static final Waiter TOMBSTONE = new Waiter(false /* ignored param */);

    @CheckForNull volatile Thread thread;
    @CheckForNull volatile Waiter next;

    /**
     * Constructor for the TOMBSTONE, avoids use of ATOMIC_HELPER in case this class is loaded
     * before the ATOMIC_HELPER. Apparently this is possible on some android platforms.
     */
    Waiter(boolean unused) {}

    Waiter() {