From: Daniel Berger <djberg96@...>
Date: 2006-06-10T00:54:50+09:00
Subject: Re: Package idea: attempt

ara.t.howard@noaa.gov wrote:
> On Fri, 9 Jun 2006, Daniel Berger wrote:
> 
>> Yep, definitely something to watch out for.  What can I say?  Use with
>> caution. :)
> 
> for what it's worth have my own version of attempt in a few near-real-time
> systems where the overriding principle is : keep going at all costs.  in 
> these
> systems the 'fail big and fail early' priciple doesn't work unless one 
> enjoys
> working on sundays - so i've got lots of stuff like attempt - it all 
> logs to
> stderr and/or logs however, so it doesn't go unnoticed.
> 
> on another note i've found that incremental sleep increse with reset is 
> almost
> always what you want.  retrying on the same interval seems to clog up 
> systems
> as you get in certain timing rythyms.  in rq i use this alot
> 
> http://codeforpeople.com/lib/ruby/rq/rq-2.3.3/lib/rq-2.3.3/sleepcycle.rb
> 
> it's a cycle that looks like a sawtooth wave - so basically on each 
> retry we
> timeout for longer than before, essentially becoming more and more 
> 'patient'
> before getting really 'impatient' again.
> 
> i've found this matched the real world pretty well since timing out a 
> bunch in
> a short period normally means you should wait longer.
> 
> cheers.
> 
> -a

Hm, interesting.  Maybe a more advanced version would use a full fledged 
class with lots of options.  Something like this:

attempt = Attempt.new{ |a|
    a.tries      = 3       # Try 3 times
    a.interval   = 30      # 30 seconds between tries but...
    a.max        = 90      # In case of nested retries
    a.increment  = 10      # add 10 seconds to the interval with each try
    a.log        = log     # Where 'log' is an IO handle
    a.warnings   = $stderr # Send caught errors to IO handle as warnings
}

attempt{ # Some op }

Attempt#max would, in theory, be used to prevent Jim Weirich's nightmare 
scenario, where you have a bunch of nested retries, all doing their own 
sleep + retry thing.

So, using the above example, if I did something like this:

attempt{
    begin
       # some op
    rescue
       sleep 500
       retry
    end
}

It would error out at 90 seconds no matter what (the value we set to 
'max').  I'm not sure if that's possible, however, or even how you would 
implement it.  Thoughts?

- Dan