title: my app gets stuck when I call performFetch some times
body: <p>I am using a CoreDataTableViewController from the Stanford course cs193p, and in my viewWillAppear I call</p>
  <pre><code>self.fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:request
                                                                      managedObjectContext:self.dataBase.managedObjectContext
                                                                        sectionNameKeyPath:nil
                                                                                 cacheName:nil];
  </code></pre>
  <p>which on some random occasions makes my app freeze (it doesn't crush, it just freezes).
  in the CoreDataTableViewController the setter makes a call [self performFetch], which looks like this:</p>
  <pre><code>- (void)performFetch
  {
      if (self.fetchedResultsController) {
          if (self.fetchedResultsController.fetchRequest.predicate) {
              if (self.debug) NSLog(@&quot;[%@ %@] fetching %@ with predicate: %@&quot;, NSStringFromClass([self class]), NSStringFromSelector(_cmd), self.fetchedResultsController.fetchRequest.entityName, self.fetchedResultsController.fetchRequest.predicate);
          } else {
              if (self.debug) NSLog(@&quot;[%@ %@] fetching all %@ (i.e., no predicate)&quot;, NSStringFromClass([self class]), NSStringFromSelector(_cmd), self.fetchedResultsController.fetchRequest.entityName);
          }
          NSError *error;
          NSLog(@&quot;before&quot;);
          [self.fetchedResultsController performFetch:&amp;error];
          NSLog(@&quot;after&quot;);
          if (error) NSLog(@&quot;[%@ %@] %@ (%@)&quot;, NSStringFromClass([self class]), NSStringFromSelector(_cmd), [error localizedDescription], [error localizedFailureReason]);
      } else {
          if (self.debug) NSLog(@&quot;[%@ %@] no NSFetchedResultsController (yet?)&quot;, NSStringFromClass([self class]), NSStringFromSelector(_cmd));
      }
      [self.tableView reloadData];
  }
  </code></pre>
  <p>and the line it get stuck on  is</p>
  <pre><code>[self.fetchedResultsController performFetch:&amp;error];
  </code></pre>
  <p>any suggestions?</p>