When called, gexiv2 will install it's own #GExiv2LogHandler which redirects all Exiv2 and gexiv2 log messages to GLib's logging calls (g_debug(), g_message(), g_warning(), and g_critical() for the respective #GExiv2LogLevel value). #GEXIV2_LOG_LEVEL_MUTE logs are dropped.
One advantage to using this is that GLib's logging control and handlers can be used rather than GExiv2's ad hoc scheme. It also means an application can use GLib logging and have all its messages routed through the same calls.
gexiv2 requires initialization before its methods are used. In particular, this call must be made in a thread-safe fashion. Best practice is to call from the application's main thread and not to use any Gexiv2 code until it has returned.