Question

I am a seemingly straightforward question that I can’t seem to find an answer to (and it is hindering my app).

I have a background thread running a paricular method:

-(void)processImage:(UIImage *)image {

  NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

  //Process image here in the background here

  [pool drain];
}

This much works great, but my question comes when I want to call another method from inside the already-background method. Does this call stay in the background? Do I need to add NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; and [pool drain]; to the new method to make it run in the background as well?

Any advice would be very helpful. I am a bit confused about this.

Many thanks,
Brett

Answer 1

It WILL stay in the background, on the same thread it was called from.

Some threading notes to consider with this:

• It may not be obvious, but if you call a timer from the background thread, and the thread exits before the timer is supposed to go off, the timer will NOT be called. Thus it is recommended you setup timers from the main thread
• You dont need another autorelease pool unless you spawn another thread.
• Any UI updates should be done on the main thread