title: How do I know when safe to ignore __cxa_throw on an All Exceptions breakpoint?
body: <p>I am on Xcode 4.5.1.  I think this is relatively new behavior I am seeing.</p>
  
  <p>I prefer to develop and test my projects with the "All Exceptions" breakpoint enabled.</p>
  
  <p>I have been running into a scenario where I am loading thumbnail images to cells in a tableview, where I am getting a __cxa_throw exception.  When I click the "Continue program execution" button, Xcode continues its merry way.  I get the thumbnails.  App seems to work fine.  I am looking for some tips on how I can determine if this is something safe to ignore.  Like maybe some pointers on understanding the stack trace?  Or something else?</p>
  
  <p>Here is the snippet of code:</p>
  
  <pre><code>    NSString *imageStr = item.thumbURL;
      imageStr = [imageStr stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
      NSURL *imageURL;
  
      if (![imageStr isEqualToString:@""]) {
          imageURL = [NSURL URLWithString:imageStr];
          NSLog(@"imageURL: %@",imageURL);
          if (imageURL == nil) {
              NSLog(@"imageUrl was nil for string: %@",imageStr);
          } else {
              UIActivityIndicatorView *spinner = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];
              //spinner.frame = CGRectMake(cell.imageView.frame.size.width/2,cell.imageView.frame.origin.y + cell.imageView.frame.size.height/2,cell.imageView.frame.size.width,cell.imageView.frame.size.height);
              spinner.frame = CGRectMake(10,20,40,40);
              [spinner startAnimating];
              [cell addSubview:spinner];
  
              dispatch_queue_t downloadQueue = dispatch_queue_create("thumbnail downloader", NULL);
              dispatch_async(downloadQueue, ^{
                  NSLog(@"Network request for tour_thumb image: %@",imageStr);
                  UIImage *img = [[UIImage alloc] initWithData:[NSData dataWithContentsOfURL:imageURL]];
                  dispatch_async(dispatch_get_main_queue(), ^{
                      [spinner removeFromSuperview];
                      UIImageView *imgView=[[UIImageView alloc] initWithFrame:CGRectMake(8, 8, cell.contentView.frame.size.width/2 - 16, cell.contentView.frame.size.height - 16)];
                      imgView.image = img;
                      [cell.contentView addSubview:imgView];
                  });
              });
              dispatch_release(downloadQueue);
          }
      }
  </code></pre>
  
  <p>Here is what I see on the stack trace:</p>
  
  <pre><code>#0  0x34a9c524 in __cxa_throw ()
  #1  0x387014ce in AddChildNode(XMP_Node*, XML_Node const&amp;, char const*, bool) ()
  #2  0x38700d22 in RDF_LiteralPropertyElement(XMP_Node*, XML_Node const&amp;, bool) ()
  #3  0x3870094e in RDF_PropertyElementList(XMP_Node*, XML_Node const&amp;, bool) ()
  #4  0x38700608 in ProcessRDF(XMP_Node*, XML_Node const&amp;, unsigned int) ()
  #5  0x3871480a in XMPMeta::ParseFromBuffer(char const*, unsigned int, unsigned int) ()
  #6  0x387095c0 in WXMPMeta_ParseFromBuffer_1 ()
  #7  0x38725578 in TXMPMeta&lt;std::string&gt;::ParseFromBuffer(char const*, unsigned int, unsigned int) ()
  #8  0x387254de in TXMPMeta&lt;std::string&gt;::TXMPMeta(char const*, unsigned int) ()
  #9  0x38722b70 in CreateMetadataFromXMPDataInternal(char const*, unsigned long, unsigned int) ()
  #10 0x38739a50 in readXMPProperties ()
  #11 0x386a01fc in readXMPData ()
  #12 0x3868cec8 in initImageJPEG ()
  #13 0x3868c2ee in _CGImagePluginInitJPEG ()
  #14 0x3867e274 in makeImagePlus ()
  #15 0x3867ddde in CGImageSourceCreateImageAtIndex ()
  #16 0x38e117b6 in _UIImageRefFromData ()
  #17 0x38e116c6 in -[UIImage initWithData:] ()
  #18 0x0004cb0a in __57-[ViewController tableView:cellForRowAtIndexPath:]_block_invoke_0 at ViewController.m:335
  #19 0x313fc792 in _dispatch_call_block_and_release ()
  #20 0x313ffb3a in _dispatch_queue_drain ()
  #21 0x313fd67c in _dispatch_queue_invoke ()
  #22 0x31400612 in _dispatch_root_queue_drain ()
  #23 0x314007d8 in _dispatch_worker_thread2 ()
  #24 0x394767f0 in _pthread_wqthread ()
  #25 0x39476684 in start_wqthread ()
  </code></pre>