Paul Bjorkstrand created SLING-12279:
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Summary: Move Sling Model cache holder for Resource and
ResourceResolver adaptables into the resource resolver property map
Key: SLING-12279
URL: https://issues.apache.org/jira/browse/SLING-12279
Project: Sling
Issue Type: Improvement
Components: Sling Models
Affects Versions: Models Implementation 1.6.4
Reporter: Paul Bjorkstrand
There have been several instances of issues with model caching over the years,
the most recent being SLING-12259 and [this
thread|https://www.mail-archive.com/[email protected]/msg131926.html] from
Jörg Hoh. These recent issues have been around cached items sticking
around for too long. In that thread, it was discussed using
{{[ResourceResolver#getPropertyMap()|https://github.com/apache/sling-org-apache-sling-api/blob/master/src/main/java/org/apache/sling/api/resource/ResourceResolver.java#L888]}}
whenever possible. This binds the cache to the lifecycle of the
ResourceResolver, avoiding the global cache altogether.
After looking at the [current
implementation|https://github.com/apache/sling-org-apache-sling-models-impl/blob/master/src/main/java/org/apache/sling/models/impl/ModelAdapterFactory.java#L341],
there is already a divergence that binds the cache for request-based models to
the request, by putting the cache in the request attribute.
This proposes to do a similar change for Resource/Resolver based models, and
use the resolver's property map to bind the cache for those adaptables to the
lifecycle of the ResourceResolver. Resources are already (largely) bound to the
lifecycle of the ResourceResolver that supplied them, and binding the models
that come from these Resources seems to be a reasonable approach.
This will greatly reduce the lifetime of model objects, reducing the likelihood
of the JVM's GC being put under pressure in cases when cached models [reference
the original adaptable using
{{@Self}}|https://sling.apache.org/documentation/bundles/models.html#a-note-about-cache-true-and-using-the-self-injector].
As a bonus, if the cache object implements {{Closeable}}, the Sling
Implementation will call {{close()}} on the cache when the resolver is closed,,
giving us further control over the lifetime of objects in the cache.
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