NSWindow keyDown: crashes - objective-c

Question

In my application, I inherited NSWindow class. This is to override default key down event.
//mywindow.h
#interface TWindow: NSWindow
{
}
- (void)keyDown: (NSEvent *)pEvent;
#end
//mywindow.mm
- (void)keyDown:(NSEvent *)theEvent
{
//Detect Control-W and Control-Q and handle them.
unsigned short keycode; ///< Key code.
NSString * charigmtch; ///< Character ignoring matches.
NSString * character;
BOOL cmdkeydown; ///< check if the command key is down.
BOOL shiftkeydown; ///< Check if shift key is down.
//Get the keycode of Control-W
keycode = [theEvent keyCode];
//get character ignoring match.
charigmtch = [theEvent charactersIgnoringModifiers];
//get character
character = [theEvent characters];
cmdkeydown = ([[NSApp currentEvent] modifierFlags] & NSCommandKeyMask) == NSCommandKeyMask;
shiftkeydown = ([[NSApp currentEvent] modifierFlags] & NSShiftKeyMask) == NSShiftKeyMask;
//Get the keycode of Control
if(cmdkeydown && 12 == keycode && ![character compare:#"q"] && ![charigmtch compare:#"q"]) {
//CloseWithConfirm shows message box confirming quit.
[self CloseWithConfirm];
} else if (keycode == 48) {
//Tab key is pressed.
//This AppDelegate is application delegate and also NSWindowDelegate.
AppDelegate * delegate; ///< Delegate.
//Get the delegate from the window.
delegate = (AppDelegate *)[self delegate];
//Shift key is not down.
if(!shiftkeydown) {
//Tab key is pressed.
[delegate TabKeyPressed];
} else {
//Shift-Tab key is pressed.
[delegate ShiftTabKeyPressed];
}
}
//Handle the other key.
[super keyDown:theEvent]; //Line E
}
When I run following sample test case:
void TestCase ()
{
MyThread thread1, thread2, thread3, thread4;
//Run thread 1
thread1.Execute();
//Run thread 2
thread2.Execute();
//Run thread 3
thread3.Execute();
//Run thread 4
thread4.Execute();
}
//Following function is executed in thread function.
void Perform ()
{
//This adds the data in table view.
AddRowInTableView ("Test");
}
This code run fines most the time. But sometimes, it crashes at Line E marked in the code.
I am not able to find the reason of this crash. Can anyone help me?
I am using Mac OS X Mavericks preview and Xcode 5 for debugging and building.

Answer 1

Do not update UI in secondary thread. All drawing and UI events must be handled on the main thread.