supervisor terminates on bad call to sc_server

[err]

Gist (same info is inline further down):
https://gist.github.com/d4cbcb6c81e9e27f38ac


I get that sc_lookup/1 is not exported by the sc_server,
but I'm not sure why this terminates the supervisor (sc_sup) process.


11> sc_server:insert(foo, bar).
ok
12> sc_server:lookup(foo).
bar
13> sc_server:insert(baz).       % sc_server:insert/1 doesn't exist!
** exception error: undefined function sc_server:insert/1
     in function  error_handler:crash/1 (error_handler.erl, line 106)
26>
=ERROR REPORT==== 11-Oct-2013::21:36:50 ===
** Generic server sc_sup terminating
** Last message in was {'EXIT',<0.104.0>,
                           {undef,
                               [{sc_server,insert,[baz],[]},
                                {error_handler,crash,1,
                                    [{file,"error_handler.erl"},{line,106}]},
                                {erl_eval,do_apply,6,
                                    [{file,"erl_eval.erl"},{line,573}]},
                                {shell,exprs,7,
                                    [{file,"shell.erl"},{line,674}]},
                                {shell,eval_exprs,7,
                                    [{file,"shell.erl"},{line,629}]},
                                {shell,eval_loop,3,
                                    [{file,"shell.erl"},{line,614}]}]}}
** When Server state == {state,
                            {local,sc_sup},
                            one_for_one,
                            [{child,<0.108.0>,sc_server,
                                 {sc_server,start_link,[]},
                                 permanent,2000,worker,
                                 [sc_server]}],
                            undefined,1000,3600,[],sc_sup,[]}
** Reason for termination ==
** {'function not exported',
       [{sc_server,insert,[baz],[]},
        {error_handler,crash,1,[{file,"error_handler.erl"},{line,106}]},
        {erl_eval,do_apply,6,[{file,"erl_eval.erl"},{line,573}]},
        {shell,exprs,7,[{file,"shell.erl"},{line,674}]},
        {shell,eval_exprs,7,[{file,"shell.erl"},{line,629}]},
        {shell,eval_loop,3,[{file,"shell.erl"},{line,614}]}]}

[Jordan Wilberding]

Very good question.

What happening here is that since you are starting it in the shell, the supervisor process is linked to the shell process. When that gen_server process crashes, that EXIT signal is propagated up to the shell which crashes the shell (then restarts it).

In order to get around this (only for educational purposes, don't actually do this for production code), you can add a function to sc_sup.erl like this:

start_shell() ->

    {ok, Pid} = supervisor:start_link(sc_sup, []),

    unlink(Pid).

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