Properly kill OS processes upon exit

oubiwann commented 3 years ago

Right now, it seems that only calling (exit) from the REPL does go through the proper termination sequence (but only sendmidi is killed; receivemidi remains running). Issuing a SIGINT or SIGTERM don't seem to executing the full termination sequence at all, when run via rebar3 and the LFE REPL. Both OS processes for sendmidi and receivemidi remain running.

Tasks:

[ ] Put this in a general-purpose module
[ ] Do the same for the already extant code that starts a non-port, one-off OS process
[ ] Refactor OS PID tracking in state (remove) and just do the lookup when needed (all that's needed is the port reference)
[ ] Maybe stop differently and watch for DOWN message?
[ ] Dig more into any OTP callbacks and/or messages specific to ports from spawned executables
[ ] Find out why one of these processes is shutting down properly (sendmidi) while the other isn't (receivemidi)
[ ] TBD ...

Related to #89

Part of epic #80

oubiwann commented 3 years ago

Take a look at these examples ... maybe something useful (from https://github.com/saleyn/erlexec/blob/master/src/exec.erl):

stop_and_wait(Pid, Timeout) when is_pid(Pid) ->
    gen_server:call(?MODULE, {port, {stop, Pid}}, Timeout),
    receive
    {'DOWN', _Ref, process, Pid, ExitStatus} -> ExitStatus
    after Timeout                            -> {error, timeout}
    end;

terminate(_Reason, State) ->
    try
        erlang:port_command(State#state.port, term_to_binary({0, {shutdown}})),
        case wait_port_exit(State#state.port) of
        0 -> ok;
        S -> error_logger:warning_msg("~w - exec process terminated (status: ~w)\n",
                [self(), S])
        end
    catch _:_ ->
        ok
    end.

wait_port_exit(Port) ->
    receive
    {Port,{exit_status,Status}} ->
        Status;
    _ ->
        wait_port_exit(Port)
    end.

notify_and_exit(true, Pid, OsPid, Reason) ->
    Pid ! {'DOWN', OsPid, process, self(), Reason},
    exit(Reason);

oubiwann commented 3 years ago

Also see How do you kill an OS process that was opened with open_port on a brutal_kill?. Highlight:

A well-behaved port should be checking the file descriptor to see if it is closed. (see #87)

ut-proj / undertone

Properly kill OS processes upon exit #88