第十八章 构造基于OTP的系统

Table of Contents

• 第十八章 构造基于OTP的系统
  • 18.1 通用的事件处理
  • 18.2 错误日志
    • 18.2.1 记录一个错误
    • 18.2.2 配置错误日志
    • 18.2.3 分析错误
  • 18.3 警报管理
  • 18.4 应用服务
    • 18.4.1 素数服务
    • 18.4.2 面积服务
  • 18.5 监控树
  • 18.6 启动整个系统
  • 18.7 应用程序
  • 18.8 文件系统的组织
  • 18.9 应用程序监视器
  • 18.10 进一步深入

第十八章 构造基于OTP的系统

18.1 通用的事件处理

%% 创建一个注册名为Name的进程, 这个进程执行my_handler函数 
make(Name) ->
    register(Name, spawn(fun() ->my_handler(fun no_op/1) end)).


%% 等待事件处理
%% 如果是{event, _}类型则调用Fun处理
%% 如果是{add, _}类型则更新处理函数 
my_handler(Fun) ->
    receive
        {add, Fun1} ->
            my_handler(Fun1);
        {event, Any} ->
            (catch Fun(Any)),
            my_handler(Fun)
    end.

%% 更新Name进程的处理函数为Fun
add_handler(Name, Fun) ->Name ! {add, Fun}.

%% 向Name进程发送事件X
event(Name, X) ->Name ! {event, X}.

%% 事件处理函数, 什么都不做
no_op(_) ->void.

运行结果:

1> c(event_handler).
{ok,event_handler}
2> event_handler:make(errors).
true
3> event_handler:event(errors, hi).
{event,hi}

为处理程序添加一个简单的回调模块

-module(motor_controller).

-export([add_event_handler/0]).

%% 更新errors进程的处理函数
add_event_handler() ->
    event_handler:add_handler(errors, fun controller/1).

%% 具体处理, 一些简单的输出
controller(too_hot) ->
    io:format("Turn off the motor~n");
controller(X) ->
    io:format("~w ignored event: ~p~n",[?MODULE, X]).

运行结果:

4> c(motor_controller).
{ok,motor_controller}
5> motor_controller:add_event_handler().
{add,#Fun<motor_controller.0.125151531>}
6> event_handler:event(errors, cool).   
motor_controller ignored event: cool
{event,cool}
7> event_handler:event(errors, too_hot).
Turn off the motor
{event,too_hot}

从这个简单的例子可以看到Erlang的强大之处:非常延迟的绑定^_^, 正如作者所说:使用这个机制, 我们可以构造一个可以随着时间推移不断演化的系统, 而演化的过程无需停机, 甚至也不需要升级代码。

18.2 错误日志

错误日志的三种视角:如何调用函数记录错误日志; 如何配置错误日志的存储; 如何对错误日志进行分析。

18.2.1 记录一个错误

# 错误日志的API 

# 向错误日志发送一个错误消息
# error_logger:error_msg(String) -> ok
8> error_logger:error_msg("An error has occurred\n").
ok
9> 
=ERROR REPORT==== 8-Nov-2013::13:22:42 ===
An error has occurred

# 向错误日志发送一个带参数的错误消息 
# error_logger:error_msg(Format, Data) -> ok
10> error_logger:error_msg("~s, An error has occurred\n", ["Joe"]).

=ERROR REPORT==== 8-Nov-2013::13:25:39 ===
Joe, An error has occurred
ok

# 向错误日志发送一个标准错误报告
# error_logger:error_report(Report) -> ok
# @type Report = [{Tag, Data} | term()] | string() | term()
# @type Tag = term()
# @type Data = term()
11> error_logger:error_report([{tag1, data1}, a_term, {tag2, data}]). 

=ERROR REPORT==== 8-Nov-2013::13:29:14 ===
    tag1: data1
    a_term
    tag2: data
ok

18.2.2 配置错误日志

• 1. 标准错误日志

    # 适合程序开发的环境
    $ erl -boot start_clean

    # 适合产品化系统的环境
    $ erl -boot start_sasl

• 2. 不进行配置的SASL

    matrix@MBP:18 $ erl -boot start_sasl
    Erlang R15B01 (erts-5.9.1) [source] [64-bit] [smp:4:4] [async-threads:0] [hipe] [kernel-poll:false]


