CALayer or CATextLayer with a nsoperationqueue

Question

I have CALayer with an image, to render/calculate the ref of this image needs a lot of time. When I am using an NSOperationQueue to do that and set the layer content in this block the image will not show immediately, it will show after around 2-3 second.

I try to set the layer for setNeedsDisplay and so one, but this option seems not be the solution for this problem.

Thanks in advance!