static JSContext issue with multiple threads

[BlixLT]

It seems that static JSContext (Iterator.rruleContext) is causing problems when there are calculations on different threads. It happens, when in some (not so rare) cases two context?.evaluateScript("var rule = new RRule({ \(ruleJSONString) })") is being called one after another and only then two dates calculations

        guard let allOccurrences = context?.evaluateScript("rule.all()").toArray() as? [Date] else {
            return []
        }

also one after another. And in such case the second new RRule({ \(ruleJSONString) }) overwrites first RRule's properties in static JSContext and first calculation uses wrong parameters.
One way to avoid this issue would be reduce evaluateScript calls (create a rule and evaluate it in one evaluateScript call. I couldn't reproduce this issue after such modification):
guard let allOccurrences = Iterator.rruleContext?.evaluateScript("new RRule({ \(ruleJSONString) }).all()").toArray() as? [Date] else {
instead of

        let _ = Iterator.rruleContext?.evaluateScript("var rule = new RRule({ \(ruleJSONString) })")
         guard let allOccurrences = Iterator.rruleContext?.evaluateScript("rule.all()").toArray() as? [Date] else {

I also implemented a test, that could help quite easily reproduce the issue: you can launch Sample app and make testRRuleIteratorMultipleThreads() call in the viewDidLoad(). There are 2 background thread that generates rrule and checks the returned dates. If everything worked as expected, then there would be no logs in console similar to print("dates mismatch, got: ", occurrences.first, ", expected: ", startDate) - first date returned by rrule's Iterator.rruleContext?.evaluateScript should be equal to its startDate. But in some 5th-10th iteration one thread overrides other's rrule parameters and wrong parameters are being used. I hope I made myself clear.