Scope leaked between contexts/optimization bug starting in Java 9

[James Laskey]

Try using the  --optimistic-types=false flag and see if that helps. 

Sent from my iPhone

> On Aug 19, 2019, at 4:48 PM, Ryan Berdeen <rberdeen at hubspot.com> wrote:
> 
> I've encountered what seems like bug introduced in Java 9 where variables
> can be leaked by the engine across separate contexts. I've extracted this
> minimal reproduction out of service I'm running in projection in Java 8.
> Gist: https://gist.github.com/also/412ce859f10f0b501bbfc43d15342dfc
> 
> Given this script
> 
> var x;
> function test() {
>  x = 1;
>  print(++test.calls);
>  eval('');
> }
> test.calls = 0;
> test();
> 
> Repeatedly running it with a new context in the same engine works fine in
> Java 8 (it will print "1" forever), but in Java 9+, things get weird. I
> tested on macOS in openjdk 12.0.2 2019-07-16 from Oracle.
> 
>    ScriptEngine engine = new
> ScriptEngineManager().getEngineByName("nashorn");
> 
>    for (int i = 0; i < 20; i++) {
>      SimpleScriptContext context = new SimpleScriptContext();
>      Bindings bindings = engine.createBindings();
>      context.setBindings(bindings, ScriptContext.ENGINE_SCOPE);
>      engine.eval(script, context);
>    }
> 
> 
> This logs
> 1
> 2
> 3
> 4
> ...
> 
> If you add a second `engine.eval(script, context);` to the loop, it starts
> to look like an optimization bug:
> 
> 1
> 1
> 2
> NaN
> 1
> 1
> 2
> NaN
> NaN
> NaN
> NaN
> NaN
> NaN
> NaN
> NaN
> NaN
> NaN
> NaN
> NaN
> NaN
> NaN
> NaN
> NaN
> NaN
> NaN
> NaN
> NaN
> NaN
> NaN
> NaN
> NaN
> NaN
> NaN
> 1
> 2
> 1
> 2
> 1
> 2
> 1
> 
> It seems to stabilize on 2, 1 after the 18th iteration. With a third call
> to "engine.eval(script, context);" in the loop, it settles sooner:
> 
> 1
> 1
> 1
> 2
> NaN
> NaN
> 1
> 1
> 1
> 1
> 1
> 1
> 
> It works as expected if you omit `context` in the calls to `engine.eval()`,
> if you omit the `x = 1;` or `eval('');` lines in the `test` function, if
> you call `print(++test.calls);` before `x = 1;`, or when using the
> "graal.js" engine.
> 
> I know GraalVM JS is probably the way forward here, but was hoping I'd be
> able to upgrade to Java 12 before making the switch.