CC to the serviceability-dev alias.
---
I have no objection to this change, anybody else care? Sundar? Alan?
If not I can file a bug, and we can decide who gets to push the change
into jdk6, and probably jdk7 too.
-kto
Keith Randall wrote:
I'm working on tracing down a ClassLoader leak in a web application I'm
working on (see
http://blogs.sun.com/fkieviet/entry/classloader_leaks_the_dreaded_java
for a description of the kind of leak I'm talking about). I'm using hat
to find sources of the leak, and I have run into a problem where hat
generates a lot of false positives of a particular form. When I list
the reference chains from the rootset for a ClassLoader, it lists lots
of chains which start at a static field of a class which was loaded by
that classloader. This isn't a real leak, however, because if the
ClassLoader is otherwise dead, the class containing that static field
will be GCed.
I propose that hat shouldn't consider static fields of classes which
aren't loaded by the root classloader as GC roots. These roots will be
found during the normal heap walk (classloader -> class -> static
field). Unless of course the classloader isn't reachable, but that is
exactly when we don't want to consider static fields in these classes as
roots.
Does this sound like a reasonable thing to do? It works for me, just
want to make sure it won't break some other use case for hat.
Possible patch (to openjdk6 build b16):
--- com/sun/tools/hat/internal/model/Snapshot.java
** 331,336 ****
--- 331,345 ----
System.out.println();
for (Root r : roots) {
r.resolve(this);
+ if (r.getType() == Root.JAVA_STATIC) {
+ JavaClass clazz = (JavaClass) r.getReferer();
+ if (clazz.getLoader() != nullThing) {
+ // this "root" will be discovered through a reference
+ // to its classloader, so we don't need to treat it as
+ // an explicit root.
+ continue;
+ }
+ }
JavaHeapObject t = findThing(r.getId());
if (t != null) {
t.addReferenceFromRoot(r);
