Erlang Supervisor

[twn39]

%%%-------------------------------------------------------------------
%% @doc erapp top level supervisor.
%% @end
%%%-------------------------------------------------------------------

-module(erapp_sup).

-behaviour(supervisor).

%% API
-export([start_link/0]).

%% Supervisor callbacks
-export([init/1]).

-define(SERVER, ?MODULE).

%%====================================================================
%% API functions
%%====================================================================

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

%%====================================================================
%% Supervisor callbacks
%%====================================================================

%% Child :: #{id => Id, start => {M, F, A}}
%% Optional keys are restart, shutdown, type, modules.
%% Before OTP 18 tuples must be used to specify a child. e.g.
%% Child :: {Id,StartFunc,Restart,Shutdown,Type,Modules}
init([]) ->
    {ok, {{one_for_one, 0, 1}, [
        #{
            id => tcp_server,
            start => {tcp_server, start_link, []},
            restart => permanent,
            shutdown => brutal_kill
        }
    ]}}.

%%====================================================================
%% Internal functions
%%====================================================================

[twn39]

init初始化函数中返回：

{ok, {<strategy>, <child_spec>}}

其中strategy:

• one_for_one - If one child process terminates and is to be restarted, only that child process is affected. This is the default restart strategy.
• one_for_all - If one child process terminates and is to be restarted, all other child processes are terminated and then all child processes are restarted.
• rest_for_one - If one child process terminates and is to be restarted, the 'rest' of the child processes (that is, the child processes after the terminated child process in the start order) are terminated. Then the terminated child process and all child processes after it are restarted.
• simple_one_for_one - A simplified one_for_one supervisor, where all child processes are dynamically added instances of the same process type, that is, running the same code.

其中child_spaec:

child_spec() = #{id => child_id(),       % mandatory
                 start => mfargs(),      % mandatory
                 restart => restart(),   % optional
                 shutdown => shutdown(), % optional
                 type => worker(),       % optional
                 modules => modules()}   % optional
    child_id() = term()
    mfargs() = {M :: module(), F :: atom(), A :: [term()]}
    modules() = [module()] | dynamic
    restart() = permanent | transient | temporary
    shutdown() = brutal_kill | timeout()
    worker() = worker | supervisor

示例：

#{id => ch3,
  start => {ch3, start_link, []},
  restart => permanent,
  shutdown => brutal_kill,
  type => worker,
  modules => [ch3]}