    =PROGRESS REPORT==== 8-Nov-2013::13:32:52 ===
              supervisor: {local,sasl_safe_sup}
                 started: [{pid,<0.34.0>},
                           {name,alarm_handler},
                           {mfargs,{alarm_handler,start_link,[]}},
                           {restart_type,permanent},
                           {shutdown,2000},
                           {child_type,worker}]

    =PROGRESS REPORT==== 8-Nov-2013::13:32:52 ===
              supervisor: {local,sasl_safe_sup}
                 started: [{pid,<0.35.0>},
                           {name,overload},
                           {mfargs,{overload,start_link,[]}},
                           {restart_type,permanent},
                           {shutdown,2000},
                           {child_type,worker}]

    =PROGRESS REPORT==== 8-Nov-2013::13:32:52 ===
              supervisor: {local,sasl_sup}
                 started: [{pid,<0.33.0>},
                           {name,sasl_safe_sup},
                           {mfargs,
                               {supervisor,start_link,
                                   [{local,sasl_safe_sup},sasl,safe]}},
                           {restart_type,permanent},
                           {shutdown,infinity},
                           {child_type,supervisor}]

    =PROGRESS REPORT==== 8-Nov-2013::13:32:52 ===
              supervisor: {local,sasl_sup}
                 started: [{pid,<0.36.0>},
                           {name,release_handler},
                           {mfargs,{release_handler,start_link,[]}},
                           {restart_type,permanent},
                           {shutdown,2000},
                           {child_type,worker}]

    =PROGRESS REPORT==== 8-Nov-2013::13:32:52 ===
             application: sasl
              started_at: nonode@nohost
    Eshell V5.9.1  (abort with ^G)
    1> error_logger:error_msg("This is an error\n").
    ok
    2> 
    =ERROR REPORT==== 8-Nov-2013::13:33:45 ===
    This is an error

• 3. 控制记录何种日志
     监管报告, 在监管进程启动或者停止被监管的进程时;进程报告, 每次OTP监管进程启动或者停止的时候;崩溃报告, 当被监管的进程退出时, 如果退出原因不是normal或者shutdown则产生此报告。

    %% elog1.config
    [{sasl, [{sasl_error_logger, false}]}].

运行结果:

    matrix@MBP:18 $ erl -boot start_sasl -config elog1
    Erlang R15B01 (erts-5.9.1) [source] [64-bit] [smp:4:4] [async-threads:0] [hipe] [kernel-poll:false]

    Eshell V5.9.1  (abort with ^G)
    1> error_logger:error_msg("This is an error\n").
    ok

    =ERROR REPORT==== 8-Nov-2013::13:40:09 ===
    This is an error

• 4. 文本文件和shell

    %% elog2.config
    [{sasl, [{sasl_error_logger, {file, "/Users/matrix/Documents/Erlang/erlp/18/error_logs/THELOG"}}]}].

运行结果:

    matrix@MBP:18 $ cat error_logs/THELOG 

    =PROGRESS REPORT==== 8-Nov-2013::13:45:27 ===
              supervisor: {local,sasl_safe_sup}
                 started: [{pid,<0.35.0>},
                           {name,alarm_handler},
                           {mfargs,{alarm_handler,start_link,[]}},
                           {restart_type,permanent},
                           {shutdown,2000},
                           {child_type,worker}]

    =PROGRESS REPORT==== 8-Nov-2013::13:45:27 ===
              supervisor: {local,sasl_safe_sup}
                 started: [{pid,<0.36.0>},
                           {name,overload},
                           {mfargs,{overload,start_link,[]}},
                           {restart_type,permanent},
                           {shutdown,2000},
                           {child_type,worker}]

    =PROGRESS REPORT==== 8-Nov-2013::13:45:27 ===
              supervisor: {local,sasl_sup}
                 started: [{pid,<0.34.0>},
                           {name,sasl_safe_sup},
                           {mfargs,
                               {supervisor,start_link,
                                   [{local,sasl_safe_sup},sasl,safe]}},
                           {restart_type,permanent},
                           {shutdown,infinity},
                           {child_type,supervisor}]

    =PROGRESS REPORT==== 8-Nov-2013::13:45:27 ===
              supervisor: {local,sasl_sup}
                 started: [{pid,<0.37.0>},
                           {name,release_handler},
                           {mfargs,{release_handler,start_link,[]}},
                           {restart_type,permanent},
                           {shutdown,2000},
                           {child_type,worker}]

    =PROGRESS REPORT==== 8-Nov-2013::13:45:27 ===
             application: sasl
              started_at: nonode@nohost

• 5. 循环日志和shell

    %% elog3.config
    [{sasl, [
             {sasl_error_logger, false},
             %% 指定输出目录
             {error_logger_mf_dir, "/Users/matrix/Documents/Erlang/erlp/18/error_logs"},
             %% 指定单个文件最大值
             {error_logger_mf_maxbytes, 10485760},
             %% 指定文件最大数量
             {error_logger_mf_maxfiles, 10}
            ]}].

