merge with latest dev and squash, to fix diff issues

src/WebJobs.Extensions.DurableTask/ContextImplementations/DurableClient.cs

@@ -83,6 +83,12 @@ internal class DurableClient : IDurableClient,
 
         string IDurableEntityClient.TaskHubName => this.TaskHubName;
 
+        /// <inheritdoc/>
+        public override string ToString()
+        {
+            return $"DurableClient[backend={this.config.GetBackendInfo()}]";
+        }
+
         /// <inheritdoc />
         HttpResponseMessage IDurableOrchestrationClient.CreateCheckStatusResponse(HttpRequestMessage request, string instanceId, bool returnInternalServerErrorOnFailure)
         {
@@ -541,10 +547,14 @@ async Task<CleanEntityStorageResult> IDurableEntityClient.CleanEntityStorageAsyn
                          tasks.Add(CheckForOrphanedLockAndFixIt(state, status.LockedBy));
                     }
 
-                    if (removeEmptyEntities && !status.EntityExists && status.LockedBy == null && status.QueueSize == 0
-                        && now - state.LastUpdatedTime > TimeSpan.FromMinutes(this.config.Options.EntityMessageReorderWindowInMinutes))
+                    if (removeEmptyEntities)
                     {
-                        tasks.Add(DeleteIdleOrchestrationEntity(state));
+                        bool isEmptyEntity = !status.EntityExists && status.LockedBy == null && status.QueueSize == 0;
+                        bool safeToRemoveWithoutBreakingMessageSorterLogic = now - state.LastUpdatedTime > this.config.MessageReorderWindow;
+                        if (isEmptyEntity && safeToRemoveWithoutBreakingMessageSorterLogic)
+                        {
+                            tasks.Add(DeleteIdleOrchestrationEntity(state));
+                        }
                     }
                 }
 

src/WebJobs.Extensions.DurableTask/ContextImplementations/DurableCommonContext.cs

@@ -22,7 +22,6 @@ internal DurableCommonContext(DurableTaskExtension config, string functionName)
         {
             this.Config = config ?? throw new ArgumentNullException(nameof(config));
             this.FunctionName = functionName;
-            this.EntityMessageReorderWindow = TimeSpan.FromMinutes(config.Options.EntityMessageReorderWindowInMinutes);
         }
 
         internal DurableTaskExtension Config { get; }
@@ -41,8 +40,6 @@ internal DurableCommonContext(DurableTaskExtension config, string functionName)
 
         internal string Name => this.FunctionName;
 
-        internal TimeSpan EntityMessageReorderWindow { get; private set; }
-
         internal bool ExecutorCalledBack { get; set; }
 
         internal void AddDeferredTask(Func<Task> function)

src/WebJobs.Extensions.DurableTask/ContextImplementations/DurableEntityContext.cs

@@ -539,7 +539,7 @@ internal void SendOutbox(OrchestrationContext innerContext, bool writeBackSucces
                     {
                         if (!operationMessage.EventContent.ScheduledTime.HasValue)
                         {
-                            this.State.MessageSorter.LabelOutgoingMessage(operationMessage.EventContent, operationMessage.Target.InstanceId, DateTime.UtcNow, this.EntityMessageReorderWindow);
+                            this.State.MessageSorter.LabelOutgoingMessage(operationMessage.EventContent, operationMessage.Target.InstanceId, DateTime.UtcNow, this.Config.MessageReorderWindow);
                         }
 
                         this.Config.TraceHelper.SendingEntityMessage(

src/WebJobs.Extensions.DurableTask/ContextImplementations/DurableOrchestrationContext.cs

@@ -1117,7 +1117,7 @@ internal void SendEntityMessage(OrchestrationInstance target, object eventConten
                         requestMessage,
                         target.InstanceId,
                         this.InnerContext.CurrentUtcDateTime,
-                        TimeSpan.FromMinutes(this.Config.Options.EntityMessageReorderWindowInMinutes));
+                        this.Config.MessageReorderWindow);
 
                     eventName = EntityMessageEventNames.RequestMessageEventName;
                 }

src/WebJobs.Extensions.DurableTask/DurabilityProvider.cs

@@ -57,6 +57,16 @@ public DurabilityProvider(string storageProviderName, IOrchestrationService serv
         /// </summary>
         public virtual bool SupportsEntities => false;
 
