Comment 55 for bug 857153

Yes, both libdbus and GDBus (in gio) will spawn a new bus with dbus-launch if it can't connect to a session bus (ie, if DBUS_SESSION_BUS_ADDRESS is unset).

I've just been bitten by this in Ubuntu with IPC xpcshell tests hanging our builds. I did some investigation of this today and found that the hangs were caused by plugin-container failing to start because it couldn't get an X connection - because of the bazillion or so dbus-launch processes (and associated buses!!) that had been spawned during the previous tests had used up all of the allowable X server connections :(

To work around this, we'll probably run all of the tests inside dbus-launch so that they have a bus already (eg, dbus-launch --exit-with-session)