运行后会在错误日志存储目录下发现已经生成了名字为1的日志文件。

• 6. 产品化环境

    %% elog4.config
    [{sasl, [
             {sasl_error_logger, false},
             %% 只记录错误日志
             {errorlog_type, error},
             %% 指定输出目录
             {error_logger_mf_dir, "/Users/matrix/Documents/Erlang/erlp/18/error_logs"},
             %% 指定单个文件最大值
             {error_logger_mf_maxbytes, 10485760},
             %% 指定文件最大数量
             {error_logger_mf_maxfiles, 10}
            ]}].

18.2.3 分析错误

使用rb模块读取错误日志

18.3 警报管理

-module(my_alarm_handler).
-behaviour(gen_event).

%% 需要自定义的gen_event的回调函数
-export([init/1, handle_event/2, handle_call/2, 
     handle_info/2, terminate/2]).

%% 完成初始化, 必须返回{ok, State}
init(Args) ->
    io:format("*** my_alarm_handler init:~p~n",[Args]),
    {ok, 0}.

%% handle_event(Event, State) -> {ok, NewState}
%% 其中Event是形如{EventType, EventArgs}的元组
%% EventType可以是set_event或clear_event
%% EventArgs是用户提供的参数

%% 设置警报 
handle_event({set_alarm, tooHot}, N) ->
    error_logger:error_msg("*** Tell the Engineer to turn on the fan~n"),
    {ok, N+1};

%% 清除警报
handle_event({clear_alarm, tooHot}, N) ->
    error_logger:error_msg("*** Danger over. Turn off the fan~n"),
    {ok, N};

%% 其它类型的警报
handle_event(Event, N) ->
    io:format("*** unmatched event:~p~n",[Event]),
    {ok, N}.

%% 其它需要实现的回调函数 
handle_call(_Request, N) ->Reply = N, {ok, Reply,  N}.

handle_info(_Info, N)    ->{ok, N}.

terminate(_Reason, _N)   ->ok.

运行结果:

matrix@MBP:18 $ erl -boot start_sasl -config elog3
Erlang R15B01 (erts-5.9.1) [source] [64-bit] [smp:4:4] [async-threads:0] [hipe] [kernel-poll:false]

Eshell V5.9.1  (abort with ^G)
1> c(my_alarm_handler).
{ok,my_alarm_handler}

# 普通的警报
2> alarm_handler:set_alarm(tooHot).
ok
3> 
=INFO REPORT==== 8-Nov-2013::14:02:43 ===
    alarm_handler: {set,tooHot}

# 使用自定义的警报 
3> gen_event:swap_handler(alarm_handler, {alarm_handler, swap}, {my_alarm_handler, xyz}).
*** my_alarm_handler init:{xyz,{alarm_handler,[tooHot]}}
ok

# 触发警报
4> alarm_handler:set_alarm(tooHot).                                                      

=ERROR REPORT==== 8-Nov-2013::14:03:51 ===
*** Tell the Engineer to turn on the fan
ok

