[erlang-questions] dirty nif and enif_make_badarg()

[Daniel Goertzen]

Thanks, that's what I will do then.

PS, the dirty schedulers are working very well for me.  I ran a cpu-bound
nif that took about an hour, and the rest of the Erlang system just kept on
ticking.


On Wed, May 28, 2014 at 2:46 PM, Steve Vinoski <vinoski@REDACTED> wrote:

>
>
>
> On Wed, May 28, 2014 at 3:19 PM, Daniel Goertzen <
> daniel.goertzen@REDACTED> wrote:
>
>> I am trying to write a dirty nif and am following the directions from
>> http://www.erlang.org/doc/man/erl_nif.html
>>
>> Exceprt:
>> "A dirty NIF may not invoke the enif_make_badarg<http://www.erlang.org/doc/man/erl_nif.html#enif_make_badarg>to raise an exception. If it wishes to return an exception, the dirty NIF
>> should pass a regular result indicating the exception details to its
>> finalizer, and allow the finalizer to raise the exception on its behalf."
>>
>> So I am doing this; here is my finalizer....
>>
>>
>> // cached atoms
>> ERL_NIF_TERM badarg;
>>
>> static ERL_NIF_TERM badarg_finalizer(ErlNifEnv* env, ERL_NIF_TERM term)
>> {
>>     if(term == badarg)
>>         return enif_make_badarg(env);
>>     else
>>         return term;
>> }
>>
>> ... and I end up with the exception context of the finalizer and not the
>> nif as desired...
>>
>>
>> 5> generate_rsa:generate_rsa_key(abc, 65537).
>> entering generate_rsa_key_nif
>>                              entering generate_rsa_key_nif_dirty
>>                                                                 entering
>> badarg_finalizer
>>
>> ** exception error: bad argument
>>      in function  generate_rsa:generate_rsa_key_nif/2
>>         called as
>> generate_rsa:generate_rsa_key_nif(badarg,18446744072346624528)   *!!!
>> should be (abc,65537)*
>>      in call from generate_rsa:generate_rsa_key/2 (src/generate_rsa.erl,
>> line 25)
>>
>>
>> The documentation implies I can provide the "exception details", but
>> enif_make_badarg() doesn't offer any extra parameters.  Is there some other
>> way to set the "exception details"?
>>
>
> "Exception details" here is just general, meaning whatever kinds of error
> information you want the finalizer to return. A NIF can raise only badarg
> via enif_make_badarg(), and there's no way for it to control any parameters
> associated with the exception. You might instead consider wrapping the NIF
> function with an actual Erlang function in your module, treating the NIF
> like an internal (non-exported) function, having the finalizer return an
> error tuple containing relevant information, and letting Erlang raise an
> exception based on that info.
>
> --steve
>
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