static JSContext issue with multiple threads

Package.swift

@@ -0,0 +1,29 @@
+// swift-tools-version:5.3
+// The swift-tools-version declares the minimum version of Swift required to build this package.
+
+import PackageDescription
+
+let package = Package(
+    name: "RRuleSwift",
+    platforms: [
+        .iOS(.v10),
+        .macOS(.v10_12),
+    ],
+    products: [
+        // Products define the executables and libraries a package produces, and make them visible to other packages.
+        .library(
+            name: "RRuleSwift",
+            targets: ["RRuleSwift-iOS"]),
+    ],
+    dependencies: [
+    ],
+    targets: [
+        // Targets are the basic building blocks of a package. A target can define a module or a test suite.
+        // Targets can depend on other targets in this package, and on products in packages this package depends on.
+        .target(
+            name: "RRuleSwift-iOS",
+            dependencies: [],
+            path: "Sources"
+        ),
+    ]
+)

RRuleSwiftExample/RRuleExampleViewController.swift

@@ -72,7 +72,60 @@ class RRuleExampleViewController: UIViewController {
         textView.delegate = self
         navigationItem.rightBarButtonItem = UIBarButtonItem(title: "Reset", style: .plain, target: self, action: #selector(resetButtonTapped(_:)))
     }
+
+    fileprivate func testRRuleIteratorMultipleThreads() {
+        DispatchQueue.global(qos: .background).async {
+            for n in 1...100
+            {
+                self.testRRuleIterator(n)
+            }
+        }
+
+        DispatchQueue.global(qos: .background).async {
+            for n in 1...100
+            {
+                self.testRRuleIterator(-n)
+            }
+        }
+    }
+
+    fileprivate func testRRuleIterator(_ n : Int) {
+        let ruleFormat = "RRULE:FREQ=WEEKLY;DTSTART=%@%@01T014500Z;INTERVAL=1;UNTIL=%@%@01T014500Z"
+        let calendar = NSCalendar.current
+        var startDateComponents = DateComponents()
+        startDateComponents.month = n;
+        let startDate = calendar.date(byAdding: startDateComponents, to: Date())
+        startDateComponents = calendar.dateComponents([.year, .month], from: startDate!)
+
+        var endDateComponents = DateComponents()
+        endDateComponents.month = 6
+        let endDate = calendar.date(byAdding: endDateComponents, to: startDate!)
+        endDateComponents = calendar.dateComponents([.year, .month], from: endDate!)
 
+        var startDateMonth = String(startDateComponents.month!)
+        if (startDateComponents.month! < 10)
+        {
+            startDateMonth = "0".appending(startDateMonth)
+        }
+        var endDateMonth = String(endDateComponents.month!)
+        if (endDateComponents.month! < 10)
+        {
+            endDateMonth = "0".appending(endDateMonth)
+        }
+
+        let rruleString = String(format: ruleFormat, String(startDateComponents.year!), startDateMonth, String(endDateComponents.year!), endDateMonth )
+
+        print ("rruleString: ", rruleString)
+        var rule = RecurrenceRule(rruleString: rruleString)!
+
+        let occurrences = rule.allOccurrences()
+        print ("occurrences for rrule: ", rruleString, ", count:", occurrences.count, ", first:", occurrences.first)
+        if !calendar.isDate(startDate!, equalTo: occurrences.first!, toGranularity: .day)
+        {
+            print("dates mismatch, got: ", occurrences.first, ", expected: ", startDate)
+        }
+    }
+
     fileprivate func testRRuleIterator() {
         let dateFormatter: DateFormatter = {
             let dateFormatter = DateFormatter()

Sources/Iterators.swift

@@ -31,8 +31,7 @@ public extension RecurrenceRule {
         }
 
         let ruleJSONString = toJSONString(endless: endlessRecurrenceCount)
-        let _ = Iterator.rruleContext?.evaluateScript("var rule = new RRule({ \(ruleJSONString) })")
-        guard let allOccurrences = Iterator.rruleContext?.evaluateScript("rule.all()").toArray() as? [Date] else {
+        guard let allOccurrences = Iterator.rruleContext?.evaluateScript("new RRule({ \(ruleJSONString) }).all()").toArray() as? [Date] else {
             return []
         }
 
@@ -67,8 +66,7 @@ public extension RecurrenceRule {
         let untilDateJSON = RRule.ISO8601DateFormatter.string(from: untilDate)
 
         let ruleJSONString = toJSONString(endless: endlessRecurrenceCount)
-        let _ = Iterator.rruleContext?.evaluateScript("var rule = new RRule({ \(ruleJSONString) })")
-        guard let betweenOccurrences = Iterator.rruleContext?.evaluateScript("rule.between(new Date('\(beginDateJSON)'), new Date('\(untilDateJSON)'))").toArray() as? [Date] else {
+        guard let betweenOccurrences = Iterator.rruleContext?.evaluateScript("new RRule({ \(ruleJSONString) }).between(new Date('\(beginDateJSON)'), new Date('\(untilDateJSON)'))").toArray() as? [Date] else {
             return []
         }