[Workflow] Add examples for reuse ID policy

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

@@ -28,9 +28,117 @@ There are several different kinds of tasks that a workflow can schedule, includi
 
 ### Workflow identity
 
-Each workflow you define has a type name, and individual executions of a workflow require a unique _instance ID_. Workflow instance IDs can be generated by your app code, which is useful when workflows correspond to business entities like documents or jobs, or can be auto-generated UUIDs. A workflow's instance ID is useful for debugging and also for managing workflows using the [Workflow APIs]({{< ref workflow_api.md >}}).
+Each workflow you define has a type name, and individual executions of a workflow require a unique _instance ID_. Only one workflow instance with a given ID can exist at any given time. Workflow instance IDs can be generated by your app code, which is useful when workflows correspond to business entities like documents or jobs, or can be auto-generated UUIDs. A workflow's instance ID is useful for debugging and also for managing workflows using the [Workflow APIs]({{< ref workflow_api.md >}}).
 
-Only one workflow instance with a given ID can exist at any given time. However, if a workflow instance completes or fails, its ID can be reused by a new workflow instance. Note, however, that the new workflow instance effectively replaces the old one in the configured state store.
+#### Reusing workflow identities
+
+If a workflow instance completes or fails, its ID can be reused by a new workflow instance. The new workflow instance effectively replaces the old one in the configured state store.
+
+**Example 1**
+
+The following example demonstrates `main` executing a workflow twice. In the example:
+1. The workflow calls a single activity with orchestration ID reuse policy.
+1. The reuse ID policy specifies the action `IGNORE_IF_RUNNING_OR_COMPLETED` and the target statuses of `RUNNING`, `COMPLETED`, `PENDING`. 
+1. The second call to create a workflow with the same instance ID is expected to be ignored if the first workflow instance is one of the target statuses.
+
+```go
+func main() {
+	r := task.NewTaskRegistry()
+	r.AddOrchestratorN("SingleActivity", func(ctx *task.OrchestrationContext) (any, error) {
+		var input string
+		if err := ctx.GetInput(&input); err != nil {
+			return nil, err
+		}
+		var output string
+		err := ctx.CallActivity("SayHello", task.WithActivityInput(input)).Await(&output)
+		return output, err
+	})
+	r.AddActivityN("SayHello", func(ctx task.ActivityContext) (any, error) {
+		var name string
+		if err := ctx.GetInput(&name); err != nil {
+			return nil, err
+		}
+		return fmt.Sprintf("Hello, %s!", name), nil
+	})
+
+	ctx := context.Background()
+	client, engine := startEngine(ctx, r)
+
+	instanceID := api.InstanceID("IGNORE_IF_RUNNING_OR_COMPLETED")
+	reuseIDPolicy := &api.OrchestrationIdReusePolicy{
+		Action:          api.REUSE_ID_ACTION_IGNORE,
+		OperationStatus: []api.OrchestrationStatus{api.RUNTIME_STATUS_RUNNING, api.RUNTIME_STATUS_COMPLETED, api.RUNTIME_STATUS_PENDING},
+	}
+
+	// Run the orchestration
+	id, err := client.ScheduleNewOrchestration(ctx, "SingleActivity", api.WithInput("World"), api.WithInstanceID(instanceID))
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	// Wait for orchestration to start
+	client.WaitForOrchestrationStart(ctx, id)
+	// Schedule again, it should ignore creating the new orchestration
+	id, err = client.ScheduleNewOrchestration(ctx, "SingleActivity", api.WithInput("World"), api.WithInstanceID(id), api.WithOrchestrationIdReusePolicy(reuseIDPolicy))
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+}
+```
+
+**Example 2**
+
+In the following example:
+1. The workflow calls a single activity with the orchestration ID reuse policy. 
+1. The reuse ID policy contains the action to `TERMINATE` and target statuses `RUNNING`, `COMPLETED`, and `PENDING`.
+1. The second call to create a workflow with the same workflow instance ID is expected to terminate the first workflow instance and create a new workflow instance if in one of the target statuses.
+
+```go
+func main() {
+	r := task.NewTaskRegistry()
+	r.AddOrchestratorN("SingleActivity", func(ctx *task.OrchestrationContext) (any, error) {
+		var input string
+		if err := ctx.GetInput(&input); err != nil {
+			return nil, err
+		}
+		var output string
+		err := ctx.CallActivity("SayHello", task.WithActivityInput(input)).Await(&output)
+		return output, err
+	})
+	r.AddActivityN("SayHello", func(ctx task.ActivityContext) (any, error) {
+		var name string
+		if err := ctx.GetInput(&name); err != nil {
+			return nil, err
+		}
+		return fmt.Sprintf("Hello, %s!", name), nil
+	})
+
+	ctx := context.Background()
+	client, engine := startEngine(ctx, r)
+
+	instanceID := api.InstanceID("IGNORE_IF_RUNNING_OR_COMPLETED")
+	reuseIDPolicy := &api.OrchestrationIdReusePolicy{
+		Action:          api.REUSE_ID_ACTION_TERMINATE,
+		OperationStatus: []api.OrchestrationStatus{api.RUNTIME_STATUS_RUNNING, api.RUNTIME_STATUS_COMPLETED, api.RUNTIME_STATUS_PENDING},
+	}
+
+	// Run the orchestration
+	id, err := client.ScheduleNewOrchestration(ctx, "SingleActivity", api.WithInput("World"), api.WithInstanceID(instanceID))
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	// Wait for orchestration to start
+	client.WaitForOrchestrationStart(ctx, id)
+	// Schedule again, it should ignore creating the new orchestration
+	id, err = client.ScheduleNewOrchestration(ctx, "SingleActivity", api.WithInput("World"), api.WithInstanceID(id), api.WithOrchestrationIdReusePolicy(reuseIDPolicy))
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+}
+```
 
 ### Workflow replay