[erlang-questions] How to get pid number in NIF code?

Jovi Zhang <>
Thu Sep 29 03:41:56 CEST 2011


Hmm, understood, Thanks very much, I will store the ErlNifPid instead
of process number.

On Thu, Sep 29, 2011 at 2:35 AM, Sverker Eriksson
<> wrote:
> Yes, ErlNifPid is typically the size of one word. You can type cast it to an
> integer type of equal size to get a "process number".
>
> /Sverker, Erlang/OTP
>
> Robert Virding wrote:
>>
>> Someone must correct if I am wrong here but I don't think that an
>> ErlNifPid takes much space. As I understand it is not the whole process
>> structure, just a reference to it. From erl_nif.h:
>>
>> #ifdef HALFWORD_HEAP_EMULATOR
>> #  define ERL_NIF_VM_VARIANT "beam.halfword" typedef unsigned int
>> ERL_NIF_TERM;
>> #else
>> #  define ERL_NIF_VM_VARIANT "beam.vanilla" typedef unsigned long
>> ERL_NIF_TERM;
>> #endif
>>
>> ...
>>
>> typedef struct
>> {
>>    ERL_NIF_TERM pid;  /* internal, may change */
>> }ErlNifPid;
>>
>> But someone more knowledgeable should confirm this.
>>
>> Robert
>>
>> ----- Original Message -----
>>
>>>
>>> On Wed, Sep 28, 2011 at 4:48 PM, Tony Rogvall <>
>>> wrote:
>>>
>>>>
>>>> I do not think there is a way to extract that number (except for a
>>>> small
>>>> hack, of course)
>>>> Care to tell the reason behind why you need it ?
>>>> /Tony
>>>>
>>>>
>>>
>>> Hmm, I'm writing a NIF library to let erlang process communicate with
>>> external hand. we call that as "hand", it is similar with erlang
>>> process, but with different number reference, hand is range from
>>> 0-65535.
>>>
>>> So in this NIF library I must remember the mapping of
>>> "process<->hand", actually I only run this in one node, with process
>>> like <0.X.0>,
>>> which I only care about process number, that's why I want to get
>>> process number, not whole pid structure.
>>>
>>> Of course I can store all "ErlNifPid<->hand index", but that will
>>> consume a lot of memory.
>>>
>>> I think erts should provide API or macro for get process number for
>>> some use case.
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>>> 
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>>>
>>
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>
>



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