add fan in/fan out

Signed-off-by: Hannah Hunter <hannahhunter@microsoft.com>

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

@@ -516,7 +516,64 @@ public class FaninoutWorkflow extends Workflow {
 <!--go-->
 
 ```go
-
+func BatchProcessingWorkflow(ctx *workflow.WorkflowContext) (any, error) {
+	var input int
+	if err := ctx.GetInput(&input); err != nil {
+		return 0, err
+	}
+	var workBatch []int
+	if err := ctx.CallActivity(GetWorkBatch, workflow.ActivityInput(input)).Await(&workBatch); err != nil {
+		return 0, err
+	}
+	parallelTasks := workflow.NewTaskSlice(len(workBatch))
+	for i, workItem := range workBatch {
+		parallelTasks[i] = ctx.CallActivity(ProcessWorkItem, workflow.ActivityInput(workItem))
+	}
+	var outputs int
+	for _, task := range parallelTasks {
+		var output int
+		err := task.Await(&output)
+		if err == nil {
+			outputs += output
+		} else {
+			return 0, err
+		}
+	}
+	if err := ctx.CallActivity(ProcessResults, workflow.ActivityInput(outputs)).Await(nil); err != nil {
+		return 0, err
+	}
+	return 0, nil
+}
+func GetWorkBatch(ctx workflow.ActivityContext) (any, error) {
+	var batchSize int
+	if err := ctx.GetInput(&batchSize); err != nil {
+		return 0, err
+	}
+	batch := make([]int, batchSize)
+	for i := 0; i < batchSize; i++ {
+		batch[i] = i
+	}
+	return batch, nil
+}
+func ProcessWorkItem(ctx workflow.ActivityContext) (any, error) {
+	var workItem int
+	if err := ctx.GetInput(&workItem); err != nil {
+		return 0, err
+	}
+	fmt.Printf("Processing work item: %d\n", workItem)
+	time.Sleep(time.Second * 5)
+	result := workItem * 2
+	fmt.Printf("Work item %d processed. Result: %d\n", workItem, result)
+	return result, nil
+}
+func ProcessResults(ctx workflow.ActivityContext) (any, error) {
+	var finalResult int
+	if err := ctx.GetInput(&finalResult); err != nil {
+		return 0, err
+	}
+	fmt.Printf("Final result: %d\n", finalResult)
+	return finalResult, nil
+}
 ```
 
 {{% /codetab %}}