BROKEN example of concurrent code. This is for comparison ONLY

ModelManager-Broken.m

//
//  ModelManager.m
//  ThreadingHell
//
//  Created by Cory D. Wiles on 10/19/12.
//  Copyright (c) 2012 Cory D. Wiles. All rights reserved.
//

#import "ModelManager.h"
#import "NSMutableString+CoryAdditions.h"

static NSString* const wsRequestErrorDomain = @"net.epb.imf.im3.request.error";
static char const *imfQueueName             = "net.epb.imf.im3.queue";
static dispatch_queue_t _imfDispatchQueue;

@implementation ModelManager

+ (void)initialize {
  _imfDispatchQueue = dispatch_queue_create(imfQueueName, DISPATCH_QUEUE_CONCURRENT);
}

+ (ModelManager *)sharedManager {

  static ModelManager *_sharedClient = nil;
  static dispatch_once_t onceToken;

  dispatch_once(&onceToken, ^{
    _sharedClient = [[self alloc] init];
  });

  return _sharedClient;
}

- (void)getAccountDetailsForAccountNumber:(NSString* )accountNumber
                          completionBlock:(IMFRequestCompletionBlock)completion {

  dispatch_sync(_imfDispatchQueue, ^{

    NSLog(@"trying to fetch information for details");

    NSMutableString *details = [NSMutableString randomStringWithCapacity:10];

    [details appendFormat:@" details"];

    NSLog(@"details string: %@", details);

    dispatch_async(dispatch_get_main_queue(), ^{

      if (completion) {

        if (details) {

          completion(details, YES, nil);

        } else {

          NSString *errorMessage = [NSString stringWithFormat:@"Failed getting details for account: %@", accountNumber];
          NSError *failerror     = [NSError errorWithDomain:wsRequestErrorDomain
                                                       code:1002
                                                   userInfo:[NSDictionary dictionaryWithObject:NSLocalizedString(errorMessage, nil)
                                                                                        forKey:NSLocalizedDescriptionKey]];
          completion(nil, NO, failerror);
        }
      }
    });
  });
}

- (void)getAccountListMetaInformation:(IMFRequestCompletionBlock)completion {

  __block NSMutableDictionary *accountList = [NSMutableDictionary new];
  __block NSMutableArray *accountDetails   = [NSMutableArray new];

  NSArray *loginResponse = @[@"account1", @"account2"];

  if (loginResponse) {

    NSLog(@"inside loginResponse");

    dispatch_sync(_imfDispatchQueue, ^{

      [loginResponse enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop){

        NSLog(@"inside account loop for obj: %@", obj);

        [self getAccountDetailsForAccountNumber:obj completionBlock:^(id obj, BOOL success, NSError *error) {

          if (success) {

            NSLog(@"success account looop");

            [accountDetails addObject:obj];

          } else {

            NSLog(@"failed to get any accont details from account: %@ %@", obj, [error localizedDescription]);
          }

        }];
      }];

      dispatch_async(dispatch_get_main_queue(), ^{

        NSLog(@"should be updating main queue");

        if (completion) {

          if (accountDetails.count) {

            completion(accountList, YES, nil);

          } else {

            NSString *errorMessage = @"There was error getting your accounts. Please login again.";
            NSError *failerror     = [NSError errorWithDomain:wsRequestErrorDomain
                                                         code:1003
                                                     userInfo:[NSDictionary dictionaryWithObject:NSLocalizedString(errorMessage, nil)
                                                                                          forKey:NSLocalizedDescriptionKey]];
            completion(nil, NO, failerror);
          }
        }
      });
    });
  }
}

@end