# 清除警报 
5> alarm_handler:clear_alarm(tooHot).

=ERROR REPORT==== 8-Nov-2013::14:04:07 ===
*** Danger over. Turn off the fan
ok

# 查看错误日志报告
6> rb:start([{max, 20}]).
rb: reading report...done.
rb: reading report...done.
rb: reading report...done.
{ok,<0.51.0>}
7> rb:list().
  No                Type   Process       Date     Time
  ==                ====   =======       ====     ====
  20            progress  <0.30.0> 2013-11-08 13:51:15
  19            progress  <0.30.0> 2013-11-08 13:51:15
  18            progress  <0.23.0> 2013-11-08 13:51:15
  17               error  <0.24.0> 2013-11-08 13:51:25
  16            progress  <0.30.0> 2013-11-08 13:55:08
  15            progress  <0.30.0> 2013-11-08 13:55:08
  14            progress  <0.30.0> 2013-11-08 13:55:08
  13            progress  <0.30.0> 2013-11-08 13:55:08
  12            progress  <0.23.0> 2013-11-08 13:55:08
  11        crash_report        rb 2013-11-08 13:55:23
  10               error  <0.24.0> 2013-11-08 13:56:16
   9        crash_report        rb 2013-11-08 13:56:20
   8            progress  <0.30.0> 2013-11-08 14:01:19
   7            progress  <0.30.0> 2013-11-08 14:01:19
   6            progress  <0.30.0> 2013-11-08 14:01:19
   5            progress  <0.30.0> 2013-11-08 14:01:19
   4            progress  <0.23.0> 2013-11-08 14:01:19
   3         info_report  <0.30.0> 2013-11-08 14:02:43
   2               error  <0.30.0> 2013-11-08 14:03:51
   1               error  <0.30.0> 2013-11-08 14:04:07
ok
8> rb:show(1).

ERROR REPORT  <0.34.0>                                      2013-11-08 14:04:07
===============================================================================

*** Danger over. Turn off the fan
ok
9> rb:show(2).

ERROR REPORT  <0.34.0>                                      2013-11-08 14:03:51
===============================================================================

*** Tell the Engineer to turn on the fan
ok

18.4 应用服务

18.4.1 素数服务

使用gen_server模块快速生成代码, 然后添加获取素数的的方法, 并添加警报处理。

-module(prime_server).
-behaviour(gen_server).

-export([new_prime/1, start_link/0]).

%% 必须自定义实现的gen_server回调函数
-export([init/1, handle_call/3, handle_cast/2, handle_info/2,
     terminate/2, code_change/3]).

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

%% 生成素数的服务, 设置了超时时间 
new_prime(N) ->
    gen_server:call(?MODULE, {prime, N}, 20000).

init([]) ->
    process_flag(trap_exit, true),
    io:format("~p starting~n",[?MODULE]),
    {ok, 0}.

handle_call({prime, K}, _From, N) ->
    {reply, make_new_prime(K), N+1}.

handle_cast(_Msg, N)  ->{noreply, N}.

handle_info(_Info, N)  ->{noreply, N}.

terminate(_Reason, _N) ->
    io:format("~p stopping~n",[?MODULE]),
    ok.

code_change(_OldVsn, N, _Extra) ->{ok, N}.

%% 生成素数时添加了警报处理 
make_new_prime(K) ->
    if
    K > 100 ->
        alarm_handler:set_alarm(tooHot),
        N = lib_primes:make_prime(K),
        alarm_handler:clear_alarm(tooHot),
        N;
    true ->
        lib_primes:make_prime(K)
    end.

18.4.2 面积服务

与素数服务代码相差无几, 但是计算面积的函数对于长方形需要提供两个参数而 hadle_call({area, Thing}, …) 只提供了对一个参数的支持。

18.5 监控树

监控树有两种类型:one-for-one, 如果一个进程失效, 它的监控进程就会重启它; all-for-one, 如果一个进程失效, 所有的工作进程都会被终止, 然后被重启。
监控树的形式:

%% RestartStrategy可以是one-for-one或all-for-one
%% MaxRestarts, Time限定了在Time时间内最多可以重启MaxRestarts次, 否则将终止所有工作进程, 以防止出现死循环
init(...) ->
    {ok, {RestartStrategy, MaxRestarts, Time},
         [Worker1, Worker2, ...]}.

实现自己的监控树:

-module(sellaprime_supervisor).
-behaviour(supervisor).

-export([start/0, start_in_shell_for_testing/0, start_link/1, init/1]).

%% 调用 supervisor:start_link 启动监控树, 将会调用自定义的init/1函数
start() ->
    spawn(fun() ->
          supervisor:start_link({local,?MODULE}, ?MODULE, _Arg = [])
      end).

start_in_shell_for_testing() ->
    {ok, Pid} = supervisor:start_link({local,?MODULE}, ?MODULE, _Arg = []),
    unlink(Pid).

start_link(Args) ->
    supervisor:start_link({local,?MODULE}, ?MODULE, Args).

init([]) ->
     %% 使用自定义的警报器 
     gen_event:swap_handler(alarm_handler, 
                                   {alarm_handler, swap},
                   {my_alarm_handler, xyz}),
    %% {ok, {SupFlags, Children}}
    %% SupFlags : {supervision_strategy(), maxR(), maxT()}
    %% supervision_strategy() : one_for_one | one_for_all | simple_one_for_one
    {ok, {{one_for_one, 3, 10},
      %% Children : [ChildStartSpecification]
      %% ChildStartSpecification : {internal_name(),
      %%                            {module(), function(), args()},
      %%                            shutdown_time(),
      %%                            child_type(),
      %%                            modules()}
      [{tag1, 
        {area_server, start_link, []},
        permanent, 
        10000, 
        worker, 
        [area_server]},
       {tag2, 
        {prime_server, start_link, []},
        permanent, 
        10000, 
        worker, 
        [prime_server]}
      ]}}.

