}

    /**
     * Returns {@code this} up-casted to the specific {@link Segment} implementation type {@code S}.
     *
     * <p>This method exists so that the {@link Segment} code can be generic in terms of {@code S},
     * the type of the concrete implementation.
     */
    abstract S self();

    /** Drains the reference queues used by this segment, if any. */
    @GuardedBy("this")