From: Jim Weirich <jim@...>
Date: 2005-07-30T00:09:24+09:00
Subject: Re: Allow retry to take arguments?


Austin Ziegler said:
> One problem that I see, Jim. In Daniel's pseudo-code, he can rescue
> specific exceptions:
>
>     begin
>       connect_to_something
>     rescue NetworkBusyException, TimeoutException
>       retry(3, 30) or raise
>     rescue NetworkUnavailableException
>       retry(5, 60) or raise
>     end

Gah!  What is the semantics of that?  What if you get a
NetworkBusyException, so you want to retry 3 times.  But the next time you
get a NetworkUnavailable exception.  Do you leave it at 3 retries or up it
to a max of 5 tries.  Or do the tries for each exception count
individually, i.e. we could have up to 8 retries, 5 for Unavailable and 3
for Busy/Timeout.  Or is a a max of 11 retries because retries for timeout
and busy count together.

> Yours just allows for one attempt wrapper and doesn't specify what
> sort of exceptions can be caught.

So use ...

   attempt([NetworkBusyException, TimeoutException] => [3,30],
            NetworkUnavailableException => [5, 60]) do
     connect_to_something
   end

or something like this ...

   Attempt = RetryController.new do |retry|
     retry.on NetworkBusyException, TimeoutException, :trys=>3, :timeout=>30
     retry.on NetworkUnavailableException, :trys=>5, :timeout=>60
   end

   # ... later in code ...

   Attempt.call { connect_to_something }

All still doable without changing the language.

-- 
-- Jim Weirich     jim@weirichhouse.org    http://onestepback.org
-----------------------------------------------------------------
"Beware of bugs in the above code; I have only proved it correct,
not tried it." -- Donald Knuth (in a memo to Peter van Emde Boas)