Erlang 生成问题

Question

我在 erlang 中遇到了“spawn”问题，似乎进程在一段时间后就死掉了。这是简单的代码:

-module(simple).
-export([server/1, client/1, owner/1, spawn_n/2, start/1, main/1]).

server(State) ->
receive
    {request,Return_PID} ->
        io:format("SERVER ~w: Client request recieved from ~w~n", [self(),Return_PID]),
        NewState = State + 1,
        Return_PID ! {hit_count,NewState},
        server(NewState);

    {server_owner,Owner_PID} ->
        io:format("SERVER ~w: Owner request recieved from ~w~n", [self(), Owner_PID]),
        Owner_PID ! {hit_count,State},
        server(State);
    reset ->
        io:format("SERVER ~w: State reset to zero.~n", [self()]),
        server(0)

end.



client(Server_Address) ->
Server_Address ! {request, self()},
receive
    {hit_count,Number} ->
        io:format("CLIENT ~w: Hit count was ~w~n", [self(),Number])
end.



owner(Server_PID) ->
timer:sleep(random:uniform(100)),
Server_PID ! {server_owner,self()},
receive 
    {hit_count,Number} when Number > 5 ->
        io:format("OWNER: Hit count is ~w , reseting counter. ~n", [Number]),
        Server_PID ! reset,
        owner(Server_PID);
    {hit_count,Number} when Number < 5 ->
        io:format("OWNER ~w: Hit count was ~w~n", [self(), Number]),
        owner(Server_PID)
end.




spawn_n(N, Server_PID) ->
if
    N>0 ->
        spawn(simple,client,[Server_PID]),
        timer:sleep(random:uniform(100)),
        spawn_n(N-1,Server_PID);
    N==0 ->
        io:format("Last client spawned. ~n")
end.



start(N) ->
Server_PID = spawn(simple,server,[0]),
spawn(simple,owner,[Server_PID]),
spawn(simple,spawn_n,[N,Server_PID]).


main([Arg]) ->
N = list_to_integer(atom_to_list(Arg)),
start(N),
init:stop().

这是我运行时得到的一个示例:

erl -noshell -s simple main 20

SERVER <0.28.0>: Client request recieved from <0.31.0>
CLIENT <0.31.0>: Hit count was 1
SERVER <0.28.0>: Owner request recieved from <0.29.0>
SERVER <0.28.0>: Client request recieved from <0.32.0>
OWNER <0.29.0>: Hit count was 1
CLIENT <0.32.0>: Hit count was 2
SERVER <0.28.0>: Owner request recieved from <0.29.0>
SERVER <0.28.0>: Client request recieved from <0.33.0>
OWNER <0.29.0>: Hit count was 2
CLIENT <0.33.0>: Hit count was 3
SERVER <0.28.0>: Owner request recieved from <0.29.0>
SERVER <0.28.0>: Client request recieved from <0.34.0>
OWNER <0.29.0>: Hit count was 3
CLIENT <0.34.0>: Hit count was 4
SERVER <0.28.0>: Owner request recieved from <0.29.0>
SERVER <0.28.0>: Client request recieved from <0.35.0>
OWNER <0.29.0>: Hit count was 4
CLIENT <0.35.0>: Hit count was 5
SERVER <0.28.0>: Owner request recieved from <0.29.0>
SERVER <0.28.0>: Client request recieved from <0.36.0>
CLIENT <0.36.0>: Hit count was 6
SERVER <0.28.0>: Client request recieved from <0.37.0>
CLIENT <0.37.0>: Hit count was 7
SERVER <0.28.0>: Client request recieved from <0.38.0>
CLIENT <0.38.0>: Hit count was 8
SERVER <0.28.0>: Client request recieved from <0.39.0>
CLIENT <0.39.0>: Hit count was 9
SERVER <0.28.0>: Client request recieved from <0.40.0>
CLIENT <0.40.0>: Hit count was 10
SERVER <0.28.0>: Client request recieved from <0.41.0>
CLIENT <0.41.0>: Hit count was 11
SERVER <0.28.0>: Client request recieved from <0.42.0>
CLIENT <0.42.0>: Hit count was 12
SERVER <0.28.0>: Client request recieved from <0.43.0>
CLIENT <0.43.0>: Hit count was 13
SERVER <0.28.0>: Client request recieved from <0.44.0>
CLIENT <0.44.0>: Hit count was 14
SERVER <0.28.0>: Client request recieved from <0.45.0>
CLIENT <0.45.0>: Hit count was 15
SERVER <0.28.0>: Client request recieved from <0.46.0>
CLIENT <0.46.0>: Hit count was 16
SERVER <0.28.0>: Client request recieved from <0.47.0>
CLIENT <0.47.0>: Hit count was 17
SERVER <0.28.0>: Client request recieved from <0.48.0>
CLIENT <0.48.0>: Hit count was 18
{error_logger,{{2011,6,27},{12,57,8}},"~s~n",["Error in process <0.28.0> with ex
it value: {terminated,[{io,format,[<0.22.0>,\"SERVER ~w: Client request recieved
 from ~w~n\",[<0.28.0>,<0.49.0>]]},{simple,server,1}]}\n"]}

