[Pas-dev] Suggestion for logging

[Kyle R. B. <mo...@vo...>]

In the Java projects I've been involved with, we've used Jakarta's
Log4j.  Probably the most important features of the logging library are
that you can tweak the logging level or the destination(s) from a
configuration file.

The logging level (fatal, error, warn, info or debug) can be set across
the entire project, on a per package or a per-object basis.  For
example, if you were trying to watch a constrained set of modules, you
could set up a configuration like:

  log4perl.logger=ERROR, file
  log4perl.logger.Org.Bgw=INFO, screen, file
  log4perl.logger.Org.Bgw.Pas.Page=DEBUG, screen, file
  log4perl.logger.Org.Bgw.Pas.Response=ERROR, file

  log4perl.logger.file=Log::Dispatch::File
  log4perl.logger.file.filename=logs/pas.log
  log4perl.logger.file.layout=Log::Log4perl::Layout::PatternLayout
  log4perl.logger.file.layout.ConversionPattern=%d %p> %F{1}:%L %M - %m%n
  
  log4perl.logger.screen=Log::Dispatch::Screen
  log4perl.logger.screen.stderr=0
  log4perl.logger.screen.layout=Log::Log4perl::Layout::SimpleLayout
  
The first section sets up the default level so only ERROR, or FATAL get
logged.  As a default for all the objects and sub-packages of
Org::Bgw, it sets up a default of INFO or more severe.  For Page
it turns the log level all the way up to DEBUG, while turning it back
down to ERROR for Response.

To make the support easier, since perl can detect the calling package,
we could centralize the configuraiton and obtaining of the logger to a
single module:

  ###
  package Org::Bgw::Log;
  ...
  use Log::Log4perl;
  Log::Log4perl->init($ENV{'PAS_BASE'}."/conf/log4perl.conf");
  # get a Log4perl log object based on the caller's package name
  sub getLogger { Log::Log4perl::get_logger( (caller)[0] ); }


Then in any random module:

  ###
  package Org::Bgw::Foo;
  ...
  my $log = Org::Bgw::Log::getLogger;

  sub somethingComplicated
  {
     my($self) = @_;

     # testing log->is_debug is an optimization so that Dumper isn't
     # called (since it could be expensive) unless the log level is set
     # to debug -- unless the level is debug, the arguments aren't
     # computed, and the log statement isn't called.
     if( $log->is_debug() ) {
       $log->debug("somethingComplicated, self = ", Dumper($self) );
     }

     eval {
       $log->info("Entering log running loop...");
       while(...) {
       }
       $log->info("major processing completed");
     };

     if($@) {
       $log->fatal("Woah, bad error in main processing, aborting: $@");
       $self->throw($@);
     }

     reutrn 1;
  }

This article gives a good overview:

  http://www.perl.com/pub/a/2002/09/11/log4perl.html

This is the main project site:

  http://log4perl.sourceforge.net/

It's also available from CPAN (http://cpan.org/modules/by-module/Log/).

The project comes with a few appenders: Screen, File and DBI.  It can
also make use of Log::Dispatch appenders, which include: Email,
FileRotate (good for keeping log files from filling up all free space),
Tk and Syslog.  One thing that could be done for production would be to
set up fatal errors to go to a File appender, and an Email appender
where the Email appender can be used for easy notification of
catastrophic errors.


The functionality is good, the downside is that this introduces another
dependency.  I had thought that Log::Dispatch::Config had these features,
but it turns out that it doens't really.

What do you guys think about switching?  It should be an easy change.

Kyle

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