<div class="secondary-content" markdown="0">

For common Bolt apps, you can call `ack()` at the beginning of a listener function this way:

@app.shortcut("callback-id-here")

run_time_consuming_operation_here()

However, if you run your app on FaaS or a similar runtime (that doesn't allow running threads/processes after returning an HTTP response), you will use the `process_before_response=True` option to hold off sending an HTTP response util completing all the tasks in a listener. In this case, all your listener functions must complete within 3 seconds.

app = App(process_before_response=True)

time.sleep(5)

To deal with this, you can use keyword args `ack: Callable` and `lazy: List[Callable]`:

* `ack: Callable` is responsible for calling `ack()`

* `lazy: List[Callable]` are unable to call `ack()` but can do any time consuming operations in a separate execution (in a thread, another AWS Lambda invocation, and so on)

Instead of acting as a decorator for a method, `App`/`AsyncApp`'s methods takes keyword args as below.

app.command("/start-process")(

lazy=[run_long_process]

)

</details>