Erlang 动态主管启动 gen_server

Question

我有创建其他主管的根主管:

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

init([]) ->
    RestartStrategy = {one_for_one, 5, 600},
    ListenerSup =
            {popd_listener_sup,
            {popd_listener_sup, start_link, []},
             permanent, 2000, supervisor, [popd_listener]},

    Children = [ListenerSup],

    {ok, {RestartStrategy, Children}}.

我有 gen_server - 听众。创建主管后，如何使用 popd_listener_sup 主管运行此 gen_server？

谢谢你。

Answer 1

根主管

-module(root_sup).
-behaviour(supervisor).
-export([start_link/0]).
-export([init/1, shutdown/0]).

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

init(_Args) ->
     RestartStrategy = {one_for_one, 10, 60},
     ListenerSup = {popd_listener_sup,
          {popd_listener_sup, start_link, []},
          permanent, infinity, supervisor, [popd_listener_sup]},
     Children = [ListenerSup],
     {ok, {RestartStrategy, Children}}.    

% supervisor can be shutdown by calling exit(SupPid,shutdown)
% or, if it's linked to its parent, by parent calling exit/1.
shutdown() ->
     exit(whereis(?MODULE), shutdown).
     % or
     % exit(normal).

如果子进程是另一个监督者，那么子规范中的 Shutdown 应该设置为 infinity 以给子树足够的时间关闭，并且 Type 应该设置为 supervisor ，这就是我们所做的。

child 监督员

-module(popd_listener_sup).
-behaviour(supervisor).
-export([start_link/0]).
-export([init/1]).

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

init(_Args) ->
    RestartStrategy = {one_for_one, 10, 60},
    Listener = {ch1, {ch1, start_link, []},
            permanent, 2000, worker, [ch1]},
    Children = [Listener],
    {ok, {RestartStrategy, Children}}.

这里，在子规范中，我们将 Shutdown 的值设置为 2000 。整数超时值意味着主管将通过调用 exit(Child,shutdown) 告诉子进程终止，然后等待退出信号，原因是从子进程关闭。

听众

-module(ch1).
-behaviour(gen_server).

% Callback functions which should be exported
-export([init/1]).
-export([handle_cast/2, terminate/2]).

% user-defined interface functions
-export([start_link/0]).

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

init(_Args) ->
     erlang:process_flag(trap_exit, true),
     io:format("ch1 has started (~w)~n", [self()]),
     % If the initialization is successful, the function
     % should return {ok,State}, {ok,State,Timeout} ..
     {ok, []}.

handle_cast(calc, State) ->
     io:format("result 2+2=4~n"),
     {noreply, State};
handle_cast(calcbad, State) ->
     io:format("result 1/0~n"),
     1 / 0,
     {noreply, State}.

terminate(_Reason, _State) ->
     io:format("ch1: terminating.~n"),
     ok.

来自 Erlang/OTP 文档:

If the gen_server is part of a supervision tree and is ordered by its supervisor to terminate, the function Module:terminate(Reason, State) will be called with Reason=shutdown if the following conditions apply:

• the gen_server has been set to trap exit signals, and
• the shutdown strategy as defined in the supervisor's child specification
  is an integer timeout value, not
  brutal_kill.

这就是我们在 erlang:process_flag(trap_exit, true) 中调用 Module:init(Args) 的原因。

sample 运行

启动根主管:

1> root_sup:start_link().
ch1 has started (<0.35.0>)
{ok,<0.33.0>}

根主管运行并自动启动它的子进程，在我们的例子中是子主管。子主管依次启动其子进程；在我们的例子中，我们只有一个 child ， ch1 。

让我们让 ch1 评估正常代码:

2> gen_server:cast(ch1, calc).
result 2+2=4
ok

现在一些不好的代码:

3> gen_server:cast(ch1, calcbad).
result 1/0
ok
ch1: terminating.

=ERROR REPORT==== 31-Jan-2011::01:38:44 ===
** Generic server ch1 terminating 
** Last message in was {'$gen_cast',calcbad}
** When Server state == []
** Reason for termination == 
** {badarith,[{ch1,handle_cast,2},
              {gen_server,handle_msg,5},
              {proc_lib,init_p_do_apply,3}]}
ch1 has started (<0.39.0>)
4> exit(normal).
ch1: terminating.
** exception exit: normal

如您所见，子进程 ch1 被子主管 popd_listener_sup 重新启动(注意 ch1 has started (<0.39.0>) )。

由于我们的 shell 和 root supervisor 是双向链接的(在 root supervisor 函数 supervisor:start_link 中调用 supervisor:start ，而不是 start_link/0 )， exit(normal) 导致 root supervisor 关闭，但它的子进程有一些时间来清理。