[erlang-questions] [Code Review] Is this a good idea? I linking 3 process manually (not using recursive)

[I Gusti Ngurah Oka Prinarjaya]

Hi Bengt,

Thank you for the idea,

I've implement your idea, from performance side, i think using two version
of function will have better performance because there's no need to
checking using IF statement.

I worry at first to implement this idea, because i think different version
of function will have different PID, hahaha it turns out exactly have same
PID.
this is  my new code https://pastebin.com/ECf3jhZ2 . Please review if
there's any improvement needs.

Thank you







Pada tanggal Min, 10 Mar 2019 pukul 05.23 bengt <cean.ebengt@REDACTED>
menulis:

> Greetings,
>
> The error happens the second time any of the three processes call
> erlang:register/2. They already registered themselves the first time. If
> you want this structure, but not the error, you have to do the register
> before starting the loop. Eg, split the functions into two. One that do the
> register and then calls the second that does the loop.
>
> bengt
>
> On 9 Mar 2019, at 14:41, I Gusti Ngurah Oka Prinarjaya <
> okaprinarjaya@REDACTED> wrote:
>
> Hi Attila Rajmund Nohl,
>
> After i implement your suggestion, i get error when execute any of
> function call_the_*_p()
> for example:
>
> 3> newbie:starter().
> <0.112.0>
> 4> newbie:call_the_second().
> =ERROR REPORT==== 9-Mar-2019::20:35:15.069388 ===
> Error in process <0.113.0> with exit value:
> {badarg,[{erlang,register,[pidsecondp,<0.113.0>],[]},
>          {newbie,the_second_p,0,
>
> [{file,"/Users/okaprinarjaya/Oprek/Erlang-Oprek/oprek-lagi/src/newbie.erl"},
>                   {line,17}]}]}
>
> {<0.113.0>,"the_second_p()","Halo second p!"}
>
> This is my new modified code https://pastebin.com/iYCxkkuz
>
>
> Pada tanggal Jum, 8 Mar 2019 pukul 21.03 Attila Rajmund Nohl <
> attila.r.nohl@REDACTED> menulis:
>
>> I Gusti Ngurah Oka Prinarjaya <okaprinarjaya@REDACTED> ezt írta
>> (időpont: 2019. márc. 8., P, 12:11):
>> >
>> > Hi Folks,
>> >
>> > I need your help to review my code. I create and linking 3 process
>> manually without using recursive. And inside p1 and p2 i using IF statement
>> to check to make sure spawning process will only once.
>> >
>> > I mean, is part code below is a good idea?
>> >
>> > IsPidExists = whereis(xxx),
>> >   if IsPidExists =:= undefined ->
>> >     Pid = spawn_link(?MODULE, the_p, []),
>> >     register(xxx, Pid);
>> >     true -> true
>> >   end,
>>
>> Generally this is not a good idea, there's a race condition between
>> checking that the process is registered (the whereis/1 call) and
>> registering the new process. A better idea is to start the process and
>> let the process itself to register. If register fails, it means that
>> there's already a process registered, so the just started process can
>> terminate. So your code could look like something like this:
>>
>> starter() ->
>>   spawn(?MODULE, the_first_p, []).
>>
>> the_first_p() ->
>>   register(pidfirstp, self()),
>>   spawn_link(?MODULE, the_second_p, []),
>>   ...
>>   the_first_p().
>>
>> Actually if the register call fails, it throws a badarg and the
>> process dies automatically, simplifying the code.
>>
> _______________________________________________
> erlang-questions mailing list
> erlang-questions@REDACTED
> http://erlang.org/mailman/listinfo/erlang-questions
>
>
> _______________________________________________
> erlang-questions mailing list
> erlang-questions@REDACTED
> http://erlang.org/mailman/listinfo/erlang-questions
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://erlang.org/pipermail/erlang-questions/attachments/20190310/aa927a73/attachment.htm>