The class cache

A. Sundararajan sundararajan.athijegannathan at
Wed Mar 12 10:30:14 UTC 2014

Actually, the plan is to get to 8u20 - which is an update release after 
jdk8 GA.

Script engine is associated with a single nashorn Context instance. One 
nashorn Context instance may be associated with multiple nashorn Global 
instances. The class sharing as of today is per global instance - after 
Hannes' change, it'll be per Context instance (and so sharing across all 
globals associated with a nashorn Context instance).

ScriptEnvironment._class_cache_size is set from --class-cache-size 
option. Currently it is interpreted as per-global cache size. After 
Hannes' change, it is per-Context class cache size.


On Wednesday 12 March 2014 03:28 PM, Tal Liron wrote:
> I did see that change come through, but I thought it was a JDK9 
> feature... great to know it is for JDK8!
> I'll note that I'm not using ScriptEngine, but instead working on the 
> Scripturian implementation. How will ScriptEngine make sure to reuse 
> the cache?
> Would it be possible to also allow a shared ClassCache instance for 
> all globals? How about a ScriptEnvironment._class_cache_size boolean 
> option to enable this?
> On 03/12/2014 05:50 PM, Hannes Wallnoefer wrote:
>> Hi Tal,
>> I'm right now pushing a change for JDK-8021350 that allows sharing 
>> script classes between global scopes. Currently, script classes are 
>> bound to the global object in various ways, so the change is not 
>> trivial, and it's not possible to share compiled scripts between 
>> global scopes with the nashorn.jar in current JDK8 builds. The script 
>> sharing feature is planned for the 8u20 release.
>> The class sharing will be per script engine, meaning that if you use 
>> multiple scopes with one script engine classes will be reused, when 
>> you use multiple script engines scripts will be recompiled for each 
>> engine.
>> I'd be interested to know whether this would work for you. If you'd 
>> like to test the class sharing feature I can help you getting started.
>> Hannes
>> Am 2014-03-12 10:27, schrieb Tal Liron:
>>> In Nashorn, the ClassCache is set per Global instance.
>>> This is fine if your application has only one global instance. 
>>> However, my application design involves creating many Global 
>>> instances. (Actually, I create and destroy them on the fly per user 
>>> request in an HTTP server scenario.) The problem is that all code 
>>> has to constantly be recompiled, and the cache is essentially never 
>>> used. Since recompilation is so very expensive in Nashorn, this 
>>> results in awful performance.
>>> How can I implement a shared ClassCache? I can't extend and modify 
>>> Global behavior, because it's a final class.
>>> I've tried to cache ScriptFunction instances myself, but I get 
>>> exceptions when I try to run them with a different Global instance 
>>> than the one that created them.

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