Rails - Nov 2005 - Threads and Active Reccord

Yeah, this is fun!

So I''m trying to check a bunch of websites to see if they''ve
been updated
since the last time I check them. I''m using threads and SizedQueue to
grab
sets of "feed" objects out of the database, then send them off to be
downloaded and compared to existing records.

I sometimes get this error, which I don''t understand:
[2005-11-04 13:10:15] ERROR SystemExit:
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.12.2/lib/active_record/base
.rb:1412:in `select''
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.12.2/lib/active_record/base
.rb:1412:in `method_missing'': undefined method `accounts'' for
#<Feed:0x25d3af8> (NoMethodError)


I don''t really even know if this is a sane approach so any suggestions
are
welcome. Since I am retrieving the feed objects in one thread, then
modifying them and saving them in a different thread, do I need to so
anything special, like pre-fetch the accounts collection somehow?



Below is the code that''s being used to produce the problems:


<code>
      
    # method run by controller
  def check_all_feeds_and_create_tells
    fill_feed_queue
    sleep(1.minute)
    
    checkers = (1..3).map do |i|
      process_feed_chunk
    end
  end


   private
   def fill_feed_queue
     last_at = 0
     @queue = SizedQueue.new(10) # with a capacity for 10
     
     # we do the queue filling in a single thread that runs until no more
items are left to add
     Thread.new do 
       loop do
         logger.debug("Fetching next block of feeds: limit
#{FEED_FETCH_LIMIT}, offset = #{last_at}")
         feeds = Feed.find(:all, :limit => FEED_FETCH_LIMIT, :offset =>
last_at)
         break if feeds == nil || feeds.length == 0
         last_at += feeds.length
         
         # add each feed found to the queue
         feeds.each do |feed|
           feed.accounts # load the accounts so they are available later as
part of this feed object (othwerwise accounts throws NoSuchMethod )
           @queue << feed
         end
         sleep(10) # 10 second break
       end #loop
     end # thread.new
   end # def
   
   def process_feed_chunk
     Thread.new do
       loop do
         feed = @queue.pop
         logger.debug("Processing feed: #{feed}")
       
         begin
            item = get_first_item feed.url
         rescue Exception
            logger.warn("The feed #{feed.url} could not be retrieved:
#{$!}")
            next
         end
    
         if ( feed.signature != item[:title] )       # if the feed appears
to have been updated
            feed.signature = item[:title]    # then save the new signature
            feed.save
       
            feed.accounts.each do |account| #### THE ERROR IS PRODUCED HERE
               tell = Tell.new
               tell.message = "[#{item[:channel_title]} ( #{item[:link]} ):
#{item[:title]} ] \n #{item[:description]} \n" +
                              "--
http://localhost:3000/accounts/#{account.id}"
               account.tells << tell
            end
         end # if feed.sig
       end # loop do
     end # Thread.new
   end # def
</code>