OQL query to find all instances and sub-instances of a given class referred to from a session

I'm trying to use jhat/OQL to trace a memory leak in our Tomcat container. The question I want to ask is:

"Show me all the instances (and sub-instances) of foo.bar.Cacheable class that are reachable from javax.servlet.http.HttpSession"

I managed to come up with the following, but this doesn't show subclasses of foo.bar.Cacheable (which is important since this is infact an interface).

select filter(reachables(s), "/foo.bar.Cacheable/(classof(it).name)") from javax.servlet.http.HttpSession s

I tried various permutations of the concept below, but just keep getting errors ("foo" is not defined).

select filter(reachables(s), classof(it) instanceof foo.bar.Cacheable) from javax.servlet.http.HttpSession s

Can anyone help me out with what I'm doing wrong to pose this question through OQL?

Solution

In jhat based OQL implementations (jHat, VisualVM) you can exploit the fact that you are not limited to the SQL like syntax but you have a complete javascript engine at your hands.

The following piece of code would do the trick

var containerSuperClass = "javax.servlet.http.HttpSession"
var elementSuperClass = "foo.bar.Cacheable"
// find the container class by name
var alClz = heap.findClass(elementSuperClass)
// retrieve all subclasses
var subClzs = alClz.subclasses()

// filter the list of objects reachables from instances of the container super class
// and all its subclasses so it contains only objects of classes from subClzs
map(heap.objects(containerSuperClass), 'filter(reachables(it), "it != null && contains(subClzs, containsClause(it))")')

// we need to externalize the contains clause because of clash in naming the closure parameter 'it'
function containsClause(rcbl) {
    return function(it) {
        if (rcbl == null || it == null) return false;
        return it.name.equals(classof(rcbl).name)
    }
}