private static Optional<Runnable> getTargetFieldOfThread(Thread t) {
        try {
            Field f = Thread.class.getDeclaredField("target");
            f.setAccessible(true);
            return Optional.ofNullable((Runnable)f.get(t));
        } catch (ReflectiveOperationException e) {
            return Optional.empty();
        }
    }
Detect and warn on threads leaked by defunct application components.
These are threads launched by components of application bundles and not stopped after subsequent component deconstruction.
The below algorithm is a heuristic and will not detect all leaked threads.
jdisc_core/src/main/java/com/yahoo/jdisc/core/ContainerWatchdog.java