我对OTP非常陌生，我正在尝试创建一个简单的示例来理解监督器行为：
这里是一个简单的增量服务器。
-module( inc_serv ).
-behaviour( gen_server ).
-export( [ start/0, inc/1, stop/0 ] ).
-export( [ init/1, handle_call/3, terminate/2 ] ).
start() ->
gen_server:start_link( { local, ?MODULE }, ?MODULE, no_args, [] ).
stop() ->
gen_server:call( ?MODULE, stop ).
inc( Num ) ->
gen_server:call( ?MODULE, { num, Num } ).
init( no_args ) ->
io:format( "~p~n", [ "Increment server started :)" ] ),
{ ok, no_state }.
handle_call( { num, Num }, _From, no_state ) ->
{ reply, Num + 1, no_state };
handle_call( stop, _From, no_state ) ->
{ stop, normal, ok, no_state }.
terminate( Reason, no_state ) ->
io:format( "~p~n", [ "Increment server stopped" ] ).
我希望用这个模块来监督它：
-module( supervisor_inc ).
-behaviour( supervisor ).
-export( [ start/0 ] ).
-export( [ init/1 ] ).
start() ->
supervisor:start_link( { local, ?MODULE }, ?MODULE, no_args ).
init( no_args ) ->
process_flag( trap_exit, true ),
Supervisor_Spec = { one_for_one, 1, 1 },
IncServ_Spec = {
inc_serv,
{ inc_serv, start, [] },
permanent, 2000, worker, [ inc_serv ] },
{ ok, { Supervisor_Spec, [ IncServ_Spec ] } }.
之后我在Erlang shell中执行了以下步骤：
1>
1> c(inc_serv).
{ok,inc_serv}
2>
2> c(supervisor_inc).
{ok,supervisor_inc}
3>
3> supervisor_inc:start().
"Increment server started :)"
{ok,<0.43.0>}
4>
4> inc_serv:inc( 7 ).
8
5> inc_serv:inc( 8 ).
9
接下来我尝试了下面的方法（如预期的一样，我遇到了错误）：
6> inc_serv:inc( bad_arg ).
"Increment server stopped"
"Increment server started :)"
=ERROR REPORT==== 23-Aug-2012::19:32:06 ===
** Generic server inc_serv terminating
** Last message in was {num,bad_arg}
** When Server state == no_state
** Reason for termination ==
** {badarith,[{inc_serv,handle_call,3,[{file,"inc_serv.erl"},{line,22}]},
{gen_server,handle_msg,5,[{file,"gen_server.erl"},{line,588}]},
{proc_lib,init_p_do_apply,3,
[{file,"proc_lib.erl"},{line,227}]}]}
=ERROR REPORT==== 23-Aug-2012::19:32:06 ===
** Generic server supervisor_inc terminating
** Last message in was {'EXIT',<0.31.0>,
{{{badarith,
[{inc_serv,handle_call,3,
[{file,"inc_serv.erl"},{line,22}]},
{gen_server,handle_msg,5,
[{file,"gen_server.erl"},{line,588}]},
{proc_lib,init_p_do_apply,3,
[{file,"proc_lib.erl"},{line,227}]}]},
{gen_server,call,[inc_serv,{num,bad_arg}]}},
[{gen_server,call,2,
[{file,"gen_server.erl"},{line,180}]},
{erl_eval,do_apply,6,
[{file,"erl_eval.erl"},{line,576}]},
{shell,exprs,7,[{file,"shell.erl"},{line,668}]},
{shell,eval_exprs,7,
[{file,"shell.erl"},{line,623}]},
{shell,eval_loop,3,
[{file,"shell.erl"},{line,608}]}]}}
** When Server state == {state,
{local,supervisor_inc},
one_for_one,
[{child,<0.48.0>,inc_serv,
{inc_serv,start,[]},
permanent,2000,worker,
[inc_serv]}],
undefined,1,1,
[{1345,739526,107495}],
supervisor_inc,no_args}
** Reason for termination ==
** {{{badarith,[{inc_serv,handle_call,3,[{file,"inc_serv.erl"},{line,22}]},
{gen_server,handle_msg,5,[{file,"gen_server.erl"},{line,588}]},
{proc_lib,init_p_do_apply,3,
[{file,"proc_lib.erl"},{line,227}]}]},
{gen_server,call,[inc_serv,{num,bad_arg}]}},
[{gen_server,call,2,[{file,"gen_server.erl"},{line,180}]},
{erl_eval,do_apply,6,[{file,"erl_eval.erl"},{line,576}]},
{shell,exprs,7,[{file,"shell.erl"},{line,668}]},
{shell,eval_exprs,7,[{file,"shell.erl"},{line,623}]},
{shell,eval_loop,3,[{file,"shell.erl"},{line,608}]}]}
** exception exit: {{badarith,[{inc_serv,handle_call,3,
[{file,"inc_serv.erl"},{line,22}]},
{gen_server,handle_msg,5,
[{file,"gen_server.erl"},{line,588}]},
{proc_lib,init_p_do_apply,3,
[{file,"proc_lib.erl"},{line,227}]}]},
{gen_server,call,[inc_serv,{num,bad_arg}]}}
in function gen_server:call/2 (gen_server.erl, line 180)
之后我期望 - 我的主管将重新启动 inc_serv。但他没有这样做：
7> inc_serv:inc( 8 ).
** exception exit: {noproc,{gen_server,call,[inc_serv,{num,8}]}}
in function gen_server:call/2 (gen_server.erl, line 180)
你能帮我理解发生了什么吗？还有我应该如何重写我的监管程序，以便能够重新启动inc_serv？
谢谢