NSApplication -runModalSession崩溃

Question

I am trying to process files loaded by the user via NSOpenPanel and then start a modal session in order to display the progress on my custom window class. At the first few dozen tries, it was running well until I've started running into random crashes. All objects I've allocated were released after each iteration, so I'm a bit stumped on how to proceed from here. Here's a code snippet for posterity:

NSModalSession m = [[NSApplication sharedApplication] beginModalSessionForWindow:progWindow];

while(index < [validImageURLS count])
{
    // Check if user presses the stop track button in pop up window
    if([[NSApplication sharedApplication] runModalSession:m] != NSModalResponseContinue)
    {
        stopProcessing = YES;
        break;
    }

    NSURL* current = [validImageURLS objectAtIndex:index];
    CGImageSourceRef imgSrc = CGImageSourceCreateWithURL((__bridge CFURLRef)current, NULL);
    CGImageRef image = CGImageSourceCreateImageAtIndex(imgSrc, 0, NULL);
    size_t img_width = CGImageGetWidth(image);
    size_t img_height = CGImageGetHeight(image);
    size_t new_size = 0.0;

    if(img_width > img_height)
    {
        new_size = img_width;
    }
    else
    {
        new_size = img_height;
    }

    float aspectRatio = img_width / (float)img_height;

    if(img_width >= img_height)
    {
        img_width  = (int)(round(log2((int)img_width)));
        img_width  = (int)(pow(2.0, img_width));

        if(img_width > 256)
        {
            img_width  = 256;
        }

        img_height = (int)(img_width / aspectRatio);
    }
    else
    {
        img_height = (int)(round(log2((int)img_height)));
        img_height = (int)(pow(2.0, img_height));

        if(img_height > 256)
        {
            img_height = 256;
        }

        img_width  = (int)(img_height * aspectRatio);
    }

    new_size = (int)(round(log2((int)new_size)) + 1);
    new_size = (int)(pow(2.0, new_size));

    GLubyte* imgDataBuffer = new GLubyte[img_width * img_height * ATLAS_NUM_CHANNELS];
    memset(imgDataBuffer, 0, img_width * img_height * ATLAS_NUM_CHANNELS);

    CGColorSpaceRef tmpColorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef imgContext = CGBitmapContextCreate(imgDataBuffer,
                                                    img_width,
                                                    img_height,
                                                    8,
                                                    img_width * 4,
                                                    tmpColorSpace,
                                                    kCGBitmapByteOrder32Host | kCGImageAlphaPremultipliedFirst);

    // Initialize bitmap context attributes
    CGContextSetBlendMode(imgContext, kCGBlendModeNormal);
    CGContextSetInterpolationQuality(imgContext, kCGInterpolationHigh);

    CGRect _c = CGRectMake(0.0, 0.0, img_width, img_height);

    CGContextDrawImage(imgContext, _c, image);

    //flip back
    CGImageRef drawnImg = CGBitmapContextCreateImage(imgContext);

    NSString* c_p = [current path];
    std::string www = std::string([c_p UTF8String]);

    NSString* c_img_name = [current lastPathComponent];
    std::string zzz = std::string([c_img_name UTF8String]);

    // Creating new input content to be put into to the input list
    // for BinPack2D to process later
    SquareContent mycontent(www);
    mycontent.img = drawnImg;

    inputContent += BinPack2D::Content<SquareContent>(mycontent,
                                                      BinPack2D::Coord(),
                                                      BinPack2D::Size((int)img_width, (int)img_height),
                                                      false);

    CGContextRelease(imgContext);
    CGColorSpaceRelease(tmpColorSpace);
    CGImageRelease(image);
    CFRelease(imgSrc);
    delete [] imgDataBuffer;


    // Update progress bar view in our pop up window
    [self UpdateTrackProgressAsync:@[[NSNumber numberWithDouble:index],
                                     [NSNumber numberWithDouble:(int)[validImageURLS count]]]];

    index++;
}

[[NSApplication sharedApplication] endModalSession:m];

Below is a screenshot of the said error:

I simply followed the structure that was presented in Apple's documentation: https://developer.apple.com/documentation/appkit/nsapplication/1428590-runmodalsession?language=objc

Reason why I need to run this via a modal session for window instead of dispatching the code in a background queue is because I'm developing this for a plugin. I want the processing to halt all other UI in the host application until the work has been finished, or the user presses a button that will trigger a stopModal call. I hope someone can point me in the right direction. Thank you and many cheers.

Answer 1

run with zombies enabled to narrow down cause of crash. (Edit scheme... diagnostics... zombie objects checkbox)

what happened to me was that endModalSession crashed when it got called recursively. No idea what's causing your problem.

Here's some (maybe unrelated) problems I encountered:

• ensure there's no recursion going on
• see endModalSession subfunction below to avoid recursive call
• be sure your app is the main app and your window is the key window

Here's some source code FWIW

- (void)endModalSession
{
   if ( modalSession )
   {
      NSModalSession tempSession = modalSession;
      modalSession = NULL;
      [NSApp endModalSession:tempSession];
   }
   appInactiveWait = NO;
}

- (BOOL) waiting { return (modalSession || appInactiveWait); }

- (void)foo
{
   while ( !done )
   {
      // Only start a modal session when app is active.
      // Otherwise you get spurious Dock bouncing when you switch between Finder and this app.
      // Particulary, Remote afp mounts send spurious FSEventStream events every 30 seconds.
      if ( [NSApp isActive] && !startedModal )
      {
         if ( [NSApp keyWindow] == remoteFileManagerWindow || [NSApp keyWindow] == [NSApp mbWindow] )
         {
            startedModal = YES;
            //DLog( @"startingModal (RemoteFileManager) cookie %d", task.readWriteCookie );
            modalSession = [NSApp beginModalSessionForWindow:remoteFileManagerWindow];
            appInactiveWait = NO;
            //DLog( @"startedModal (RemoteFileManager) cookie %d", task.readWriteCookie );
         }
         else
         {
            DLog( @"deferring modal (RemoteFileManager) to keyWindow %@", [NSApp keyWindow] );
         }
      }

      if ( ![self waiting] )
         break;

      if (blah blah blah )
         done = true;

      if ( [self waiting] )
      {             
         if ( modalSession )
         {
            if ([NSApp runModalSession:modalSession] != NSModalResponseContinue)
               break;
         }
         else
         {
            [[NSRunLoop currentRunLoop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:0.1]];
         }
      }

      [self processDelayedQueue];
   }
   [self setCurrentTask:nil];

   [self endModalSession];