AFNetworking and NSURLConnection on main thread

Question

EDIT: The highlighted row in the screenshot is what I have a problem with, why is NSURLConnection running on [NSThread main] when I'm not calling it, AFNetworking is.

I'm using AFNetworking for my project, but when running Time Profiler in Instruments I'm seeing a lot of activity on the main thread for NSURLConnection, I have a feeling this is not what I want.

My method is

- (void)parseArticles {   
    NSMutableArray *itemsToParse = [[FMDBDataAccess sharedDatabase] getItemsToParse];

    NSMutableArray *operations = [[NSMutableArray alloc] init];


    for (Post *p in itemsToParse) {

        NSMutableString *strURL = [NSMutableString new];
        [strURL appendString:@"http://xxxxxxxxxxxxxxxxxxxxxx.php?url="];
        [strURL appendString:[p href]];

        NSURL *url = [NSURL URLWithString:strURL];
        NSURLRequest *request = [NSURLRequest requestWithURL:url];

        AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:request];
        [[ParserClient sharedInstance] registerHTTPOperationClass:[AFHTTPRequestOperation class]];

        [operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {

            dispatch_async(loginParseQueue, ^{

                Parser *parse = [[Parser alloc] init];
                [parse parseLink:responseObject rowID:[p rowID]];
            });
        } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
            NSLog(@"%@",error);
        }];
        [operations addObject:operation];
    }
    NSOperationQueue *operationQueue = [[NSOperationQueue alloc] init];
    [operationQueue setMaxConcurrentOperationCount:3];
    [operationQueue addOperations:operations waitUntilFinished:NO];
}

Why would AFNetworking be using the main thread? and how do I fix it.

Answer 1

AFNetworking is running on a child thread not in main thread, but every thread has a main method, which is on the image you post. This is not the main thread.Now tell me What do you want to fix?

Answer 2

It's because AFNetworking uses "successCallbackQueue" to route the completion block :

AFHTTPRequestOperation.m :

self.completionBlock = ^{
    if (self.error) {
        if (failure) {
            dispatch_async(self.failureCallbackQueue ?: dispatch_get_main_queue(), ^{
                failure(self, self.error);
            });
        }
    } else {
        if (success) {
            dispatch_async(self.successCallbackQueue ?: dispatch_get_main_queue(), ^{
                success(self, self.responseData);
            });
        }
    }
};

You can simply assign a different thread to success and failure completion blocks :

dispatch_queue_t backgroundQueue = dispatch_queue_create("com.name.bgqueue", NULL);
AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:request];
operation.successCallbackQueue = backgroundQueue;
operation.failureCallbackQueue = backgroundQueue;

Answer 3

EDIT:

Here is some code to run operations in a background thread. Use of any function called from the UI thread will run on on the UI thread. You can use a technique similar to the one specified below to run your operation on a background thread, and then dispatch the result back to the UI thread for later use.

Here is the technique I used, you may replace my sendSynchronousRequest call with your AFHTTPRequestOperation :

Specify a special type (a block) so you can pass blocks of code around.

typedef void (^NetworkingBlock)(NSString* stringOut);

Then, you need to dispatch to a background thread, so as not to freeze your UI thread.

Here's a function to call stuff in a background thread, and then wait for a response, and then call a block when done without using the UI thread to do it:

- (void) sendString:(NSString*)stringIn url:(NSString*)url method:(NSString*)method completion:(NetworkingBlock)completion {
    //build up a request.
    NSMutableURLRequest* request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:url]];
    NSData *postData = [stringIn dataUsingEncoding:NSUTF8StringEncoding];
    [request setHTTPMethod:method];
    [request setValue:[NSString stringWithFormat:@"%d", postData.length] forHTTPHeaderField:@"Content-Length"];
    [request setValue:@"application/json" forHTTPHeaderField:@"Content-Type"];  //or whatever
    [request setHTTPBody:postData];

    //dispatch a block to a background thread using GCD (grand central dispatch)
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        NSURLResponse *response;
        NSError* error;

        //request is sent synchronously here, but doesn't block UI thread because it is dispatched to another thread.
        NSData* responseData = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];

        //call complete, so now handle the completion block.
        if (completion) {
            //dispatch back to the UI thread again
            dispatch_async(dispatch_get_main_queue(), ^{
                if (responseData == nil) {
                    //no response data, so pass nil to the stringOut so you know there was an error.
                    completion(nil);
                } else {
                    //response received, get the content.
                    NSString *content = [[NSString alloc] initWithBytes:[responseData bytes] length:responseData.length encoding:NSUTF8StringEncoding];
                    NSLog(@"String received: %@", content);

                    //call your completion handler with the result of your call.
                    completion(content);
                }
            });
        }
    });
}

Use it like this:

- (void) myFunction {
    [self sendString:@"some text in the body" url:@"http://website.com" method:@"POST" completion:^(NSString *stringOut) {
        //stringOut is the text i got back
    }];
}