Preempting the main thread

[Alton Hernandez]

Hi,
Is it possible for the main thread or the intial thread to be preempted while its children are not?
Thanks

[Jim Yingst]

Not sure what you mean. To me in order for a thread to be pre-empted the thread must have been running in the first place. Only one thread can run at a time. So if a thread is pre-empted, no other threads are pre-empted at the same time, since no other threads were actually running.
That probably isn't what you meant, so can you rephrase?

[Alton Hernandez]

Sorry for the confussion.
What I meant is something like this:

class A extends Thread {
  public static void main (String [] args ) {
     A a = new A();
     a.start();           // 1
  }
}

When I type java A, a main thread is created. When the program reaches line 1, a child thread is created. So now there are two threads, the main and the child.
My question now is can the main thread be swapped-out (that is moved out from the running state) but its child remains running?
Thanks.

[Jim Yingst]

Well, the way the JVM deals with threads, it doesn't really care about the parent-child relationship. The JVM just keeps running as long as there are non-daemon threads still running. It starts with one thread, main, starts another thread (call it thread-1), mean ends, but the JVM doesn't care, it just knows that it's still got one (non-daemon) thread running, so it keeps on going until that ends (assuming no other threads are spawned).
Does that answer your question, or did I misunderstand again?

[Alton Hernandez]

Yes, that answer it Thank you.
I was thinking along the line on how most OS swap programs out.