One engine per worker thread would definitely work - this is maximum
isolation. This mode even avoids sharing script classers / loaders.
If that is not workable in your use-case, you can use a separate
ENGINE_SCOPE bindings (or separate ScriptContext) per thread. This will
separate ECMAScript globals to be thread specific. This mode allows for
script Class (compiled/loaded script Class objects) to be shared -- but
global state is not. This is partial sharing - but safe.
If you do share the default ScriptContext of the script engine across
threads, then it is up to you to take care of MT access/modification of
globals -- you could still carefully structure code to run script
functions in a such a way to avoid concurrent global modifications - but
it'd be practically difficult.
Hope this helps,
-Sundar
On 12/9/2015 2:58 PM, Frantzius, Jörg wrote:
Hi,
we’re using Oracle JDK’s Nashorn in a web application, where it is used to
render HTML markup in HTTP worker threads.
I remember having read somewhere that the creation of a ScriptEngine (i.e.
invocation of ScriptEngineFactory.getScriptEngine()) may have considerable
performance overhead, so probably it should be avoided to do this with every
incoming HTTP request. This is why we’ll go for keeping a ScriptEngine per
thread in a ThreadLocal.
On the other hand this may result in a large memory footprint, as there can be
200 HTTP worker threads, but we don’t have any experience with it yet.
The ScriptEngineFactory.getParameter()
Javadocs<http://docs.oracle.com/javase/8/docs/jdk/api/nashorn/jdk/nashorn/api/scripting/NashornScriptEngineFactory.html#getParameter-java.lang.String->
does list some interesting parameters for the key „THREADING“, that seem to make it
possible to have a singleton ScriptEngine instead, which could be used concurrently
from multiple threads. However, I have no clue whether this is either supported by
Nashorn, nor how to set this parameter on engine creation.
Is there per chance some recommended usage pattern for ScriptEngine in a web
server?
Thanks for any insights,
Jörg
---
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