Calling a http Request in background failing inside dispatch serial queue - objective-c

Question

I have a http request to make whenever a new location has been found asynchronously, for handling request, i have create a class called background requester which takes care of all these requests. The following code sample is as follows.
- (void)locationManager:(CLLocationManager *)manager
didUpdateToLocation:(CLLocation *)newLocation
fromLocation:(CLLocation *)oldLocation
{
dispatch_queue_t queue;
queue = dispatch_queue_create("com.test.sample", NULL); //create a serial queue can either be null or DISPATCH_QUEUE_SERIAL
dispatch_async(queue,
^{
if (bgTask == UIBackgroundTaskInvalid)
{
bgTask=[[UIApplication sharedApplication]
beginBackgroundTaskWithExpirationHandler:
^{
DDLogInfo(#"Task =%d",bgTask);
DDLogInfo(#"Ending bground task due to time expiration");
[[UIApplication sharedApplication] endBackgroundTask:bgTask];
bgTask = UIBackgroundTaskInvalid;
}];
}
BackgroundRequester *request = [[BackgroundRequester alloc] initwithLocation:self.currentLocation];
[request start];
DDLogInfo(#"Task =%d",bgTask);
DDLogInfo(#"bg Task remaining time=%f",[[UIApplication sharedApplication] backgroundTimeRemaining]);
});
}
//background requester class
//the start function will inturn calll the callAsynchrnously method.
-(void) callAsynchronously:(NSString *)url
{
DDLogInfo(#"Calling where am i from background");
DDLogInfo(#"Url =%#",reqURL);
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:url] cachePolicy:NSURLCacheStorageNotAllowed timeoutInterval:20.0f];
responseData = [[NSMutableData alloc] init];
connect = [NSURLConnection connectionWithRequest:request delegate:self];
[connect start];
}

Answer 1

You cannot use connectionWithRequest from a background queue (without scheduling the connection in some runloop). Either
use sendSynchronousRequest (which is fine to do if you're using it from a background queue like this), or
schedule the connection in a run loop. If you dig through the AFNetworking code, you'll see they create a run loop on a dedicated thread, which strikes me as the most elegant solution if you really need the NSURLConnectionDataDelegate methods.
You can also use the main run loop (though I'm less crazy about that solution), e.g., something like:
connect = [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:NO];
[connect scheduleInRunLoop:[NSRunLoop mainRunLoop] forMode:NSRunLoopCommonModes];
[connect start];
Also note, I'm not using connectionWithRequest (because that starts the connection immediately, which is incompatible with your calling of start; only use start if you use initWithRequest with a startImmediately of NO). If you try to do start in conjunction with connectionWithRequest, it can cause problems.
I think the sendSynchronousRequest is simplest (and saves you from having to write any of the NSURLConnectionDataDelegate methods, too). But if you need the NSURLConnectionDataDelegate methods (e.g. you need progress updates, you're using a streaming protocol, etc.), then use the scheduleInRunLoop method.