gen_tcp:connect will close when using supervisor.

I have a simple gen_server which connects to a tcp port, when I run gen_server directly:

erl -noshell  -s ttest start

it works fine, But when I run:

erl -noshell -s tt_sup start_link 

the connection will be closed instantly, it will work if I unlink the supervisor.

How could I run my simple gen_server with supervisor ?





-module(tt_sup).

-behaviour(supervisor).

-export([init/1, start_link/0, start_shell/0]).



start_link() ->

    io:format("Supervisor started with PID~p~n", [self()]),

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

    io:format("Supervisor PID=~p~n", [Pid]),

    {ok, Pid}.



start_shell() ->

    io:format("Supervisor started with PID~p~n", [self()]),

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

    io:format("Supervisor PID=~p~n", [Pid]),

    unlink(Pid),

    {ok, Pid}.



init(_Args) ->

    SupFlags = #{strategy => one_for_one},

    Child = [#{id => ttest, start => {ttest, start, []},

               restart => permanent, shutdown => brutal_kill,

               type => worker, modules => [ttest]}],

    {ok, {SupFlags, Child}}.





-module(ttest).

-export([start/0,init/1,handle_cast/2,handle_call/3,handle_info/2,terminate/2,connect/1]).

-behaviour(gen_server).



start() ->

       io:format("gen_server start id is ~p~n",[self()]),

       {ok,Pid} = gen_server:start_link({local,ttest},ttest,[],[]),

       io:format("gen_server id is ~p~n",[Pid]),

       connect(Pid),

       {ok,Pid}.



init(_Args) ->

    io:format("init id is ~p~n",[self()]),

        {ok,[]}.       

handle_call({tcp,Socket,Bin},_From,States) ->

        {reply,States,States}.

handle_info({tcp,Socket,Bin},States) ->

        io:format("got info msg"),

        {noreply,States}.



handle_cast({send,Msg},States) ->

        {reply,States}.



connect(I) ->

    io:format("connect id is ~p~n",[self()]),

        {ok,Socket} =gen_tcp:connect("localhost",6000,[binary,{active,true}]),

        gen_tcp:controlling_process(Socket,I).



terminate(shutdown, State) ->

    io:format("terminating"),

    ok.