Is there any way that the application can be set to be disabled while it is busy fetching data, without disabling this at the start of the fetch and enabling once the data is back. This is ok if you have a simple app, but can get very difficult to manage in large scale applications.
you could create a 'please wait' popup, set modal to true which'll disallow all usage of the application below it, on the Result of the HTTPService simply remove the popup.
you could just do 'this.enabled = false' in the main script, set it to true after the result.
it really doesn't matter what size the app is.
You can add a click blocker over the entire app, if you want to prevent user clicking around while the data is loading. You can also put a small loader animation or something and don't forget to set a timeout for it so that in case something goes wrong with the service app doesn't stay unclickable.
You can use Application.application.enabled = false; anywhere throughout your application to disable the whole application ...and Application.application.enabled = true; to enable the application back..