The main difference is that networks are inherently unreliable. Threaded or multi-processed applications can also be unreliable but for different reasons. The

The main difference is that networks are inherently unreliable. Threaded or multi-processed applications can also be unreliable but for different reasons. The goal should be to inform the caller of the types of errors that may pop up. Obviously, with network or RPC calls, the caller should handle the case where the network is down. With threaded apps, the potential errors are more subtle, but the caller should definitely be aware that it's not a synchronous call. The function header you proposed is a bit clumsy due to the c semantics, but gets the general point across well enough.