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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?
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A process can terminate itself by calling one of the BIFs exit(Reason), erlang:error(Reason), erlang:error(Reason, Args), erlang:fault(Reason) or erlang:fault(Reason, Args). The process then terminates with reason Reason for exit/1 or {Reason,Stack} for the others.
Erlang processes are light-weight (grow and shrink dynamically) with small memory footprint, fast to create and terminate and the scheduling overhead is low.
Each process in erlang has a process identifier ( Pid ) in this format <x.x.x> , x being a natural number. Below is an example of a Pid <0.1252.0> Pid can be used to send messages to the process using 'bang' ( ! ), also Pid can be bounded to a variable, both are shown below. MyProcessId = self().
spawn() creates a new process and returns the pid. The new process starts executing in Module:Name(Arg1,...,ArgN) where the arguments are the elements of the (possible empty) Args argument list.
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.
44
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).
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