面对软件错误构建可靠的分布式系统_笔记13

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