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From Felipe Schnack <feli...@ritterdosreis.br>
Subject Re: servlets
Date Tue, 28 Jan 2003 21:54:35 GMT
  Yes... now I see :-))
  But there must be a way!!!

On Tue, 2003-01-28 at 19:52, Jon Wingfield wrote:
> Problem with serialization:
> 1) Client asks for singleton from webapp and stores it as an instance 
> variable.
> 2) Client get serialized to some persistance store (db, jms message 
> queue, whatever)
> 3) webapp goes away (dies, gets shutdown, whatever)
> 4) webapp restored
> 5) Client deserialized.
> 
> Which version of the singleton does the Client then use? ;)
> 
> Felipe Schnack wrote:
> >>> If I write an servlet and DO NOT implement the SingleThreadModel, I
> >>>have a guarantee that I'll have only one instance of it? If not, here is
> >>>a way to do this?
> >>
> >>No, there's no guarantee. As far as I can tell, there's no guarantee even
> >>with SingleThreadModel.
> > 
> >   As far as I understand it, if you implement  SingleThreadModel you can 
> > actually  guarantee that you have more than one instance :-)
> > 
> > 
> >>Only way to ensure this would be to make the Servlet itself simply a facade
> >>(Front end) to a different class that is basically a Singleton.
> > 
> >   Hmmm... wow
> >  
> > 
> >>Mind you this won't work if more than one JVM is perhaps involved, and
> >>Singletons can bring up painful issues regarding serialization of sessions
> >>if they happen to get stuck in one.
> > 
> >   I don't think multiple VMs is an issue... you would certainly have, in this
> > case, multiple singletons loaded (one for each VM), but all of your other 
> > classes would be isolated from one of them anyway
> >   Why there are problems with serialization?
> >  
> > 
> >>Otherwise, it would be straightforward, but you'll be synchronizing like a
> >>mad man, so don't expect a lot of throughput to multiple clients.
> >>
> >>Of course, the real question is not whether it's possible, but why is it
> >>necessary?
> >>
> >>Regards,
> >>
> >>Will Hartung
> >>(willh@msoft.com)
> >>
> >>
> >>
> >>
> >>--
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> >>
> 
> 
> 
> 
> 
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> 
-- 

Felipe Schnack
Analista de Sistemas
felipes@ritterdosreis.br
Cel.: (51)91287530
Linux Counter #281893

Centro Universitário Ritter dos Reis
http://www.ritterdosreis.br
ritter@ritterdosreis.br
Fone/Fax.: (51)32303341


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