NSRunAlertPanel caused performance issue on multithreading

Question

Occasionally I have to do a popup alert window in my Cocoa code segments. Previously I used NSAlert directly then have runModal to go while I found that the NSRunAlertPanel is more easier to achieve my goal. So I decided to switch all my alert functions to NSRunAlertPanel. It seemed okay at most time。

Now I'm adding multithreading. I found that NSRunAlertPanel appears clearly slower than NSAlert when calling back in the main thread.

Code segments:

Firstly I create a thread:

[NSThread detachNewThreadSelector: @selector(tryRunLoop:) toTarget:self withObject:nil];

Then this functiontryRunLoop in this thread call the alert window function in the main thread:

while(1)
[self performSelectorOnMainThread:@selector(showAlert:) withObject:anObject waitUntilDone:YES]; 

The function showAlert in main thread do the rest things:

NSRunAlertPanel(@"Warning:",@"Just testing", @"YES", nil, nil);

As time goes by the response of the popup window appears slower and slower.If I use NSAlert instead of NSRunAlertPanel, or did not run the popup method in main thread, the symptom should disappear.

I also found that the CPU usage was also different between these two methods. Obviously NSAlert costs low CPU usage while hitting the button all the time.

Is someone able to explain these phenomenons?

PS: I was not allowed to put the whole original project online so that I've created a simple Cocoa project in Github to simulate the symptom and the URL ,please take a look at the Known issues in Readme file at first.

Answer 1

Alright, the short answer is don't use NSRunAlertPanel. That family of functions have been discouraged for some time now, and superseded by NSAlert. Use NSAlert instead.

(Unfortunately the class reference for NSRunAlertPanel etc. doesn't mention this; I'm trying to remember where it was first documented; perhaps a release note)