我不明白。进程就死掉了还是怎么的？它不应该终止! 我正在 Windows 7 上运行，如果它可能与 Windows 相关的话。

谢谢

编辑:这是执行 application:start(sasl) 时发生的情况。之前:

C:\Program Files\erl5.8.4\bin>erl
Eshell V5.8.4  (abort with ^G)
1> application:start(sasl).
ok

=PROGRESS REPORT==== 27-Jun-2011::16:03:55 ===
          supervisor: {local,sasl_safe_sup}
             started: [{pid,<0.37.0>},
                       {name,alarm_handler},
                       {mfargs,{alarm_handler,start_link,[]}},
                       {restart_type,permanent},
                       {shutdown,2000},
                       {child_type,worker}]
2>
=PROGRESS REPORT==== 27-Jun-2011::16:03:55 ===
          supervisor: {local,sasl_safe_sup}
             started: [{pid,<0.38.0>},
                       {name,overload},
                       {mfargs,{overload,start_link,[]}},
                       {restart_type,permanent},
                       {shutdown,2000},
                       {child_type,worker}]
2>
=PROGRESS REPORT==== 27-Jun-2011::16:03:55 ===
          supervisor: {local,sasl_sup}
             started: [{pid,<0.36.0>},
                       {name,sasl_safe_sup},
                       {mfargs,
                           {supervisor,start_link,
                               [{local,sasl_safe_sup},sasl,safe
                       {restart_type,permanent},
                       {shutdown,infinity},
                       {child_type,supervisor}]
2>
=PROGRESS REPORT==== 27-Jun-2011::16:03:55 ===
          supervisor: {local,sasl_sup}
             started: [{pid,<0.39.0>},
                       {name,release_handler},
                       {mfargs,{release_handler,start_link,[]}}
                       {restart_type,permanent},
                       {shutdown,2000},
                       {child_type,worker}]
2>
=PROGRESS REPORT==== 27-Jun-2011::16:03:55 ===
         application: sasl
          started_at: nonode@nohost
2> simple:main(['20']).
ok
SERVER <0.42.0>: Client request recieved from <0.45.0>
3> CLIENT <0.45.0>: Hit count was 1
3> SERVER <0.42.0>: Owner request recieved from <0.43.0>
3> SERVER <0.42.0>: Client request recieved from <0.47.0>
3> OWNER <0.43.0>: Hit count was 1
3> CLIENT <0.47.0>: Hit count was 2
3> SERVER <0.42.0>: Owner request recieved from <0.43.0>
3> SERVER <0.42.0>: Client request recieved from <0.48.0>
3> OWNER <0.43.0>: Hit count was 2
3> CLIENT <0.48.0>: Hit count was 3
3> SERVER <0.42.0>: Owner request recieved from <0.43.0>
3> SERVER <0.42.0>: Client request recieved from <0.49.0>
3> OWNER <0.43.0>: Hit count was 3
