Service interface

[Leo Simons <ma...@leosimons.com>]

what's our definition of a Service? We used to have a nice one, no?
Can't find it....

- Leo

from javadoc:
"This is a marker interface that all Services must implement. A Service is a
behavioural contract that an object implements."

from blockinfo spec:
"The services section documents the services that this block can offer other
Blocks. The service instances indicate an interface and a version. The
interface MUST extend org.apache.phoenix.Service. This section is optional
and a Block can choose to not offer any services."

from turbine:
"Services are singletons within the Turbine Framework which have pluggable
implementation, and are capable of participating in the Turbine startup and
shutdown. As Services are Singletons, there is only one instance of each
service in the system. Memory or connections are allocated once only and the
internal state is common to all requesting clients. Services can access
ServletConfig at system startup time to process relative paths and similar
functionality, they can also access RunData on the first Turbine doGet
execution to get the environment Turbine is operating under and with.
Services can also initialize themselves before they are requested by the
client for the first time. A Service that is never used will not allocate
resources to itself. A Service can also execute actions upon the system
being shutdown, such as closing open connections. The Singleton pattern also
allows for the Services to be accessed from anywhere within your code.

The Life Cycle of a Service begins with the Services constructor. A Service
does not do much in it's contructor. Especially it should not allocate any
costly resources like large memory structure, DB or Network connections,
etc. The Service may be in the properties file, but unless a client using
the application needs the Service in question, there is no point starting
the Service."


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Re: Service interface

[Peter Donald <do...@apache.org>]

On Wed, 22 Aug 2001 16:34, Leo Simons wrote:
> what's our definition of a Service? 

A behavioural or "work" interface. ie An interface a client can use to do 
something. Not sure how to make that more clearer though ;) Maybe if we 
described service as the java interface for a Role ??? Not sure.

It differs from turbines definition in a few key points. Turbine combines 
lifecycle management and work interface, two othogonal concepts. Phoenix 
allows multiple instances and implementations of a Service to be inside same 
JVM. Turbine implementation mandates a specific access approach while Phoenix 
can theoretically be accessed via any method (since it uses ComponentManager 
abstraction) ... however not sure if this is really needed.

> We used to have a nice one, no? Can't find it....

not sure. My definition is in my head. Are you volunteering to write a sane 
description ? ;)

>
> - Leo
>
> from javadoc:
> "This is a marker interface that all Services must implement. A Service is
> a behavioural contract that an object implements."
>
> from blockinfo spec:
> "The services section documents the services that this block can offer
> other Blocks. The service instances indicate an interface and a version.
> The interface MUST extend org.apache.phoenix.Service. This section is
> optional and a Block can choose to not offer any services."
>
> from turbine:
> "Services are singletons within the Turbine Framework which have pluggable
> implementation, and are capable of participating in the Turbine startup and
> shutdown. As Services are Singletons, there is only one instance of each
> service in the system. Memory or connections are allocated once only and
> the internal state is common to all requesting clients. Services can access
> ServletConfig at system startup time to process relative paths and similar
> functionality, they can also access RunData on the first Turbine doGet
> execution to get the environment Turbine is operating under and with.
> Services can also initialize themselves before they are requested by the
> client for the first time. A Service that is never used will not allocate
> resources to itself. A Service can also execute actions upon the system
> being shutdown, such as closing open connections. The Singleton pattern
> also allows for the Services to be accessed from anywhere within your code.
>
> The Life Cycle of a Service begins with the Services constructor. A Service
> does not do much in it's contructor. Especially it should not allocate any
> costly resources like large memory structure, DB or Network connections,
> etc. The Service may be in the properties file, but unless a client using
> the application needs the Service in question, there is no point starting
> the Service."
>
>
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> To unsubscribe, e-mail: avalon-dev-unsubscribe@jakarta.apache.org
> For additional commands, e-mail: avalon-dev-help@jakarta.apache.org

-- 
Cheers,

Pete

*-----------------------------------------------------*
* "Faced with the choice between changing one's mind, *
* and proving that there is no need to do so - almost *
* everyone gets busy on the proof."                   *
*              - John Kenneth Galbraith               *
*-----------------------------------------------------*

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