Lazy listeners do not work with Chalice local testing server

I want to perform operations when a member has joined a channel which takes more than 5 seconds, but I'm getting BrokenPipeError: [Errno 32] Broken pipe.

The minimal step to reproduce the same has been shown below while using the lazy listener it waits for 10 seconds before responding back.

Reproducible in:

from chalice import Chalice, Response
from slack_bolt import App
from slack_bolt.adapter.aws_lambda.chalice_handler import ChaliceSlackRequestHandler

bolt_app = App(process_before_response=True)
app = Chalice(app_name='chalice_app_name')
slack_handler = ChaliceSlackRequestHandler(app=bolt_app, chalice=app)


@bolt_app.event("message")
def handle_message_events(body, logger):
    logger.info(body['event']['text'])


def respond_to_slack_within_3_seconds(ack):
    ack("Accepted!")


def say_it(say):
    time.sleep(10)
    say("Done!")


bolt_app.event("member_joined_channel")(
    ack=respond_to_slack_within_3_seconds, lazy=[say_it]
)


@app.route(
    "/slack/events",
    methods=["POST"],
    content_types=["application/x-www-form-urlencoded", "application/json"],
)
def events() -> Response:
    return slack_handler.handle(app.current_request)

The slack_bolt version

slack-bolt==1.9.1
slack-sdk==3.11.1

Python runtime version

Python 3.6.15

OS info

Ubuntu 20.04.3 LTS

Steps to reproduce:

1. While handling of any Slack event (e.g. handle_member_joined event)
2. Use lazy listener and wait for more than 3 seconds before responding back to Slack

Expected result:

Since the event is acknowledging the Slack within 3 seconds irrespective of the lazy listener function time, it should have processed the same.

Actual result:

Requirements

Please read the Contributing guidelines and Code of Conduct before creating this issue or pull request. By submitting, you are agreeing to those rules.

Comienza en el punto de entrada de ChaliceSlackRequestHandler y reproduce el evento member_joined_channel con process_before_response habilitado y un listener lazy que duerma durante 10 segundos. Comprueba el comportamiento del servidor de pruebas local en torno a la respuesta de /slack/events y confirma que el listener lazy se completa sin BrokenPipeError después de enviar la confirmación.