Preventing provisioning duplicate Web Parts instances on Feature reactivation

http://blog.mastykarz.nl/preventing-provisioning-duplicate-web-parts-instances-on-feature-reactivation/

using (SPSite site = new SPSite("http://sharepoint"))
{
  SPList list = site.GetCatalog(SPListTemplateType.MasterPageCatalog);
  SPListItemCollection items = list.Items;
  List<string> webParts = new List<string>();

  // find the right Page Layout
  foreach (SPListItem item in items)
  {
    if (item.Name.Equals("CustomPageLayout.aspx",
      StringComparison.CurrentCultureIgnoreCase))
    {
      SPFile file = item.File;
      // get the Web Part Manager for the Page Layout
      SPLimitedWebPartManager wpm =
        file.GetLimitedWebPartManager(PersonalizationScope.Shared);
      // iterate through all Web Parts and remove duplicates
      while (wpm.WebParts.Count > 0)
      {
        StringBuilder sb = new StringBuilder();
        XmlWriterSettings xws = new XmlWriterSettings();
        xws.OmitXmlDeclaration = true;
        XmlWriter xw = XmlWriter.Create(sb, xws);
        System.Web.UI.WebControls.WebParts.WebPart wp =
          wpm.WebParts[0];
        wpm.ExportWebPart(wp, xw);
        xw.Flush();
        string md5Hash = getMd5Hash(sb.ToString());
        if (webParts.Contains(md5Hash))
          wpm.DeleteWebPart(wp);
        else
          webParts.Add(md5Hash);
      }
    }
  }
}