When is UITableView's reloadData Synchronous?

When is an UITableView's reloadData method synchronous vs. asynchronous? Apple's documentation does not mention anything about it, and I've seen the reloadData function perform both synchronously as well as asynchronously, which really confuses me.

How does Ap开发者_StackOverflowple make the distinction about which scheme to use? Does anyone know?

The update to the UI is always synchronous but you its possible to update the data asynchronously before calling reloadData and incurring the synchronous UI update.