On Wednesday, November 28, 2012, Robert Hailey wrote:
>
> I've read the "everyone out of the pool" blog post, but have not been able
> to find an example of how to best use per-thread value on a page or service
> (seems like what's provided is an internal tapestry case).
>
>
As always. Some of the best examples are in the Tapestry source code.
> As a (lazy?) tapestry developer, my first thought is to try this:
>
> @Inject
> private PerThreadValue<Integer> widgetRenderCount;
>
>
Although Tapestry could be extended to support this pattern, it is not so
out of the box.
> Which probably isn't the expected use-case, because it doesn't work: "no
> service implements PerThreadValue interface" (or thereabout)
>
> I then though I was probably looking one abstraction layer too deep (as
> the article does talk about transparent perthread access)... so then I
> thought of this:
>
> @Inject
> @PerThread
> private Integer widgetRenderCount;
>
> Which made a degree of sense because "Persist" is deprecated, but no such
> annotation exists.
>
> So then I thought I could create my own perthreadvalue-providing service
> (to realize the first example) like this:
>
> public void contributeMasterObjectProvider(
> OrderedConfiguration<ObjectProvider> configuration,
> final PerthreadManager perthreadManager
> )
> {
> configuration.add("PerThreadValue", new ObjectProvider() {
> public <T> T provide(Class<T> tClass, AnnotationProvider
> annotationProvider, ObjectLocator objectLocator) {
> return (T)perthreadManager.createValue();
> }
> });
> }
>
> ... but that fails due to the "MasterObjectProvider somehow depends on
> itself" error message and what's probably a blindingly-obvious lack of
> knowledge on my part concerning how tapestry actually provides virtually
> interfaced objects.
>
> So now I have fallen back to patterns like this, that seem to work, but
> seem to be much clunkier than I would expect:
>
> @Inject
> private PerThreadManager perThreadManager;
> private static PerThreadValue<Integer> widgetRenderCount;
>
> void afterRender() {
> if (widgetRenderCount==null) {
> widgetRenderCount=perthreadManager.createValue();
> }
> int count=widgetRenderCount.get(0);
> count++;
> log.debug("{} widgets have now rendered in this request!",
> count);
> widgetRenderCount.set(count);
> }
>
>
> Am I missing something? If so, how is PerThreadValue intended to be used?
The path of least resistance is to define your own service for tracking
this kind of per-request information. You can then inject this service into
any page or component that wants it.
The scope annotation can be used to configure that service as per-thread
http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/ioc/annotations/Scope.html
http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/ioc/ScopeConstants.html
>
> --
> Robert Hailey
>
>
>
--
Howard M. Lewis Ship
Creator of Apache Tapestry
The source for Tapestry training, mentoring and support. Contact me to
learn how I can get you up and productive in Tapestry fast!
(971) 678-5210
http://howardlewisship.com
