[erlang-questions] OTP Design Pattern Question/gen_server with different parameters?

Daniel Goertzen <>
Tue Mar 10 18:51:06 CET 2009


I wonder if you are throwing too many processes and servers at the problem.
Can the solution be implemented by plain old functions within a single
process?

Dan.

2009/3/10 Jonathan Palley <>

> All -   I've got this running in straight Erlang, but trying to understand
> how to apply to the OTP pattern.
>
> Wondering the best practice for a system like this:
>
>
> event comes in (external source) -> various event handlers get sent the
> event based on the event type. -> these event handlers will filter the event
> to determine if they should send it on (via an http request).
>
> The trick is this: there is an interface to add and delete event handlers
> with a filter.
>
> In straight erlang I:
>   - Created a new process for each handler.  The handler would be init with
> the filters.
>   - A central event processor stored the PID of each handler and the event
> type it was subscribed to.  As an event would come in it would re-broadcast
> to the different handlers.
>   - Each handler would then use its custom filter to determine whether to
> send it on.
>
>
> Now, I would like all the robustness that comes with OTP.  Perhaps I am
> approaching this incorrectly, but what I can't figure out is:
>
> - If I start multiple instances of gen_event (with different filters each)
> and add it to a supervisor tree, there doesn't seem to be a way to identify
> the one handler I want to delete (if I want to remove the handler)
> - If I create only one gen_event for each event type and make the
> event_handlers be gen_server, I run into a similar problem (how do I call
> all the gen_servers that I want).
>
> Thanks for any ideas!
> JP
>
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Daniel Goertzen
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