void sd_bus_close(sd_bus *bus);
int sd_bus_flush(sd_bus *bus);
sd_bus_flush() synchronously writes out all outgoing queued message on a bus connection if there are any. This function call may block if the peer is not processing bus messages quickly.
Before a program exits it is usually a good idea to flush any pending messages with sd_bus_flush() and then close connections with sd_bus_close() to ensure that no unwritten messages are lost, no further messages may be queued and all incoming but unprocessed messages are released. After both operations have been done, it is a good idea to also drop any remaining references to the bus object so that it may be freed. Since these three operations are frequently done together a helper call sd_bus_flush_close_unref(3) is provided that combines them into one.
sd_bus_default_flush_close() is similar to sd_bus_flush_close_unref(), but does not take a bus pointer argument and instead iterates over any of the "default" buses opened by sd_bus_default(3), sd_bus_default_user(3), sd_bus_default_system(3), and similar calls. sd_bus_default_flush_close() is particularly useful to clean up any buses opened using those calls before the program exits.