Async event delivery is undocumented/unsupported about gen_stage

[talentdeficit]

this needs tests obviously, but is there any reason this couldn't be merged?

https://github.com/talentdeficit/gen_stage/tree/async_events

[josevalim]

The producer doesn't have to answer immediatialy. It is totally fine to
store the demand and serve that later on. That's why all callbacks can
potentially return events. The GenEvent example in the examples folder and
in the announcement does that.

The notification is used for other goals. You can check the Naiad project
from Microsoft, which is where we got the notifications from, but in
summary it can be used to notifiy consumers that the source has exhausted
or halted or to notify a new window of processing has started and so on. It
has the property of keep the ordering from events, even if those events
have been buffered somewhere.

On Thursday, July 14, 2016, alisdair sullivan [email protected]
wrote:

As far as I can tell if a consumer requests events the producer must
immediately return that many events in the handle_demand callback or the
producer has to drop down to the raw message protocol to send events
asynchronously. Otherwise the consumer has to issue another request in
order to ever receive any events.

Is async_notify/sync_notify meant to be used for this purpose? how is an
callback module supposed to handle notify messages? raw interpretation of
the notify message in handle_info?

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José Valim
www.plataformatec.com.br
Skype: jv.ptec
Founder and Director of R&D

[josevalim]

To further expand, you never want to send events asynchronously because it
means we won't be able to track the demand and you will lose ordering in
case there are buffers. If you send events async, the consumer will
eventually complain it has gotten more events than it has asked for.

José Valim
www.plataformatec.com.br
Skype: jv.ptec
Founder and Director of R&D

[talentdeficit]

i understand now why i wouldn't want to send events directly to a client async and i guess if i want to produce events asynchronously i could use handle_call/3, thanks

[josevalim]

@talentdeficit you would need to send those messages to the producer so it finally sends them downstream or figure out a way of having multiple producers so you could leverage concurrency from this other angle.