How can I capture terminal abort exit and execute a function before termination?

Questions / Help
, ,
1

This is my supervisor.

-module(my_web_app_sup).

-behaviour(supervisor).

-export([start_link/0]).

-export([init/1]).

-define(SERVER, ?MODULE).

start_link() ->
 
    supervisor:start_link({local, ?SERVER}, ?MODULE, []).

init([]) ->
     TerminalLogger = {terminal_logger, {terminal_logger, start_link, []}, permanent, 2000, worker, [terminal_logger]}, % Add terminal logger
      % gen_event:start({local, error_man}),
      % gen_event:add_handler(error_man, terminal_logger, []),
   Childern = [TerminalLogger],
RestartStrategy = {one_for_one, 8, 10},
	{ok, {RestartStrategy, Childern}}.


handle() ->
    receive        
        'sigtstp' ->
            io:format("Exit signal received. Goodbye!\n")
             end.

This is my module which im trying to capture exit signals.

-module(terminal_logger).
-moduledoc false.
-behaviour(gen_event).
-export([start/0, init/1,
         handle_event/2, handle_call/2, handle_info/2,
         terminate/2, code_change/3]).

-record(state,{}).

start() ->
    %% add signal handler
    case whereis(erl_signal_server) of
        %% in case of minimal mode
        undefined -> ok;
        _ ->
            gen_event:add_handler(erl_signal_server, terminal_logger, [])
    end.

init(_Args) ->
    {ok, #state{}}.

handle_event(sigusr1, S) ->
    erlang:halt("Received SIGUSR1"),
    {ok, S};
handle_event(sigquit, S) ->
    erlang:halt(),
    {ok, S};
handle_event(sigterm, S) ->
    error_logger:info_msg("SIGTERM received - shutting down~n"),
    ok = init:stop(),
    {ok, S};
handle_event(_SignalMsg, S) ->
            io:format("~n handle_event(_SignalMsg, S) ~n"),

    {ok, S}.

handle_info(_Info, S) ->
        io:format("~n handle_info(_Info, S) ->~n"),
    {ok, S}.

handle_call(_Request, S) ->
            io:format("~n handle_call(_Request, S)  ~n"),

    {ok, ok, S}.

code_change(_OldVsn, S, _Extra) ->
    {ok, S}.

terminate(_Args, _S) ->
        io:format("~nterminated~n"),

    ok.

This my terminal output.

rebar3 shell
===> Verifying dependencies...
===> Analyzing applications...
src/amf_sup.erl:49:1: Warning: function terminate/2 is unused

Erlang/OTP 26 [erts-14.1] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [jit:ns]
1> terminal_logger:start().
ok
2> 
BREAK: (a)bort (A)bort with dump (c)ontinue (p)roc info (i)nfo
       (l)oaded (v)ersion (k)ill (D)b-tables (d)istribution
a
2

Start MFA in children spec is ‘{terminal_logger, start_link, }’, but ‘start_link/0’ is not exported in ‘terminal_logger’

Also, seems like your suporvisor isn’t started. Make sure to have your app listed in shell config in rebar.config

1 Like
3

Thank you for your reply,I made few changes and now Im able to start it with my supervisor but Im still unable to capture exit signals.

This is my supervisor.

-module(shell_exit_sup).

-behaviour(supervisor).

-export([start_link/0]).

-export([init/1]).

-define(SERVER, ?MODULE).

start_link() ->
    supervisor:start_link({local, ?SERVER}, ?MODULE, []).

init([]) ->
    SupFlags = #{strategy => one_for_all,
                 intensity => 0,
                 period => 1},
 ChildSpecs = [
        #{id => shell_termination,
          start => {shell_termination, start, []},
          restart => permanent,
          shutdown => 5000,
          type => worker}
    ],    {ok, {SupFlags, ChildSpecs}}.

This is my gen_event module

-module(shell_termination).
-behaviour(gen_event).
-export([start/0, init/1,
         handle_event/2, handle_call/2, handle_info/2,
         terminate/2, code_change/3]).

