Query related to Multithreading?

Hi

I am working on an MFC based SDI (Explorer type) application which searches for 2 headers (BMP & JPG) in the logical drive selected by the user.

The searching headers job i am doing in a UI Thread.

As soon as any header is found i add it to a Linked list maintained by me and then i send messages to the mainframe & leftview class to update the interface..

In the mainframe class in the message handler function i update the progress bar in the statusbar pane 0 & headers found count in the statusbar pane 1.

In the leftview message handler function i create a folder by the name of the header found (ex: BMP) & add it to the tree.

Now after half of the logical drive processed 2 folder exists in the left view - BMP & JPG.

So far so good.....................

Now when the user clicks on any folder(for ex: BMP) in the leftview, i will show the thumbnails of the various bmp's found so far by the searching process & stored in the linked list.

I have used a worker thread to show the thumbnails.

Now there are two problems related to the above discussion:

1-----> When the thumbnails are being shown by the worker thread, the header searching UI threads hangs untill all thumnails are displayed. Please have a look at the code for the worker thread:

 UINT      LoadingThumbnails_WorkerThread(LPVOID pParam)
{
      CSPhApp      *pApp = ( CSPhApp* )AfxGetApp();

      HWND      hHandle      =      (HWND)pParam;

      CWaitCursor      obj;

      while(pApp->pTemp)
      {
            if(pApp->pTemp->dwParentId      ==      pApp->dwCurrentlySelected_Dirs_FileId)
            {
                  BOOL      ret_Value = PostMessage(hHandle, WM_THUMBNAILS, 0, 0);

                  Sleep(500);
            }
            pApp->pTemp      =      pApp->pTemp->next;
      }//end of while..

      //When control comes here, loading of thumbnails is done.
      pApp->LoadingThumbNails      =      FALSE;            

      return 0;
}


Y is my UI thread hanging.

Waiting for suggestions

Regards