I'm probably missing something obvious

[Dave Thomas]

but the Registry module seems to require to be called by name, and not by pid. Given that, I can see a way of using it between nodes.

I wanted to replace the now-deprecated GenEvent with Registry, but this seems to be a roadblock.

As I said, I must be missing something obvious.

Dave

[Michał Muskała]

The Registry module provides local registration. It does not provide global registration. Since a better global registry is something the OTP team is working on, there was little use in doubling the effort.

That said, you can call a named GenServer on another node using {server_name, node_name} as "reference".

Michał.

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[Dave Thomas]

Sure. 

So rather than remove GenEvent, could it be spun out as a Hex module? I don't really want to reinvent the wheel and write my own servers that do what it already does.

Dave

[Pedro Medeiros]

Dave, you can always use the gen_event from erlang. If you you are having a more complex logic I guess that use GenStage is the way to go. As it is suggested on the master docs https://hexdocs.pm/elixir/master/GenEvent.html#content

Furthermore, I totally agree to open source GenEvent for those how can't afford to change the code right now. But with a warning that this module will no longer be maintained as it used to be.

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[Dave Thomas]

I read the docs. None of the suggestions is a replacement for GenEvent (apart from writing a replacement yourself). Registry, however, is. So I was assuming that GenEvent would only be deprecated if there was a replacement, and that Registry was intended to act as that. Changing the interface to registry to accept a pid as well as a name would achieve that.

Dave

On Tuesday, March 14, 2017 at 2:24:03 PM UTC-5, Pedro Medeiros wrote:

Dave, you can always use the gen_event from erlang. If you you are having a more complex logic I guess that use GenStage is the way to go. As it is suggested on the master docs https://hexdocs.pm/elixir/master/GenEvent.html#content

Furthermore, I totally agree to open source GenEvent for those how can't afford to change the code right now. But with a warning that this module will no longer be maintained as it used to be.

On Tue, Mar 14, 2017 at 4:13 PM, Dave Thomas <da...@pragdave.me> wrote:

Sure. 

So rather than remove GenEvent, could it be spun out as a Hex module? I don't really want to reinvent the wheel and write my own servers that do what it already does.

Dave

On Tuesday, March 14, 2017 at 12:36:00 PM UTC-5, Michał Muskała wrote:

The Registry module provides local registration. It does not provide global registration. Since a better global registry is something the OTP team is working on, there was little use in doubling the effort.

That said, you can call a named GenServer on another node using {server_name, node_name} as "reference".

Michał.

On 14 Mar 2017, 18:27 +0100, Dave Thomas <da...@pragdave.me>, wrote:

but the Registry module seems to require to be called by name, and not by pid. Given that, I can see a way of using it between nodes.

I wanted to replace the now-deprecated GenEvent with Registry, but this seems to be a roadblock.

As I said, I must be missing something obvious.

Dave

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[José Valim]

The only direct replacement for GenEvent is :gen_event.

Registry, GenStage or using supervisors require you to rethink your design and consider the trade-offs. In the Registry case, it was designed for decentralized reads so it doesn't work on PIDs. The point of registry is to not have to rely on a process.

But with :gen_event, you only need to replace "use GenEvent" by "@behaviour :gen_event" and implement the missing callbacks (which will become warnings).

And FWIW the OTP team is discussing about making callbacks optional so by the time GenEvent is actually removed from Elixir, which is still a long time ahead, migrating to :gen_event should be even more straight-forward.

José Valim

www.plataformatec.com.br

Skype: jv.ptec

Founder and Director of R&D

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