Added workflow concurrency example for .NET

Signed-off-by: Whit Waldo <[email protected]>

daprdocs/content/en/developing-applications/building-blocks/workflow/workflow-patterns.md

@@ -586,7 +586,60 @@ The key takeaways from this example are:
 - The number of parallel tasks can be static or dynamic
 - The workflow itself is capable of aggregating the results of parallel executions
 
-While not shown in the example, it's possible to go further and limit the degree of concurrency using simple, language-specific constructs. Furthermore, the execution of the workflow is durable. If a workflow starts 100 parallel task executions and only 40 complete before the process crashes, the workflow restarts itself automatically and only schedules the remaining 60 tasks.
+Furthermore, the execution of the workflow is durable. If a workflow starts 100 parallel task executions and only 40 complete before the process crashes, the workflow restarts itself automatically and only schedules the remaining 60 tasks.
+
+It's possible to go further and limit the degree of concurrency using simple, language-specific constructs.
+
+{{< tabs ".NET" >}}
+
+{{% codetab %}}
+<!-- .NET -->
+```csharp
+public static class TaskExtensions
+{
+  public static async Task<IEnumerable<T>> WhenAllWithLimitAsync<T>(this IEnumerable<Task<T>>> tasks, int maxDegreeOfParallelism)
+  {
+    var results = new List<T>();
+    var inFlight = new HashSet<Task<T>>();
+    foreach (var task in tasks)
+    {
+      if (inFlight.Count > maxParallelism)
+      {
+        var finishedTask = await Task.WhenAny(inFlight);
+        results.Add(finishedTask.Result);
+        inFlight.Remove(finishedTask);
+      }
+
+      inFlight.Add(context.CallActivityAsync(task))
+    }
+
+    //Wait for all the remaining tasks to complete
+    await Task.WhenAll(inFlight);
+  }
+}
+
+//Revisiting the earlier example...
+// Get a list of N work items to process in parallel.
+object[] workBatch = await context.CallActivityAsync<object[]>("GetWorkBatch", null);
+
+// Schedule the parallel tasks, but don't wait for them to complete yet
+var parallelTasks = new List<Task<int>>();
+foreach (var workItem in workBatch)
+{
+  var task = context.CallActivityAsync<int>("ProcessWorkItem", workItem);
+  parallelTasks.Add(task);
+}
+
+// This is where we diverge from the previous example and use our new extension method above to limit concurrency to 5 tasks at a time
+var result = await Task.WhenAllWithLimitAsync(parallelTasks, 5);
+
+var sum = result.Sum(t => t);
+await context.CallActivityAsync("PostResults", sum);
+```
+
+{{% /codetab %}}
+
+{{< /tabs >}}
 
 ## Async HTTP APIs