gistfile1.txt

          concurrent_iterator :on_field => 'variable_urls', :to_f => "variable_url" do
            participant :ref => 'convert_variable' 
          end



      engine.register_participant 'convert_variable' do |workitem|
        mutex = Nesstar::Mutexer.available
        
        begin
          mutex = Nesstar::Mutexer.available
          sleep 2 if mutex.nil?
        end while mutex.nil? 
                        
        @@curl_count += 1
        puts "found a free curl conn #{@@curl_count}"
        
        #we looks for a study's variables
        variable_url = workitem.fields['variable_url']
        var_file_name = variable_url.split(".").last

        `curl -o #{$xml_dir}#{var_file_name} --compressed "#{variable_url}"`

        variables_list = RDF::Parser.parse_variables("#{$xml_dir}/#{var_file_name}")
              
        variables_list.each do |var_hash|
          variable = Variable.store_with_fields(var_hash)
        end

        mutex.unlock

#....
end
 

 class Mutexer

    LIMIT = 10
    CURL_MUTEXES = []
    
    [0..LIMIT].each {CURL_MUTEXES << Mutex.new}
    
    def self.available
      for mutex in CURL_MUTEXES
        available = mutex if not mutex.locked?
        break if available
      end
      
      available.lock if available          
      puts "**** \n\n offering a mutex" if available          
      
      available
    end
  end