How to wait for consumer to complete poll function after stop

[mikicho]

Background

TL;DR:
The start function is sync but leaves "open" promise that users can't await for.

Example:

I have a consumer that prints a log on the message_processed event:

consumer.on('message_processed', (message) => {
    console.log('Yay');
});

The problem is that my tests (and the process in production) are completed before the listener gets executed because the stop function doesn't wait for poll function to complete.

Objectives

stop function should wait for the poll function to complete.

OR

Emit shutdown event only after the poll function is complete instead of inside the stop function. so users will be able to await for shutdown event

[mikicho]

It may somewhat related to #392

[nicholasgriffintn]

Hey! Sorry for the late reply.

This is something that we have had raised before and we have noted it as a future exploration task, due to how Consumer works though, this is slightly tricky.

[mikicho]

This is why I think we should emit another event when polling actually stops:
e.g. here: https://github.com/bbc/sqs-consumer/blob/main/src/consumer.ts#L178

[nicholasgriffintn]

Yeah so currently there's no way of actually knowing how if there's a soon to be active timer, they should be cancelled on stop, but this is there to catch the cases where sometimes they don't get cancelled.

We'd have to rewrite the queuing in order to know if there's anything in it or not.

[mikicho]

Oh.. are you worried about inflight messages?

[nicholasgriffintn]

Yes that's basically the reason.

[mikicho]

Maybe we can keep a counter?

[barwin]

I've taken a stab at this with #454 -- There are a few different ways to go about this, so I'm happy to rework this PR with some guidance if maintainers are opposed to this approach.