From: Gin Mendi <gin18em@...>
Date: 2009-09-08T13:09:26+09:00
Subject: Re: Problems with cross-thread violation

Eleanor McHugh wrote:
>> I'm unsure if get_live_feed uses a seperate thread. I just have the  
>> dll
>> and no source. If get_live_feed does use a seperate thread how would I
>> make a seperate feed handle? Does that mean I need to declare a new
>> callback and pass that each time I call live feed?
> 
> Not necessarily, but it's certainly an experiment I'd consider as part
> of taming the problem. If you know C reasonably well I also recommend
> taking a peak through /ext/dl in the Ruby sources. That's not for the
> faint-hearted though.

I'm only learning C now as I was trying to look at the source code. At 
first glance I couldn't understand anything there but I'll study it if I 
run out of ideas. Anything in particular that I should study?

> No, it just means that while garbage collection is disabled your
> unreferenced objects will remain in memory. Once you reenable it all
> those dead objects will then be dealt with during the next collection
> cycle, including freeing up any memory associated with DataPtr objects
> you may have created with DL::malloc.

what about the pointers in the callback will those remain unreferrenced 
or are they automatically freed when the callback ends?

Well I tried disabling GC as you suggested but I got the same result. 
Here's what I did:

require 'feed_library'

module live_feed

  # my callback for the live feed
  fc = DL.callback('0PL') { |result_list, count| }
    if result_list
      record = FeedRecord.new(result_list)
      puts record.code
    end
  }

  # handle used to request for a feed
  handle = FeedLibrary::log_on("user", "password")

  if handle
    GC.disable

    session = get_live_feed(handle, fc)

    loop do
    end

    GC.enable
  end

end

I still got the cross-thread violation on rb_thread_schedule()

I tried changing the callback. Instead of using the struct class 
FeedRecord I instead used the struct! method. So I made it simple just 
to access 3 fields from the data structure:

  fc = DL.callback('0PL') { |result_list, count| }
    if result_list
      result_list.struct('C16FF', :code, :value, :stat)
      puts result_list[:code].pack('C16')
      puts result_list[:value]
    end
  }

I instead got a crash where I would see the printout of the callback 
with mixed in letters forming segmentation fault. Other runs would just 
flat out crash back to the command prompt.
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