[jira] [Resolved] (JENA-1029) Add a Jena-wide subsystem lifecycle

["Andy Seaborne (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/JENA-1029?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Andy Seaborne resolved JENA-1029.
---------------------------------
    Resolution: Done

> Add a Jena-wide subsystem lifecycle
> -----------------------------------
>
>                 Key: JENA-1029
>                 URL: https://issues.apache.org/jira/browse/JENA-1029
>             Project: Apache Jena
>          Issue Type: Improvement
>    Affects Versions: Jena 3.0.0
>            Reporter: Andy Seaborne
>
> A subsystem lifecyclefor Jena would provide the hook for:
> * basic wiring together e.g. wiring RIOT into Jena core
> * initialization e.g. {{TDB.init()}} becomes redundant
> * starting and stopping in large systems, e.g. starting and stopping Fuseki2 when in a Tomcat server
> This proposal is as simple as possible. It is for system bootstrap and basic lifecycle. It is not intended to work for a mixture of jars from different Jena releases.
> *Sub-system Interface*
> {code:title=JenaSubsystemLifecycle|borderStyle=solid}
> public interface JenaSubsystemLifecycle {
>     public void start() ;
>     public void stop() ;
> }
> {code}
> {{stop}} would not be called normally as part of JVM exit (code can do that itself anyway). It is in support of start-stop-(re)start and only called if there is a hook for such a cycle. {{stop}} is more of a placeholder for the moment.
> *Registry*
> There is a single registry:
> {code:title=JenaSubsystemRegistry|borderStyle=solid}
> public class JenaSubsystemRegistry {
>     public static void add(JenaSubsystemLifecycle module) ;
>     public static boolean isRegistered(JenaSubsystemLifecycle module) ;
>     public static void remove(JenaSubsystemLifecycle module) ;
>     public static int size() ;
>     public static boolean isEmpty() ;
>     public static void forEach(Consumer<JenaSubsystemLifecycle> action) ;
> }
> {code}
> *Ensuring initialization*
> Jena core provides a "system init" that is cheap to call if initialization has already occurred. It should attempt the first call  as early as possible.
> When initializing, it runs a {{ServiceLoader}} cycle to discover any {{JenaSubsystemLifecycle}} implementations described in a {{META-INF/services/...}} file and populates the registry. Then the registry is 
> used to call {{start()}} in some unspecified order.



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