[jira] [Closed] (TAP5-795) Tapestry IoC should provide an OrderedConfiguration for EagerLoaded services

["Jochen Kemnade (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/TAP5-795?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Jochen Kemnade closed TAP5-795.
-------------------------------

    Resolution: Not a Problem

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> Tapestry IoC should provide an OrderedConfiguration for EagerLoaded services
> ----------------------------------------------------------------------------
>
>                 Key: TAP5-795
>                 URL: https://issues.apache.org/jira/browse/TAP5-795
>             Project: Tapestry 5
>          Issue Type: Improvement
>          Components: tapestry-ioc
>    Affects Versions: 5.1
>         Environment: Any
>            Reporter: Peter Stavrinides
>            Priority: Minor
>              Labels: bulk-close-candidate
>
> It is mentioned in the documentation that the order in which services are created is not defined when using eagerLoad(). This is somewhat counter productive in a sense as you can get into serious trouble If ordering of eagerloaded services is important (and very often it is, as the very concept implies ordering and availability before other services), yet ordering is ignored for eagerloaded services? 
> So by using :
> binder.bind(SomeService.class).eagerLoad(); you can produce a NPE or potentially work just fine and this IoC quirk goes undetected, which is a ticking time bomb. Perhaps this method should be renamed to eagerLoadUnordered() or better yet removed entirely, and another way of ordering these should be introduced.
> An illustrative example is given below with two eagerloaded services (SiteInitialise sets up database connections and the connection pool, ImageService loads a cache of image data, so implicitly ImageService requires SiteInitialise to be loaded first).
> //Example: The shell of the eagerloaded ImageService service
> public class ImageService {
>                  /** Cache to hold thumbnail images */
>                  private static ConcurrentHashMap<Integer, Thumbnail>
> imageCache_ = new ConcurrentHashMap<Integer, Thumbnail>();
>  
>                  public void preloadImageCache() {
>                                  DbConnection connection = null;
>                                  try {
>                         //This can potentially  turn into a Null Pointer Exception as the startup order is arbitrary
>                                     connection = DatabaseConnection.getReadConnection();
>                                                  //database query
>                                  } catch (Exception e) {
>                                                  //handle exception
>                                  }
>                  }
>                  public static ImageService build() {
>                                  return new ImageService();
>                  }
>                  public ImageService() {
>                                  preloadImageCache();
>                  }
>  }
> //Workaround: adding a dependency on the other eagerloaded service will solve
> it, but this is not a practical solution if there are many of these services
> public class ImageService {
>                  /** Cache to hold thumbnail images */
>                  private static ConcurrentHashMap<Integer, Thumbnail>
> imageCache_ = new ConcurrentHashMap<Integer, Thumbnail>();
>  
>                  public void preloadImageCache() {
>                                  DbConnection connection = null;
>                                  try {
>                                                  connection =
> DatabaseConnection.getReadConnection();
>                                                  //database query
>                                  } catch (Exception e) {
>                                                  //handle exception
>                                  }
>                  }
>                  public static ImageService build(SiteInitialise
> siteInitialise) {
>                                  return new ImageService(siteInitialise);
>                  }
>                  public ImageService(SiteInitialise siteInitialise) {
>                                  if(siteInitialise.isConnectionOk())
>                                                  preloadImageCache();
>                  }
>  }



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