I am using iOS 7 NSURLSession to do some simple GET to a RESTful service. This is what i did:
NSURLSessionConfiguration *sessionConfig = [NSURLSessionConfiguration ephemeralSessionConfiguration];
_session = [NSURLSession sessionWithConfiguration:sessionConfig delegate:nil delegateQueue:[NSOperationQueue mainQueue]];
// create your url at this line
NSURLRequest *request = [NSURLRequest requestWithURL:url];
NSURLSessionTask *task = [self.session dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
// do something with the result
}];
[task resume];
All of the above code works fine. The completionHandler should get called in the main queue.
However, if i use this in GCD, like so:
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
// do some heavylifting in the background
for (int i = 0; i < 10000000; i++) ;
dispatch_async(dispatch_get_main_queue(), ^{
// do the exact same thing as the above NSURLSession call
NSURLSessionConfiguration *sessionConfig = [NSURLSessionConfiguration ephemeralSessionConfiguration];
_session = [NSURLSession sessionWithConfiguration:sessionConfig delegate:nil delegateQueue:[NSOperationQueue mainQueue]];
// create your url at this line
NSURLRequest *request = [NSURLRequest requestWithURL:url];
NSURLSessionTask *task = [self.session dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
// do something with the result
}];
[task resume];
});
});
Now, i thought i run that code within the dispatch_get_main_queue(), which should be the same as [NSOperationQueue mainQueue] as specified in the session's delegateQueue?? Tt should be effectively running in the main thread just like the 1st set of code. However, what i discovered is that the completionHandler is never called. And if i remove the GCD code, it works again.
Has anyone tried to do this before? Should this work? or I have misunderstanding where the work had dispatched to which queue?