Question

我需要保持gen_mod进程运行，因为它每分钟循环并进行一些清理。但是每隔几天它就会崩溃，我将不得不再次手动启动它。

我可以使用在ejabberd_sup中实现主管的基本示例，以便它可以继续。我正在努力理解使用gen_server的例子。

感谢您的帮助。

Answer 1

这是一个结合了ejabberd的gen_mod和OTP的gen_server的示例模块。代码中内联了解释。

-module(cleaner).

-behaviour(gen_server).
-behaviour(gen_mod).

%% gen_mod requires these exports
-export([start/2, stop/1]).

%% these are exports for gen_server
-export([start_link/0]).
-export([init/1, handle_call/3, handle_cast/2, handle_info/2,
         terminate/2, code_change/3]).

-define(INTERVAL, timer:minutes(1)).

-record(state, {}).

%% ejabberd calls this function when this module is loaded
%% basically it adds gen_server defined by this module to 
%% ejabberd main supervisor
start(Host, Opts) ->
    Proc = gen_mod:get_module_proc(Host, ?MODULE),
    ChildSpec = {Proc,
                 {?MODULE, start_link, [Host, Opts]},
                 permanent,
                 1000,
                 worker,
                 [?MODULE]},
    supervisor:start_child(ejabberd_sup, ChildSpec).

%% this is called by ejabberd when module is unloaded, so it
%% does the opposite of start/2 :)
stop(Host) ->
    Proc = gen_mod:get_module_proc(Host, ?MODULE),
    supervisor:terminate_child(ejabberd_sup, Proc),
    supervisor:delete_child(ejabberd_sup, Proc).

%% it will be called by supervisor when it is time to start
%% this gen_server under control of supervisor
start_link(_Host, _Opts) ->
    gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).

%% it is an initialization function for gen_server
%% it starts a timer, which sends 'tick' message periodically to itself
init(_) ->
    timer:send_interval(?INTERVAL, self(), tick),
    {ok, #state{}}.

handle_call(_Request, _From, State) ->
    Reply = ok,
    {reply, Reply, State}.

handle_cast(_Msg, State) ->
    {noreply, State}.

%% this function is called whenever gen_server receives a 'tick' message
handle_info(tick, State) ->
    State2 = do_cleanup(State),
    {noreply, State2};

handle_info(_Info, State) ->
    {noreply, State}.

terminate(_Reason, _State) ->
    ok.

code_change(_OldVsn, State, _Extra) ->
    {ok, State}.


%% this function is called by handle_info/2 when tick message is received
%% so put all cleanup code here
do_cleanup(State) ->
    %% do all cleanup work here
    State.

This blog post很好地解释了gen_servers的工作原理。当然，请务必在gen_server和supervisor上重新阅读OTP设计原则。

Ejabberd的模块开发描述为here

ejabberd主管模块

1 个答案: