timer:send_after

gen_server 代码片段
 init([Host, _Opts]) -> 
       timer:send_after(5000, self(), {writing_db}),      
      {ok, #state{}}.     
 handle_info({writing_db}, State) ->
       timer:send_after(5000, self(), {writing_db}),  
       ...............

{noreply, State};