📜  Erlang-驱动程序

📅  最后修改于: 2020-11-04 06:01:14             🧑  作者: Mango


有时我们想在Erlang运行系统中运行外语程序。在这种情况下,程序被编写为共享库,该库被动态链接到Erlang运行时系统中。链接的驱动程序在程序员看来像是端口程序,并且服从与端口程序完全相同的协议。

创建驱动程序

创建链接驱动程序是将外语代码与Erlang接口的最有效方法,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。

以下是Erlang中的驱动程序实现示例-

-module(helloworld). 
-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; 
   
      {'EXIT', Port, Reason} -> 
      io:format("~p ~n" , [Reason]), 
      exit(port_terminated) 
   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。