Philip Withnall af6dbece87 tests: Wait until unwatching the gdbus-testserver name has completed
Previously, the code in `ensure_gdbus_testserver_up()` created a proxy
object and watched its `name-owner` to see when the
`com.example.TestService` name appeared.

This ended up subscribing to three signals (one of them for name
ownership, and two unused for properties of the proxy), and was racy. In
particular, the `name-owner` property could be set before all D-Bus
messages had been processed — it could have been derived from getting
the owner of the name, for example.

This left unprocessed messages hanging around in the `context`, but that
context was never iterated again, which essentially leaked the
references held by those messages. That included a reference to the
`GDBusConnection`.

The first part of the fix is to simplify the code to use
`g_bus_watch_name_on_connection()`, so there’s only one signal
subscription to worry about.

The second part of the fix is to use the `GDestroyNotify` callback for
the watch data to be notified of when all D-Bus traffic has been
processed and the signal unsubscription is complete. At this point, it’s
guaranteed that there are no idle callbacks pending in the
`GMainContext`, since the `GDestroyNotify` callback is the last one
invoked on the `GMainContext`.

Essentially, this commit uses the `GDestroyNotify` callback as a
synchronisation message between the D-Bus worker thread and the thread
calling `ensure_gdbus_testserver_up()`.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Fixes: #1515
2020-02-24 09:01:03 +00:00
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