[erlang-questions] gproc and gen_event

Andrew Berman <>
Sat May 19 21:00:17 CEST 2012


Awesome, thanks for the explanation Ulf!  I'm going to give it a shot.

--Andrew

On Sat, May 19, 2012 at 2:40 AM, Ulf Wiger <> wrote:

>
> On 19 May 2012, at 01:38, Andrew Berman wrote:
>
> Ok, cool, thanks Garrett.
>
> Do you have any experience using gproc for pub/sub?
>
>
> Gproc does do pub/sub fairly well, but if I may, the main purpose of
> gproc initially was to serve as a form of "property index" for processes.
>
> It had dawned on me that complex signaling applications tended to
> end up with a lot of code that basically provided different sorts of
> mappings to allow you to locate the right processes. Having so many
> different mappings complicated debugging, and obscured many
> aspects of the architecture.
>
> When we started using (the predecessor of) gproc in some Ericsson
> projects, there was significant code reduction. The nice thing was that
> the developers picked it up themselves; there wasn't really any central
> decision to go with it.
>
> One of the things I like about gproc is that it allows you to publish the
> 'interaction features' of a process: registered aliases say much about
> what services a process can perform, and properties illustrate its
> dependencies on other processes. The registry can be queried with
> select operations or QLC, or simply with gproc:i() from the shell.
>
> In short, there are many fine ways of doing pub/sub, but if you use
> gproc consistently for this sort of thing, and similar things, it can help
> clarify runtime aspects of your system, making it more transparent and
> easier to debug.
>
> This also explains why gproc relies on a central registry (which is a
> challenge in the global case). The registry itself is much of the point.
>
> Of course, for a distributed pub/sub, you don't really need to turn on
> the distributed parts of gproc. Running a local gproc instance on each
> node, you can publish like so:
>
> publish(Event, Data) ->
>    rpc:eval_everywhere(
>       gproc, send,
>       [{p, l, {?MODULE, Event}}, {?MODULE, Event, Data}]).
>
> BR,
> Ulf W
>
> Ulf Wiger, Co-founder & Developer Advocate, Feuerlabs Inc.
> http://feuerlabs.com
>
>
>
>
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