From: Robert Klemme <bob.news@...>
Date: 2005-10-08T00:31:50+09:00
Subject: Re: Customizing Exception, but only when an error is raised

Berger, Daniel wrote:
>> -----Original Message-----
>> From: Robert Klemme [mailto:bob.news@gmx.net]
>> Sent: Friday, October 07, 2005 6:52 AM
>> To: ruby-talk ML
>> Subject: Re: Customizing Exception, but only when an error is raised
>
> <snip>
>
>> It would be interesting to learn what real world problem
>> Daniel wants to solve...
>>
>> Kind regards
>>
>>     robert
>
> I was trying to emulate Perl's $SIG{__DIE__} handler for reports
> running via cron where, whenever an error occurred, an email would be
> sent to me (or whoever).

I'm not too familiar with $SIG{__DIE__} but I assume it's called whenever
the program executes a die.  If this is the case, there are several
alternatives in Ruby:

1. wrap your complete script in begin;rescue;end and handle the exception
appropriately at this top level.

1b. like 1 but catch only SystemExit

2. You can use at_exit to set an exit handler
http://www.ruby-doc.org/core/classes/Process.html#M001763

3. Use Signal.trap
http://www.ruby-doc.org/core/classes/Signal.html#M001593

4. In certain circumstances you might be able to use END {}

>  While I can log errors to a file, I still
> have to check the log files periodically to make sure they ran as
> expected.  Every once in a while something goes awry - network
> glitch, database glitch - whatever.
>
> No, I don't want to run a separate program to tail log files looking
> for errors. :)
>
> My initial plan (which I had nearly complete) was to do something like
> this:
>
> # At the top of your program
> require "exception/mail"
> Exception.mail_host = "mailhost.foo.com"
> Exception.mail_to   = "person@foo.com"
>
> Then, whenever an error was raised anywhere in my program an email
> would be sent out.  There are plenty of other options you could
> configure, btw, though the others all have reasonable defaults.
>
> The problem, I realized, was that even if I wanted to ignore an error
> (or handle it some other way), an email would still be sent out. Now
> I'm thinking that maybe I should redefine Kernel#raise instead.

I would refrain from that and use one of the other approaches as fiddling
with such core features might lead to surprising effects (for example, if
you alias this method but 0/0 doesn't even invoke it but raises exceptions
differently) and incompatibilities.

Kind regards

    robert