I've got a procedure that is responsible for performing the following operations on a richtextbox
1) determining what parts of the text to forma
2) formatting specific ranges of text a specific color

I need to do this whenever the contents of the richtextbox change. The algorithm is quite fast as I have built in some speed saving optimizations, but i need to do some more, I was wondering if anybody could give me any suggestions? So far, I've coded it to
* - retrieve information about all ranges 'as of now' but only setting the format of ones that are new / only unsetting the format of ones that were there but aren't no
* - only set the format of ranges that are visible. For this, I use the message EM_GETFIRSTVISIBLELINE to get the first visible line, and the line count by dividing the height by the height of a line (got by GetTextMetrics). But then I need to do a rescan of ranges to format on vscroll aswell as on textchange, which is a bit bad as it's slow when you scroll

I was thinking of having some sort of 'lazy updater' type thing that either runs for, say, 100 milliseconds each second, or in a different thread, to update the RTB for the ranges that are off the visible range once all the others have been done, but I can't get my head round how to handle the synchronicity with the fact that when the richtextbox's contents change, the ranges will change too. Should I consider this a thing that takes 'a long time' to happen? Or can anyone else lend a hand with the obviously huge amount of sideways thinking I'm having to do!!

It's for a syntax highlighting control, right now I'm just trying to get it to be able to parse c-style block comments, line comments and quotes (red.

Any ideas on performance in this area
Have posted to C++ groups as although I am writing the app in c# I am non too averse to turn my hand to c++

Thanks