One process open multiple threads on multiple CPUs

[kfcnhl]

I am using the code below to open up multiple threads (20+).
However, it seems that all the threads are running on 1 CPU when I do have 4 cores(according to task manager).
I am guessing there is a limitation on where my threads can be run.
In other word, threads can only be open up on the CPU where the original process started.
Obviously something have gone wrong some where.
Anybody got some suggestions?
Thanks a lot in advance :)

Additional information on platform:
I am using Eclipse to code.
Have tried to run on both windows 7 and XP, none works.

Runnable runnable = new XThread();
Thread thread = new Thread(runnable);
thread.start();

public class XThread implements Runnable
{
public void run()
{
}
}

[kjkrum]

It could be that your particular JVM is using lightweight threads instead of OS-level threads. See if there's a JVM option to change it, try a different JVM, or switch to Linux.

[JosAH]

It could be that your particular JVM is using lightweight threads instead of OS-level threads.

That would be so unlikely for recent versions of the JVM; more likely is that the 'affinity' of the JVM process is set to a single core. It can be changed with the task manager.

kind regards,

Jos