About Sync and Async Sub-Flows

Overview

A Sub-Flow is a Flow that runs like a Step within the course of another Flow. A Sub-Flow may also be referred to as a "Child Flow" and the primary Flow as a "Parent Flow."

A Sub-Flow may be set to run in one of two ways:

1. The Sync method: allows the Sub-Flow and Main Flow to run sequentially.

2. The Async method: allows the primary Flow to run independently while the Sub-Flow completes.

Each method has benefits for use in different scenarios; part of Flow design planning should be to decide which method works for a specific scenario. The key difference is that the Sync method allows the Flows to run in sequence. The Async method allows the Sub Flow to run independently of the Parent Flow. With Async, control is immediately given back to the primary Flow. The consequence of this method is that the relationship between the two Flows is "asynchronous", meaning that the Sub Flow is now an independently executing Flow and has no necessary output data to deliver to the primary Flow. Below are a few examples and further information regarding the different types of sub-flows.

Async Flows

Start Linked Flow Async

In the screenshot below, the gray-colored Process Flow is a Linked Flow Async step. In this example, the Sub Flow is designed to run independently from the Primary Flow. The primary purpose of Async Flows is for use in instances where the Primary Flow needs to delegate a task to the Sub Flow. 

In this example, whenever an email is found, it is delegated to the Process workflow to be filtered by a user-set Rule. In this case, the Async method allows the Primary Flow to check for Emails while the Child Flow processes each one individually.

The table below represents each of the available Properties provided by the Start Linked Flow Async step: 

Viewing Thread Jobs from Start Linked Flow Async 

To view the Thread Jobs from a Start Linked Flow Async Subflow:

1. From the Decisions Studio, navigate to System > Administration > System Tools.
2. Open the Event Viewer.
   
3. Navigate to the THREAD JOBS tab. 
4. Scroll to the bottom of the end of the Active Thread Jobs to view the Thread Jobs for the Subflow. 

Start Linked Flow Async Flows in Multi-Node Environments

Thread Jobs are not shared across the Server Cluster when utilizing a multi-node environment. Instead, they are completely discrete; this means that an Async Job that is started on one Server will stay on and be executed on that specific Server. The information from these Jobs is not shared across Servers in any way. The load balance directs the work so that each Server has its own specific Queue and Thread Jobs.

Run Flow Async And Wait

The Run Flow Async And Wait is a check box configuration on the Run Flow step. This configuration does not run the sub Flow independently from the parent process but executes it on a separate thread. This check box configuration does three things: spawns a new process, runs the Flow on a separate thread, and returns the data to the main Flow. This is helpful in scenarios involving multiple steps involving a loop or branch that would usually run synchronously, such as API calls or adding numbers. Run Flow Async and Wait allow these tasks to be executed parallel to save time.  

One difference between the Run Flow Async and Wait step and the Start Linked Flow Async is that the Run Flow Async and Wait returns data while the Start Linked Flow Async does not. Run Flow Async and Wait are most commonly used to assist API calls that return large amounts of data. 

Go Async Flow Step

Go Async step's purpose is to move the current execution of the Flow to a different thread. This allows users more fine-tuning when directing which portion of a Flow is running Async. Users may run portions of a Flow as Async without moving the process. For more information, review Running Steps Asynchronously With The Go Async Component.

Synchronous Flows

Sync Flows help handle processes that require the main Flow and Sub Flow to occur one after the other. For instance, within the Async Flow above, the Email handling process is split into multiple synchronous Sub Flows depending on how the Email is evaluated. In the example below, after reaching the Email Process Folder, an Email is evaluated as either an invoice, resume, or another type and sent to its respective Sub Flow. This allows running a Sub Flow midway through the process before proceeding to the next step and returning data to the parent Flow. This can be especially helpful if manager approval or a user response is required in the process. It also allows each sequence in the Flow to be evaluated and easily troubleshoot, as they are split up separately. 

Checking Flow Attribute 

To determine if a Flow is Sync or Async after it has been created without opening it, users may utilize the information provided by the Element Attribute in the Flow's Properties. This Property provides information on the selected Designer Element, such as its Type and run behavior.
 
This information is located in the Information Panel that appears upon selecting any space within the Designer Project's Report row for that specific Flow.