DEvil0000
Linking a port / exit normal in case of kill -X <os_pid>
Hi there,
I want to open a os process from elixir and get informed in case it crashes. I tried it with port and link but when I kill the external os process the exit always reports normal.
I was expecting to get something else then normal when it exits abnormal like in kill -9 or kill -15.
Since I am actually using elixir 1.5 my test code looks like:
:erlang.process_flag(:trap_exit, true)
port = Port.open({:spawn, "sleep 360"}, [:exit_status])
Process.link port
:erlang.monitor :port, port
And I get the following:
{#Port<0.6363>, {:exit_status, 137}}
{:EXIT, #Port<0.6363>, :normal}
{:DOWN, #Reference<0.3242658756.1180172289.143115>, :port, #Port<0.6363>, :normal}
The only thing I could use as a workaround is the exit status as it looks like.
Does one of you have a good idea how to get link working for this case?
Is this a bug or a feature?
Communication with os processes, killing them or sending signals is quite tricky anyway in erlang…
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grych
Everything works as expected.
When you kill the process in unix, its exit status is set to non-zero value, depending on the signal you’ve sent (128 + signal number, so in your case it is 128+9=137).
OvermindDL1
It’s not possible to know it segfaulted, and a return code from an application may not actually be an error but could be returning valid information that is actually wanted (this is done quite commonly), only the user can know.
grych
I think you are missing the difference between OS and Erlang processes.
This is an exit of the erlang process, not the unix one. Port.open creates an erlang process, which runs the external command and waits for it to end. From the erlang point of view, the port process finished normally - it did the job.
DEvil0000
I was expecting those cases would also get reflected in the exit beeing not normal so link would make sense.
March 12
Everything works as expected.
DEvil0000:
{#Port<0.6363>, {:exit_status, 137}}
When you kill the process in unix, its exit status is set to non-zero value, depending on the signal you’ve sent (128 + signal number, so in your case it is 128+9=137).
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