Rubymotion Dispatch exiting early

Question

I'm executing a fairly vanilla dispatch queue in Rubymotion, however it is apparently exiting early. It never gets past the initWithContentsOfURL call. However, removing the Dispatch::Queue wrapper and putting the calls in the main thread works.

The application in the simulator exits with no stack trace or indication of what went wrong. Am I mis-using the dispatch queue?

def foo
  Dispatch::Queue.concurrent.async do
    error_ptr = Pointer.new(:object)
    data = NSData.alloc.initWithContentsOfURL(
      NSURL.URLWithString(url), options:NSDataReadingUncached, error:error_ptr)
    unless data
      p error_ptr[0]
      return
    end
    json = NSJSONSerialization.JSONObjectWithData(data, options:0, error:error_ptr)
    unless json
      presentError error_ptr[0]
      return
    end
    Dispatch::Queue.main.sync { print_results(json) }
  end
end

def print_results(json)
  p "#{json}"
end

Answer 1

I think I tracked down the issue. It was because I was declaring url in the method

def foo
url = "www.google.com"
  Dispatch
    take action on url
  end
end

By moving the url declaration in to the Dispatch thread, it works. I think it was a matter of a method local variable going out of scope before the task had time to execute.

def foo
  Dispatch
    url = "www.google.com"
    take action on url
  end
end