No notification received for terminal application

There’s two answers here:

• In general I recommend that you ‘park’ your main thread using dispatch_main [1]. This is the modern way to do things, and it seems to work in your specific case (see the code pasted in below).

• In some circumstances you’ll find code that relies on an actual main thread run loop. This is a bit of a pain because, as you’ve noted, NSRunLoop will exit if it has no run loop sources. I generally get around this by scheduling a timer that fires at +[NSDate distantFuture].

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—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware
let myEmail = "eskimo" + "1" + "@apple.com"

[1] dispatch_main doesn’t actually park the thread, but rather it saves resources by terminating the thread while leaving your process alive. Neat-o-rama!

@import Foundation;
 
@interface Main : NSObject
@end
 
@implementation Main 
 
- (void)run {
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(timeZoneDidChange:) name:NSSystemTimeZoneDidChangeNotification object:nil];
    dispatch_main();
}
 
- (void)timeZoneDidChange:(NSNotification *)note {
    NSLog(@"time zone changed");
}
 
@end
 
int main(int argc, char **argv) {
    @autoreleasepool {
        [[[Main alloc] init] run];
        return EXIT_SUCCESS;
    }
}

Thanks eskimo for the sample. Though I am testing the code directly in application, The class will eventually be in a static library that will be picked up by a cocoa or terminal application. Because of the nature of the application, the class can be used either from a main thread or indirectly from another worker thread.

Is there any other way to get this working from a worker thread?

Is there any other way to get this working from a worker thread?

NSSystemTimeZoneDidChangeNotification

is posted on the main queue, so that notification is never generated if the main queue is not being serviced. Personally I would make that a requirement of your library. It’s likely that lots of other system APIs that you depend on have similar limitations.

If you absolutely have to support programs that don’t run the main queue then you can be notified of time zone changes by using the BSD notify API with the

kNotifyTimeZoneChange

key. But, to reiterate, I would not do this in your case because it’s just papering over one of potentially many cracks.

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—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware

let myEmail = "eskimo" + "1" + "@apple.com"

Eskimo,

I tried the notify method but I am still not getting the notification. I copied the sample at the below github gist

/anonymous/eb1c5dbbab2b048ffe676d2556122f9d

I will also keep the dispatch_main option as well. Also a newbie question on this how do I terminate the app while the dispatch_main() is running?

I took a quick look at your gist and couldn’t see what was wrong (honestly, it was a lot more code than I was expecting). Here’s a program that works on my machine:

@import Foundation;
 
#include <notify.h>
#include <notify_keys.h>
 
int main(int argc, char **argv) {
    int token;
    uint32_t status;
 
    status = notify_register_dispatch(kNotifyTimeZoneChange, &token, dispatch_get_main_queue(), ^(int blockToken) {
        NSLog(@"notified");
    });
    assert(status == 0);
 
    dispatch_main();
 
    return EXIT_SUCCESS;
}

Also a newbie question on this how do I terminate the app while the

dispatch_main

is running?

Call

exit

.

Share and Enjoy
—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware

let myEmail = "eskimo" + "1" + "@apple.com"

Thanks that helped me. I used the wrong key in my source. I can now receive the change notifications without any issues.