Re: ThreadGroup merge

[Bryce McKinlay]

Hi John,

Thanks for your comments.

John Keiser wrote:

> 1. setMaxPriority(): the JavaDoc seems to indicate you can set max priority
> as high as you want up to MAX_PRIORITY.  Why does GCJ only make it smaller
> and not larger?

The JCL says that you can only use this method to lower the maximum priority
of a thread group, not raise it. This makes sense to me, because the purpose
of setMaxPriority() is to limit what a thread can do with setPriority(). If a
thread could raise its own maximum priority (ie using
currentThread.getThreadGroup().setMaxPriority()) then there wouldn't really be
much point!

> 2. activeCount(): It seems activeCount() should only count live threads,
> right?  Why count all threads?

Because as far as I can tell, and despite what the JCL suggests, "active
thread" just means "any thread that is in the threadgroup", regardless of
whether that thread has been started yet. When a thread finishes, it will
automatically removes itself from its group and thus be consided inactive.

> 3. activeGroupCount(): Similar question here--though I can see how
> Classpath's is probably wrong as well, counting all threads instead of all
> active groups.

I've assumed that "Active ThreadGroup" means "any threadgroup that isn't
destroyed" because its simpler and consistent with the assumption above.

> 4. synchronized: I noticed a lot of synchronized keywords were removed from
> one to the other.  Do y'all feel they were unnecessary for thread safety?
> (Seems like if anything should be threadsafe, it's ThreadGroup and Thread.)

Oops. Somehow I dropped some synchronized flags. Certainly they should be at
least synchronized to the extent specified in the JCL. I guess things like
destroy() should be synchronized wrt addThread(). Will fix.

I've attached a couple of test cases for your points 1,2,3 above. These tests
run identically on JDK1.1.8, JDK1.2.2, and libgcj on Linux.

regards

  [ bryce ]



public class TG
{
  public static void main(String args[])
  {
    ThreadGroup tg = new ThreadGroup("fooz");
    System.out.println (tg.isDaemon());       // false
    System.out.println (tg.isDestroyed());    // false
    tg.setDaemon(true);
    System.out.println (tg.isDaemon());       // true
    System.out.println (tg.isDestroyed());    // false

    tg = new ThreadGroup("jsaz");
    tg.setMaxPriority(2);
    System.out.println (tg.getMaxPriority()); // 2
    tg.setMaxPriority(3);
    System.out.println (tg.getMaxPriority()); // 2
    ThreadGroup tg2 = new ThreadGroup(tg, "pfiz");
    System.out.println (tg2.getMaxPriority()); // 2
    tg = Thread.currentThread().getThreadGroup();
    tg.list();
    /*
    java.lang.ThreadGroup[name=main,maxpri=10]
        Thread[main,5,main]
        java.lang.ThreadGroup[name=fooz,maxpri=10]
        java.lang.ThreadGroup[name=jsaz,maxpri=2]
            java.lang.ThreadGroup[name=pfiz,maxpri=2]
    */
  }
}

public class TGCount implements Runnable
{
  public static void main(String[] args) throws InterruptedException
  {
    new TGCount();
  }
  
  public void run() {}
  
  public TGCount() throws InterruptedException
  {
    ThreadGroup tg = new ThreadGroup("foo");
    System.out.println (tg.activeCount());      // 0
    Thread t = new Thread(tg, this);
    System.out.println (tg.activeCount());      // 1
    System.out.println (t.isAlive());           // false
    t.start();
    Thread.sleep(100);
    System.out.println (t.isAlive());           // false
    System.out.println (tg.activeCount());      // 0
    tg.destroy();
    tg = new ThreadGroup("foo");
    ThreadGroup tg2 = new ThreadGroup(tg, "bar");
    System.out.println (tg.activeGroupCount()); // 1
    tg2.destroy();
    System.out.println (tg.activeGroupCount()); // 0    
  }
}