ScheduleAtFixedRate in ScheduledThreadPoolExecutor not accurate in windows

Question

I am using the scheduleAtFixedRate method in ScheduledThreadPoolExecutor class to run a task periodically,but I found it not run accurately,here's a sample code:
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
public class TestThreadPool {
     private static SimpleDateFormat dateformat = new SimpleDateFormat("HH:mm:ss.SSS");
     * @param args
     public static void main(String[] args) {
          Calendar cal = Calendar.getInstance();
          cal.add(Calendar.MINUTE, 1);
          cal.set(Calendar.SECOND, 0);
          cal.set(Calendar.MILLISECOND, 0);
          System.out.println(cal.getTime());
          ScheduledThreadPoolExecutor threadpool = new ScheduledThreadPoolExecutor(1);
          threadpool.scheduleAtFixedRate(new Runnable(){
               public void run() {
                    System.out.println(dateformat.format(new Date()));
          }, (cal.getTimeInMillis()-System.currentTimeMillis()),5000, TimeUnit.MILLISECONDS);
I want to it to work at next minute,then every 5 sencods like 0,5,15,20 seconds and so on.but the actually run time is plus,and it will not run at 5 based time,
is it the windows platoform problem,I use windows xp sp2,but when I test this code
in redhat enterprise server 4,it works well after serveral hours,can anybody tell me why and how to solve this problem ? Need your help!
Edited by: allenzhuyi on Jul 6, 2008 11:03 PM

Answer 1

ejp,Thanks for you advice,I will recalc next run time after the task has finished,here's my code:
public class TestRescheduleTask2 {
private static ScheduledThreadPoolExecutor threadpool = new ScheduledThreadPoolExecutor(1);
public static long nextRunTime;
public static long interval = 20000;
     public static void main(String[] args) {
          Calendar cal= Calendar.getInstance();
          cal.add(Calendar.MINUTE, 1);
          cal.set(Calendar.SECOND, 0);
          cal.set(Calendar.MILLISECOND, 0);
          nextRunTime = cal.getTimeInMillis();
          resubmit();
     public static void resubmit() {
          threadpool.schedule(new Task12(),
                    (nextRunTime-System.currentTimeMillis()),TimeUnit.MILLISECONDS);
          nextRunTime = nextRunTime + interval;
class Task12 implements Runnable{
     public void run() {
          System.out.println(new Date());
          TestRescheduleTask2.resubmit(); //afer finish the task,I reschedule the task
}