[erlang-questions] cnode interface memory allocation

[Guilherme Andrade]

You can always use a secondary channel to transmit the heavier data;
serialising libs like Protocol Buffers et. al. come to mind. As a very
unsafe alternative, you can also use enif_make_new_binary() first and
only then write your data over the allocated area. But, in my limited
experience, I wouldn't recomend it.


On 08/09/14 11:35, Dror Mein wrote:
> I'll try to clarify the problem.
> I have a char * in my code, which I want to erl_send to the erlang
> node. The erl_send function accepts as input an ETERM* pointer. I need
> to turn char* to ETERM*. The current way is by erl_mk_binary, which
> allocates memory.
> Is there a way to pass the char * to erl_send without the unnecessary
> memory allocation.
>
> I thought of pre-creating an ETERM struct, and only changing the
> binary pointer to the char* (before running erl_send). This way I can
> send multiple char* buffers without the need to create multiple ETERM
> pointers.
>
> The point of all this is to reduce run-time for the erl_send process
>
>
> On Monday, September 8, 2014 12:55 PM, Guilherme Andrade
> <g@REDACTED> wrote:
>
>
> (Sorry, missed the subject -- you are indeed talking about a C node.
> Please ignore some of my previous phrasing.)
>
> On 08/09/14 10:34, Guilherme Andrade wrote:
> Hi Drod,
>
> Assuming your application is a C node, and that the library codebase
> is the same as for NIFs and whatnot, I'd expect that allocating
> structures / copying data is the appropriate behaviour when creating
> Erlang terms -- it's the simple way to transfer that data back to
> Erlang avoiding ownership issues and mutable state (or at least making
> it much harder to unintentionally do it.)
>
> I've only dealt with NIFs though, and am not an expert on them, so
> probably someone else can probably clarify this better.
>
>
> Cheers,
>
> On 08/09/14 10:08, Dror Mein wrote:
>> Hi all,
>> I'm writing a c application that communicates with an erlang node. In
>> order to send messages to the node I need to create erlang terms
>> (ETERM structure).
>> it appears that all functions in the C library "erl_eterm" allocate
>> memory when creating erlang terms. 
>> For example, erl_mk_binary copies the binary provided to it, instead
>> of only creating the pointer.
>> I want to prevent this memory allocation to optimize speed. 
>> Has anyone done this before? 
>> Is there a better way to create eterms?
>>
>> Thanks
>>
>>
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>
> -- 
> Guilherme
>
> https://www.gandrade.net/
> PGP: 0x35CB8191 / 1968 5252 3901 B40F ED8A  D67A 9330 79B1 35CB 8191
>
>
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>
> -- 
> Guilherme
>
> https://www.gandrade.net/
> PGP: 0x35CB8191 / 1968 5252 3901 B40F ED8A  D67A 9330 79B1 35CB 8191
>
>

-- 
Guilherme

https://www.gandrade.net/
PGP: 0x35CB8191 / 1968 5252 3901 B40F ED8A  D67A 9330 79B1 35CB 8191

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