Async calls in the ConnectToPersistentSubscription EventAppeared action

EventStoreDB
1

For example, is there any benefit to:

private async void OnEventReceived(EventStorePersistentSubscriptionBase subscription, ResolvedEvent resolvedEvent)
{
var thing = new Thing();
var result = await _repository.SaveAsync(thing);

}

``

versus just waiting/blocking the current thread:

private void OnEventReceived(EventStorePersistentSubscriptionBase subscription, ResolvedEvent resolvedEvent)

{

var thing = new Thing();

var result = _repository.SaveAsync(thing).Result; // or .Wait() etc...

}

``

Will EventStore make use of the original thread if the async operation is awaited or is this just a bad idea? Assuming if this was intended to be Async the EventAppeared would be a function that returned a Task…not an action.

When providing an “EventAppeared” method for ConnectToPersistentSubscription I have calls on the EventReceived that are async calls. Like saving a record to Elastic etc… Is there anything to be gained by making the event appeared method async and awaiting these calls, or is the expected pattern that I will simply “.Wait()” the contained async calls.

2

Use manual acking then ack in your async callback...

3

Greg, do you see that pattern as advantageous over blocking until the handler finishes?

Thanks,

4

Yes for async handlers as they can be async (and you get retry mechanisms etc)

5

Cool thanks