[erlang-questions] Implement standard API (was process hierarchy and passing references)

Schneider <>
Fri Aug 15 19:27:56 CEST 2014


I know I can cascade the gen_server behaviour, and I’ve got it working already with the new –callback syntax. 

I was wondering if there is a way to ‘import’ the init, handle_call etc callback definitions from gen_server so I don’t have to retype them in my new behaviour and, most importantly, they will keep in sync with future updates of the gen_server behaviour. 

Also, what is the performance impact using the cascading approach?

 

Thanks for the input,

 

Frans

 

 

Van: Vance Shipley [mailto:] 
Verzonden: vrijdag 15 augustus 2014 19:10
Aan: Frans Schneider
CC: Ladislav Lenart; Questions erlang-questions
Onderwerp: Re: [erlang-questions] Implement standard API (was process hierarchy and passing references)

 

Yes. ;)

On Aug 15, 2014 7:46 PM, "Frans Schneider" <> wrote:

Yes, I guess defining my own behaviour is what I am looking for.
Found Cascading Behaviours (http://erlangcentral.org/wiki/index.php?title=Cascading_Behaviours) which seems to do the trick.
It is a little dated and still uses behaviour_info(). Is it possible to reuse the callback definitions from gen_server?

Frans


On 08/15/2014 04:02 PM, Ladislav Lenart wrote:

Hello.


On 15.8.2014 11:49, Frans Schneider wrote:

Hi list,

Now that I got the supervision working, I am looking for a way to
implement a standard API for every "main" server. The API implements a
way for the main gen_server to call the RPC middleman and should also
define standard callbacks for the main server the middleman can use. The
API would also use some internal state. In a previous life, I would have
used inheritance to accomplish this, but how can I do this in Erlang?
I had a look at the supervisor implementation, but was wondering if
there is a easier way to accomplish this.

I am not sure I follow you completely. However, if you want to parametrize
process behavior in Erlang (i.e. something similar to OO inheritance that you
mentioned), you can define your own behaviour (a module) and define different
callback modules that all implement it. The pattern is the same as with a
gen_server behaviour.

If this is not what you need, please provide us with a concrete example(s) that
you currently struggle with.


HTH,
Ladislav Lenart



Thanks

Frans


On 08/14/2014 05:16 PM, Ladislav Lenart wrote:

Hello again.


On 14.8.2014 17:00, Ladislav Lenart wrote:

Hello.

What about the following solution:
* Put all three processes under one supervisor.
* Set its restart strategy to one_for_all.

Or rest_for_one. This one may better suite your needs. For more info, refer to
the official documentation at: http://www.erlang.org/doc/man/supervisor.html

* Pass supervisor's PID to its children.
* Each worker process can lookup PID of its relevant sibling via
supervisor:which_children/1.

HTH,

Ladislav Lenart



On 14.8.2014 16:48, Schneider wrote:

Hi list,

Since I am very new to Erlang, I am not sure how to layout process
hierarchies in the following case:

Besides the domain specific functionality, every program has a RPC
middleman and an XML-RPC interface, each implemented as gen_servers. In
the current setup, the main gen_server process starts the RPC middleman,
passing it its Pid, and the RPC gen_server starts the XML-RPC server
which is passed the RPC middleman's Pid.
Using the passed in Pid's, the XML-RPC server can do a
gen_server:call()/cast() back to the RPC server which on its turn can
call the main server. Works ok, but I would like to have the RPC
middleman and XML-RPC controller under the control of a supervisor. The
main supervisor should start the main gen_server process plus a
supervisor that on its turn should start the RPC midleman and the
XML-RPC handler.
The thing I can't figure out is how the XML-RPC process should find the
RPC middleman process and how that process should locate the main server
when using supervision. Since there can be many RPC middlemen and
XMP-RPC servers around, each belonging to different main servers, naming
and registering seems a little hard.
So how to pass references around?

Any help will be very much appreciated.

Frans
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