more wip

src/Orleans.Core.Abstractions/Timers/TimerCreationOptions.cs

@@ -36,8 +36,14 @@ namespace Orleans.Runtime;
     public bool Interleave { get; init; }
 
     /// <summary>
-    /// Gets a value indicating whether callbacks scheduled by this timer should keep the grain activation active. Defaults to <see langword="false"/>.
+    /// Gets a value indicating whether callbacks scheduled by this timer should extend the lifetime of the grain activation. Defaults to <see langword="false"/>.
     /// </summary>
+    /// <remarks>
+    /// If this value is <see langword="false"/>, timer callbacks will not extend a grain activation's lifetime.
+    /// If a grain is only processing timer callbacks and no other messages, the grain will be collected after its idle collection period expires.
+    /// If this value is <see langword="true"/>, timer callback will extend a grain activation's lifetime.
+    /// If the timer period is shorter than the grain's idle collection period, the grain will not be collected due to idleness.
+    /// </remarks>
     public bool KeepAlive { get; init; }
 
 }

src/Orleans.Runtime/Timers/GrainTimer.cs

@@ -95,6 +95,8 @@ protected void ScheduleTickOnActivation()
         _grainContext.ReceiveMessage(msg);
     }
 
+    protected abstract Task InvokeCallback();
+
     private ValueTask<Response> InvokeTickAsync(CancellationToken cancellationToken)
     {
         try
@@ -110,16 +112,20 @@ private ValueTask<Response> InvokeTickAsync(CancellationToken cancellationToken)
             // If the task is not completed, we need to await the tick asynchronously.
             if (task is { IsCompletedSuccessfully: false })
             {
+                // Complete asynchronously.
                 return AwaitCallbackTask(task, cancellationToken);
             }
-
-            if (Logger.IsEnabled(LogLevel.Trace))
+            else
             {
-                Logger.LogTrace((int)ErrorCode.TimerAfterCallback, "Completed timer callback for timer {TimerName}", this);
+                // Complete synchronously.
+                if (Logger.IsEnabled(LogLevel.Trace))
+                {
+                    Logger.LogTrace((int)ErrorCode.TimerAfterCallback, "Completed timer callback for timer {TimerName}", this);
+                }
+
+                OnTickCompleted();
+                return new(Response.Completed);
             }
-
-            OnTickCompleted();
-            return new(Response.Completed);
         }
         catch (Exception exc)
         {