ios：队列在后台阻塞，并在网络可用时执行

I am developing an app using parse.com API (hosted backend which provides API to save data on their servers). I want to be able to use the app seamlessly online and offline. For this I would need to use a queue where I can place blocks that require network access. When network does become available, the blocks should be executed serially and when the network goes offline, then the queue processing should be suspended.I am developing an app using parse.com API (hos