+        /// <summary>
+        /// Specifies whether the backend's WaitForOrchestration is implemented without polling.
+        /// </summary>
+        public virtual bool SupportsPollFreeWait => false;
+
+        /// <summary>
+        /// Specifies whether this backend delivers messages in order.
+        /// </summary>
+        public virtual bool GuaranteesOrderedDelivery => false;
+
         /// <summary>
         /// JSON representation of configuration to emit in telemetry.
         /// </summary>
@@ -87,6 +97,11 @@ public DurabilityProvider(string storageProviderName, IOrchestrationService serv
         /// <inheritdoc/>
         public int MaxConcurrentTaskActivityWorkItems => this.GetOrchestrationService().MaxConcurrentTaskActivityWorkItems;
 
+        internal string GetBackendInfo()
+        {
+            return this.GetOrchestrationService().ToString();
+        }
+
         private IOrchestrationService GetOrchestrationService()
         {
             if (this.innerService == null)
@@ -278,7 +293,7 @@ public virtual Task<IList<OrchestrationState>> GetAllOrchestrationStatesWithFilt
         /// <returns>Returns a task which completes when the state has been fetched.</returns>
         public virtual Task<IList<OrchestrationState>> GetOrchestrationStateWithInputsAsync(string instanceId, bool showInput = true)
         {
-            throw this.GetNotImplementedException(nameof(this.GetOrchestrationStateAsync));
+            throw this.GetNotImplementedException(nameof(this.GetOrchestrationStateWithInputsAsync));
         }
 
         /// <summary>
@@ -418,5 +433,51 @@ internal virtual bool ConnectionNameMatches(DurabilityProvider durabilityProvide
         {
             return this.ConnectionName.Equals(durabilityProvider.ConnectionName);
         }
+
+        /// <summary>
+        /// Returns the instance id of the entity scheduler for a given entity id.
+        /// </summary>
+        /// <param name="entityId">The entity id.</param>
+        /// <returns>The instance id of the scheduler.</returns>
+        protected string GetSchedulerIdFromEntityId(EntityId entityId)
+        {
+            return EntityId.GetSchedulerIdFromEntityId(entityId);
+        }
+
+        /// <summary>
+        /// Reads the state of an entity from the serialized entity scheduler state.
+        /// </summary>
+        /// <param name="state">The orchestration state of the scheduler.</param>
+        /// <param name="serializerSettings">The serializer settings.</param>
+        /// <param name="result">The serialized state of the entity.</param>
+        /// <returns>true if the entity exists, false otherwise.</returns>
+        protected bool TryGetEntityStateFromSerializedSchedulerState(OrchestrationState state, JsonSerializerSettings serializerSettings, out string result)
+        {
+            if (state != null
+                && state.OrchestrationInstance != null
+                && state.Input != null)
+            {
+                var schedulerState = JsonConvert.DeserializeObject<SchedulerState>(state.Input, serializerSettings);
+
+                if (schedulerState.EntityExists)
+                {
+                    result = schedulerState.EntityState;
+                    return true;
+                }
+            }
+
+            result = null;
+            return false;
+        }
+
+        /// <summary>
+        /// Converts the DTFx representation of the orchestration state into the DF representation.
+        /// </summary>
+        /// <param name="orchestrationState">The orchestration state.</param>
+        /// <returns>The orchestration status.</returns>
+        protected DurableOrchestrationStatus ConvertOrchestrationStateToStatus(OrchestrationState orchestrationState)
+        {
+            return DurableClient.ConvertOrchestrationStateToStatus(orchestrationState);
+        }
     }
 }

