有时我们想在Erlang运行系统中运行foreign-language程序，在这种情况下，程序被编写为共享库，该库动态链接到Erlang运行时系统中。
创建驱动程序
创建链接驱动程序是将foreign-language代码与Erlang连接的最有效方法，但也是最危险的，链接驱动程序中的任何致命错误都将使Erlang系统崩溃。
-module(helloLearnfk).
-export([start/0, stop/0]).
-export([twice/1, sum/2]).
start() ->
start("example1_drv" ).
start(SharedLib) ->
case erl_ddll:load_driver("." , SharedLib) of
ok -> ok;
{error, already_loaded} -> ok;
_ -> exit({error, could_not_load_driver})
end,
spawn(fun() -> init(SharedLib) end).
init(SharedLib) ->
register(example1_lid, self()),
Port=open_port({spawn, SharedLib}, []),
loop(Port).
stop() ->
example1_lid ! stop.
twice(X) -> call_port({twice, X}).
sum(X,Y) -> call_port({sum, X, Y}). call_port(Msg) ->
example1_lid ! {call, self(), Msg}, receive
{example1_lid, Result} ->
Result
end.
LINKED-IN DRIVERS 223
loop(Port) ->
receive
{call, Caller, Msg} ->
Port ! {self(), {command, encode(Msg)}}, receive
{Port, {data, Data}} ->
Caller ! {example1_lid, decode(Data)}
end,
loop(Port);
stop -> Port !
{self(), close},
receive
{Port, closed} ->
exit(normal)
end;
</span><span class="pun">{</span><span class="str">EXIT</span><span class="pun">,</span><span class="pln"> </span><span class="typ">Port</span><span class="pun">,</span><span class="pln"> </span><span class="typ">Reason</span><span class="pun">}</span><span class="pln"> </span><span class="pun">-></span><span class="pln">
io</span><span class="pun">:</span><span class="pln">format</span><span class="pun">(</span><span class="str">"~p ~n"</span><span class="pln"> </span><span class="pun">,</span><span class="pln"> </span><span class="pun">[</span><span class="typ">Reason</span><span class="pun">]),</span><span class="pln">
</span><span class="kwd">exit</span><span class="pun">(</span><span class="pln">port_terminated</span><span class="pun">)</span><span class="pln">
end.
encode({twice, X}) -> [1, X];
encode({sum, X, Y}) -> [2, X, Y]. decode([Int]) -> Int.
请注意，使用驱动程序极为复杂，在使用驱动程序时应格外小心。
