From: Eric Hodel <drbrain@...7.net>
Date: 2005-07-24T08:15:50+09:00
Subject: Re: Catching DRb exceptions ??

On 23 Jul 2005, at 01:10, john casu wrote:

> I have a simple problem.
> I want to launch a DRb server from my program (in my case a  
> parallel MPI program,
> where the zero rank process is the actual DRb server), and then  
> connect to it.
>
> If I place a long enough sleep before invoking DRbObject.new, then  
> everything
> is groovy, and things proceed as intended.  If I don't, then I get  
> a DRbConnError
> exception when DRB tries to connect to the server (which hasn't  
> started up yet)
>
> My problem is that I am unable to catch the exception that  
> DRbObject.new raises
> (i.e, I never see the "got exception" message in the attached code  
> below), and
> hence I am at the mercy of race conditions for this to work in a  
> consistent way
> without an excessively long sleep.
>
> Can anyone please point out to me where I'm being a moron, and what  
> I'm doing wrong ?
> I'm running ruby-1.8.3 on Fedora Core 4 Linux.

$ ruby drb.rb
/usr/local/lib/ruby/1.8/drb/drb.rb:733:in `open': druby://hobbes:7777  
- #<SocketError: getaddrinfo: No address associated with nodename>  
(DRb::DRbConnError)
         from /usr/local/lib/ruby/1.8/drb/drb.rb:726:in `each'
         from /usr/local/lib/ruby/1.8/drb/drb.rb:726:in `open'
         from /usr/local/lib/ruby/1.8/drb/drb.rb:1186:in `initialize'
         from /usr/local/lib/ruby/1.8/drb/drb.rb:1166:in `open'
         from /usr/local/lib/ruby/1.8/drb/drb.rb:1082:in  
`method_missing'
         from /usr/local/lib/ruby/1.8/drb/drb.rb:1081:in `with_friend'
         from /usr/local/lib/ruby/1.8/drb/drb.rb:1081:in  
`method_missing'
         from drb.rb:5
              ^^^^^^^^
[ ~ ]
[16:14] drbrain@kaa$ cat -n drb.rb
      1  require 'drb'
      2
      3  DRb.start_service
      4  foo = DRbObject.new(nil, 'druby://hobbes:7777')
      5  puts foo.call_remote_foo(0, "run")
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      6

DRb doesn't attempt to connect until you try to use the remote object.

You may want to look into Rinda to automatically find live DRb services:

http://segment7.net/projects/ruby/drb/rinda/ringserver.html

-- 
Eric Hodel - drbrain@segment7.net - http://segment7.net
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