Program a supervisor process that can be used to start the frequency server, and restart it whenever it has terminated unexpectedly.
In adding the supervisor you will need to think about the state of the server when it is restarted. The following discussion may help you to think about that.
In a typical client-server scenario, the clients are not under the control of the supervisor: any client can connect to the server as long as it knows the name (or the Pid) of the server. So, we can’t expect the supervisor to restart the clients; on the other hand we can ensure that if the server terminates unexpectedly then the clients do too.
Using the observer tool as described in the previous exercise, observe how your system behaves when some of the constituent processes – including the supervisor itself – are killed.
Recall that to run the observer, type observer:start() in the Erlang shell,
and that we use exit(Pid,kill) to kill the process with pid Pid.