How can you trigger flows asynchronously from a parent flow?

• A. By calling a sub-flow directly
• B. With the Async scope
• C. Using a Poll scope
• D. With the Sync scope

Answer: (B)

Asynchronous processing in Mule is achieved by using the Async scope. Placing a Flow Reference (or the work you want to run) inside this scope runs that work on a separate thread, so the parent flow continues immediately without waiting for it to finish. This is the mechanism that lets you trigger another flow asynchronously from the parent flow and keep the main processing responsive or throughput-focused.

The other options don’t fit because they don’t offload work to a separate thread. Calling a sub-flow directly executes inline on the same thread, which is synchronous. The Poll scope is meant for repeatedly checking a source (polling), not for kicking off asynchronous work. The Sync scope enforces synchronous execution, opposite of what you need for asynchronous triggering.