You might all be familiar with the popular message bus system i.e. DBus. It is an inter-process communication (IPC) and remote procedure call (RPC) mechanism that allows communication between multiple computer programs concurrently running on the same machine.
DigiKam earlier used DBus under Linux system, but its support under Windows and OS X made digiKam unstable. The database core implementation based on DBUS was only used with old KIOSalve which is now removed.
In the current version, DBus is now optional for Linux and completely removed for Windows and OS X. It is now a thread, not a separate process.
After more than 1 year of development, digiKam 5.0.0 release plan updated and finalized… Do take a look!