Main thread watchdog

gistfile1.m

- (void)watchdog {
    NSTimeInterval pingInterval = 1.0/60.0;
    NSTimeInterval watchdogInterval = 1.0/30.0;

    __block NSTimeInterval lastPing = 0;

    NSProcessInfo *pi = [NSProcessInfo processInfo];

    dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, dispatch_get_main_queue());
    dispatch_source_set_timer(timer, DISPATCH_TIME_NOW, pingInterval * NSEC_PER_SEC, 0);
    dispatch_source_set_event_handler(timer, ^{
        lastPing = [pi systemUptime];
    });
    dispatch_resume(timer);

    dispatch_source_t watchdog = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0));
    dispatch_source_set_timer(watchdog, DISPATCH_TIME_NOW, pingInterval * NSEC_PER_SEC, 0);
    NSLog(@"Set timer to %f", pingInterval * NSEC_PER_SEC);
    dispatch_source_set_event_handler(watchdog, ^{
        NSTimeInterval now = [pi systemUptime];
        NSTimeInterval delta = now - lastPing;
        if(delta > watchdogInterval) {
            NSLog(@"Jammed for %f seconds", delta);
        }
    });
    dispatch_resume(watchdog);

    CFBridgingRetain(timer);
    CFBridgingRetain(watchdog);
}