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| ng at snipsnap.edfac.unim |
 Posted: Thu Aug 19, 1999 12:40 pm |
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Guest
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G'day,
I am trying to export some C functions to Erlang and at the same time getting
those C functions to invoke Erlang functions in the same program. Like that
of the calback functions. How can this be done in IC ?? if possible at all...
thanks,
mark
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| tobbe at serc.rmit.edu.au |
| Posted: Thu Aug 19, 1999 2:12 pm |
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Guest
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> I am trying to export some C functions to Erlang and at the same time getting
> those C functions to invoke Erlang functions in the same program. Like that
> of the calback functions. How can this be done in IC ?? if possible at all...
Sorry, I know I shouldn't promote IG (since it is obsolete) but
I can't help myself. Actually I would also be interested in how
you would do it with IC. Anyway, here is how you do it with IG:
example.h
--------------------------------------------------------------
#ifndef _EXAMPLE_H
#define _EXAMPLE_H
#include <stdio.h>
#ifdef HIDE
/*
* C functions we want to call from Erlang
*/
IG_fun FILE *fopen(IG_string path, IG_string mode);
IG_fun int fclose( FILE *);
#endif
#endif
--------------------------------------------------------------
Run this through IG:
erl-shell> ig:gen(example).
Compile the result:
gcc -ansi -pedantic -Wall
-I /usr/local/lib/erlang/usr/include
-L /usr/local/lib/erlang/usr/lib
-o example example_stub.c
/usr/local/lib/erlang/usr/lib/igio.o
/usr/local/lib/erlang/usr/lib/igmain.o -lerl_interface
erlc example.erl
Now you can call those functions from Erlang:
--------------------------------------------------------------
23:57 ~/junk> ls
example* example.beam example.erl example.h example_stub.c
23:57 ~/junk> erl
Erlang (BEAM) emulator version 47.4.1
Eshell V47.4.1 (abort with ^G)
1> S=example:start().
<0.30.0>
2> {ok,Fd} = example:fopen(S,"TOUCH_ME","wb").
{ok,134618608}
3> example:fclose(S,Fd).
{ok,0}
4>
BREAK: (a)bort (c)ontinue (p)roc info (i)nfo (l)oaded
(v)ersion (k)ill (D)b-tables (d)istribution
a
23:58 ~/junk> ls
TOUCH_ME example* example.beam example.erl example.h example_stub.c
23:58 ~/junk>
--------------------------------------------------------------
To call an Erlang function from C is a bit more complicated,
but basically: add the following to example.h:
--------------------------------------------------------------
/*
* Erlang function we want to call from C
*/
typedef struct { /* First a data type to store */
int hour; /* the result from erlang:time/0 */
int minute;
int second;
} etime;
IG_call etime get_etime(void);
--------------------------------------------------------------
Run IG again. This time you will also get an 'example.hrl' out
from IG. As per default, IG will assume you are implementing
your callback Erlang functions in example_cb.erl, so create
this file:
--------------------------------------------------------------
-module(example_cb).
-export([get_etime/1]).
-include("example.hrl").
get_etime(_Pid) ->
{H,M,S} = time(),
#etime{hour = H, minute = M, second = S}.
--------------------------------------------------------------
The hardest part is to write a C program that can trigger
this code. I leave this as an exercise for you... ;-)
Cheers /Tobbe
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| ng at snipsnap.edfac.unim |
| Posted: Fri Aug 20, 1999 12:23 pm |
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Guest
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On Fri, Aug 20, 1999 at 12:12:29AM +1000, Torbjorn Tornkvist wrote:
>
> Sorry, I know I shouldn't promote IG (since it is obsolete) but
I have played with it a bit, and like it more than IC for some
tasks. :)
> I can't help myself. Actually I would also be interested in how
> you would do it with IC. Anyway, here is how you do it with IG:
>
<example snipped>
Thanks for the example, but I am really after is something like
where I can pass a lambda to a C function and get that C function
to invoke this piece of Erlang code.
The IC manual has examples on how to call "static" Erlang functions
from C, but not dynamic ones.
mark
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| dgud at erix.ericsson.se |
| Posted: Fri Aug 20, 1999 1:49 pm |
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Guest
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Something like this should be doable I guess.
Define in IDL:
#include <erlang.idl>
module dynamic
{
interface dyn_erl
{
Status erlApply(in string module,
in string function,
in erlang::term listOfArgs,
in out erlang::term res);
}
}
And in the erlang callback module:
erl_apply(State, Mod, Fun, Args) ->
case catch apply(list_to_atom(Mod),
list_to_atom(Fun), Args) of
{'EXIT', R} ->
{reply, {error, []}, State}};
Result ->
{reply, {ok, Result}, State}}
end.
In 'C' the call would look something like
ETERM * result, empty;
empty = erl_mk_empty_list();
status = dynamic_erlApply(NULL, "erlang", "date", empty, &result, env);
See the erl_interface doc about handling erlang data types in C.
/Dan
Mark NG writes:
> On Fri, Aug 20, 1999 at 12:12:29AM +1000, Torbjorn Tornkvist wrote:
> >
> > Sorry, I know I shouldn't promote IG (since it is obsolete) but
>
> I have played with it a bit, and like it more than IC for some
> tasks. 
>
>
> > I can't help myself. Actually I would also be interested in how
> > you would do it with IC. Anyway, here is how you do it with IG:
> >
>
> <example snipped>
>
> Thanks for the example, but I am really after is something like
> where I can pass a lambda to a C function and get that C function
> to invoke this piece of Erlang code.
>
> The IC manual has examples on how to call "static" Erlang functions
> from C, but not dynamic ones.
>
>
> mark
>
--
Dan Gudmundsson Project: Mnesia, Erlang/OTP
Ericsson Utvecklings AB Phone: +46 8 727 5762
UAB/F/P Mobile: +46 70 519 9469
S-125 25 Stockholm Visit addr: Armborstv 1
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