-record(state,{}).

start() ->
    %% add signal handler
    case whereis(erl_signal_server) of
        %% in case of minimal mode
        undefined -> ok;
        _ ->
            gen_event:add_handler(erl_signal_server, erl_signal_handler, [])
    end,
    {ok,self()}.

init(_Args) ->
    {ok, #state{}}.

handle_event(sigusr1, S) ->
    erlang:halt("Received SIGUSR1"),
    {ok, S};
handle_event(sigquit, S) ->
    erlang:halt(),
    {ok, S};
handle_event(sigterm, S) ->
    error_logger:info_msg("SIGTERM received - shutting down~n"),
    ok = init:stop(),
    {ok, S};
handle_event(_SignalMsg, S) ->
        io:format("handle_info called "),

    {ok, S}.

handle_info(_Info, S) ->
    io:format("handle_info called "),
    {ok, S}.

handle_call(_Request, S) ->
        io:format("handle_info called "),

    {ok, ok, S}.

code_change(_OldVsn, S, _Extra) ->
    {ok, S}.

terminate(_Args, _S) ->
        io:format("handle_info called "),

    ok.

This is my terminal output.

rebar3 shell
===> Verifying dependencies...
===> Analyzing applications...
===> Compiling shell_exit
Erlang/OTP 26 [erts-14.1] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [jit:ns]

Eshell V14.1 (press Ctrl+G to abort, type help(). for help)
===> Booted shell_exit
1> 
BREAK: (a)bort (A)bort with dump (c)ontinue (p)roc info (i)nfo
       (l)oaded (v)ersion (k)ill (D)b-tables (d)istribution
a
4

In the example you’re trying to send SIGINT, right? It is intercepted by erlang shell and I don’t know if it’s forwarded to the user program. Try sending other signals which aren’t used by erang shell.

Also, make sure that os:set_signal/2 sets those signals to ‘handle’

1 Like
5

Thank you for your reply,I read somewhere that when I abort the rebar3 shell it behaves like erlang:halt() function,so I’m trying to capture whatever the signal it sends before exiting and execute a cleanup type function just before the exit of the program ,as per your suggestion I did set the os:set_signal(’ ',‘handle’) in fact I set all the options to handle and yet Im unable to capture the exit.

This is my module

-module(shell_termination).
-behaviour(gen_event).
-export([start/0, init/1,
         handle_event/2, handle_call/2, handle_info/2,
         terminate/2, code_change/3]).

-record(state,{}).

start() ->
    os:set_signal('sighup','handle'),
    os:set_signal('sigquit','handle'),
    os:set_signal('sigabrt' ,'handle'),
    os:set_signal('sigalrm','handle'),
    os:set_signal('sigterm','handle'),
    os:set_signal('sigusr1','handle'),
    os:set_signal('sigusr2','handle'),
    os:set_signal('sigchld','handle'),
    os:set_signal('sigstop','handle'),
    os:set_signal('sigtstp','handle'),




    %% add signal handler
    case whereis(erl_signal_server) of
        %% in case of minimal mode
        undefined -> ok;
        _ ->
            gen_event:add_handler(erl_signal_server, erl_signal_handler, [])
    end,
    {ok,self()}.

init(_Args) ->
    {ok, #state{}}.

handle_event(sigusr1, S) ->
    
    io:format("handle_info called "),
    % erlang:halt("Received SIGUSR1"),
    {ok, S};
handle_event(sigquit, S) ->
    io:format("handle_info called "),
    % erlang:halt(),
    {ok, S};
handle_event(sigterm, S) ->
    io:format("SIGTERM received - shutting down~n"),
    ok = init:stop(),
    {ok, S};
handle_event(_SignalMsg, S) ->
        io:format("handle_info called "),

    {ok, S}.

handle_info(_Info, S) ->
    io:format("handle_info called "),
    {ok, S}.

handle_call(_Request, S) ->
        io:format("handle_info called "),

    {ok, ok, S}.

code_change(_OldVsn, S, _Extra) ->
    {ok, S}.

terminate(_Args, _S) ->
        io:format("handle_info called "),

    ok.

This is my terminal output:

rebar3 shell
===> Verifying dependencies...
===> Analyzing applications...
===> Compiling shell_exit
Erlang/OTP 26 [erts-14.1] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [jit:ns]

Eshell V14.1 (press Ctrl+G to abort, type help(). for help)
===> Booted shell_exit
1> 
BREAK: (a)bort (A)bort with dump (c)ontinue (p)roc info (i)nfo
       (l)oaded (v)ersion (k)ill (D)b-tables (d)istribution
a