How does Linux top command determine the state of a Java process?

Question

[Update: in top, after I pressed shift+H, which shows threads rather than processes, it then shows the Java thread as R and using 100% CPU time, which is what I expected before posting this question.]

Since a Java process has multiple threads, each of which might be in a different state, then how does Linux top command determine the Java process state?

If I run the following code,

public class Test{
  public static void main(String[] args){
     while (true){
       int n = (int)(Math.random() * 1000);
     }
  }
}

Then, running top shows that the process state is S, and it's using 100% CPU time.

Also, running strace shows and only shows:

futex(0x7f6ba759c9d0, FUTEX_WAIT, 26060, NULL

However, running jstack shows that the main thread is RUNNABLE:

"main" prio=10 tid=0x00007fd7ec007800 nid=0x669b runnable [0x00007fd7f5754000]
  java.lang.Thread.State: RUNNABLE
    at Test.main(Test.java:5)

jstack also shows that, there are only two threads in WAITING state:

"Finalizer" daemon prio=10 tid=0x00007fd7ec080000 nid=0x66a6 in Object.wait() [0x00007fd7f0252000]
    java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x00000007ad001310> (a java.lang.ref.ReferenceQueue$Lock)
        at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:133)
        - locked <0x00000007ad001310> (a java.lang.ref.ReferenceQueue$Lock)
        at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:149)
        at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:177)

"Reference Handler" daemon prio=10 tid=0x00007fd7ec07e000 nid=0x66a5 in Object.wait() [0x00007fd7f0353000]
    java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x00000007ad0011e8> (a java.lang.ref.Reference$Lock)
        at java.lang.Object.wait(Object.java:502)
        at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:133)
        - locked <0x00000007ad0011e8> (a java.lang.ref.Reference$Lock)

Answer 1

A JVM has many threads running to do "housekeeping" like garbage collection, etc. Those are in sleep state most of the time.