NSTimer from secondary NSThread doesn't work - ios

Question

As per the documentation of Run Loop if there is any input source NSThread will be running otherwise it will go to sleep. I configured the timer same as provided under "Configuring Timer Sources" in above link but its not triggering. I am using below code.
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
[NSThread detachNewThreadSelector:#selector(testOnThread) toTarget:self withObject:nil];
}
- (void) testThread
{
NSLog(#"Test");
}
-(void)testOnThread
{
#autoreleasepool {
NSRunLoop* myRunLoop = [NSRunLoop currentRunLoop];
// Create and schedule the first timer.
NSDate* futureDate = [NSDate dateWithTimeIntervalSinceNow:1.0];
NSTimer* myTimer = [[NSTimer alloc] initWithFireDate:futureDate
interval:0.1
target:self
selector:#selector(testThread)
userInfo:nil
repeats:YES];
[myRunLoop addTimer:myTimer forMode:NSDefaultRunLoopMode];
}
}
Above code never prints "Test".
But timer is firing every time if I put [[NSRunLoop currentRunLoop] run]; at the end of -(void)testOnThread methods it works fine(Stackoverflow Question). My query is if we are already providing timer input Source to run loop than what is the need to explicitly start it using [[NSRunLoop currentRunLoop] run];

Answer 1

I'll let others answer the question why you have to run the runloop yourself. But I'd like to suggest an alternative:
If you want to run timer on background thread, using dispatch timer is easiest, IMHO, with no runloop required at all. Just define timer property:
#property (nonatomic, strong) dispatch_source_t timer;
And then schedule the timer to run on a custom queue:
dispatch_queue_t queue = dispatch_queue_create("com.domain.app.timer", 0);
self.timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
dispatch_source_set_timer(self.timer, dispatch_walltime(NULL, 0), 20ull * NSEC_PER_SEC, 1ull * NSEC_PER_SEC);
dispatch_source_set_event_handler(timer, ^{
// code to be performed periodically on background thread here
});
dispatch_resume(self.timer);