👀 Views: 41 💬 Answers: 1 📅 Created: 2025-06-18

objective-c ios nsurlconnection gcd Objective-C

I'm sure I'm missing something obvious here, but I'm encountering an unexpected behavior when using `NSURLConnection` alongside Grand Central Dispatch (GCD) in my Objective-C application on iOS 16.3. Specifically, I have a method that fetches data from a URL and processes the response on a background queue. However, I noticed that the completion handler I registered with `NSURLConnection` sometimes executes on the main thread, leading to race conditions with UI updates that occur simultaneously. Here's a simplified version of my implementation: ```objective-c - (void)fetchDataFromURL:(NSURL *)url { NSURLRequest *request = [NSURLRequest requestWithURL:url]; NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self]; [connection start]; } - (void)connectionDidFinishLoading:(NSURLConnection *)connection { dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ // Simulate processing data [self processData]; }); } - (void)processData { // Update UI (e.g., reload table view) dispatch_async(dispatch_get_main_queue(), ^{ [self.tableView reloadData]; }); } ``` I've added logging statements to check the thread of execution: ```objective-c NSLog(@"Current Thread: %@", [NSThread currentThread]); ``` Sometimes it logs that the current thread is the main thread, which conflicts with my expectation that the processing should happen on a background thread. I tried wrapping the `NSURLConnection` call in a background queue as well but it didn't resolve the issue. Is there something I'm missing here regarding how `NSURLConnection` handles its callbacks? Any insights on best practices for handling network requests and threading in Objective-C would be greatly appreciated. I'm working with Objective-C in a Docker container on Linux. Any pointers in the right direction?