[erlang-questions] can a program launched with open_port({spawn, Cmd}, Options) remain running after the port closes?

Erik Søe Sørensen eriksoe@REDACTED
Thu Sep 27 04:20:44 CEST 2012

It is the responsibility of the port program to shut down when stdin
reaches EOF.
This behaviour/expectation confused me too at some point, but it probably
has its merits: not all software is designed for "let it crash", so simply
killing the port program might be too crude in some circumstances.
Den 26/09/2012 23.55 skrev "Tim Watson" <watson.timothy@REDACTED>:

> I'm seeing this happen, and it's most confusing. The program is not
> launched using nohup/setsid or anything to send it to the background. The
> arguments passed to open_port/2 are thus:
> [{args, Args}, {env, Env}, exit_status, hide, stderr_to_stdout, use_stdio,
> {line, 16384}]
> The script that is being run essentially does this:
> # fiddle around with some environment variables, then
> exec erl \
>     -pa ${EBIN_ROOT} \
>     -sname ${NODENAME} \
>     -boot start_sasl \
>     ${CONFIG_ARG} \
>     +W w \
>     ${SERVER_ERL_ARGS} \
>     ${LISTEN_ARG} \
>     "$@"
> After some tests are run, the port is closed (using close_port). The
> connected process for the port is a gen_server, so it's *possible* that
> this exits without cleanly shutting down, but I'm under the impression
> (from experimentation) that if the connected process dies, the port is
> closed anyway. Nevertheless, I'm seeing *stuck nodes* that survive the test
> run and are locked up because some code on the node (which should be dead
> after the port goes) is stuck in an io:format/2 call which will never
> return because stdout is not responding - hardly surprising under the
> circumstances.
> Can someone explain to me what's going on here? Is this an issue with the
> exec call, and if so what is the problem with it? I've got a minimal
> example using exec that doesn't behave like this, so I'm a bit bemused.
> What's really confusing is that the process the port is used to open should
> presumably be closed regardless of what some sub-process is doing, and I
> thought that exec returned the stdout of the subprocess anyway!?
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