3> CLIENT <0.49.0>: Hit count was 4
3> SERVER <0.42.0>: Owner request recieved from <0.43.0>
3> SERVER <0.42.0>: Client request recieved from <0.50.0>
3> OWNER <0.43.0>: Hit count was 4
3> CLIENT <0.50.0>: Hit count was 5
3> SERVER <0.42.0>: Owner request recieved from <0.43.0>
3> SERVER <0.42.0>: Client request recieved from <0.51.0>
3> CLIENT <0.51.0>: Hit count was 6
3> SERVER <0.42.0>: Client request recieved from <0.52.0>
3> CLIENT <0.52.0>: Hit count was 7
3> SERVER <0.42.0>: Client request recieved from <0.53.0>
3> CLIENT <0.53.0>: Hit count was 8
3> SERVER <0.42.0>: Client request recieved from <0.54.0>
3> CLIENT <0.54.0>: Hit count was 9
3> SERVER <0.42.0>: Client request recieved from <0.55.0>
3> CLIENT <0.55.0>: Hit count was 10
3> SERVER <0.42.0>: Client request recieved from <0.56.0>
3> CLIENT <0.56.0>: Hit count was 11
3> SERVER <0.42.0>: Client request recieved from <0.57.0>
3> CLIENT <0.57.0>: Hit count was 12
3> SERVER <0.42.0>: Client request recieved from <0.58.0>
3> CLIENT <0.58.0>: Hit count was 13
3> SERVER <0.42.0>: Client request recieved from <0.59.0>
3> CLIENT <0.59.0>: Hit count was 14
3> SERVER <0.42.0>: Client request recieved from <0.60.0>
3> CLIENT <0.60.0>: Hit count was 15
3> SERVER <0.42.0>: Client request recieved from <0.61.0>
3> CLIENT <0.61.0>: Hit count was 16
3> SERVER <0.42.0>: Client request recieved from <0.62.0>
3> CLIENT <0.62.0>: Hit count was 17
3> SERVER <0.42.0>: Client request recieved from <0.63.0>
3> CLIENT <0.63.0>: Hit count was 18
3> {error_logger,{{2011,6,27},{16,3,58}},"~s~n",["Error in proc
 exit value: {terminated,[{io,format,[<0.23.0>,\"SERVER ~w: Cli
ved from ~w~n\",[<0.42.0>,<0.64.0>]]},{simple,server,1}]}\n"]}

Answer 1

另一个答案是正确的，但没有解释原因。

这是一个棘手的问题，答案(在某种程度上)在您的日志输出中:

{error_logger,{{2011,6,27},{12,57,8}},"~s~n",["Error in process <0.28.0> with exit value: {terminated,[{io,format,[<0.22.0>,\"SERVER ~w: Client request recieved from ~w~n\",[<0.28.0>,<0.49.0>]]},{simple,server,1}]}\n"]}

第一个线索是 io:format/3 退出并带有“终止”和一些数据。

查看文档并搜索终止并没有给出任何结果。不过，查看 io.erl 内部给了我们答案。

当 io 设备关闭时，io.erl 的第 456 和 462 行返回 {error, Termination}。现在我们知道 io:format 可能会以终止状态退出。进一步观察，我们可以看到这个返回值变成了上面第 74 行的错误消息(带有上下文):

case request(Io, Request) of
{error, Reason} ->
    [_Name | Args] = tuple_to_list(to_tuple(Request)),
    {'EXIT',{undef,[_Current|Mfas]}} = (catch erlang:error(undef)),
        MFA = {io, Func, [Io | Args]},
        exit({conv_reason(Func, Reason),[MFA|Mfas]});

如果您遵循 request/2 的调用路径，您会发现一个可能的分支位于前面提到的 {error, returned} 处。

所以，长话短说，标准输出下降了。

很可能是因为您使用 init:stop() 终止了系统。