Why does my HTTP request (bubble wrap) fail to execute in a Grand Central Dispatch queue?

Question

I am doing this inside my RubyMotion application:

Dispatch::Queue.concurrent('google').async {
  BubbleWrap::HTTP.get("http://google.com") do |response|
    p response.body.to_str
  end
}

This call does not complete.

However if I take the BubbleWrap code outside of the Dispatch queue, it completes fine.

Answer 1

BubbleWrap::HTTP is an abstraction over NSURLConnection, which depends on a RunLoop for its asynchronous processing. Unfortunately RunLoops aren't set up on GCD queues, and I haven’t figured out how to start a runloop on a GCD queue. When I've needed the above, I've resorted to instantiating a new NSThread, and started the run loop manually instead:

action = lambda do
  runLoop = NSRunLoop.currentRunLoop

  BW::HTTP.get("http://www.google.com") do |response|
    NSLog("Fetched Google!")
  end

  runLoop.run
end

thread = NSThread.alloc.initWithTarget action, selector:"call", object:nil
thread.start

This answer is a rehash of my blogpost on the same topic and Cocoa In The Shell