Erlang gen_server:如何捕获错误？

Question

我是Erlang开发的新手,我对流程关系很感兴趣.

如果我们连接两个进程P1和P2与process_flag(trap_exit, true)和使用建筑像Pid ! msg和receive .. after .. end-有可能赶上P1错误,如badarith第二进程P2.

但是如果我们使用gen_server与P2链接的进程P1,则P1在P2失败后终止.

那么,如何exit()使用gen_server 捕获错误？

提前致谢!

PS测试代码.

P1:

-module(test1).
-compile(export_all).
-behaviour(gen_server).

start() ->
  gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).

init([]) -> Link = self(),
            spawn(fun() ->
              process_flag(trap_exit, true),
              link(Link),
              test2:start(Link)
            end),
            {ok, "lol"}.

handle_call(stop, From, State) ->
  io:fwrite("Stop from ~p. State = ~p~n",[From, State]),
  {stop, normal, "stopped", State};

handle_call(MSG, From, State) ->
  io:fwrite("MSG ~p from ~p. State = ~p~n",[MSG, From, State]),
  {reply, "okay", State}.

handle_info(Info, State) -> io:fwrite("Info message ~p. State = ~p~n",[Info, State]), {noreply, State}.

terminate(Reason, State) -> io:fwrite("Reason ~p. State ~p~n",[Reason, State]), ok.

P2:

-module(test2).
-compile(export_all).

start(Mod) ->
  io:fwrite("test2: Im starting with Pid=~p~n",[self()]),
  receiver(Mod).

receiver(Mod)->
  receive
    stop ->
      Mod ! {goodbye},
      io:fwrite("Pid: I exit~n"),
      exit(badarith);
    X ->
      io:fwrite("Pid: I received ~p~n",[X])
  end.

结果:test2进程因badarith退出test2后失败.

38> 
38> c(test1).                    
test1.erl:2: Warning: export_all flag enabled - all functions will be exported
{ok,test1}
39> c(test2).                    
test2.erl:2: Warning: export_all flag enabled - all functions will be exported
{ok,test2}
40> test1:start().               
test2: Im starting with Pid=<0.200.0>
{ok,<0.199.0>}
41> <0.200.0> ! stop.            
Pid: I exit
Info message {goodbye}. State = "lol"
stop
** exception exit: badarith
42> gen_server:call(test1, stop).
** exception exit: {noproc,{gen_server,call,[test1,stop]}}
     in function  gen_server:call/2 (gen_server.erl, line 215)
43> 

Answer 1

链接是双向的,但陷阱退出不是; 你需要process_flag(trap_exit, true)在P1中调用(你当前的代码在P2中执行),然后处理表单{'EXIT', FromPid, Reason}中的消息handle_info(将P2的pid放入State帮助中).

在这种情况下,如果P1确实P2停止是有意义的,否则我建议使用监视器而不是链接.

附注:

1. 使用spawn_link而不是spawn+ link.

2. 搬进spawn去的风格更好test2:start.