面对软件错误构建可靠的分布式系统_笔记13

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6.5通用监督者Supervisor

gen_sup

6.5.1通用监督者

(1)supervisor:start_link(Name1, Mod, Arg) -> Result

(2)Mod:init(Arg) -> SupStrategy

SupStrategy监督树，参见后面例子

-module(thesis_simple_sup).
-behaviour(supervisor).
-export([start/0, init/1]).

start() ->
supervisor:start_link({local, thesis_simple_sup}, ?MODULE, nil).

init(_) ->
{ok,
{%%one_for_one:或型监督树，如果1000秒内被监督者重启超过5次，则监督者本身也错误

    {one_for_one, 5, 1000},
   [
    {packet, %%被监督节点名称，要树内唯一
     {thesis_packet_assembler, start,[]}, %%被监督者模块、启动命令和参数

      %%permanent表示如果出错则自动重启，500指关停协议中Timer=500ms，worker指工作进程，最后是模块名称
     permanent, 500, worker, [thesis_packet_assembler]},
    {server,
     {thesis_kv, start, []},
     permanent, 500, worker,[thesis_kv]},
    {logger,
     {thesis_simple_logger, start, []},
     permanent, 500, worker, [thesis_simple_logger]
    }
   ]
  }}.

监督者通过调用shutdown(Pid,How)终止一个工作者，遵从停止协议：shutdown protocol

shutdown(Pid, brutal_kill) -> ％％无条件杀死Pid进程

exit(Pid, kill);

shutdown(Pid, infinity) -> %%发送shutdown消息，并等待回应

exit(Pid, shutdown),

receive

{'EXIT',Pid, shutdown} -> true

end;

shutdown(Pid, Time) -> %%发送shutdown消息，并等待回应，如果超时则无条件杀死,前面例子中，就是500ms

exit(Pid, shutdown),

receive

{'EXIT', Pid, shutdown} -> true

after Time ->

exit(Pid, kill)

end.

eg:将前面几个模块作为工作进程

-module(thesis_simple_sup).
-behaviour(supervisor).
-export([start/0, init/1]).

start() ->
supervisor:start_link({local, thesis_simple_sup}, ?MODULE, nil).

init(_) ->
{ok,
  {{one_for_one, 5, 1000},
   [
    {packet,
     {thesis_assember, start,[]},
     permanent, 500, worker, [thesis_assember]},
    {server,
     {thesis_kv, start, []},
     permanent, 500, worker,[thesis_kv]},
    {logger,
     {thesis_logger, start, []},
     permanent, 500, worker, [thesis_logger]}
   ]
  }}.

6.6通用应用的原理

负责打包、安装。没有Mod的回调函数，由应用描述文件.app，定义

6.6.1通用应用API

*.app

{application, Application,

[ {description, Description},

{vsn, Vsn},

{id, Id},

{modules, [Module1,,,ModuleN]},

{maxT, MaxT},

{registered, [Name1,...NameN]},

{applications, [Appl1,..ApplN]},

{included_applications, [Appl1,,,,ApplN]},

{evn, [{Par1,Val1},,,,{ParN,ValN}]},

{mod, {Module, StartArgs}},

{start_phases, [{Phase1,PhaseArgs1],,,,{PhaseN,PhaseArgsN}]}]}.

均是可选项

6.6.2通用应用的例子

thesis_simple.app

{application, 'thesis_simple',
    [ {description, "A simple application"},
      {vsn,          "1.0"},
      {modules,     [thesis_simple,thesis_kv,thesis_logger,
           thesis_assember,thesis_simple_sup]},
      {maxT,         infinity},
      {registered,   [thesis_kv,my_simple_event_logger,my_simple_packet_assembler]},
      {applications, []},
      {included_applications, []},
      {evn,            []},
      {mod,            {thesis_simple, go}}]}.

定义thesis_simple.erl

-module(thesis_simple).
-behaviour(application).

-export([start/2]).
start(_,_) -> thesis_simple_sup:start().

启动：

1> application:start(thesis_simple, temporary).
Packet assembler starting
Key-Value server starting
Logger starting
ok
2> thesis_kv:store("yes","test").
ack
3> thesis_logger:log("hello").
ok
4> thesis_assember:send_header(2).
ok
5> thesis_assember:send_data("h")
5> .
ok
6> thesis_assember:send_data("h").
Got data:hh
ok
7> application:stop(thesis_simple).

=INFO REPORT==== 29-Jan-2009::20:59:07 ===
    application: thesis_simple
    exited: stopped
    type: temporary
ok