From: Mark Hubbart <discord@...>
Date: 2004-08-09T17:06:48+09:00
Subject: Re: Problem with exception not beeing caught


On Aug 9, 2004, at 12:16 AM, Michael Mueller wrote:

> Dear rubyists!
>
> I have a problem with a small programm, that's fetching emails from my
> account and then goes to sleep for X seconds.
> The code looks somehow like this:
>
> loop do
>   begin
>     load FILTERFILE
>     BOXES.each{|box| check_mailbox(box)}
>     $log.debug("Gehe f�r #{SLEEPTIME} Sekunden schlafen!")
>     sleep(SLEEPTIME)
>   rescue
>     $log.warn("Fehler aufgetreten:#{$!}\n#{$!.backtrace}")
>   end
> end
>
> From time to time I get an exception in check_mailbox because the 
> mailserver
> doesn't respond so I'm gettin:
> mi@ceres:~$ mail-forward.rb -n
> /usr/local/lib/ruby/1.8/timeout.rb:42:in `new': execution expired
> (Timeout::Error)
>         from /usr/local/lib/ruby/1.8/net/protocol.rb:83:in `connect'
>         from /usr/local/lib/ruby/1.8/net/protocol.rb:82:in `timeout'
>         from /usr/local/lib/ruby/1.8/timeout.rb:55:in `timeout'
>         from /usr/local/lib/ruby/1.8/net/protocol.rb:82:in `connect'
>         from /usr/local/lib/ruby/1.8/net/protocol.rb:64:in `initialize'
>         from /usr/local/lib/ruby/1.8/net/pop.rb:427:in `open'
>         from /usr/local/lib/ruby/1.8/net/pop.rb:427:in `do_start'
>         from /usr/local/lib/ruby/1.8/net/pop.rb:415:in `start'
>         from /home/mi/bin/mail-forward.rb:45:in `check_mailbox'
>         from /home/mi/bin/mail-forward.rb:89
>         from /home/mi/bin/mail-forward.rb:89:in `each'
>         from /home/mi/bin/mail-forward.rb:89
>         from /home/mi/bin/mail-forward.rb:86:in `loop'
>         from /home/mi/bin/mail-forward.rb:86
>
> I guess that's kinda normal, but: Why isn't this exception caught???? I
> expected the exception in my logfile and the program to continue, but
> obviously the program exits before getting into the rescue block??
>
> Any ideas what i'm doing wrong?

When you don't specify an exception class to rescue from, it defaults 
to StandardError. Timeout::Error doesn't inherit from StandardError, so 
it goes uncaught:

   # show the ancestors: no StandardError!
   Timeout::Error.ancestors
     ==>[Timeout::Error, Interrupt, SignalException, Exception, Object, 
Kernel]

   # test rescuing the lowest exception class possible: Exception.
   begin
     raise Timeout::Error
   rescue Exception
     p 'rescued!'
   end
   "rescued!"
     ==>nil

   # test an unspecified exception class:
   begin
     raise Timeout::Error
   rescue
     p 'rescued!'
   end
   (irb):9:in `irb_binding': Timeout::Error (Timeout::Error)
         from /usr/local/lib/ruby/1.9/irb/workspace.rb:52:in 
`irb_binding'
         from /usr/local/lib/ruby/1.9/irb/workspace.rb:52

In fact, this made IRB die off on me; IRB didn't catch the error either.

HTH,
Mark