Configuration to throw an exception when an orchestration is in an ex…

…isting dedupe state (#334)

src/DurableTask.AzureStorage/AzureStorageOrchestrationService.cs

@@ -1271,6 +1271,11 @@ public async Task CreateTaskOrchestrationAsync(TaskMessage creationMessage, Orch
             if (existingInstance != null && dedupeStatuses != null && dedupeStatuses.Contains(existingInstance.OrchestrationStatus))
             {
                 // An instance in this state already exists.
+                if (settings.ThrowExceptionOnInvalidDedupeStatus)
+                {
+                    throw new InvalidOperationException($"An Orchestration instance with the status {existingInstance.OrchestrationStatus} already exists.");
+                }
+
                 return;
             }
 

src/DurableTask.AzureStorage/AzureStorageOrchestrationServiceSettings.cs

@@ -172,6 +172,11 @@ public class AzureStorageOrchestrationServiceSettings
         /// </summary>
         public BehaviorOnContinueAsNew EventBehaviourForContinueAsNew { get; set; } = BehaviorOnContinueAsNew.Carryover;
 
+        /// <summary>
+        /// When true, will throw an exception when attempting to create an orchestration with an existing dedupe status.
+        /// </summary>
+        public bool ThrowExceptionOnInvalidDedupeStatus { get; set; } = false;
+
         /// <summary>
         /// Returns bool indicating is the TrackingStoreStorageAccount has been set.
         /// </summary>