How to restart app if it unexpectedly shutdown

Question

Skype update text contains next:

App auto restarts if unexpectedly shut down

How is possible to perform that via SDK?

Answer 1

Skype does exactly this:

1. Registers it's TCP sockets for VoIP.
2. Logs in.
3. Upon nonzero exit code the app will be relaunched by iOS (Because VoIP applications need to stay running in order to receive incoming calls, the system automatically relaunches the application if it exits with a nonzero exit code.).
4. It then immediately starts a background task (Relaunched apps remain suspended).
5. Next it registers it's login socket for VoIP.
6. It logs back in.