Hi Joao,
the following test fails immediately for me with "java.lang.RuntimeException:
Expected: Thread[ForkJoinPool.commonPool-worker-4,5,main], received:
Thread[main,5,main]":
@Test
public void testClosureThreadSafety() throws ScriptException {
final ScriptEngine engine = new
ScriptEngineManager().getEngineByName("nashorn");
String testJsFunction = (
" (function outerFunction(currentThreadName) {\n" +
" function innerFunction() {\n" +
" return currentThreadName;\n" +
" }\n" +
" return innerFunction;\n" +
" })(java.lang.Thread.currentThread().toString())\n");
ScriptObjectMirror jsFunction = (ScriptObjectMirror)
engine.eval(testJsFunction);
IntConsumer invokeAndTest = i-> {
String currentThreadName = Thread.currentThread().toString();
Object received = jsFunction.call(jsFunction);
if (!currentThreadName.equals(received)) {
throw new RuntimeException("Expected: " + currentThreadName +
", received: " + received);
}
};
IntStream.range(0, 10).parallel().forEach(invokeAndTest);
}
The outer function returns its inner function, which contains „currentThread“
as a reference to its closure (i.e. a reference to outerFunction’s
„currentThread“ parameter). That closure property „currentThread“ will be set
to the name of the current thread only once (in engine.eval(testJsFunction)),
and subsequent calls to innerFunction will always return the name of that
thread (and not of the current thread that calls innerFunction).
If your Javascript code is under your control, this may not be a problem, as
you can change the code. In our case, we are using an existing Javascript
library „Handlebars“ that we cannot change, which seems to be keeping function
objects with closures around just like the above code does in Java.
Regards,
Jörg
Am 20.02.2017 um 13:00 schrieb João Paulo Varandas
<joaovaran...@inpaas.com<mailto:joaovaran...@inpaas.com>>:
Hi Jorg.
Could you send us a code snippet?
I have never seem such problem when using closures. In my project, I use a
single engine for whole web application. My tomcat is running with 150
maxThreads and it seems to be working fine. I test that in each build by
running the test case below:
https://gist.github.com/joaovarandas/f80a9cb5548a9d620e4da1ace2729911
The idea in this test is to use a single engine and run a closure from
one-thread or multiple-threads simultaneously and then read data from those
closures.
PS.: Should I send the source code directly in the mail body for future readers?
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2017-02-19 18:30 GMT-03:00 Frantzius, Jörg
<joerg.frantz...@aperto.com<mailto:joerg.frantz...@aperto.com>>:
… to correct myself, with code that contains closures, it’s probably
global-per-thread on a single engine that remains as the least
resource-consuming option (we were using a single global on single engine for
all threads, in order to share expensively computed Javascript state between
them).
From what I understand, global-per-thread could be implemented e.g. by having a
ThreadLocal<ScriptContext> and always using that as the context in
ScriptEngine.eval(script, context).
It would be good to know then whether global-per-thread on single engine still
allows for sharing Nashorn’s code optimization between threads? That would
already be great (and as Nashorn *is* great, I’m positive here :)
Regards,
Jörg
Am 19.02.2017 um 00:47 schrieb Frantzius, Jörg
<joerg.frantz...@aperto.com<mailto:joerg.frantz...@aperto.com><mailto:joerg.frantz...@aperto.com<mailto:joerg.frantz...@aperto.com>>>:
Hi,
it begins to dawn on me that closures aren’t thread-safe, at least that would
explain crosstalk issues we’re seeing in JMeter tests (with a single engine for
multiple threads).
It would be good to know (and I guess for others as well) if somebody can
confirm this?
Perhaps thread-safety of closures was thinkable if Nashorn somehow stored
closure state in ThreadLocals, but I guess that’s neither happening nor planned?
From what I understand, closures are pervasive in Javascript code out there,
and anybody using such code will currently be forced to use engine-per-thread.
Thanks for any hints,
Jörg
---
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