Do Java Threads need any cleanup?

Question

I see that all the stop and destroy and anything else that deals with cleanup methods have been deprecated.

If I have a new Thread() or a class that extends Thread running, do I need to do anything in its run() method other than let it get to the end of regular execution? Or is there a background mechanism that understands that the Thread has run through all its tasks and can be destroyed?

Answer 1

When you call start() on your thread, native mechanism in JVM close to the operating system are starting your thread, eventually executing run(). When run() finishes, JVM takes care of everything.

You might be concerned about garbage collection or other resources cleanup. Of course if you open file/network connection inside a thread, it must be closed like everywhere else. Also the garbage collector, while analyzing live objects, takes into account objects referred from running threads. But the moment thread finishes, all the objects referenced by it (or by Runnable implementation passed to the thread) are eligible for garbage collection.

quick&dirty edit for exit method of Thread, as visible contextClassLoader is missing x.x

private void exit() {
    if (group != null) {
        group.remove(this);
        group = null;
    }
    /* Aggressively null out all reference fields: see bug 4006245 */
    target = null;
    /* Speed the release of some of these resources */
    threadLocals = null;
    inheritableThreadLocals = null;
    inheritedAccessControlContext = null;
    blocker = null;
    uncaughtExceptionHandler = null;
}