Feature/queue performance

[jacobgardner]

This includes my other PR, #4. Created two to keep the review separate.

Things:

• To build an index, you need to explicitly set the createIndex flag to true on MessageQueue
• The place I created the index is not optimal, but I think the best place without being a breaking change.

[wonderlic-stephene]

Not sure I understand this. Does the await on line 93 not actually keep line 97 from starting the polling?

[jacobgardner]

It's to avoid a "race condition" when registerWorker is called twice in quick succession, which is what everyone will probably be doing anyway, including us.

// _pollingIntervalId is undefined
mq.registerWorker('typeOne', (queueItem) => {...});
// _startPolling called => !_pollingIntervalId === true => createIndex awaiting
mq.registerWorker('typeTwo', (queueItem) => {...});
// _startPolling called => !_pollingIntervalId === true => createIndex awaiting again
// first createIndex finishes => _pollingIntervalId updated and setInterval called
// second createIndex finishes => _pollingIntervalId changed (first one lost) and setInterval called again. 

This is a pretty awkward place to be creating the index as it is...
I think I would rather do a major version bump, have the database promise passed in through the constructor and do a createIndex once that gets fulfilled and then start the poller (if register worker has been called).

[wonderlic-stephene]

Ok, that makes more sense now. Let's sleep on it and discuss further tomorrow.

[jacobgardner]

Updated based on feedback. I need to test these changes still.