Threading Problem with Nashorn

[Attila Szegedi]

Hi,

thanks for experimenting with Nashorn!

As far as your example is concerned, Nashorn is not thread safe by design. Indeed, if you evaluate 

	new NashornScriptEngineFactory().getParameter("THREADING")

it'll return null, which means "the engine implementation is not thread safe, and cannot be used to execute scripts concurrently on multiple threads" -- see <http://docs.oracle.com/javase/7/docs/api/javax/script/ScriptEngineFactory.html#getParameter(java.lang.String)>

Nashorn library internals themselves are thread safe to the degree that we're using synchronized and concurrent data structures for various internal static caches et cetera, but JavaScript programs executing within a single engine instance are not thread safe.

As I said, this is by design. ECMAScript 5.1 language specification doesn't define multithreading semantics for programs written in the language; they are inherently single threaded. If we were to make them thread safe, we'd be sacrificing single threaded performance for a behavior that falls outside of the specification. You can always create one script engine per thread using the same factory - that should work in a multithreaded scenario.

Actually, in your above example, since the JavaScript program has no explicit guarding of concurrent access to variable `i` you seem like you would actually even expect to have an engine that has "THREAD-ISOLATED" as its threading model instead of the simpler "MULTITHREADED" - that' very rare in an engine, usually hard to implement efficiently (do you clone all of the data up front? do you implement a copy-on-write semantics?) , and is functionally simpler to just have a non-threadsafe engine and let the users manage their own thread isolation by creating one engine instance per thread.

Cheers,
  Attila.

On Jul 9, 2013, at 10:01 AM, Tobias Schlottke <tobias.schlottke at gmail.com> wrote:

> 
> Hi there,
> 
> we're currently planning to switch our infrastructure from Rhino to Nashorn but are experiencing some threading Issues that nobody addressed so far.
> I tweeted with Jim Laskey and he kindly asked me to post it to this list.
> 
> Example:
> 
> https://gist.github.com/tobsch/5955518
> 
> Could could you check this example and check if this really is a problem in your eyes or if it is supposed to be this way?
> 
> Best,
> 
> Tobias
>