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Running NSTimer on Separate Thread

I’ve been working in something requiring an NTimer to fire every second. The documentation says that an NSTimer needs to be attached to a NSRunLoop to fire. So I started off with the following:

NSTimer* timer = [NSTimer timerWithTimeInterval:1.0 target:self selector:@selector(timerTick:) userInfo:nil repeats:YES];
[[NSRunLoop currentRunLoop] addTimer:timer forMode:NSEventTrackingRunLoopMode];

So, what I am doing here is creating a new NSTimer which fires in 1 second intervals and sends the timerTick message to self every time it fires. On the 2nd line, I am attaching the NSTimer object to the current runloop. This all worked fine. Until…!

It turns out in UI applications, the NSRunLoop is responsible for getting input from all the input devices/timers that are attached to it. The timer would fire and the tickerTick message got sent as expected until the runloop got busy doing something else. For example if I pressed a button on the UI and kept it pressed, the runloop was busy reading the mouse down input and the timer ticks would get ignored completely.

So, the solution was to run the NSTimer in a separate thread so it can have a NSRunLoop dedicated to responding to it and nothing else.

Here is the code:

-(void) startTimer
{
NSThread* timerThread = [[NSThread alloc] initWithTarget:self selector:@selector(startTimerThread) object:nil]; //Create a new thread
[timerThread start]; //start the thread
}

//the thread starts by sending this message
-(void) startTimerThread
{
NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init];
NSRunLoop* runLoop = [NSRunLoop currentRunLoop];
[[NSTimer scheduledTimerWithTimeInterval: 1.0
target: self
selector: @selector(timerTick:)
userInfo: nil
repeats: YES] retain];

[runLoop run];
[pool release];
}


- (void)timerTick:(NSTimer *)timer
{
NSLog(@"Tick!");
}

The NSRunLoop for the new thread needs to be explicitly set to run. If this is not done, the thread will start the timer, and then duly exit the function (and therefore the thread) and no ticks will be received. Also, the NSAutoreleasePool object needs to be created to manage the objects that are created in the new thread.

Cheers