erlang并行服务器错误？

Question

我决定通过将服务器更改为并行服务器（如本书中所述）来修改this thread中的代码，但它无法正常工作。根据“Erlang编程”一书，下面的代码应该是presto-chango但是我在第17行得到了一个错误。这是并行服务器代码（完成的并行服务器在底部，这只是对最后一个线程上的旧服务器代码），

startp() ->
    {ok, Listen} = gen_tcp:listen(4042, [binary, {packet, 0},  
                     {reuseaddr, true},
                     {active, true}]),                       
                     spawn(fun() -> par_connect(Listen) end).

par_connect(Listen) ->      
        {ok, Socket} = gen_tcp:accept(Listen),
        spawn(fun() -> par_connect(Listen) end),
        loop(Socket).

这是错误，

=ERROR REPORT==== 12-Feb-2013::23:05:13 ===
Error in process <0.35.0> with exit value: {{badmatch,{error,einval}},[{ps1,loop,1,[{file,"ps1.erl"},{line,17}]}]}

以下是并行服务器代码，我认为调用循环（Socket）第14行的参数出错了。也许是别的东西，我不知道？

-module(ps1).
-compile(export_all).
-import(lists, [reverse/1]).

startp() ->
    {ok, Listen} = gen_tcp:listen(4042, [binary, {packet, 0},  
                     {reuseaddr, true},
                     {active, true}]),                       
                     spawn(fun() -> par_connect(Listen) end).

par_connect(Listen) ->      
        {ok, Socket} = gen_tcp:accept(Listen),
        spawn(fun() -> par_connect(Listen) end),
        loop(Socket).

loop(Listen) ->
    {ok, Socket} = gen_tcp:accept(Listen),
    receive
    {tcp, Socket, Bin} ->
        io:format("Server received binary = ~p~n",[Bin]),
        Str = binary_to_term(Bin), 
        io:format("Server (unpacked)  ~p~n",[Str]),
        Reply = string:to_upper(Str),  
        io:format("Server replying = ~p~n",[Reply]),
        gen_tcp:send(Socket, term_to_binary(Reply)),  
        loop(Listen);
    {tcp_closed, Socket} ->
        io:format("Server socket closed~n")
    end.

接下来是客户端代码，它最终也会等待回复

c1:nano("list_to_tuple([2+3*4,10+20])").
nano got not answer to "list_to_tuple([2+3*4,10+20])"
{error,timeout}

-module(c1).
-compile(export_all).
-import(lists, [reverse/1]).

%old port 2345
nano(Str) ->
    {ok, Socket} = 
    gen_tcp:connect("localhost", 4042,
            [binary, {packet, 0}]),
    ok = gen_tcp:send(Socket, term_to_binary(Str)),
    R = receive
        {tcp,Socket,Bin} ->
            io:format("Client received binary = ~p~n",[Bin]),
            Val = binary_to_term(Bin),
            io:format("Client result = ~p~n",[Val]),
            {ok,Val}
        after 5000 ->
            io:format("nano got no answer to ~p~n",[Str]),
            {error,timeout}
    end,
%   gen_tcp:close(Socket),
    R.

Answer 1

根据文档说明，你得到的错误描述有点奇怪：

  

EINVAL

Attempt to delete the current directory. On some platforms, eacces is returned instead.

我必须说它没有多大帮助。

无论如何，您不需要在循环中回忆{ok, Socket} = gen_tcp:accept(Listen)，而在par_connect(Listen)中已经完成了。但在这种情况下，循环的参数将是Socket而不是Listen。你在per_connect中进行了修正，但没有在循环中进行修正（这是你得到错误的原因）。

执行此操作时，第一个服务器是spawn，它使用gen_tcp：listen初始化连接，并等待与gen_tcp：accept的连接。一旦建立连接，就会启动一个新进程，等待接受，并在当前进程中调用循环，并将连接端口作为参数。

现在你应该写一个比我建议更聪明的客户端，它可以使用相同的开放连接循环一段时间：o）

-module(socket_examples).
-compile(export_all).

nano_client_eval(Str) ->
    {ok, Socket} = gen_tcp:connect("localhost", 2345,[binary, {packet, 0}]),
    nano_client_eval(Str,10,Socket).

nano_client_eval(_,0,Socket) ->
    gen_tcp:close(Socket);
nano_client_eval(Str,N,Socket) ->
    ok = gen_tcp:send(Socket, term_to_binary(Str ++ " loop " ++ integer_to_list(N))),
    receive
        {tcp,Socket,Bin} ->
            io:format("Client received binary = ~p on socket ~p~n",[Bin,Socket]),
            Val = binary_to_term(Bin),
            io:format("Client result = ~p~n",[Val]),
            timer:sleep(1000),
            nano_client_eval(Str,N-1,Socket)
        after 5000 ->
            io:format("nano_client_eval got not answer to ~p~n",[Str]),
            {error,timeout}
    end.

start_nano_server() ->
    {ok, Listen} = gen_tcp:listen(2345, [binary, {packet, 0},{reuseaddr, true},{active, true}]),                       
    spawn(fun() -> par_connect(Listen) end).

par_connect(Listen) ->      
    {ok, Socket} = gen_tcp:accept(Listen),
    spawn(fun() -> par_connect(Listen) end),
    loop(Socket).                    

loop(Socket) ->
    receive
    {tcp, Socket, Bin} ->
        io:format("Server received binary = ~p~n",[Bin]),
        Str = binary_to_term(Bin),  %% (9)
        io:format("Server (unpacked)  ~p~n",[Str]),
%        Reply = lib_misc:string2value(Str),  %% (10)
        Reply = string:to_upper(Str),  %% (10)
        io:format("Server replying = ~p~n",[Reply]),
        gen_tcp:send(Socket, term_to_binary(Reply)),  %% (11)
        loop(Socket);
    {tcp_closed, Socket} ->
            io:format("Server socket ~p closed by request~n",[Socket])
    after 60000 ->
            gen_tcp:close(Socket),
            io:format("Server socket ~p closed, no more activity~n",[Socket])
    end.