Macos Application hangs when using NSDistributedNotificationCenter and CFRunLoopAddSource

Question

I have MacOS application built using Qt. There I have created NSDistributedNotificationCenter to be notified when accessibility settings change (observing "com.apple.accessibility.api" ). Also I have CFRunLoopAddSource to monitor key pressed events.

However when I run the program and I change accessibility application hangs and I cannot run it normally.

Could someone help to see why that is happening?

This is the code:

Here I am creating observer: Creation/deletion is controlled by button click

- (void)createObserver
{
[[NSDistributedNotificationCenter defaultCenter] addObserver:self
            selector:@selector(didToggleAccessStatus:)
                name:@"com.apple.accessibility.api"
              object:nil
  suspensionBehavior:NSNotificationSuspensionBehaviorDeliverImmediately];
}

And this is how I add key event logger:

// Create an event tap to retrieve keypresses.
CGEventMask eventMask = (CGEventMaskBit(kCGEventKeyDown) | 
CGEventMaskBit(kCGEventFlagsChanged) |
                          CGEventMaskBit(kCGEventLeftMouseDown) |
                          CGEventMaskBit(kCGEventRightMouseDown) |
                          CGEventMaskBit(kCGEventMouseMoved) |
                          CGEventMaskBit(kCGEventScrollWheel));
                                  //| CGEventMaskBit(kCGEventLeftMouseDragged)
                                  //| CGEventMaskBit(kCGEventRightMouseDragged)
                                  //| CGEventMaskBit(kCGEventOtherMouseDragged););
CFMachPortRef           m_eventTap = nullptr;
CFRunLoopSourceRef      m_runLoopSource = nullptr;
 m_eventTap = CGEventTapCreate(
     kCGSessionEventTap, kCGHeadInsertEventTap, kCGEventTapOptionDefault,
     eventMask, myCGEventCallback, nullptr);

 if (m_eventTap != Q_NULLPTR) {
    NSLog(@"CGEventTap created");
    // Create a run loop source and add enable the event tap.
    m_runLoopSource = CFMachPortCreateRunLoopSource(kCFAllocatorDefault, m_eventTap, 0);
    CFRunLoopAddSource(CFRunLoopGetCurrent()/*CFRunLoopGetMain()*/, m_runLoopSource, kCFRunLoopCommonModes);
    CGEventTapEnable(m_eventTap, true);
    //CFRunLoopRun();
 }
 else {
     m_runLoopSource = Q_NULLPTR;
     NSLog(@"Error creating CGEventTap");
 }

Any ideas please?

Thanks in advance and regards

The hang sounds like Qt's event loop isn't getting processed when the new RunLoop is active. — TheDarkKnight, Feb 21 '20 at 10:51
What new RunLoop? If I create only keylogger everything works and I think Qt event loop is active as well — RuLoViC, Feb 21 '20 at 16:34
"application hangs" — Hangs *doing what*? Look at the stack trace. — seth, Feb 21 '20 at 17:48
Actually is not really hang. Mouse and keyboard stop responding and I have to reboot the laptop — RuLoViC, Feb 21 '20 at 18:12
*What new RunLoop?* - Is CFRunLoopRun() commented out when it stops responding? — TheDarkKnight, Feb 24 '20 at 10:21
Not really. I finally took another way to achieve what I needed but I am still interested in what is wrong in this code. Do you have any clue? — RuLoViC, Mar 19 '20 at 19:45
@KrishnaMaru no, finally I took different approach but I would like to know why it was hanging — RuLoViC, May 01 '20 at 11:53

Macos Application hangs when using NSDistributedNotificationCenter and CFRunLoopAddSource

0 Answers0