Open in Compare Editor -- over a minute of CPU time

Question

I've got a 947-line MXML file that seems to require over a
minute of CPU time to "Open in Compare Editor".
Specifically, I'm using Flex Builder 3 as an Eclipse 3.3.2
plug-in with Subclipse 1.2.4. If I synchronize with repository that
runs in a few seconds. If I then try to view the diff for the file
in question (main.mxml), the CPU goes to 100% and eclipse.exe piles
up about 1:19 of CPU time.
I tried a few experiments with chopping out parts of the
file. Here are times to Open in Compare Editor single-line diffs
with only the first N lines of the file in question:
400 lines: 56 seconds
200 lines: 15 seconds
150 lines: 4 seconds
100 lines: instantaneous
Executive summary: OUCH!

Answer 1

A sleeping thread uses no CPU. Try the following, both with and without the for loop. If you see a constant high CPU usage, even when the thread is sleeping, it's probably that the CPU usage is measured as an average over the last second or several seconds, so when the tasks you're performing are intense and take a significant fraction of the time you're sleeping, the average CPU usage doesn't go down that much.
public class Sleeper {
    public static void main(String[] args) throws Exception {
        while(true) {
            for (int ix = 0; ix < 100000000; ix++) {
                int jx = ix * 2;
                ix = --jx;
            Thread.sleep(5 * 1000* 60);
}