You are viewing a plain text version of this content. The canonical link for it is here.
Posted to users@tomcat.apache.org by Antonio Fiol Bonnín <fi...@terra.es> on 2003/06/15 17:21:37 UTC
Singleton across multiple contexts
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
Re: Singleton across multiple contexts
Posted by Dan Tran <da...@hotmail.com>.
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" <ma...@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
> > >>
> > >>
> >
> >
---------------------------------------------------------------------
To unsubscribe, e-mail: tomcat-user-unsubscribe@jakarta.apache.org
For additional commands, e-mail: tomcat-user-help@jakarta.apache.org
Re: Singleton across multiple contexts
Posted by Mike Johnson <de...@miketec.org>.
On Sun, 2003-06-15 at 10:51, Antonio Fiol Bonnín wrote:
> 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.
>
With good reason. :-)
> I do have a database. Databases are supposed to store data, aren't they? ;-)
Application or workflow state is data, isn't it?
> 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.
The Tomcat user's list isn't the best place to discuss the design of
your application, but it seems there's no good way to use a singleton
across webapps. (Not that I searched the archives...)
Also, I guess you are relying on method synchronization/instantiation to
ensure that work gets done just once. That's one way of locking logic
(the easiest) but -- as you know -- it falls apart when you use multiple
classloaders. But there are other ways of locking, external file locks
or maybe database bits you can use to keep tack of state and future
actions.
The only other thing I can suggest is to consider your options carefully
before continuing. I don't have a clear understanding of what you've
already designed, but I'd avoid doing something hackish like sockets
inside Tomcat at pretty much any cost. If it can't be avoided, then I
guess you write it and debug the snot out of it.
Heck, I'd probably choose poll a queue table every three seconds before
writing socket layers. :-)
Anyway, you seem to know what you're doing, so good luck to you.
--
Mike Johnson <de...@miketec.org>
---------------------------------------------------------------------
To unsubscribe, e-mail: tomcat-user-unsubscribe@jakarta.apache.org
For additional commands, e-mail: tomcat-user-help@jakarta.apache.org
RE: Singleton across multiple contexts
Posted by Jacob L E Blain Christen <ja...@entheal.com>.
> I do have a database. Databases are supposed to store data,
> aren't they? ;-)
Yeah, which is why ...
> 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.
... you should use one here. You are describing state changes that need
to happen in an atomic manner and "exist" in one and only one place.
The semantics of db interactions are perfectly suited for what you are
trying to do.
--
Jacob L E Blain Christen
Entheal LLC
---------------------------------------------------------------------
To unsubscribe, e-mail: tomcat-user-unsubscribe@jakarta.apache.org
For additional commands, e-mail: tomcat-user-help@jakarta.apache.org
Re: Singleton across multiple contexts
Posted by Antonio Fiol Bonnín <fi...@terra.es>.
This seems a good idea. Would it be possible to reload this class
without trashing the whole Tomcat?
I don't think so... At least, I cannot imagine how it would be done.
I have just come across another possibility:
Store the singleton instance in the system properties.
What do you think of this? Is it calling for trouble?
Antonio Fiol
(This time w/o certificate)
Filip Hanik wrote:
>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
>>>>
>>>>
>>>>
>>>>
>>
>>
>
>
>---------------------------------------------------------------------
>To unsubscribe, e-mail: tomcat-user-unsubscribe@jakarta.apache.org
>For additional commands, e-mail: tomcat-user-help@jakarta.apache.org
>
>
>
>
---------------------------------------------------------------------
To unsubscribe, e-mail: tomcat-user-unsubscribe@jakarta.apache.org
For additional commands, e-mail: tomcat-user-help@jakarta.apache.org
RE: Singleton across multiple contexts
Posted by Filip Hanik <ma...@filip.net>.
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
> >>
> >>
>
>
---------------------------------------------------------------------
To unsubscribe, e-mail: tomcat-user-unsubscribe@jakarta.apache.org
For additional commands, e-mail: tomcat-user-help@jakarta.apache.org
Re: Singleton across multiple contexts
Posted by Antonio Fiol Bonnín <fi...@terra.es>.
