Cost/benefit of multi-threaded text processing

Question

I am working on a real-time syntax highlighter for the iPhone and I have created a custom UIView that takes a string, parses it and then highlights it in its drawRect: method. I've also implemented a blinking cursor. However, it is starting to get a little slow and I think that when I implement multi-line processing and chunk-processing, it will slow it down more. However, I tried placing the [formattedTextView setNeedsDisplayInRect:] call in a function in my view controller and then calling on a separate thread using [self performSelectorInBackground:@selector(updateDisplay) withObject:nil]. The keyboard is more responsive now, but this seems like a bad use of threads on a single-core processor.

Are there any problems with doing something like this?

Thanks

Answer 1

As you pointed out yourself, on a single processor multithreading will not bring a huge performance boost, but will come with a stability and complexity penalty.

On-the-fly Syntax-coloring is a hard problem, stuffed with possibilites for optimization:

• Are you applying a bunch of Regexes on the whole text? (bad) or do you parse the text to be held in an efficient datastructure like an ast?
• Are you limiting the colorized painting to the visible area?

Greets

Seb

Answer 2

I am working on a real-time syntax highlighter

Are you doing keyword highlighting or have you written a BNF parser?

For the latter, why not have it running in a thread; the GUI simply displays the colouring of all that's been decoded so far. That way you get instant update but delayed colouring.