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

Sun Mar 10 23:38:21 CET 2019

Hi Bengt,

Thank you very much for all of your hints and suggestions. It's clear now.

Pada tanggal Sen, 11 Mar 2019 05.20, bengt <cean.ebengt@REDACTED> menulis:

> I think your code is about learning erlang. Do that first. OTP is the next
> step.
>
> Yes, splitting a gen_server into callback module and interface module is
> not the OTP way (as described in documentation), so while good for a
> beginner it can be considered bad style by experienced programmers.
>
> Sorry, but I have not seen any tutorial about how to avoid thinking the
> same function/module is always in the same process. It is a very
> fundamental concept (them not being) in Erlang, so just keep it in mind.
> One way would be to try and make all your three functions the same
> function, just have different arguments to the loop. Then you must think
> about it.
>
>
> On 10 Mar 2019, at 11:11, I Gusti Ngurah Oka Prinarjaya <
> okaprinarjaya@REDACTED> wrote:
>
> Hi Bengt,
>
> Thank you for your review :)
>
> I don't quite understand with some of your thought. Then i hope you not
> mind to give more explanation.
>
> >> Seasoned Erlang programmers will tell you this is not the OTP way, or a
> waste of modules
> Did you mean my code here: https://pastebin.com/ECf3jhZ2 wasn't the OTP
> way?
> I learn from here: https://learnyousomeerlang.com/errors-and-processes
> and i do really a beginner at programming with erlang.
>
> >> So only do this until you have a better understanding.
> What is that? Did you mean *doing one module with the interface functions
> to a gen_server and one module for the gen_server callbacks.?*
> or what?
>
> >> Conflating the function (or even more often, module) and the process is
> a common mistake in the beginning. When my fellow programmers are
> experienced, but not used >> to process oriented programming.
>  Any tutorials / reference for me to avoid this mistake ?
>
> Thank you :)
>
>
>
>
>
>
>
>
> Pada tanggal Min, 10 Mar 2019 pukul 14.49 bengt <cean.ebengt@REDACTED>
> menulis:
>
>> Conflating the function (or even more often, module) and the process is a
>> common mistake in the beginning. When my fellow programmers are
>> experienced, but not used to process oriented programming, I have found
>> that it helps to put the code that is run in different process in different
>> modules. Ex: one module with the interface functions to a gen_server and
>> one module for the gen_server callbacks. Seasoned Erlang programmers will
>> tell you this is not the OTP way, or a waste of modules. So only do this
>> until you have a better understanding.
>>
>> bengt
>>
>> On 10 Mar 2019, at 04:57, I Gusti Ngurah Oka Prinarjaya <
>> okaprinarjaya@REDACTED> wrote:
>>
>> 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.
>>>>
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