>
>
>>- 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
>>
>>
Re: Singleton across multiple contexts
Posted by Mike Johnson <de...@miketec.org>.
Hi Antonio,
> - 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.
> - Extract the component into another context, and connect to it via HTTP.
>
yuck.
This isn't for locking or something is it? I get the feeling you're
trying to use a class for storing or accessing something the way most
people use a database...
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
--
Mike Johnson <de...@miketec.org>
---------------------------------------------------------------------
To unsubscribe, e-mail: tomcat-user-unsubscribe@jakarta.apache.org
For additional commands, e-mail: tomcat-user-help@jakarta.apache.org
Re: Singleton across multiple contexts
Posted by Tim Funk <fu...@joedog.org>.
Place the jar (or class) in common/lib (or common/classes) and all will be
"ok". That is - until you need to make a change to your singleton class (or
a class used by it) - in which case you will need to restart tomcat. (and not
restart your webapp)
-Tim
Antonio Fiol Bonnín wrote:
> This is the best I could find:
> --------------
> Each application is loaded with sepperate classloaders, so as long as the
> servlets are in the same application and the singleton is in it's classpath
> too it works.
> --------------
>
> My singleton has to work *across* applications.
>
> Any ideas?
>
>
> Thank you very much.
>
>
> Antonio Fiol
>
>
>
> Tim Funk wrote:
>
>> Look in the archives and search for past Singleton discussions.
>>
>> http://marc.theaimsgroup.com/?l=tomcat-user&w=2&r=1&s=singleton&q=b
>> http://marc.theaimsgroup.com/?l=tomcat-dev&w=2&r=1&s=singleton&q=b
>>
>> Otherwise ...
>> - EJB (???)
>> - Use a custom JNDI Factory (see tomcat jndi docs)
>>
>> -Tim
>>
>> 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
>>
>>
>>
>>
>> ---------------------------------------------------------------------
>> To unsubscribe, e-mail: tomcat-user-unsubscribe@jakarta.apache.org
>> For additional commands, e-mail: tomcat-user-help@jakarta.apache.org
>>
>>
>
---------------------------------------------------------------------
To unsubscribe, e-mail: tomcat-user-unsubscribe@jakarta.apache.org
For additional commands, e-mail: tomcat-user-help@jakarta.apache.org
Re: Singleton across multiple contexts
Posted by Antonio Fiol Bonnín <fi...@terra.es>.
This is the best I could find:
--------------
Each application is loaded with sepperate classloaders, so as long as the
servlets are in the same application and the singleton is in it's classpath
too it works.
--------------
My singleton has to work *across* applications.
Any ideas?
Thank you very much.
Antonio Fiol
Tim Funk wrote:
> Look in the archives and search for past Singleton discussions.
>
> http://marc.theaimsgroup.com/?l=tomcat-user&w=2&r=1&s=singleton&q=b
> http://marc.theaimsgroup.com/?l=tomcat-dev&w=2&r=1&s=singleton&q=b
>
> Otherwise ...
> - EJB (???)
> - Use a custom JNDI Factory (see tomcat jndi docs)
>
> -Tim
>
> 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
>
>
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: tomcat-user-unsubscribe@jakarta.apache.org
> For additional commands, e-mail: tomcat-user-help@jakarta.apache.org
>
>
Re: Singleton across multiple contexts
Posted by Tim Funk <fu...@joedog.org>.
Look in the archives and search for past Singleton discussions.
http://marc.theaimsgroup.com/?l=tomcat-user&w=2&r=1&s=singleton&q=b
http://marc.theaimsgroup.com/?l=tomcat-dev&w=2&r=1&s=singleton&q=b
Otherwise ...
- EJB (???)
- Use a custom JNDI Factory (see tomcat jndi docs)
-Tim
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
---------------------------------------------------------------------
To unsubscribe, e-mail: tomcat-user-unsubscribe@jakarta.apache.org
For additional commands, e-mail: tomcat-user-help@jakarta.apache.org