主管：
-module(mod_guild_chapter_sup).
-include("guild_dungeon.hrl").
-behaviour(supervisor).
%% API
-export([start_link/0]).
%% Supervisor callbacks
-export([init/1]).
-define(SERVER, ?MODULE).
%%%===================================================================
%%% API functions
%%%===================================================================
%%--------------------------------------------------------------------
%% @doc
%% Starts the supervisor
%%
%% @spec start_link() -> {ok, Pid} | ignore | {error, Error}
%% @end
%%--------------------------------------------------------------------
start_link() ->
supervisor:start_link({local, ?SERVER}, ?MODULE, []).
%%%===================================================================
%%% Supervisor callbacks
%%%===================================================================
%%--------------------------------------------------------------------
%% @private
%% @doc
%% Whenever a supervisor is started using supervisor:start_link/[2,3],
%% this function is called by the new process to find out about
%% restart strategy, maximum restart frequency and child
%% specifications.
%%
%% @spec init(Args) -> {ok, {SupFlags, [ChildSpec]}} |
%% ignore |
%% {error, Reason}
%% @end
%%--------------------------------------------------------------------
init([]) ->
RestartStrategy = simple_one_for_one,
MaxRestarts = 1000,
MaxSecondsBetweenRestarts = 3600,
SupFlags = {RestartStrategy, MaxRestarts, MaxSecondsBetweenRestarts},
Restart = transient,
Shutdown = 60000,
Type = worker,
ModGuildChapter = {'guild_chapter', {'mod_guild_chapter', start_link, []},
Restart, Shutdown, Type, ['mod_guild_chapter']},
{ok, {SupFlags, [ModGuildChapter]}}.
孩子：
-module(mod_guild_chapter).
-record(state, {}).
start_link(GuildId, ChapterId) ->
gen_server:start_link(?MODULE, [GuildId, ChapterId], []).
init([GuildId, ChapterId]) ->
case condition() of
true -> ignore;
false -> {ok, #state{})
end.
...omit other callbacks...
supervisor:which_children(mod_guild_chapter_sup)：
[{undefined,<0.9635.0>,worker,[mod_guild_chapter]},
{undefined,<0.9539.0>,worker,[mod_guild_chapter]},
{undefined,<0.9475.0>,worker,[mod_guild_chapter]},
{undefined,<0.9493.0>,worker,[mod_guild_chapter]},
{undefined,<0.9654.0>,worker,[mod_guild_chapter]},
{undefined,undefined,worker,[mod_guild_chapter]},
{undefined,<0.9658.0>,worker,[mod_guild_chapter]},
{undefined,<0.9517.0>,worker,[mod_guild_chapter]},
{undefined,<0.9567.0>,worker,[mod_guild_chapter]}]
收到时的异常shutdown：
2015-07-03 14:56:33 =CRASH REPORT====
crasher:
initial call: mod_guild_chapter:init/1
pid: <0.9475.0>
registered_name: []
exception exit: {{function_clause,[{supervisor,'-monitor_dynamic_children/2-fun-1-',[undefined,[100062,10003],{{set,3,16,16,8,80,48,{[],[],[],[],[],[],[],[],[],[],[],[],[],[],[],[]},{{[],[],[],[],[],[],[],[<0.9658.0>],[],[],[<0.9517.0>],[],[<0.9567.0>],[],[],[]}}},{dict,0,16,16,8,80,48,{[],[],[],[],[],[],[],[],[],[],[],[],[],[],[],[]},{{[],[],[],[],[],[],[],[],[],[],[],[],[],[],[],[]}}}}],[{file,"supervisor.erl"},{line,992}]},{dict,fold_bucket,3,[{file,"dict.erl"},{line,441}]},{dict,fold_seg,4,[{file,"dict.erl"},{line,437}]},{dict,fold_segs,4,[{file,"dict.erl"},{line,433}]},{supervisor,terminate_dynamic_children,3,[{file,"supervisor.erl"},{line,959}]},{gen_server,terminate,6,[{file,"gen_server.erl"},{line,719}]},{proc_lib,init_p_do_apply,3,[{file,"proc_lib.erl"},{line,239}]}]},[{gen_server,terminate,6,[{file,"gen_server.erl"},{line,744}]},{proc_lib,init_p_do_apply,3,[{file,"proc_lib.erl"},{line,239}]}]}
ancestors: [mod_guild_chapter_sup,mod_guild_sup,yg_sup,<0.82.0>]
messages: []
links: []
dictionary: []
trap_exit: true
status: running
heap_size: 1598
stack_size: 27
reductions: 6586
neighbours:
如您所见，有一个undefined不应该存在的pid。
文档中有两个地方对此进行了解释，但它们之间存在冲突。
temporary如果孩子不是，即使它返回，子规范将由主管保留ignore。
start 定义用于启动子进程的函数调用。它必须是用作 apply(M,F,A) 的模块函数参数元组 {M,F,A}。
start 函数必须创建并链接到子进程，并且必须返回 {ok,Child} 或 {ok,Child,Info} 其中 Child 是子进程的 pid 和 Info 一个被主管忽略的任意术语。
如果子进程由于某种原因无法启动，启动函数也可以返回忽略，在这种情况下，子进程将由主管保留（除非它是临时子进程），但不存在的子进程将被忽略。
simple_one_for_one如果启动时返回，pid 将不会添加到主管ignore。
如果子进程启动函数返回忽略，则将子规范添加到主管（除非主管是 simple_one_for_one 主管，请参见下文），将 pid 设置为 undefined 并且函数返回 {ok,undefined}。
在 simple_one_for_one 监督者的情况下，当子进程启动函数返回忽略函数返回 {ok,undefined} 并且没有子进程添加到监督者。
我被文件弄糊涂了。我选择transient重启策略是因为孩子在崩溃时应该重启。但是我怎样才能在这里避免这个异常呢？