I haven't had the time to study your question in detail yet, but I would start by directing you here: http://www.python.org/doc/current/library/logging.html#module-logging hslogger is heavily based upon an earlier version of the Python logging module. I had some experience with it and found it to work well, and thus based the hslogger design upon it. -- John Marc Weber wrote:
Following the advice on the hslogger wiki (http://software.complete.org/software/wiki/hslogger) I'm posting my thoughts about hslogger here:
What is wired? This piece of code (src/System/Log/Logger.hs):
parentHandlers name = let pname = (head . drop 1 . reverse . componentsOfName) name in do [...] next <- parentHandlers pname return ((handlers parent) ++ next)
Why? Because when logging to "A.B.C" it splits the String once to get ["A","B","C"], then it drops the last part and runs the same again for "A.B" and so on.. So A string is split > 3 times for one logging action. I think this is a waste of cpu cycles.. I'm going to improve this. While reading the code i noticed two issues:
====================================================================== issue 1
That's not the most awkward thing: When logging to "A.B.C" hslogger does add 3 loggers to the global logger Map: "A" "A.B" "A.B.C" all three inheriting the default priority level of the default rootLogger ""
A test application illustrating this (feature ?)
module Main where -- packages: hslogger import System.Log.Logger as HL import System.Log.Handler.Simple as HL
main = do -- the default logger logs to stderr level WARNING -- that's why the following message should be shown
-- a) logM "A.B.C" HL.ALERT "ALERT test, should be shown and should create the sublogger"
-- b) updateGlobalLogger rootLoggerName (setLevel EMERGENCY)
logM "A.B.C" HL.ALERT "ALERT test, should not be shown cause we have changed to EMERGENCY"
which prints:
tmp %./test1 /tmp nixos ALERT test, should be shown and should create the sublogger ALERT test, should not be shown cause we have changed to EMERGENCY
which is quite confusing because I haven't told hslogger explicitely to use a log level printing ALERTs on "A.B.C". so I'd expect that only the first message is shown. This behaviour is explained by the inheritance of the loglevel when hslogger creates them (without attaching handlers) automatically.
I don't want the logging behaviour depend on wether a log line has been emitted before or not. Do you agree? Have I missed something?
solution:
replacing
data Logger = Logger { level :: Priority, handlers :: [HandlerT], name :: String}
type LogTree = Map.Map String Logger
by a real log tree:
data LogTree = LogTree { level :: Priority, -- level only applies to handlers, not to subLoggers handlers :: [HandlerT], subLoggers :: Map.Map String LogTree }
====================================================================== issue 2
The second ineresting point is (bug or feature?) that you can make the root logger shut up by setting different log levels to sub loggers:
this sample does illustrate it:
module Main where -- packages: hslogger import System.Log.Logger as HL import System.Log.Handler.Simple as HL
main = do updateGlobalLogger "" (setLevel DEBUG) updateGlobalLogger "A" (setLevel EMERGENCY) logM "A" HL.ALERT "ALERT test, should not be shown cause we have changed to EMERGENCY"
It doesn't print anything although the default log handler on root (="") is set to loglever DEBUG. So there is no way to get all logmessages without removing all all setLevel calls to subloggers? Is this desirable?
====================================================================== my conclusion:
About issue 1 I think its a bug About issue 2 I don't know. I think there should be a way to get all log messages. So I feel this is a bug as well.
I neither have checkeg the logcxx nor log4j nor the reference implementation in python.
Thoughts?
Sincerly Marc Weber