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

Robert Virding <>
Wed Sep 28 15:15:08 CEST 2011


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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