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From "Dan Tran" <dantt...@hotmail.com>
Subject Re: Singleton across multiple contexts
Date Sun, 15 Jun 2003 18:22:17 GMT
Antonio, remove your email digital certificate.  Most of us can not answer
your question since the reply forcing us to have a digital certificate as
well.

-Dan

----- Original Message ----- 
From: "Filip Hanik" <mail@filip.net>
Newsgroups: Tomcat
Sent: Sunday, June 15, 2003 10:59 AM
Subject: RE: Singleton across multiple contexts


> I have not followed this thread,
> but putting the class in common/lib or shared/lib should make it a
singleton
> across contexts
>
> Filip
>
> > -----Original Message-----
> > From: Antonio Fiol Bonnín [mailto:fiol.bonnin@terra.es]
> > Sent: Sunday, June 15, 2003 10:52 AM
> > To: Tomcat Users List
> > Subject: Re: Singleton across multiple contexts
> >
> >
> > >
> > >
> > >>- Extract the component into a separate JVM, and connect to it
> > via socket.
> > >>
> > >>This is what I'd do, but I'd also write a client class to get access.
I
> > >>suppose you could use RMI or something, but I'm not familiar with
that.
> > >>Whatever you're comfortable with, I guess.
> > >>
> > >>You could also spin off this class in it's own thread inside one of
your
> > >>classloaders. That way it would shutdown and start up with the server
> > >>(or maybe that's a drawback...) and you wouldn't have to add the
> > >>overhead of another VM.
> > >>
> >
> > In fact, it *is* a thread. It starts and stops with the server.
> > Everything was really beautiful until I had to split my app in four
> > contexts.
> >
> > What I dislike is having to go out of the app to do app-internal calls.
> > RMI, socket, CORBA, HTTP, ... I don't mind: I just dislike the idea.
> >
> > >>- Extract the component into another context, and connect to it
> > via HTTP.
> > >>
> > >>
> > >
> > >yuck.
> > >
> > >
> > >This isn't for locking or something is it?
> > >
> >
> > Nope. ;-)
> >
> > > I get the feeling you're
> > >trying to use a class for storing or accessing something the way most
> > >people use a database...
> > >
> >
> > I do have a database. Databases are supposed to store data,
> > aren't they? ;-)
> >
> > Now seriously... My application includes a web interface to a "kind of"
> > workflow system.
> >
> > This component is the "workflow engine", which is in charge for
> > automatic (background) state changes and actions. When my
> > business/persistence logic changes a state, new potential tasks for this
> > "engine" arise. So it has to be notified (=called) from any context that
> > may change a state.
> >
> >
> >
> > >
> > >On Sun, 2003-06-15 at 08:21, Antonio Fiol Bonnín wrote:
> > >
> > >
> > >>Hello,
> > >>
> > >>This question is probably not specific to Tomcat, but a
Tomcat-specific
> > >>answer could well suit my needs.
> > >>
> > >>I have an application which I have split in several different
contexts.
> > >>I have done so, to allow different kinds of access to the app,
> > depending
> > >>on the web server the requests are coming from.
> > >>
> > >>However, I need a common unique component that "ties" all the contexts
> > >>together.
> > >>
> > >>There must be a *single* instance of this component, otherwise
> > >>inconsistencies or duplicate work might arise. OTOH, it must be
> > >>accessible from all the contexts.
> > >>
> > >>Calls to this component are very simple (calls to void methods) but
> > >>moderately frequent.
> > >>
> > >>I have thought of several possibilities:
> > >>
> > >>- Extract the component into a separate JVM, and connect to it
> > via socket.
> > >>- Extract the component into another context, and connect to it
> > via HTTP.
> > >>--- I like none of those.
> > >>
> > >>- Create the instance from the first context needing it, and making it
> > >>available to all of them.
> > >>--- I like this best, but I have no idea of how to do that.
> > >>
> > >>
> > >>Yours sincerely,
> > >>
> > >>
> > >>Antonio Fiol
> > >>
> > >>
> >
> >

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