Add @volatile on start field and synchronized block for full thread safety

Author: Shamyyoun

iterableapi/src/main/java/com/iterable/iterableapi/EmbeddedImpressionData.kt

@@ -9,7 +9,7 @@ data class EmbeddedImpressionData(
     val placementId: Long,
     var displayCount: Int = 0,
     var duration: Float = 0.0f,
-    var start: Date? = null
+    @Volatile var start: Date? = null
 ) {
     constructor(
         messageId: String,

iterableapi/src/main/java/com/iterable/iterableapi/EmbeddedSessionManager.kt

@@ -108,13 +108,15 @@ public class EmbeddedSessionManager {
     }
 
     private fun updateDisplayCountAndDuration(impressionData: EmbeddedImpressionData): EmbeddedImpressionData {
-        val start = impressionData.start
-        if (start != null) {
-            impressionData.displayCount = impressionData.displayCount.plus(1)
-            impressionData.duration =
-                impressionData.duration.plus((Date().time - start.time) / 1000.0)
-                    .toFloat()
-            impressionData.start = null
+        synchronized(impressionData) {
+            val start = impressionData.start
+            if (start != null) {
+                impressionData.displayCount = impressionData.displayCount.plus(1)
+                impressionData.duration =
+                    impressionData.duration.plus((Date().time - start.time) / 1000.0)
+                        .toFloat()
+                impressionData.start = null
+            }
         }
         return impressionData
     }