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Posted to dev@commons.apache.org by Oliver Heger <Ol...@t-online.de> on 2003/11/03 21:00:21 UTC
Re: [configuration] thread-safe?
Charles,
as I see nobody of the commiters has answered you so far. Then I will
try to give you a hint though I don't have written this code. So what
follows need not to be 100% correct.
Well, at the heart of the implementation of all so far existing
Configuration classes is an instance of the class SequencedHashMap from
common collections. So thread safety of [configuration] boils down to
the thread-safety of this class. The documentation in [collections]
states that the class is not thread safe, but this statement probably
refers to manipulation in multiple threads and not to read only access.
So it may be worth to ask the [collections] guys if read only access of
a SequencedHashMap instance from multiple threads is safe.
IMHO usage of ConfigurationFactory from a singleton is a good idea - if
it comes out that thread-safety is guaranteed and access is read only. I
think that is the easiest way of allowing application wide (okay:
classloader wide) access to the configuration. Maybe it would make sense
to support such a singleton like access directly in [configuration]?
I hope I could help you.
Oli
Charles Crouch wrote:
> Hi
>
> I'm looking to use the configuration package and wanted to wrap it in
> my own Singleton e.g.
> MyConfiguration.getInstance().getProperty(key). The
> ConfigurationFactory, referencing various Properties files, would get
> setup in the constructor of MyConfiguration.
>
> If I do not intend to add properties at run time, is it ok to use
> MyConfiguration in a mutli-threaded environment, i.e. once the
> ConfigurationFactory has been loaded up, is it safe for multiple
> threads to retrieve properties at the same time.
>
> I'd really appreciate some advice if the Singleton pattern is not the
> recommend approach. I'm trying to centralise where the Configuration
> is setup and also trying to ensure that the Properties files would
> only get read in once, rather than each call to retrieve a property.
>
> Thanks in advance
> Charles
>
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Re: [configuration] thread-safe?
Posted by Oliver Heger <Ol...@t-online.de>.
Eric,
I haven't thought about the details of accessing properties in a
singleton yet.
In the first line I was interested in the advantages such an approach
would have for initialization of the configuration framework. On its
creation the singleton instance could locate the configuration
description file by some criteria (to be defined, e.g. by the searching
the class path), set up a ConfigurationFactory and then load all
specified configuration sources. This would be a great help for developers.
I had a look at the code you pointed out, but because I don't know
anything about Avalon and Turbine I don't fully understand what's going
on there. But I think the configure() method of
DefaultConfigurationService performs some tasks that would have to be
done by our singleton, too. Am I right?
To come back to thread safety once more: In my opionion it is important
that the configuration classes guarantee to be thread-safe in read only
accesses. Well, I am quite sure that this is already the case, but it
would be certainly a good idea to make a corresponding note somewhere in
the documentation.
Oli
Eric Pugh wrote:
>Good reply Oliver. Are you thinking of some sort of SingletonConfiguration
>object that just has a single static Configuration object.. So, whether you
>call it as SingletonCongifuration.getString("test.value") or create an
>object singletonConfiguration.getString() you get the same thing?
>
>Something to look at is an Avalon wrapper I tossed out in Fulcrum[1]. This
>provides a "singleton" in terms of the Container being responsible for
>returning just one instance of the object, verus loading multiple. It seems
>to me that as long as we are talking readonly, then it doesn't matter how
>many threads read, correct? And, if you want to write, just toss a
>sychronize keyword?
>
>Eric
>
>
>[1]
>http://jakarta.apache.org/turbine/fulcrum/fulcrum-configuration/index.html
>
>
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RE: [configuration] thread-safe?
Posted by Eric Pugh <ep...@upstate.com>.
Good reply Oliver. Are you thinking of some sort of SingletonConfiguration
object that just has a single static Configuration object.. So, whether you
call it as SingletonCongifuration.getString("test.value") or create an
object singletonConfiguration.getString() you get the same thing?
Something to look at is an Avalon wrapper I tossed out in Fulcrum[1]. This
provides a "singleton" in terms of the Container being responsible for
returning just one instance of the object, verus loading multiple. It seems
to me that as long as we are talking readonly, then it doesn't matter how
many threads read, correct? And, if you want to write, just toss a
sychronize keyword?
Eric
[1]
http://jakarta.apache.org/turbine/fulcrum/fulcrum-configuration/index.html
> -----Original Message-----
> From: Oliver Heger [mailto:Oliver.Heger@t-online.de]
> Sent: Monday, November 03, 2003 9:00 PM
> To: Jakarta Commons Developers List
> Subject: Re: [configuration] thread-safe?
>
>
> Charles,
>
> as I see nobody of the commiters has answered you so far. Then I will
> try to give you a hint though I don't have written this code. So what
> follows need not to be 100% correct.
>
> Well, at the heart of the implementation of all so far existing
> Configuration classes is an instance of the class
> SequencedHashMap from
> common collections. So thread safety of [configuration] boils down to
> the thread-safety of this class. The documentation in [collections]
> states that the class is not thread safe, but this statement probably
> refers to manipulation in multiple threads and not to read
> only access.
> So it may be worth to ask the [collections] guys if read only
> access of
> a SequencedHashMap instance from multiple threads is safe.
>
> IMHO usage of ConfigurationFactory from a singleton is a good
> idea - if
> it comes out that thread-safety is guaranteed and access is
> read only. I
> think that is the easiest way of allowing application wide (okay:
> classloader wide) access to the configuration. Maybe it would
> make sense
> to support such a singleton like access directly in [configuration]?
>
> I hope I could help you.
>
> Oli
>
> Charles Crouch wrote:
>
> > Hi
> >
> > I'm looking to use the configuration package and wanted to
> wrap it in
> > my own Singleton e.g.
> > MyConfiguration.getInstance().getProperty(key). The
> > ConfigurationFactory, referencing various Properties files,
> would get
> > setup in the constructor of MyConfiguration.
> >
> > If I do not intend to add properties at run time, is it ok to use
> > MyConfiguration in a mutli-threaded environment, i.e. once the
> > ConfigurationFactory has been loaded up, is it safe for multiple
> > threads to retrieve properties at the same time.
> >
> > I'd really appreciate some advice if the Singleton pattern
> is not the
> > recommend approach. I'm trying to centralise where the
> Configuration
> > is setup and also trying to ensure that the Properties files would
> > only get read in once, rather than each call to retrieve a property.
> >
> > Thanks in advance
> > Charles
> >
> > _________________________________________________________________
> > Sign-up for a FREE BT Broadband connection today!
> > http://www.msn.co.uk/specials/btbroadband
> >
> >
> >
> ---------------------------------------------------------------------
> > To unsubscribe, e-mail: commons-dev-unsubscribe@jakarta.apache.org
> > For additional commands, e-mail: commons-dev-help@jakarta.apache.org
> >
> >
>
>
>
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