Ruby - share logger instance among module/classes

Question

Working on a little Ruby script that goes out to the web and crawls various services. I\'ve got a module with several classes inside:

module Crawler
  class          


        

Answer 1

Based on your comment

All of this could be avoided if you could just dynamically change the output location of an already-instantiated Logger (similar to how you change the log level).

If you are not restricted to the default logger you may use another log-gem.

As an example with log4r:

require 'log4r' 

module Crawler
  LOGGER = Log4r::Logger.new('mylog')
  class Runner
    def initialize
        LOGGER.info('Created instance for %s' % self.class)
    end
  end
end

ARGV << 'test'  #testcode

#...
case ARGV.first
  when 'test'
    Crawler::LOGGER.outputters = Log4r::StdoutOutputter.new('stdout')
  when 'prod'
    Crawler::LOGGER.outputters = Log4r::FileOutputter.new('file', :filename => 'test.log') #append to existing log
end
#...
Crawler::Runner.new

In prod mode the logging data are stored in a file (attached to existing file, but there are options to create new log files or implement rolling log files).

The result:

 INFO main: Created instance for Crawler::Runner

If you use the inheritance mechanism of log4r (a), you may define a logger for each class (or in my following example for each instance) and share the outputter.

The example:

require 'log4r' 

module Crawler
  LOGGER = Log4r::Logger.new('mylog')
  class Runner
    def initialize(id)
      @log = Log4r::Logger.new('%s::%s %s' % [LOGGER.fullname,self.class,id])
      @log.info('Created instance for %s with id %s' % [self.class, id])
    end
  end
end

ARGV << 'test'  #testcode

#...
case ARGV.first
  when 'test'
    Crawler::LOGGER.outputters = Log4r::StdoutOutputter.new('stdout')
  when 'prod'
    Crawler::LOGGER.outputters = Log4r::FileOutputter.new('file', :filename => 'test.log') #append to existing log
end
#...
Crawler::Runner.new(1)
Crawler::Runner.new(2)

The result:

 INFO Runner 1: Created instance for Crawler::Runner with id 1
 INFO Runner 2: Created instance for Crawler::Runner with id 2

(a) A logger name like A::B has the name B and is a child of the logger with the name A. As far as I know this is no object inheritance.

One advantage of this approach: If you want to use a single logger for each class, you need only to change the name of the logger.

Answer 2

I like to have a logger method available in my classes, but I don't like sprinkling @logger = Logging.logger in all my initializers. Usually, I do this:

module Logging
  # This is the magical bit that gets mixed into your classes
  def logger
    Logging.logger
  end

  # Global, memoized, lazy initialized instance of a logger
  def self.logger
    @logger ||= Logger.new(STDOUT)
  end
end

Then, in your classes:

class Widget
  # Mix in the ability to log stuff ...
  include Logging

  # ... and proceed to log with impunity:
  def discombobulate(whizbang)
    logger.warn "About to combobulate the whizbang"
    # commence discombobulation
  end
end

Because the Logging#logger method can access the instance that the module is mixed into, it is trivial to extend your logging module to record the classname with log messages:

module Logging
  def logger
    @logger ||= Logging.logger_for(self.class.name)
  end

  # Use a hash class-ivar to cache a unique Logger per class:
  @loggers = {}

  class << self
    def logger_for(classname)
      @loggers[classname] ||= configure_logger_for(classname)
    end

    def configure_logger_for(classname)
      logger = Logger.new(STDOUT)
      logger.progname = classname
      logger
    end
  end
end

Your Widget now logs messages with its classname, and didn't need to change one bit :)

Answer 3

How about wrapping the logger in a singleton then you could access it using MyLogger.instance