Thread.sleep takes a lot of CPU time!

Question

Hi,
I have the run method like this:
public void run()
while(true)
//some set of operations
Thread.sleep(5*1000*60);
The above code's performance was measured under stress test. . The sleep operation seems to take a lot of CPU time
though ideally sleep is like a no-operation mode, meaning since no operation
is done when a thread sleeps, it should not use any/minimal CPU time.
But it seems to take over 30% of CPU time!
Any ideas on why such a weird thing's happening?
In fact, in one more similar method also, sleep is taking similar CPU
time.

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);
}