rabbit_log.erl

%% The contents of this file are subject to the Mozilla Public License
%% Version 1.1 (the "License"); you may not use this file except in
%% compliance with the License. You may obtain a copy of the License
%% at http://www.mozilla.org/MPL/
%%
%% Software distributed under the License is distributed on an "AS IS"
%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
%% the License for the specific language governing rights and
%% limitations under the License.
%%
%% The Original Code is RabbitMQ.
%%
%% The Initial Developer of the Original Code is GoPivotal, Inc.
%% Copyright (c) 2007-2014 GoPivotal, Inc.  All rights reserved.
%%

-module(rabbit_log).

%% 该模块主要是控制日志打印的范围，根据配置来打印日志，这样能够控制日志的数据量

-export([log/3, log/4, debug/1, debug/2, info/1, info/2, warning/1,
         warning/2, error/1, error/2]).
-export([with_local_io/1]).

%%----------------------------------------------------------------------------

-ifdef(use_specs).

-export_type([level/0]).

-type(category() :: atom()).
-type(level() :: 'debug' | 'info' | 'warning' | 'error').

-spec(log/3 :: (category(), level(), string()) -> 'ok').
-spec(log/4 :: (category(), level(), string(), [any()]) -> 'ok').

-spec(debug/1   :: (string()) -> 'ok').
-spec(debug/2   :: (string(), [any()]) -> 'ok').
-spec(info/1    :: (string()) -> 'ok').
-spec(info/2    :: (string(), [any()]) -> 'ok').
-spec(warning/1 :: (string()) -> 'ok').
-spec(warning/2 :: (string(), [any()]) -> 'ok').
-spec(error/1   :: (string()) -> 'ok').
-spec(error/2   :: (string(), [any()]) -> 'ok').

-spec(with_local_io/1 :: (fun (() -> A)) -> A).

-endif.

%%----------------------------------------------------------------------------
%% Category：类别(目前只有四种类别：channel(rabbit_channel进程) connection(rabbit_reader进程) federation(插件使用) mirroring(高可用队列相关))
log(Category, Level, Fmt) -> log(Category, Level, Fmt, []).


log(Category, Level, Fmt, Args) when is_list(Args) ->
	case level(Level) =< catlevel(Category) of
		false -> ok;
		true  -> F = case Level of
						 debug   -> fun error_logger:info_msg/2;
						 info    -> fun error_logger:info_msg/2;
						 warning -> fun error_logger:warning_msg/2;
						 error   -> fun error_logger:error_msg/2
					 end,
				 %% 使用本节点的IO系统执行Fun函数将日志发送到error_logger事件中心中
				 with_local_io(fun () -> F(Fmt, Args) end)
	end.


debug(Fmt)         -> log(default, debug,    Fmt).
debug(Fmt, Args)   -> log(default, debug,    Fmt, Args).
info(Fmt)          -> log(default, info,    Fmt).
info(Fmt, Args)    -> log(default, info,    Fmt, Args).
warning(Fmt)       -> log(default, warning, Fmt).
warning(Fmt, Args) -> log(default, warning, Fmt, Args).
error(Fmt)         -> log(default, error,   Fmt).
error(Fmt, Args)   -> log(default, error,   Fmt, Args).


%% 从配置文件中得到类别对应的日志等级
catlevel(Category) ->
	%% We can get here as part of rabbitmqctl when it is impersonating
	%% a node; in which case the env will not be defined.
	CatLevelList = case application:get_env(rabbit, log_levels) of
					   {ok, L}   -> L;
					   undefined -> []
				   end,
	level(proplists:get_value(Category, CatLevelList, info)).

%%--------------------------------------------------------------------
%% 根据日志类型得到日志等级
level(debug)   -> 4;
level(info)    -> 3;
level(warning) -> 2;
level(error)   -> 1;
level(none)    -> 0.

%% Execute Fun using the IO system of the local node (i.e. the node on
%% which the code is executing). Since this is invoked for every log
%% message, we try to avoid unnecessarily churning group_leader/1.
%% 使用本节点的IO系统执行Fun函数将日志发送到error_logger事件中心中
with_local_io(Fun) ->
	GL = group_leader(),
	Node = node(),
	case node(GL) of
		Node -> Fun();
		_    -> group_leader(whereis(user), self()),
				try
					Fun()
				after
					group_leader(GL, self())
				end
	end.