Swift UITableView reloadData in a closure

UIKit isn't thread safe. The UI should only be updated from main thread:

dispatch_async(dispatch_get_main_queue()) {
    self.tableView.reloadData()
}

Update. In Swift 3 and later use:

DispatchQueue.main.async {
    self.tableView.reloadData()
}

You can also reload UITableView like this

self.tblMainTable.performSelectorOnMainThread(Selector("reloadData"), withObject: nil, waitUntilDone: true)