From: Charles Oliver Nutter <headius@...>
Date: 2011-04-20T07:45:18+09:00
Subject: Re: How do I trap Ctrl-C so it doesn't reach spawned threads?

At this point you might want to take this to a JRuby bug
(http://bugs.jruby.org) and we can sort out what you need and what
we're not doing right. I will note that we've been making various
fixes for process management recently, so this is very timely.

- Charlie

On Thu, Apr 14, 2011 at 3:27 AM, Jens Carlberg
<jens.carlberg@ericsson.com> wrote:
> I have now tried both fork and spawn, and my confusion have reached new
> levels. :-)
>
> Fork and ruby
> =============
> Worked as a charm. Too bad I need to use jruby due to JMX dependencies.
>
>
> Fork and jruby
> ==============
> Fork seems to be considered dangerous when used in jruby. I have found info
> about enabling it, but are having very limited success in doing that.
>
> I have started jirb two ways:
>
> 1. jirb -J-Djruby.fork.enabled=true
>
> Results in "IRB::UnrecognizedSwitch: Unrecognized switch:
> -J-Djruby.fork.enabled=true"
>
> 2. jruby -J-Djruby.fork.enabled=true -S jirb
>
> Results in "NotImplementedError: fork is not available on this platform".
>
> The jruby.fork.enabled property isn't listed when I do jruby --properties
> either. Has it been removed?
>
>
> Spawn and jruby
> ===============
> 1. Process.spawn("xeyes")
> Do not protect the spawned process from Ctrl-C.
>
> 2. Process.spawn("xeyes", :pgroup=>true)
> Gives the xeyes usage message; the option is used as a part of the command.
> How do jruby separates options for the command and options for
> Process.spawn?
>
> Just to test that I read the Rdoc page for Process right:
>
> 3. spawn({"FOO"=>"BAR", "BAZ"=>nil}, "xeyes")
> Errno::ENOENT: No such file or directory - {"FOO"=>"BAR", "BAZ"=>nil}
>
>
> ///Best regards, Jens Carlberg
>
> -----Original Message-----
> From: Charles Oliver Nutter [mailto:headius@headius.com]
> Sent: den 11 april 2011 01:32
> To: ruby-talk@ruby-lang.org
> Cc: Jens Carlberg
> Subject: Re: How do I trap Ctrl-C so it doesn't reach spawned threads?
>
> On Fri, Apr 8, 2011 at 2:53 AM, Jens Carlberg <jens.carlberg@ericsson.com>
> wrote:
>> Hi!
>>
>> I'm having trouble trapping Ctrl-C. I have a CLI that spawns processes I
> would like to survive the CLI, but if I press Ctrl-C the spawns dies along
> with the CLI. I have experimented with trap(INT), and have boiled down the
> problem into a small example program. I run this on Linux.
> ...
>> I don't understand the behaviour. The jruby version feels more consistent,
> but is far away from what I need. The ruby version feels strange, but I
> could handle my needs by spawning a dummy process if I didn't need jmx4r
> (which as far as I understand requires jruby).
>>
>> 1. How is trapping of SIGINT supposed to work? How is the passing of
> SIGINT supposed to work?
>> 2. Why does it differs between ruby and jruby?
>> 3. Anyone with a suggestion how to spawn processes not affected by a
> SIGINT?
>
> In MRI, I *believe* SIGINT is sent to the process that currently controls
> the TTY, so in the case of system() it's sent to your program that's
> running.
>
> In JRuby, child processes don't usually share the TTY streams (JVM isolates
> child process streams from the parent using pipes), so Ctrl-C is sent to
> JRuby (the JVM itself, really, since we don't trap INT in JRuby and allow
> JVM to handle it) and it shuts down taking the active child process with it.
>
> Perhaps you can try to use posix_spawn or 1.9's "spawn"?
>
> - Charlie
>