list_to_atom use in kernel/error_logger.erl

Serge Aleynikov <>
Fri Feb 3 15:57:39 CET 2006


Gunilla,

Gunilla Arendt wrote:
> Clarification: I should have added that I think list_to_atom/1 is in 
> error_logger for *historical reasons*, i.e. my guess is that it's a 
> remnant from a time when erlang:display/1 displayed strings as list of 
> ascii codes. Nowadays, erlang:display/1 can handle strings as well as 
> atoms and the call to list_to_atom/1 is indeed superfluous.

Thanks for clarification!  I agree with your thinking, however, since 
this simple error_logger is replaced with a standard error handler at 
startup, I assume it's logging is only essential for the startup 
functionality of the application_controller, which is a pretty 
imprortant place in troubleshooting startup issues.

> That said, I would like to point out that messages to error_logger could 
> be sent from any process, so it is (was) not an application_controller 
> issue. It is true that application_controller sends lists to 
> error_logger, but so could any other process. Also, the code snippet you 
> refer to actually has to do with the exit reason of the 
> application_controller process, not an error report.

As far as I understand you cannot use io_lib's functions for formatting 
error reports in that error_logger as they lead to a deadlock.  Given 
so, I believe, it is extremely useful to see the failure reason printed 
  readably.

On the other hand, perheps when you are exposed to Erlang for quite a 
while, the difference between

       [80,114,111,116,111,99,111,108] and "Protocol"

starts to evaporate, and you begin to think that the green flickering 
symbols on computer terminals in the "Matrix" movie do resemble people 
behind them...    ;-)

Serge

P.S. I did apply the patch to my application_controller.erl, and I am 
quite happy now as I can read the starup failure reasons without opening 
erl and copying/pasting the failure printouts in the shell like this:

()2> [80,114,111,116,111,99,111,108].
"Protocol"

> Serge Aleynikov wrote:
> 
>> I believe what you are referring to is actually a small issue with the 
>> application_controller rather than error_logger.  If the following 
>> patch is applied to the application_controller then the logging 
>> problem at system startup that you indicated will be more readable and 
>> you could remove the list_to_atom(L) in the error_logger.erl.
>>
>> --- kernel-2.10.12/src/application_controller.erl Fri Jan 27 17:17:31 
>> 2006
>> +++ lib/kernel/src/application_controller.erl Thu Feb  2 10:12:01 2006
>> @@ -1932,6 +1932,6 @@
>>               true ->
>>                   Term;
>>               false ->
>> -                 lists:flatten(io_lib:write(Term))
>> +                 lists:flatten(io_lib:format("~p", [Term]))
>>           end,
>>      lists:sublist(Str, 199).
>>
>> Regards,
>>
>> Serge
>>
>> Gunilla Arendt wrote:
>>
>>> Serge Aleynikov wrote:
>>>
>>>>
>>>> Thank you for clarification.  The reason I looked into the 
>>>> error_logger's code was indeed related to the ugly format of the 
>>>> displayed message upon an unsuccessful startup with a -boot option.
>>>>
>>>> Though I still don't understand the need for list_to_atom(L) there.  
>>>> Why not just return the list L?  It does work either way.
>>>>
>>>
>>> I haven't tried to verify this, but my guess would be that someone tried
>>> to make the output from error_logger more readable in the case where
>>> the Erlang run-time system fails to start.
>>>
>>> For example, if an application in the boot script fails to start, you
>>> will see something like this:
>>>
>>> $ erl
>>> {error_logger,{{2006,2,2},{14,11,52}},'Protocol: ~p: register error: 
>>> ~p~n',[inet_tcp,{{badmatch,{error,duplicate_name}},[{inet_tcp_dist,listen,1},{ne 
>>>
>>> t_kernel,start_protos,4},{net_kernel,start_protos,3},{net_kernel,init_node,2},{n 
>>>
>>> et_kernel,init,1},{gen_server,init_it,6},{proc_lib,init_p,5}]}]}
>>> ...
>>>
>>> which is of course somewhat more readable than
>>>
>>> {error_logger,{{2006,2,2},{14,11,52}},[80,114,111,116,111,99,111,108,58,32,126,1 
>>>
>>> 12,58,32,114,101,103,105,115,116,101,114,32,101,114,114,111,114,58,32,126,112,12 
>>>
>>> 6,110],[inet_tcp,{{badmatch,{error,duplicate_name}},[{inet_tcp_dist,listen,1},{ne 
>>>
>>> t_kernel,start_protos,4},{net_kernel,start_protos,3},{net_kernel,init_node,2},{n 
>>>
>>> et_kernel,init,1},{gen_server,init_it,6},{proc_lib,init_p,5}]}]}
>>> ...
>>>
>>> / Gunilla
>>>
>>>
>>>
>>
> 
> 




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