src/WebJobs.Extensions.DurableTask/DurableTaskExtension.cs

@@ -189,6 +189,9 @@ public string HubName
 
         internal MessagePayloadDataConverter ErrorDataConverter { get; private set; }
 
+        internal TimeSpan MessageReorderWindow
+            => this.defaultDurabilityProvider.GuaranteesOrderedDelivery ? TimeSpan.Zero : TimeSpan.FromMinutes(this.Options.EntityMessageReorderWindowInMinutes);
+
         internal static MessagePayloadDataConverter CreateMessageDataConverter(IMessageSerializerSettingsFactory messageSerializerSettingsFactory)
         {
             bool isDefault;
@@ -215,6 +218,11 @@ private MessagePayloadDataConverter CreateErrorDataConverter(IErrorSerializerSet
             return new MessagePayloadDataConverter(errorSerializerSettingsFactory.CreateJsonSerializerSettings(), isDefault);
         }
 
+        internal string GetBackendInfo()
+        {
+            return this.defaultDurabilityProvider.GetBackendInfo();
+        }
+
         /// <summary>
         /// Internal initialization call from the WebJobs host.
         /// </summary>
@@ -725,7 +733,7 @@ private async Task EntityMiddleware(DispatchMiddlewareContext dispatchContext, F
                                 else
                                 {
                                     // run this through the message sorter to help with reordering and duplicate filtering
-                                    deliverNow = entityContext.State.MessageSorter.ReceiveInOrder(requestMessage, entityContext.EntityMessageReorderWindow);
+                                    deliverNow = entityContext.State.MessageSorter.ReceiveInOrder(requestMessage, this.MessageReorderWindow);
                                 }
 
                                 foreach (var message in deliverNow)

src/WebJobs.Extensions.DurableTask/HttpApiHandler.cs

@@ -181,9 +181,34 @@ private static TemplateMatcher GetInstanceRaiseEventRoute()
 
             IDurableOrchestrationClient client = this.GetClient(request);
             Stopwatch stopwatch = Stopwatch.StartNew();
+
+            // This retry loop completes either when the
+            // orchestration has completed, or when the timeout is reached.
             while (true)
             {
-                DurableOrchestrationStatus status = await client.GetStatusAsync(instanceId);
+                DurableOrchestrationStatus status = null;
+
+                if (client is DurableClient durableClient && durableClient.DurabilityProvider.SupportsPollFreeWait)
+                {
+                    // For durability providers that support efficient (poll-free) waiting, we take advantage of that API
+                    try
+                    {
+                        var state = await durableClient.DurabilityProvider.WaitForOrchestrationAsync(instanceId, null, timeout, CancellationToken.None);
+                        status = DurableClient.ConvertOrchestrationStateToStatus(state);
+                    }
+                    catch (TimeoutException)
+                    {
+                        // The orchestration did not complete.
+                        // Depending on the implementation of the backend, we may get here before the full timeout has elapsed,
+                        // so we recheck how much time has elapsed below, and retry if there is time left.
+                    }
+                }
+                else
+                {
+                    // For durability providers that do not support efficient (poll-free) waiting, we do explicit retries.
+                    status = await client.GetStatusAsync(instanceId);
+                }
+
                 if (status != null)
                 {
                     if (status.RuntimeStatus == OrchestrationRuntimeStatus.Completed)
@@ -706,6 +731,12 @@ private static bool TryGetIntQueryParameterValue(NameValueCollection queryString
                 TimeSpan? timeout = GetTimeSpan(request, "timeout");
                 TimeSpan? pollingInterval = GetTimeSpan(request, "pollingInterval");
 
+                // for durability providers that support poll-free waiting, we override the specified polling interval
+                if (client is DurableClient durableClient && durableClient.DurabilityProvider.SupportsPollFreeWait)
+                {
+                    pollingInterval = timeout;
+                }
+
                 if (timeout.HasValue && pollingInterval.HasValue)
                 {
                     return await client.WaitForCompletionOrCreateCheckStatusResponseAsync(request, id, timeout.Value, pollingInterval.Value);