[jira] [Commented] (SLING-4801) Add support for Nashorn in the JavaScript Scripting Engine

["Radu Cotescu (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SLING-4801?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14600897#comment-14600897 ] 

Radu Cotescu commented on SLING-4801:
-------------------------------------

While researching how to implement this I've also worked on a Sightly JavaScript Use Provider using the Nashorn implementation. The Sightly performance tests only showed a 25% performance increase of running the same JavaScript code on Nashorn instead of Rhino.

However my opinion is that we should instead try to optimise the Rhino implementation (see SLING-913 and SLING-915) due the multiple environment restrictions that Nashorn currently imposes:

* run Sling on JRE > =1.8.0_45 (Nashorn had performance problems before)
* there's no way to currently provide the same JS implementation of the Resource API
* Nashorn has to be configured specifically for Sling's use case so that all its caching strategies are turned on; for Sling's use case - running multiple small JavaScript scripts repeatedly - Nashorn is not necessarily the best option due to its relatively slow warmup

For further reference I've attached a patch that provides the following features:
* a new {{org.apache.sling.scripting.javascript.nashorn}} bundle that only runs on JRE >= 1.8
* a new {{org.apache.sling.scripting.sightly.js.provider.nashorn}} bundle that takes advantage of the Nashorn features
* it exposes the {{jdk.nashorn.api.scripting;version="0.0.0.1_008_JavaSE"}} package for JRE 1.8
* it provides a way to test the performance improvements through the Sightly performance tests, which is currently the most important consumer for the JavaScript scripting engine



> Add support for Nashorn in the JavaScript Scripting Engine
> ----------------------------------------------------------
>
>                 Key: SLING-4801
>                 URL: https://issues.apache.org/jira/browse/SLING-4801
>             Project: Sling
>          Issue Type: Improvement
>          Components: Scripting
>    Affects Versions: Scripting JavaScript 2.0.16
>            Reporter: Radu Cotescu
>            Assignee: Radu Cotescu
>             Fix For: Scripting JavaScript 2.0.18
>
>
> The {{org.apache.sling.scripting.javascript}} bundle should attempt to use Nashorn, if available on the user's platform, for running JS code. Alternatively it should switch to Rhino if the JRE is < 1.8.
> Requirements:
> * need to expose the {{jdk.nashorn.api.scripting;version="0.0.0.1_008_JavaSE"}} package on JRE >= 1.8 in Sling's {{launchpad/base/src/main/resources/jre-1.8.properties}} properties files
> * the Rhino and Nashorn implementations need to co-exist, so that customers still running on Java < 8 can use the Rhino implementation; the switch from Rhino to Nashorn should happen automatically but should also be made configurable in case customers really want to use a specific implementation; while the Nashorn implementation requires Java 8 (and this can easily be handled through the {{Require-Capability}} \[0\] and {{Bundle-RequiredExecutionEnvironment}} \[1\] manifest headers) and the bundle implementing Nashorn support won't start if the detected Java version is < 8, a non-sticky run mode / configuration should handle the switch if customers would still like to use the Rhino implementation on Java >= 8
> * need to find a way to inject custom properties to all instances of a class, similar to Rhino's host objects \[2\] (thread open on Nashorn's dev list at \[3\]); this is needed in order to assure JavaScript API backwards compatibility with the JS API exposed through the Rhino implementation currently available in {{org.apache.sling.scripting.javascript}}; it seems that Nashorn's public API only allows proxying an object, not all instances of a class



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