* </p>
     *
     * @param disposable
     *            A disposable resource. Must not be {@literal null}.
     */
    public static synchronized void addFirst(final Disposable disposable) {
        assertArgumentNotNull("disposable", disposable);
        disposables.addFirst(disposable);
    }

    /**
     * Unregisters a disposable resource.
     *
     * @param disposable