ScriptEngine reusing arguments? - kotlin

Question

I've been running into weird issues with Kotlins JSR-223 implementation for ScriptEngine (kotlin-scripting-jsr223)
Basically, i have a condition, which i parse and compile into a CompiledScript:
fun parse(clazz: KClass<out GenericEvent>, condition: String): String {
val simpleName = clazz.simpleName
return """
import ${clazz.java.name}
val condition: $simpleName.() -> Boolean = { ${trimQuotes(condition)} }
fun check(event: $simpleName) = condition.invoke(event)
""".trimIndent()
}
I then compile the resulting string using (engine as Compilable).compile(code) into a CompiledScript.
Now, whenever i try to eval() these CompiledScripts multiple times in a very short period of time:
listener.compiledScript.eval()
return#Callable (engine as Invocable).invokeFunction("check", event)
It seems to reuse old previously used arguments. First i thought it was a thread-safety issue (Because it heavily looks like one), but using a Mutex or a single threaded executor to compile the script didn't change this behavior.
Full code:
override suspend fun onEvent(e: GenericEvent) {
val events = listeners[e.javaClass] ?: return
events.forEach { listener ->
try {
val event = e.javaClass.cast(e)
if (listener.compiledScript != null) {
val result = executor.submit(Callable { // executor = Executors.newSingleThreadExecutor()
println(Thread.currentThread().id) // confirms it's always the same thread
listener.compiledScript.eval()
return#Callable (engine as Invocable).invokeFunction("check", event)
}).get()
if (result is Boolean && result)
listener.method.callSuspend(listener.instance, event)
} else {
listener.method.callSuspend(listener.instance, event)
}
} catch (throwable: Throwable) {
log.error("An error occurred while evaluating listener condition!", throwable)
}
}
}
At first, this works as expected
Condition: message.contentRaw == "first"
Is actually: first
but it creates weird, but always the same patterns afterwards.
Condition: message.contentRaw == "first"
Is actually: second
Condition: message.contentRaw == "second"
Is actually: second
Condition: message.contentRaw == "first"
Is actually: second
Condition: message.contentRaw == "second"
Is actually: second
Condition: message.contentRaw == "first"
Is actually: second
Condition: message.contentRaw == "second"
Is actually: second
(These messages shouldn't be printed if the condition isn't true)
I did some debugging earlier in which i printed the condition and the actual event in the compiled code itself, and it did reuse the previous event parameter in check(), even though i actually used an entirely different one into it.

Answer 1

Fixed it by creating a new SimpleScriptContext, passing it into the eval() method of CompiledScript, and then calling ScriptEngine#setContext with the newly created context before calling invokeFunction()
Crazy stuff!