Threads CPU time

Question

Hi
I have some simple test porgram:
class ThreadTest extends Thread
   private ThreadMXBean tmbean  =  ManagementFactory.getThreadMXBean();
   public ThreadTest()
       super("ReceiveThread");
   public void run()
      new MyTest();
      long time = tmbean.getCurrentThreadCpuTime();
      System.out.println("Time: " + time);
}and
public class RunTest
  public static void main(String[] args)
      int count = 0;
      while(count < 5)
          new ThreadTest().start();
         count++;
}In each thread i create object MyTest - some simple calculations, but in some cases CPU time is 0.
How is this possible? Method 'getCurrentThreadCpuTime()' returns time in nanoseconds. Is something wrong in this way of creating ThreadMXBean object or something?
Thanks for any help

Answer 1

Try this one it may explain your problem
import java.lang.management.*;
public class CPUTimeTest{
    public static void main(String args[]){
        long vals[] = null;
        final ThreadMXBean tbe  =  ManagementFactory.getThreadMXBean();
        try{
            vals = new long[Integer.parseInt(args[0])];
            if(tbe.isCurrentThreadCpuTimeSupported()){
                tbe.setThreadCpuTimeEnabled(true);
            else{
                 System.out.println("Function not Supported");
                 return;
         catch(RuntimeException re){
             System.out.println("Usage :java CPUTimeTest num_samples");
             return;
         for(int i =0;i<vals.length;i++){
             Thread t = new Thread(){
                 public void run(){
                     System.out.println("Time = "+tbe.getCurrentThreadCpuTime());
             t.start();
         System.out.println("Total Time = "+tbe.getCurrentThreadCpuTime());
}I got the following results
java CPUTimeTest 10
Time = 10000000
Time = 0
Time = 0
Time = 0
Time = 0
Time = 0
Time = 0
Time = 0
Time = 0
Total Time = 410000000
Time = 0
My system is a linux red hat 7.2 with pentium II 233Mhz java 1.5
I think its because you are not doing anything in those threads