gistfile1.txt

log4r-kaboom.rb

=begin
I'm writing a small framework to help me with building some things,
and I'd like to give every class in the framework opt-in access to
logging. First I do that by defining a Log class which uses Singleton
to ensure that there's only one instance of a Log for the whole
application:
=end

require 'log4r'

module Constructify
 class Log
   include Singleton
   include Log4r

   def initialize
     Logger['global'].level = DEBUG
     fmt = PatternFormatter.new(:pattern => "%d [%5l] (%c) %M",
       :date_pattern => "%y-%m-%d %H:%M:%S")
     StderrOutputter.new('stderr', :level => Log4r::INFO, :formatter => fmt)
   end

   def log_init(name, level, target)
     Logger.new(name, Log4r.const_get(level)).outputters = target
     Logger[name]
   end
 end
end

=begin
Next, I add a has_logging method to every class:
=end

class Module
 def has_logging(level='DEBUG', target=['stderr'])
   class_eval {
     @log = Constructify::Log.instance.log_init(self.name,
"#{level}", target.dup)
     def log
       self.class.instance_variable_get :@log
     end
   }
 end
end

=begin
Now, one should be able to add logging to a particular class like this:
=end

class Foo
 has_logging
end

=begin
But instead, I get this:

/home/johnf/dev/constructify/lib/constructify/logging.rb:31:in
`class_eval': deadlock; recursive locking (ThreadError)
       from <internal:prelude>:6:in `synchronize'
       from <internal:prelude>:20:in `exclusive'
       from /home/johnf/.rvm/gems/ruby-1.9.1-p378@standard/gems/log4r-1.1.7/src/log4r/repository.rb:34:in
`[]'
       from /home/johnf/.rvm/gems/ruby-1.9.1-p378@standard/gems/log4r-1.1.7/src/log4r/repository.rb:75:in
`block in find_ancestor'
       from <internal:prelude>:21:in `block in exclusive'
       from <internal:prelude>:8:in `synchronize'
       from <internal:prelude>:20:in `exclusive'
       from /home/johnf/.rvm/gems/ruby-1.9.1-p378@standard/gems/log4r-1.1.7/src/log4r/repository.rb:73:in
`find_ancestor'
       from /home/johnf/.rvm/gems/ruby-1.9.1-p378@standard/gems/log4r-1.1.7/src/log4r/logger.rb:62:in
`deal_with_inheritance'
       from /home/johnf/.rvm/gems/ruby-1.9.1-p378@standard/gems/log4r-1.1.7/src/log4r/logger.rb:36:in
`initialize'
       from /home/johnf/dev/constructify/lib/constructify/logging.rb:17:in `new'
       from /home/johnf/dev/constructify/lib/constructify/logging.rb:17:in `log_init'
       from (eval):2:in `logger'
       from /home/johnf/dev/constructify/lib/constructify/logging.rb:31:in
`class_eval'
=end

=begin
I have temporarily worked around the problem by defining a MockLog class instead:
=end

module Constructify
  class MockLog
    def self.log_stub_method(*args)
      args.each do |a|
        define_method "#{a}" do |msg|
          t = Time.now.strftime("%Y-%m-%d %H:%M:%S")
          $stderr.puts "[#{a.upcase}] \u00bb [#{t}] #{msg}"
        end
      end
    end
    
    log_stub_method :fatal, :error, :warn, :info, :debug
  end
end

class Module
  def has_logging(level='DEBUG', target=['stderr'])
    class_eval {
      # @log = Constructify::Log.instance.log_init(self.name, "#{level}", target.dup)
      @log = Constructify::MockLog.new   # Use MockLog instead of Log4r.
      def log
        self.class.instance_variable_get :@log
      end
    }
  end
end

=begin
Commenting out the Log4r instantiation, not surprisingly, fixes the issue.
=end