PCL not updating

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I am able to view my lidar pointcloud using this script but not update it. viewer-> spin() does not seem to be work. Any help will be appreciated.

void callback(const ImageConstPtr& image1, const boost::shared_ptr<const sensor_msgs::PointCloud2>& input)

       pcl::PCLPointCloud2 pcl_pc2;
       pcl_conversions::toPCL(*input,pcl_pc2);
       pcl::PointCloud<pcl::PointXYZ>::Ptr temp_cloud(new pcl::PointCloud<pcl::PointXYZ>);
       pcl::fromPCLPointCloud2(pcl_pc2,*temp_cloud);
       pcl::visualization::CloudViewer viewer ("Simple Cloud Viewer");
       viewer.showCloud(temp_cloud);
       while (!viewer.wasStopped ())
       {

       {