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From: Robert Klemme on 21 Jun 2010 07:27
2010/6/21 Martin Hansen <mail(a)maasha.dk>:
> Hm, I am not making myself clear :o( -

Apparently.

> It is the status of the ruby
> script at hand I want to log. $? is probably barking up the wrong tree
> and adding confusion. In Perl I would do this trapping the signal.
>
>> trap in your Ruby script will trap signals for this process not the
>> forked process - unless you use the block form of fork in which case I
>> believe the child inherits all signal handlers.
>
> #!/usr/bin/env ruby
>
> signal = nil
>
> trap("INT") { signal = "interupted"; exit }
> #trap("TERM") { signal = "terminated"; exit }
>
> at_exit { puts "Put this in logfile: #{signal}" }

IMHO it's bad practice to simply exit from a signal handler because
you do not know what the application currently does. It is less
dramatic in Ruby because exit really throws an exception in the
interrupted thread:

$ ruby19 -e 'trap("INT"){ puts "int"; exit 1 }; begin; sleep 20;
rescue Exception => e; p e; end'
int
#<SystemExit: exit>
$

But if you have multiple active threads they are not properly cleaned up:

$ ruby19 -e 'trap("INT"){ puts "INT #{Thread.current}"; exit 1 };
2.times { Thread.new { begin; sleep 20; rescue Exception => e; p e;
ensure p Thread.current; end } }; sleep 30'
INT #<Thread:0x1004e2a4>
#<Thread:0x10042a90 run>
#<Thread:0x10042978 run>
$

Notice how all three threads are terminated but the two background
threads obviously do not see an exception.

In this case it is generally better to somehow globally communicate
that the process is asked to shut down so all parties can properly end
their business.

> sleep 5
>
> I have two issues with this: I loose the stack trace that is normally
> printed to stderr (I still want that printed to stderr):
>
> ./test.rb:10:in `sleep': Interrupt
>        from ./test.rb:10:in `<main>'
>
>
> And I fail setting signal as a global variable (if that can be done?) so
> I can use it from within a class without getting errors like this:
>
> in `block in <class:Biopieces>': undefined local variable or method
> `signal' for Biopieces:Class (NameError)

It seems there is a much simpler solution to what you want - you don't
even need a signal handler for this:

$ ruby19 -e 'begin; sleep 60; rescue Exception => e; p e.class, e,
e.backtrace; end' &
[1] 2664
$ echo $!
2664
$ kill -INT $!
$ Interrupt
Interrupt
["-e:1:in `sleep'", "-e:1:in `<main>'"]
[1]+ Done ruby19 -e 'begin; sleep 60; rescue
Exception => e; p e.class, e, e.backtrace; end'

$

Cheers

robert

--
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

From: Martin Hansen on 21 Jun 2010 08:48
> It seems there is a much simpler solution to what you want - you don't
> even need a signal handler for this:
>
> $ ruby19 -e 'begin; sleep 60; rescue Exception => e; p e.class, e,
> e.backtrace; end' &
> [1] 2664
> $ echo $!
> 2664
> $ kill -INT $!
> $ Interrupt
> Interrupt
> ["-e:1:in `sleep'", "-e:1:in `<main>'"]
> [1]+ Done ruby19 -e 'begin; sleep 60; rescue
> Exception => e; p e.class, e, e.backtrace; end'
>

That indeed looks very clever. But I note that if the script is
terminated I get "SignalException" and not "Terminated". Also, I note
that backtrace is a list, and I was wondering what method Ruby normally
uses to reformat and pretty print that (Ruby is not simply printing and
indenting the lines).

However, I fail to see how this exception handling should be integrated
in practice with my code that currently relies on an at_exit call (line
84):

http://code.google.com/p/biopieces/source/browse/trunk/code_ruby/Maasha/lib/biopieces.rb

And just a reminder that I am trying to create super simplified scripts
of this type:

http://pastie.org/1013476


Cheers,


Martin

--
Posted via http://www.ruby-forum.com/.

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