Killing a process connected to an erlang's port

Question

I want to write a some kind of supervisor and I'm trying to implement function that closes an external program. The external process is connected to an erlang's code with a port. I have no idea how to close this program, by sending a signal or anything else. Closing a port is not a solution, becouse I've checked that many programs doesn't exit on SIGPIPE. Have you got any ideas how to do it?

Answer 1

You can kill external process if you kill linked erlang process. Use this way:

-module(portest).
-export([start/1, init/1, kill/0]).

start(ExtPrg) ->
   spawn(?MODULE, init, [ExtPrg]).

init(ExtPrg) ->
   process_flag(trap_exit, true),
   Port = open_port({spawn, ExtPrg}, [{packet, 2}]),
   register(extport, self()),
   loop(Port).

kill() ->
   exit(whereis(extport), kill).

But you cannot kill external process which blocked with IO read.

Answer 2

You can use

{os_pid, OsPid} = erlang:port_info(Port, os_pid). 

to get the pid of the process in the OS (see http://erlang.org/doc/man/erlang.html#port_info-1 - I think you may need a recent version of Erlang for this to be included, I think the one installed by apt-get on Ubuntu 12.04 isn't recent enough, I know R15B02 has it though) and then

os:cmd(io_lib:format("kill -9 ~p", [OsPid])).

to kill it (http://erlang.org/doc/man/os.html#cmd-1).