18.6 启动整个系统

1> sellaprime_supervisor:start_in_shell_for_testing().
*** my_alarm_handler init:{xyz,error}
area_server starting
prime_server starting
true

# 正常计算面积
2> area_server:area({square, 10}).
100

# 错误的参数
3> area_server:area({rectangle, 10, 20}).
area_server stopping
area_server starting
** exception exit: {{function_clause,[{area_server,compute_area,
                                                   [{rectangle,10,20}],
                                                   [{file,"area_server.erl"},{line,44}]},
                                      {area_server,handle_call,3,
                                                   [{file,"area_server.erl"},{line,32}]},
                                      {gen_server,handle_msg,5,
                                                  [{file,"gen_server.erl"},{line,588}]},
                                      {proc_lib,init_p_do_apply,3,
                                                [{file,"proc_lib.erl"},{line,227}]}]},
                    {gen_server,call,[area_server,{area,{rectangle,10,20}}]}}
     in function  gen_server:call/2 (gen_server.erl, line 180)
4> 
=ERROR REPORT==== 8-Nov-2013::14:52:19 ===
** Generic server area_server terminating 
** Last message in was {area,{rectangle,10,20}}
** When Server state == 1
** Reason for termination == 
** {function_clause,[{area_server,compute_area,
                                  [{rectangle,10,20}],
                                  [{file,"area_server.erl"},{line,44}]},
                     {area_server,handle_call,3,
                                  [{file,"area_server.erl"},{line,32}]},
                     {gen_server,handle_msg,5,
                                 [{file,"gen_server.erl"},{line,588}]},
                     {proc_lib,init_p_do_apply,3,
                               [{file,"proc_lib.erl"},{line,227}]}]}

# 求阶乘
5> prime_server:new_prime(20).  
Generating a 20 digit prime .................................
46877940609417488267

# 触发警报 
6> prime_server:new_prime(120). 
Generating a 120 digit prime .
=ERROR REPORT==== 8-Nov-2013::14:58:22 ===
*** Tell the Engineer to turn on the fan

=ERROR REPORT==== 8-Nov-2013::14:58:22 ===
*** Tell the Engineer to turn on the fan
......................................

=ERROR REPORT==== 8-Nov-2013::14:58:22 ===
*** Danger over. Turn off the fan
296183949730132038037133059736194002935394554326329071373943691961695511107247366466697700357121237051115084833162714631

=ERROR REPORT==== 8-Nov-2013::14:58:22 ===
*** Danger over. Turn off the fan

# 查看错误日志报告
7> rb:start([{max, 20}]).
rb: reading report...done.
{ok,<0.96.0>}
8> rb:list().            
  No                Type       Process       Date     Time
  ==                ====       =======       ====     ====
  20               error      <0.24.0> 2013-11-08 14:52:19
  19        crash_report   area_server 2013-11-08 14:52:19
  18   supervisor_report      <0.24.0> 2013-11-08 14:52:19
  17            progress      <0.24.0> 2013-11-08 14:52:19
  16               error      <0.24.0> 2013-11-08 14:53:17
  15        crash_report  prime_server 2013-11-08 14:53:17
  14   supervisor_report      <0.24.0> 2013-11-08 14:53:17
  13            progress      <0.24.0> 2013-11-08 14:53:17
  12               error      <0.24.0> 2013-11-08 14:54:48
  11        crash_report  prime_server 2013-11-08 14:54:48
  10   supervisor_report      <0.24.0> 2013-11-08 14:54:48
   9            progress      <0.24.0> 2013-11-08 14:54:48
   8               error      <0.24.0> 2013-11-08 14:57:28
   7        crash_report  prime_server 2013-11-08 14:57:28
   6   supervisor_report      <0.24.0> 2013-11-08 14:57:28
   5            progress      <0.24.0> 2013-11-08 14:57:28
   4               error      <0.30.0> 2013-11-08 14:58:22
   3               error      <0.30.0> 2013-11-08 14:58:22
   2               error      <0.30.0> 2013-11-08 14:58:22
   1               error      <0.30.0> 2013-11-08 14:58:22
ok
9> rb:show(19).

