[kaffe] Bug in ThreadGroup
Dalibor Topic
robilad at yahoo.com
Wed Apr 9 08:47:01 PDT 2003
Hi Hervé,
--- Hervé_Roussain <Herve.Roussain at univ-ubs.fr> wrote:
> Hi!
>
> The 'parentOf' method doesn't work
thanks for the bug report and the fix.
> The method is
> final public boolean parentOf(ThreadGroup g) {
> return ((parent == g) ||
> (parentOf(g.getParent())));
> }
>
> but should be something like this:
> final public boolean parentOf(ThreadGroup g) {
> return (g != null && this == g.getParent())
> || parentOf(g.getParent());
> }
I've expanded your test class a bit to cover two
fringe cases as well: null, and self.
class ThreadGroupTest {
public static void main(String[] args) {
ThreadGroup daddy = new ThreadGroup("daddy");
ThreadGroup child = new ThreadGroup(daddy,
"child");
System.out.println("daddy.parentOf(child)=" +
daddy.parentOf(child));
System.out.println("child.parentOf(daddy)=" +
child.parentOf(daddy));
System.out.println("child.parentOf(child)=" +
child.parentOf(child));
System.out.println("child.parentOf(null)=" +
child.parentOf(null));
}
}
I think that your fix fails the null test and the self
test.
A better fix is:
final public boolean parentOf(ThreadGroup g) {
return (g != null)
&& ((this == g) ||(parentOf(g.getParent())));
}
which passes all four tests.
By the way, Classpath developers didn't implement the
method in a recursive fashion. In my opinion their
approach to walk the parent group chain in a loop is
better, as it does all the work within a single stack
frame. But that's a matter of taste, I guess.
cheers,
dalibor topic
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