all of the effort spent ensuring that this algorithm would be
correctly threadsafe, I messed up the order of operations within a
single thread when porting to the new approach.
Fix that up.
Also: fix some overzealous asserting in the testcases. Since shutdown
is now lazy, we can never surely say !is_running at any particular point
in time.
There was a theoretical deadlock between the worker trying to emit a
signal at the same time as we were waiting for it to shutdown the
notification (while holding the lock).
The deadlock was particularly annoying because we didn't really need to
wait for the shutdown and because it wasn't possible to signals to
arrive while waiting for a start. Attempting to deal with start and
stop in an asymmetric way could have lead to other weird situations,
however.
Drop the lock while waiting for the worker thread to start. This means
that we face the possibility of multiple waiters on the cond at the same
time, so we need to make more of a state machine.
https://bugzilla.gnome.org/show_bug.cgi?id=742599
Add a new internal helper called GContextSpecificGroup.
This is a mechanism for helping to maintain a group of context-specific
monitor objects (eg: GAppInfoMonitor, GUnixMountMonitor).
https://bugzilla.gnome.org/show_bug.cgi?id=742599