CRASH REPORT  <0.56.0>                                      2013-11-08 14:52:19
===============================================================================
Crashing process                                                               
   initial_call                              {area_server,init,['Argument__1']}
   pid                                                                 <0.56.0>
   registered_name                                                  area_server
   error_info
         {exit,
            {function_clause,
                [{area_server,compute_area,
                     [{rectangle,10,20}],
                     [{file,"area_server.erl"},{line,44}]},
                 {area_server,handle_call,3,
                     [{file,"area_server.erl"},{line,32}]},
                 {gen_server,handle_msg,5,
                     [{file,"gen_server.erl"},{line,588}]},
                 {proc_lib,init_p_do_apply,3,
                     [{file,"proc_lib.erl"},{line,227}]}]},
            [{gen_server,terminate,6,[{file,"gen_server.erl"},{line,747}]},
             {proc_lib,init_p_do_apply,3,
                 [{file,"proc_lib.erl"},{line,227}]}]}
   ancestors                                   [sellaprime_supervisor,<0.43.0>]
   messages                                                                  []
   links                                                             [<0.55.0>]
   dictionary                                                                []
   trap_exit                                                               true
   status                                                               running
   heap_size                                                                610
   stack_size                                                                24
   reductions                                                               176

ok

18.7 应用程序

应用程序信息文件

%% 名称
{application, sellaprime,
 %% 概述  
 [{description, "The Prime Number Shop"},
  %% 版本 
  {vsn, "1.0"},
  %% 包含的模块
  {modules, [sellaprime_app, sellaprime_supervisor, area_server, 
         prime_server, lib_lin, lib_primes, my_alarm_handler]}, 
  %% 注册进程
  {registered,[area_server, prime_server, sellaprime_super]},
  %% 依赖的应用程序
  {applications, [kernel,stdlib]},
  %% 模块
  {mod, {sellaprime_app,[]}},
  {start_phases, []}
 ]}.

应用程序回调模块

-module(sellaprime_app).
-behaviour(application).
-export([start/2, stop/1]).


start(_Type, StartArgs) ->
    sellaprime_supervisor:start_link(StartArgs).

stop(_State) ->
    ok.

运行结果:

# 显示加载的应用程序 
1> application:loaded_applications(). 
[{kernel,"ERTS  CXC 138 10","2.15.1"},
 {sasl,"SASL  CXC 138 11","2.2.1"},
 {stdlib,"ERTS  CXC 138 10","1.18.1"}]

# 加载指定的应用程序
2> application:load(sellaprime). 
ok
3> application:loaded_applications().
[{kernel,"ERTS  CXC 138 10","2.15.1"},
 {sasl,"SASL  CXC 138 11","2.2.1"},
 {stdlib,"ERTS  CXC 138 10","1.18.1"},
 {sellaprime,"The Prime Number Shop","1.0"}]

# 启动应用程序 
4> application:start(sellaprime).    
*** my_alarm_handler init:{xyz,{alarm_handler,[]}}
area_server starting
prime_server starting
ok

# 停止应用程序
5> application:stop(sellaprime). 
prime_server stopping
area_server stopping
ok
6> 
=INFO REPORT==== 8-Nov-2013::15:12:35 ===
    application: sellaprime
    exited: stopped
    type: temporary

# 卸载应用程序
7> application:unload(sellaprime).
ok
8> application:loaded_applications().
[{kernel,"ERTS  CXC 138 10","2.15.1"},
 {sasl,"SASL  CXC 138 11","2.2.1"},
 {stdlib,"ERTS  CXC 138 10","1.18.1"}]

18.8 文件系统的组织

18.9 应用程序监视器

使用appmon:start()启动图形界面的查看程序。

18.10 进一步深入

5、5、5版文档
gen_server, gen_event, supervisors
http://www.erlang.org/documentation/doc-5.5.5/pdf/design_principles-5.5.5.pdf
如何创建一个启动文件
http://www.erlang.org/documentation/doc-5.5.5/pdf/system_principles-5.5.5.pdf
应用程序监视器
http://www.erlang.org/documentation/doc-5.5.5/pdf/appmon-2.1.9.pdf
更多文档
http://www.erlang.org/documentation/

文章永久链接：https://tech.souyunku.com/?p=23541