[Embedlets-dev] Re: Sync vs Async

[Andrzej J. T. <an...@ch...>]

Chris observes:

> That all makes sense for events that can afford to fail (logs, user
> interaction etc.) For those that cannot there needs to be a queue-bypass
> path that can complete in a given amount of time. Fortunately the
> synchronous event stack depth would be deterministic since a given event
> would have a known path based on the consumers that are registered. The
> last event in the path may be asynchronous as in a logging event, user
> notification. This mix and match of sync/async events is central to real
> time operation with external client processes.

I absolutely agree....and Synchronous event sending is now implemented.  The 
next version to go up (this weekend) will have that in place.

> But you would use an interrupt driven event to notify critical embedlets
> that something needs to be done NOW! This kind of event could occur on
> sub-millisecond to an hour or more interval. The important thing is that
> there is a mechanism to define the mission critical event and guarantee
> its immediate delivery. This way the developer does not have to 'punt' too
> early in the game because Embedlets cannot deliver!

Yup....but I see the interrupt-generation and initial receipt as being a 
device driver issue (JAPL?) which will then send a Synchronous event to an 
Embedlet to do something useful with the interrupt notification.

I'll give some thought to a way of grabbing a global async thread lock so 
that all other threads get blocked while the synchronous event is being 
propagated, for the ultra-critical events.  Otherwise, even a synchronous 
event propagation can be pre-empted by an async thread execution.

> This makes the most sense in core Embedlet communication. This makes the
> 'wires' a solid connection between produce and consumers and ensures
> prompt processing of events. Async events will be very important as well
> to off load communication between more loosely coupled processes to lower
> priority services.

Yup!  And we now have both.

> We should probably put together a 'When to use Sync/Async events' document
> based on this discussion thread.

For sure....this would be very useful.
Andrzej Jan Taramina
Chaeron Corporation: Enterprise System Solutions
http://www.chaeron.com