系列:
Erlang/Elixir: 外部通信之-NIF
Erlang/Elixir: 外部通信之-端口驱动
Erlang/Elixir: 外部通信之-C节点
本文阐述了如何使用rebar3
来构建一个简单的NIF(内建函数)
使用Makefile模板
让我们从创建一个新的名为test_nif
的lib
, 使用test_nif
项目中的cmake
模板开始
$ rebar3 new lib test_nif
===> Writing test_nif/src/test_nif.erl
===> Writing test_nif/src/test_nif.app.src
===> Writing test_nif/rebar.config
===> Writing test_nif/.gitignore
===> Writing test_nif/LICENSE
===> Writing test_nif/README.md
$ cd test_nif
$ rebar3 new cmake
===> Writing c_src/Makefile
设置钩子
{erl_opts, [debug_info]}.
{deps, []}.
{pre_hooks,[
{"(linux|darwin|solaris)", compile, "make -C c_src"},
{"(freebsd)", compile, "gmake -C c_src"}
]}.
{post_hooks,[
{"(linux|darwin|solaris)", clean, "make -C c_src clean"},
{"(freebsd)", clean, "gmake -C c_src clean"}
]}.
Makefile
是由rebar3 new cmake
命令创建的.
下面是一个NIF, 包含一个repeat
函数, 接受一个pid
和一个erlang term作为参数, 向该pid
发送消息:
c_src/test_nif.c
#include "erl_nif.h"
ERL_NIF_TERM
mk_atom(ErlNifEnv* env, const char* atom)
{
ERL_NIF_TERM ret;
if(!enif_make_existing_atom(env, atom, &ret, ERL_NIF_LATIN1))
{
return enif_make_atom(env, atom);
}
return ret;
}
ERL_NIF_TERM
mk_error(ErlNifEnv* env, const char* mesg)
{
return enif_make_tuple2(env, mk_atom(env, "error"), mk_atom(env, mesg));
}
static ERL_NIF_TERM
repeat(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
{
ErlNifEnv* msg_env;
ErlNifPid pid;
ERL_NIF_TERM copy;
if(argc != 2)
{
return enif_make_badarg(env);
}
if(!enif_is_pid(env, argv[0]))
{
return mk_error(env, "not_a_pid");
}
if(!enif_get_local_pid(env, argv[0], &pid))
{
return mk_error(env, "not_a_local_pid");
}
msg_env = enif_alloc_env();
if(msg_env == NULL)
{
return mk_error(env, "environ_alloc_error");
}
copy = enif_make_copy(msg_env, argv[1]);
if(!enif_send(env, &pid, msg_env, copy))
{
enif_free(msg_env);
return mk_error(env, "error_sending_term");
}
enif_free_env(msg_env);
return mk_atom(env, "ok");
}
static ErlNifFunc nif_funcs[] = {
{"repeat", 2, repeat}
};
ERL_NIF_INIT(test_nif, nif_funcs, NULL, NULL, NULL, NULL);
测试代码 src/test_nif.erl
-module(test_nif).
-export([repeat/2]).
-on_load(init/0).
-define(APPNAME, test_nif).
-define(LIBNAME, test_nif).
repeat(_, _) ->
not_loaded(?LINE).
init() ->
SoName = case code:priv_dir(?APPNAME) of
{error, bad_name} ->
case filelib:is_dir(filename:join(["..", priv])) of
true ->
filename:join(["..", priv, ?LIBNAME]);
_ ->
filename:join([priv, ?LIBNAME])
end;
Dir ->
filename:join(Dir, ?LIBNAME)
end,
erlang:load_nif(SoName, 0).
not_loaded(Line) ->
exit({not_loaded, [{module, ?MODULE}, {line, Line}]}).
运行 rebar3 shell
$ rebar3 shell
===> Verifying dependencies...
===> Compiling test_nif
Erlang/OTP 17 [erts-6.3] [source] [64-bit] [smp:4:4] [async-threads:0] [kernel-poll:false]
Eshell V6.3 (abort with ^G)
1> test_nif:repeat(self(), hello).
ok
2> receive X -> X end.
hello