[erlang-questions] Behaviours in a module

[Nuku Ameyibor]

Hello List ,
Hope everyone is cool.

i noticed a few patterns in some tutorials i was going through and wanted
some insight .
How many application behaviors can you attach to a single module and how
does this affect  the behavior of the module .

i saw these examples

-module(a).
-behaviour(application).
-export([start/2, stop/1, start_pool/3)

start(normal, _Args) ->
    ppool_supersup:start_link().

.....

%%%%and b below

*-*module(b).
-behaviour(application).
-behaviour(supervisor).

-export([start/2, stop/1]).
-export([init/1]).
start() ->application:start(?MODULE).

.......

in module a

 i know the start function will call the top level supervisor

and the top level supervisor will start itself and possibly children etc...

in module b

i know the  start function will be run and run application:start(?module) .

what happens after that  because the function seems to be calling
itself which is causing me to scratch my head .

what happens to the supervisor behavior  also .

can you put different behaviors into a single module and evoke them
and make that one module have all the behaviours eg. can a single
module be a gen_server,supervisor  or are there some special instances
where this is allowed .(genserver and supervisor both have one init
function so i was beginning to doubt this but what if your behaviors
have different names):

i.e. create your own custom behaviours

an unrelated question

does a socket closing  send a  message to the controlling process
immediately . i get the {tcp_closed, _Socket} message only when i am
sending a message to a closed socket . it there a way the controlling
process is immediately notified of a closed socket and not nessaringly
when you tring sending a message to it


thanks !!!
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