Sets the callback function storing the data as a refcounted callback
"object". This is used internally. Note that calling
g_source_set_callback_indirect() assumes
an initial reference count on @callback_data, and thus
@callback_funcs->unref will eventually be called once more
than @callback_funcs->ref.
It is safe to call this function multiple times on a source which has already
been attached to a context. The changes will take effect for the next time
the source is dispatched after this call returns.
Sets the callback function storing the data as a refcounted callback "object". This is used internally. Note that calling g_source_set_callback_indirect() assumes an initial reference count on @callback_data, and thus @callback_funcs->unref will eventually be called once more than @callback_funcs->ref.
It is safe to call this function multiple times on a source which has already been attached to a context. The changes will take effect for the next time the source is dispatched after this call returns.