Worker Thread iOS

Question

I want to create a background thread on the iPhone that executes some code every 10msec. But before I get lost in the concurrency programming guide and the threading program

Answer 1

NSRunLoop is the missing link.

You will have to setup the thread's run loop to repeat, or you can control this from your thread's entry. the thread hosts the timer (the timer will die with the run loop if it's still alive).

NSRunLoop is a pretty small class - check it and the related samples out.

Answer 2

It's possible to do this using the method you outline, but have you looked at using Grand Central Dispatch? It can make some of this a lot easier:

dispatch_queue_t backgroundQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_async(backgroundQueue, ^{
    while ([self shouldKeepProcessingInBackground]) {
        [self doBackgroundWork];
        usleep(1e4);
    }
})

You can also use a timer dispatch source to do work periodically:

dispatch_queue_t backgroundQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_source_t timerSource = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, backgroundQueue);
dispatch_source_set_timer(timerSource, dispatch_time(DISPATCH_TIME_NOW, 0), 0.01*NSEC_PER_SEC, 0*NSEC_PER_SEC);
dispatch_source_set_event_handler(timerSource, ^{
    [self doBackgroundWork];
});
dispatch_resume(timerSource);

Answer 3

You could easily use GCD (grand central dispatch) for that. First create a selector that will be called in the background. From here call whatever method you want.

- (void)backgroundSelector
{
    // do whatever you want to do
    [self performSelector:@selector(backgroundSelector) withObject:nil afterDelay:0.01];
}

After that just fire this method for the first time like this

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0), ^{
    [self backgroundSelector];
});

Let me know if that works for you.

Answer 4

It is pretty simple and clean if you do it with NSThread. With no need to subclass it.

- (void)backgroundStuff {
    while (!self.cancelThread) {
        // do your work
        [NSThread sleepForTimeInterval:0.01];
    }
}

Just an ordinary function. cancelThread is a member variable you declare. Start it with

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

and you can cancle the thread anytime with self.cancelThread = true;